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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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need help repairing old Heathkit weather computer
Hey all;
I'm working on repairing a Heath weather computer. Initially, none of the funcitons really worked (temp, pressure, clock, etc.) I got it to the point last night where everything was working except the clock, which kept time, but I couldn't actually set it. So, I (stupidly?) poked around a little more to try to get the clock going. I noticed a 4066 with some black stuff on the pins, and some weird voltages around it, so I pulled it out, fired the unit up, and checked the voltages again. They were still weird, but when I put it back in and turned it on again, the pressure and temperature stayed at 0. I was messing around with it again tonite, and the pressure and temperature readings were more normal, but I noticed a couple of opamps (in different locations) that were hot to the touch. There were no shorts in either of them, and the voltages around them pretty much matched the schematic. I now get bad readings in the temperature (-40) and pressure (0). I'm guessing the opamps are at least part of the problem. Any idea why they are getting so hot? Any other suggestions? Thanks |
#2
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need help repairing old Heathkit weather computer
"tempus fugit" wrote in message ... Hey all; I'm working on repairing a Heath weather computer. Personally, I always suspect 4066's, and as for op-amps I always suspect 324's If things are getting hot, then are you sure that the supplies are present and correct and that nothing is shorted. If the opamps are getting hot, then it's a possibility they're drawing a lot of current, and that will affect the operation of the entire unit. You might also get some useful info from this page http://www.heathkit-museum.com/support.shtml |
#3
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need help repairing old Heathkit weather computer
Thanks Nigel.
Guess what kind of opamps they are - yup, LM324. When you say "suspect" do you mean you suspect they have failed? I've been toying with the idea of replacing the opamps with a 074, but I don't want to end up just burning another opamp. I'm wondering whether other components have caused the opamp failure, although everything around them seems to be testing OK. "Nigel" wrote in message ... "tempus fugit" wrote in message ... Hey all; I'm working on repairing a Heath weather computer. Personally, I always suspect 4066's, and as for op-amps I always suspect 324's If things are getting hot, then are you sure that the supplies are present and correct and that nothing is shorted. If the opamps are getting hot, then it's a possibility they're drawing a lot of current, and that will affect the operation of the entire unit. You might also get some useful info from this page http://www.heathkit-museum.com/support.shtml |
#4
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need help repairing old Heathkit weather computer
"tempus fugit" wrote in message ... Hey all; I'm working on repairing a Heath weather computer. Initially, none of the funcitons really worked (temp, pressure, clock, etc.) I got it to the point last night where everything was working except the clock, which kept time, but I couldn't actually set it. So, I (stupidly?) poked around a little more to try to get the clock going. I noticed a 4066 with some black stuff on the pins, and some weird voltages around it, so I pulled it out, fired the unit up, and checked the voltages again. They were still weird, but when I put it back in and turned it on again, the pressure and temperature stayed at 0. I was messing around with it again tonite, and the pressure and temperature readings were more normal, but I noticed a couple of opamps (in different locations) that were hot to the touch. There were no shorts in either of them, and the voltages around them pretty much matched the schematic. I now get bad readings in the temperature (-40) and pressure (0). I'm guessing the opamps are at least part of the problem. Any idea why they are getting so hot? Any other suggestions? Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
#5
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need help repairing old Heathkit weather computer
Thanks tweet.
The black stuff is actually on quite a few of the components - diode leads, resistors, ICs, etc. I never really looked too close at it, but it almost looks like black paint. The opamps are HOT. They start out cold, and after about 2 minutes are too hot to touch. I have the original schematic, as well as the manual, but have noticed some errors on the schem (or the circuit board, I don't know which). One thing that I have noticed on a lot of components (mostly xsistors) is odd voltage readings. There might be 5v on one side of a bias resistor, and 0.3v on the other (xsistor) side, but the xsistor checks out OK with a diode test (i.e., not leaky or shorted). Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
#6
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need help repairing old Heathkit weather computer
"tempus fugit" wrote in message
... Thanks tweet. The black stuff is actually on quite a few of the components - diode leads, resistors, ICs, etc. I never really looked too close at it, but it almost looks like black paint. The opamps are HOT. They start out cold, and after about 2 minutes are too hot to touch. I have the original schematic, as well as the manual, but have noticed some errors on the schem (or the circuit board, I don't know which). One thing that I have noticed on a lot of components (mostly xsistors) is odd voltage readings. There might be 5v on one side of a bias resistor, and 0.3v on the other (xsistor) side, but the xsistor checks out OK with a diode test (i.e., not leaky or shorted). Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Undoubtedly, the "black stuff" that you see on the leads is tarnish. It's not dangerous to the components, but if it's interfering with mating of component contacts, it will certainly prevent the circuit from operating correctly. This could be the problem with the opamps. There's something seriously out of whack if the opamps are too hot to touch.. Don't allow it to run for more than just a few seconds until you get it fixed.. the opamps will be destroyed, if they are not defective already. I can't tell a thing from your voltage measurements without seeing the schematic along with the voltages. It certainly would be a big help if you could scan the schematic and post it somewhere. Without it, it's pretty much a waste of time here. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
#7
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need help repairing old Heathkit weather computer
Thanks again.
Unforunately, I don't think I can scan the schem (it's huge for one thing). As for the voltages, they don't match up with what's indicated on the schem in a lot of places (even when I had most of it working), so I don't know which to trust. I'll try removing the tarnish and checking for continuity though. Thanks "Tweetldee" wrote in message ... "tempus fugit" wrote in message ... Thanks tweet. The black stuff is actually on quite a few of the components - diode leads, resistors, ICs, etc. I never really looked too close at it, but it almost looks like black paint. The opamps are HOT. They start out cold, and after about 2 minutes are too hot to touch. I have the original schematic, as well as the manual, but have noticed some errors on the schem (or the circuit board, I don't know which). One thing that I have noticed on a lot of components (mostly xsistors) is odd voltage readings. There might be 5v on one side of a bias resistor, and 0.3v on the other (xsistor) side, but the xsistor checks out OK with a diode test (i.e., not leaky or shorted). Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Undoubtedly, the "black stuff" that you see on the leads is tarnish. It's not dangerous to the components, but if it's interfering with mating of component contacts, it will certainly prevent the circuit from operating correctly. This could be the problem with the opamps. There's something seriously out of whack if the opamps are too hot to touch.. Don't allow it to run for more than just a few seconds until you get it fixed.. the opamps will be destroyed, if they are not defective already. I can't tell a thing from your voltage measurements without seeing the schematic along with the voltages. It certainly would be a big help if you could scan the schematic and post it somewhere. Without it, it's pretty much a waste of time here. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
#8
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need help repairing old Heathkit weather computer
On Fri, 24 Oct 2003 23:18:04 -0400, tempus fugit wrote:
Hey all; I'm working on repairing a Heath weather computer. Initially, none of the funcitons really worked (temp, pressure, clock, etc. Thanks Please get on this Heathkit list. You will find a great deal of help there. "Heathkit List" Send for info to : |
#9
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need help repairing old Heathkit weather computer
You don't need to worry about the tarnish on the soldered component leads..
just the socketed components, such as ICs and transistors. If there are any connectors that appear to be tarnished, then you should clean those as well. BTW, have you checked the power supply output(s) with your multimeter? If the supply voltages aren't correct, then you can't expect the rest of the circuit to operate properly. How abot ripple on the PS lines? If there's a lot of ripple, then there will be all sorts of chaos in the circuit. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... Thanks again. Unforunately, I don't think I can scan the schem (it's huge for one thing). As for the voltages, they don't match up with what's indicated on the schem in a lot of places (even when I had most of it working), so I don't know which to trust. I'll try removing the tarnish and checking for continuity though. Thanks "Tweetldee" wrote in message ... "tempus fugit" wrote in message ... Thanks tweet. The black stuff is actually on quite a few of the components - diode leads, resistors, ICs, etc. I never really looked too close at it, but it almost looks like black paint. The opamps are HOT. They start out cold, and after about 2 minutes are too hot to touch. I have the original schematic, as well as the manual, but have noticed some errors on the schem (or the circuit board, I don't know which). One thing that I have noticed on a lot of components (mostly xsistors) is odd voltage readings. There might be 5v on one side of a bias resistor, and 0.3v on the other (xsistor) side, but the xsistor checks out OK with a diode test (i.e., not leaky or shorted). Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Undoubtedly, the "black stuff" that you see on the leads is tarnish. It's not dangerous to the components, but if it's interfering with mating of component contacts, it will certainly prevent the circuit from operating correctly. This could be the problem with the opamps. There's something seriously out of whack if the opamps are too hot to touch.. Don't allow it to run for more than just a few seconds until you get it fixed.. the opamps will be destroyed, if they are not defective already. I can't tell a thing from your voltage measurements without seeing the schematic along with the voltages. It certainly would be a big help if you could scan the schematic and post it somewhere. Without it, it's pretty much a waste of time here. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
#10
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need help repairing old Heathkit weather computer
The PS voltages were the 1st thing I checked. They were pretty saggy, so I
replaced the main filter caps. That helped, but didn't fix the problem, so I moved on to the regulators, and found that the -15v regulator was out of commission, so I replaced it. This improved matters somewhat, but there were still problems, so I kept poking, and found a shorted PNP on the CPU board, which I replaced. I have a scope, but am kind of new to it. I basically attached the ground clip to the case and probed the regulator's output, which showed no ripple (which seemed a little unrealistic to me). Is this the proper method for checking for ripple? As for the tarnish issue, I'm just going to check for continuity from the IC's pins to the connections on the solder side of the board. Thanks again, and keep those suggestions comin' "Tweetldee" wrote in message ... You don't need to worry about the tarnish on the soldered component leads.. just the socketed components, such as ICs and transistors. If there are any connectors that appear to be tarnished, then you should clean those as well. BTW, have you checked the power supply output(s) with your multimeter? If the supply voltages aren't correct, then you can't expect the rest of the circuit to operate properly. How abot ripple on the PS lines? If there's a lot of ripple, then there will be all sorts of chaos in the circuit. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... Thanks again. Unforunately, I don't think I can scan the schem (it's huge for one thing). As for the voltages, they don't match up with what's indicated on the schem in a lot of places (even when I had most of it working), so I don't know which to trust. I'll try removing the tarnish and checking for continuity though. Thanks "Tweetldee" wrote in message ... "tempus fugit" wrote in message ... Thanks tweet. The black stuff is actually on quite a few of the components - diode leads, resistors, ICs, etc. I never really looked too close at it, but it almost looks like black paint. The opamps are HOT. They start out cold, and after about 2 minutes are too hot to touch. I have the original schematic, as well as the manual, but have noticed some errors on the schem (or the circuit board, I don't know which). One thing that I have noticed on a lot of components (mostly xsistors) is odd voltage readings. There might be 5v on one side of a bias resistor, and 0.3v on the other (xsistor) side, but the xsistor checks out OK with a diode test (i.e., not leaky or shorted). Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Undoubtedly, the "black stuff" that you see on the leads is tarnish. It's not dangerous to the components, but if it's interfering with mating of component contacts, it will certainly prevent the circuit from operating correctly. This could be the problem with the opamps. There's something seriously out of whack if the opamps are too hot to touch.. Don't allow it to run for more than just a few seconds until you get it fixed.. the opamps will be destroyed, if they are not defective already. I can't tell a thing from your voltage measurements without seeing the schematic along with the voltages. It certainly would be a big help if you could scan the schematic and post it somewhere. Without it, it's pretty much a waste of time here. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
#11
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need help repairing old Heathkit weather computer
Yeah, your scope connection will be with the ground connection of the probe
going to power supply return (most likely connected to the case, but not always) and the probe tip to the circuit point you're monitoring. if you saw no ripple there, then the PS is probably OK. How long has this unit been out of commission? Is it possible that it a lightening strike or power surge may have caused its demise? If so, then it's possible that most, if not all, of the semiconductors in the unit are bad. If the sensors are outside, and close to a power line or phone line, then it's possible that may have been the cause of failure. It's going to be a bit difficult to diagnose it without a schematic to reference, but if you can adequately describe the circuits and their symptoms, then we may be able to get it going again. I searched all the usual places for freebie downloads, but no joy. + Cheers!!!!!!!!!!!!! -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... The PS voltages were the 1st thing I checked. They were pretty saggy, so I replaced the main filter caps. That helped, but didn't fix the problem, so I moved on to the regulators, and found that the -15v regulator was out of commission, so I replaced it. This improved matters somewhat, but there were still problems, so I kept poking, and found a shorted PNP on the CPU board, which I replaced. I have a scope, but am kind of new to it. I basically attached the ground clip to the case and probed the regulator's output, which showed no ripple (which seemed a little unrealistic to me). Is this the proper method for checking for ripple? As for the tarnish issue, I'm just going to check for continuity from the IC's pins to the connections on the solder side of the board. Thanks again, and keep those suggestions comin' "Tweetldee" wrote in message ... You don't need to worry about the tarnish on the soldered component leads.. just the socketed components, such as ICs and transistors. If there are any connectors that appear to be tarnished, then you should clean those as well. BTW, have you checked the power supply output(s) with your multimeter? If the supply voltages aren't correct, then you can't expect the rest of the circuit to operate properly. How abot ripple on the PS lines? If there's a lot of ripple, then there will be all sorts of chaos in the circuit. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... Thanks again. Unforunately, I don't think I can scan the schem (it's huge for one thing). As for the voltages, they don't match up with what's indicated on the schem in a lot of places (even when I had most of it working), so I don't know which to trust. I'll try removing the tarnish and checking for continuity though. Thanks "Tweetldee" wrote in message ... "tempus fugit" wrote in message ... Thanks tweet. The black stuff is actually on quite a few of the components - diode leads, resistors, ICs, etc. I never really looked too close at it, but it almost looks like black paint. The opamps are HOT. They start out cold, and after about 2 minutes are too hot to touch. I have the original schematic, as well as the manual, but have noticed some errors on the schem (or the circuit board, I don't know which). One thing that I have noticed on a lot of components (mostly xsistors) is odd voltage readings. There might be 5v on one side of a bias resistor, and 0.3v on the other (xsistor) side, but the xsistor checks out OK with a diode test (i.e., not leaky or shorted). Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Undoubtedly, the "black stuff" that you see on the leads is tarnish. It's not dangerous to the components, but if it's interfering with mating of component contacts, it will certainly prevent the circuit from operating correctly. This could be the problem with the opamps. There's something seriously out of whack if the opamps are too hot to touch.. Don't allow it to run for more than just a few seconds until you get it fixed.. the opamps will be destroyed, if they are not defective already. I can't tell a thing from your voltage measurements without seeing the schematic along with the voltages. It certainly would be a big help if you could scan the schematic and post it somewhere. Without it, it's pretty much a waste of time here. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
#12
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need help repairing old Heathkit weather computer
Once again, thanks for your reply.
I have no idea how long it has been dead. My brother in law got it for free (!) at a garage sale this summer, and was told that it was working. I was messing around with it again tonite, and I noticed a gross error. Remember I said I pulled a 4066 out because the voltage readings were way off from the schem? Well, it wasn't a 4066, it was a 4016, and (this is the embarrassing part) I had put it in backwards when I reinstalled it. Anyway, the good news is that (now that it is in the right way) the opamps are running at a normal temperature (slightly warm). I'm wondering though, if that part isn't screwed (the 4016) because when I say the voltages are off, I mean the wrong polarity as well as the wrong voltage. Maybe I'll pop a new one in and see what happens. Here's another thought: this thing was designed in the 70's, so maybe the CPU has a Y2K problem. I found a site that mentioned that the time was an issue because of this for this unit, but it didn't describe the symptoms I've got. "Tweetldee" wrote in message ... Yeah, your scope connection will be with the ground connection of the probe going to power supply return (most likely connected to the case, but not always) and the probe tip to the circuit point you're monitoring. if you saw no ripple there, then the PS is probably OK. How long has this unit been out of commission? Is it possible that it a lightening strike or power surge may have caused its demise? If so, then it's possible that most, if not all, of the semiconductors in the unit are bad. If the sensors are outside, and close to a power line or phone line, then it's possible that may have been the cause of failure. It's going to be a bit difficult to diagnose it without a schematic to reference, but if you can adequately describe the circuits and their symptoms, then we may be able to get it going again. I searched all the usual places for freebie downloads, but no joy. + Cheers!!!!!!!!!!!!! -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... The PS voltages were the 1st thing I checked. They were pretty saggy, so I replaced the main filter caps. That helped, but didn't fix the problem, so I moved on to the regulators, and found that the -15v regulator was out of commission, so I replaced it. This improved matters somewhat, but there were still problems, so I kept poking, and found a shorted PNP on the CPU board, which I replaced. I have a scope, but am kind of new to it. I basically attached the ground clip to the case and probed the regulator's output, which showed no ripple (which seemed a little unrealistic to me). Is this the proper method for checking for ripple? As for the tarnish issue, I'm just going to check for continuity from the IC's pins to the connections on the solder side of the board. Thanks again, and keep those suggestions comin' "Tweetldee" wrote in message ... You don't need to worry about the tarnish on the soldered component leads.. just the socketed components, such as ICs and transistors. If there are any connectors that appear to be tarnished, then you should clean those as well. BTW, have you checked the power supply output(s) with your multimeter? If the supply voltages aren't correct, then you can't expect the rest of the circuit to operate properly. How abot ripple on the PS lines? If there's a lot of ripple, then there will be all sorts of chaos in the circuit. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... Thanks again. Unforunately, I don't think I can scan the schem (it's huge for one thing). As for the voltages, they don't match up with what's indicated on the schem in a lot of places (even when I had most of it working), so I don't know which to trust. I'll try removing the tarnish and checking for continuity though. Thanks "Tweetldee" wrote in message ... "tempus fugit" wrote in message ... Thanks tweet. The black stuff is actually on quite a few of the components - diode leads, resistors, ICs, etc. I never really looked too close at it, but it almost looks like black paint. The opamps are HOT. They start out cold, and after about 2 minutes are too hot to touch. I have the original schematic, as well as the manual, but have noticed some errors on the schem (or the circuit board, I don't know which). One thing that I have noticed on a lot of components (mostly xsistors) is odd voltage readings. There might be 5v on one side of a bias resistor, and 0.3v on the other (xsistor) side, but the xsistor checks out OK with a diode test (i.e., not leaky or shorted). Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Undoubtedly, the "black stuff" that you see on the leads is tarnish. It's not dangerous to the components, but if it's interfering with mating of component contacts, it will certainly prevent the circuit from operating correctly. This could be the problem with the opamps. There's something seriously out of whack if the opamps are too hot to touch.. Don't allow it to run for more than just a few seconds until you get it fixed.. the opamps will be destroyed, if they are not defective already. I can't tell a thing from your voltage measurements without seeing the schematic along with the voltages. It certainly would be a big help if you could scan the schematic and post it somewhere. Without it, it's pretty much a waste of time here. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
#13
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need help repairing old Heathkit weather computer
Here's another thought: this thing was designed in the 70's, so maybe the CPU has a Y2K problem. I found a site that mentioned that the time was an issue because of this for this unit, but it didn't describe the symptoms I've got. Does it keep track of the date? If not then obviously it doesn't have a Y2K problem, even if it did, the worst it would do is roll over to 1901, highly unlikely that it keeps track of the year beyond 2 digits. |
#14
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need help repairing old Heathkit weather computer
If you plugged the 4016 in backwards, then it's probably damaged.. replace
it for sure. The 4066 can be used in place of the 4016, with better performance in some applications. As I said in an earier post, opamps usually don't run hot, or even warm. If a new 4016 doesn't fix your problem, you might replace those opamps and see how it works. Does the unit keep track of time and date? If yes, then you may have a Y2K issue with the date display, but I doubt that could be causing your operational problem. Worst case, the date would be wrong, probably jumping back somewhere in the 1900's. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... Once again, thanks for your reply. I have no idea how long it has been dead. My brother in law got it for free (!) at a garage sale this summer, and was told that it was working. I was messing around with it again tonite, and I noticed a gross error. Remember I said I pulled a 4066 out because the voltage readings were way off from the schem? Well, it wasn't a 4066, it was a 4016, and (this is the embarrassing part) I had put it in backwards when I reinstalled it. Anyway, the good news is that (now that it is in the right way) the opamps are running at a normal temperature (slightly warm). I'm wondering though, if that part isn't screwed (the 4016) because when I say the voltages are off, I mean the wrong polarity as well as the wrong voltage. Maybe I'll pop a new one in and see what happens. Here's another thought: this thing was designed in the 70's, so maybe the CPU has a Y2K problem. I found a site that mentioned that the time was an issue because of this for this unit, but it didn't describe the symptoms I've got. "Tweetldee" wrote in message ... Yeah, your scope connection will be with the ground connection of the probe going to power supply return (most likely connected to the case, but not always) and the probe tip to the circuit point you're monitoring. if you saw no ripple there, then the PS is probably OK. How long has this unit been out of commission? Is it possible that it a lightening strike or power surge may have caused its demise? If so, then it's possible that most, if not all, of the semiconductors in the unit are bad. If the sensors are outside, and close to a power line or phone line, then it's possible that may have been the cause of failure. It's going to be a bit difficult to diagnose it without a schematic to reference, but if you can adequately describe the circuits and their symptoms, then we may be able to get it going again. I searched all the usual places for freebie downloads, but no joy. + Cheers!!!!!!!!!!!!! -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... The PS voltages were the 1st thing I checked. They were pretty saggy, so I replaced the main filter caps. That helped, but didn't fix the problem, so I moved on to the regulators, and found that the -15v regulator was out of commission, so I replaced it. This improved matters somewhat, but there were still problems, so I kept poking, and found a shorted PNP on the CPU board, which I replaced. I have a scope, but am kind of new to it. I basically attached the ground clip to the case and probed the regulator's output, which showed no ripple (which seemed a little unrealistic to me). Is this the proper method for checking for ripple? As for the tarnish issue, I'm just going to check for continuity from the IC's pins to the connections on the solder side of the board. Thanks again, and keep those suggestions comin' "Tweetldee" wrote in message ... You don't need to worry about the tarnish on the soldered component leads.. just the socketed components, such as ICs and transistors. If there are any connectors that appear to be tarnished, then you should clean those as well. BTW, have you checked the power supply output(s) with your multimeter? If the supply voltages aren't correct, then you can't expect the rest of the circuit to operate properly. How abot ripple on the PS lines? If there's a lot of ripple, then there will be all sorts of chaos in the circuit. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... Thanks again. Unforunately, I don't think I can scan the schem (it's huge for one thing). As for the voltages, they don't match up with what's indicated on the schem in a lot of places (even when I had most of it working), so I don't know which to trust. I'll try removing the tarnish and checking for continuity though. Thanks "Tweetldee" wrote in message ... "tempus fugit" wrote in message ... Thanks tweet. The black stuff is actually on quite a few of the components - diode leads, resistors, ICs, etc. I never really looked too close at it, but it almost looks like black paint. The opamps are HOT. They start out cold, and after about 2 minutes are too hot to touch. I have the original schematic, as well as the manual, but have noticed some errors on the schem (or the circuit board, I don't know which). One thing that I have noticed on a lot of components (mostly xsistors) is odd voltage readings. There might be 5v on one side of a bias resistor, and 0.3v on the other (xsistor) side, but the xsistor checks out OK with a diode test (i.e., not leaky or shorted). Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Undoubtedly, the "black stuff" that you see on the leads is tarnish. It's not dangerous to the components, but if it's interfering with mating of component contacts, it will certainly prevent the circuit from operating correctly. This could be the problem with the opamps. There's something seriously out of whack if the opamps are too hot to touch.. Don't allow it to run for more than just a few seconds until you get it fixed.. the opamps will be destroyed, if they are not defective already. I can't tell a thing from your voltage measurements without seeing the schematic along with the voltages. It certainly would be a big help if you could scan the schematic and post it somewhere. Without it, it's pretty much a waste of time here. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
#15
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need help repairing old Heathkit weather computer
Yea, it does keep track of the time and date, but I can't actually set these
parameters. Maybe I'll try replacing the ICs and go from there. The opamps are LM324s. I've got a spare TL074 around - do you think this would be an OK replacement, or should I replace them with the originals? Thanks again "Tweetldee" wrote in message ... If you plugged the 4016 in backwards, then it's probably damaged.. replace it for sure. The 4066 can be used in place of the 4016, with better performance in some applications. As I said in an earier post, opamps usually don't run hot, or even warm. If a new 4016 doesn't fix your problem, you might replace those opamps and see how it works. Does the unit keep track of time and date? If yes, then you may have a Y2K issue with the date display, but I doubt that could be causing your operational problem. Worst case, the date would be wrong, probably jumping back somewhere in the 1900's. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... Once again, thanks for your reply. I have no idea how long it has been dead. My brother in law got it for free (!) at a garage sale this summer, and was told that it was working. I was messing around with it again tonite, and I noticed a gross error. Remember I said I pulled a 4066 out because the voltage readings were way off from the schem? Well, it wasn't a 4066, it was a 4016, and (this is the embarrassing part) I had put it in backwards when I reinstalled it. Anyway, the good news is that (now that it is in the right way) the opamps are running at a normal temperature (slightly warm). I'm wondering though, if that part isn't screwed (the 4016) because when I say the voltages are off, I mean the wrong polarity as well as the wrong voltage. Maybe I'll pop a new one in and see what happens. Here's another thought: this thing was designed in the 70's, so maybe the CPU has a Y2K problem. I found a site that mentioned that the time was an issue because of this for this unit, but it didn't describe the symptoms I've got. "Tweetldee" wrote in message ... Yeah, your scope connection will be with the ground connection of the probe going to power supply return (most likely connected to the case, but not always) and the probe tip to the circuit point you're monitoring. if you saw no ripple there, then the PS is probably OK. How long has this unit been out of commission? Is it possible that it a lightening strike or power surge may have caused its demise? If so, then it's possible that most, if not all, of the semiconductors in the unit are bad. If the sensors are outside, and close to a power line or phone line, then it's possible that may have been the cause of failure. It's going to be a bit difficult to diagnose it without a schematic to reference, but if you can adequately describe the circuits and their symptoms, then we may be able to get it going again. I searched all the usual places for freebie downloads, but no joy. + Cheers!!!!!!!!!!!!! -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... The PS voltages were the 1st thing I checked. They were pretty saggy, so I replaced the main filter caps. That helped, but didn't fix the problem, so I moved on to the regulators, and found that the -15v regulator was out of commission, so I replaced it. This improved matters somewhat, but there were still problems, so I kept poking, and found a shorted PNP on the CPU board, which I replaced. I have a scope, but am kind of new to it. I basically attached the ground clip to the case and probed the regulator's output, which showed no ripple (which seemed a little unrealistic to me). Is this the proper method for checking for ripple? As for the tarnish issue, I'm just going to check for continuity from the IC's pins to the connections on the solder side of the board. Thanks again, and keep those suggestions comin' "Tweetldee" wrote in message ... You don't need to worry about the tarnish on the soldered component leads.. just the socketed components, such as ICs and transistors. If there are any connectors that appear to be tarnished, then you should clean those as well. BTW, have you checked the power supply output(s) with your multimeter? If the supply voltages aren't correct, then you can't expect the rest of the circuit to operate properly. How abot ripple on the PS lines? If there's a lot of ripple, then there will be all sorts of chaos in the circuit. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... Thanks again. Unforunately, I don't think I can scan the schem (it's huge for one thing). As for the voltages, they don't match up with what's indicated on the schem in a lot of places (even when I had most of it working), so I don't know which to trust. I'll try removing the tarnish and checking for continuity though. Thanks "Tweetldee" wrote in message ... "tempus fugit" wrote in message ... Thanks tweet. The black stuff is actually on quite a few of the components - diode leads, resistors, ICs, etc. I never really looked too close at it, but it almost looks like black paint. The opamps are HOT. They start out cold, and after about 2 minutes are too hot to touch. I have the original schematic, as well as the manual, but have noticed some errors on the schem (or the circuit board, I don't know which). One thing that I have noticed on a lot of components (mostly xsistors) is odd voltage readings. There might be 5v on one side of a bias resistor, and 0.3v on the other (xsistor) side, but the xsistor checks out OK with a diode test (i.e., not leaky or shorted). Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Undoubtedly, the "black stuff" that you see on the leads is tarnish. It's not dangerous to the components, but if it's interfering with mating of component contacts, it will certainly prevent the circuit from operating correctly. This could be the problem with the opamps. There's something seriously out of whack if the opamps are too hot to touch.. Don't allow it to run for more than just a few seconds until you get it fixed.. the opamps will be destroyed, if they are not defective already. I can't tell a thing from your voltage measurements without seeing the schematic along with the voltages. It certainly would be a big help if you could scan the schematic and post it somewhere. Without it, it's pretty much a waste of time here. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
#16
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need help repairing old Heathkit weather computer
Without seeing the schematic, it's a hard call as to whether the TL074 would
be a good replacement. I haven't looked at the spec sheets of either unit, but I do know the the TL074 is a JFET input amps, whereas the LM324 is not. I assume the pinout is the same.. you will need to check that out. Probably wouldn't hurt anything to try the substitution, but couldn't guarantee they would work. Is the CPU in the unit a programmed chip or does it have a PROM/EPROM/EEPROM to store the code? If it's a programmed CPU, then you might surf around on Google to see if there are any replacements available. The switches that are used to set the time/date, etc, may be tarnished and not making contact. Check all of the switches for good, solid (not intermittent) low-resistance contact. But, going back to the original problem, I would continue to look at the areas that may be affected by the tarnishing of the contacts on IC's, transistors, or any other components that may be socketed. Also, you should look for components that are loose. Sometimes, the plating on the leads of components comes off, and effectively breaks the connection. If there are any suspect soldered connections like that, then do the obvious and resolder them. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... Yea, it does keep track of the time and date, but I can't actually set these parameters. Maybe I'll try replacing the ICs and go from there. The opamps are LM324s. I've got a spare TL074 around - do you think this would be an OK replacement, or should I replace them with the originals? Thanks again "Tweetldee" wrote in message ... If you plugged the 4016 in backwards, then it's probably damaged.. replace it for sure. The 4066 can be used in place of the 4016, with better performance in some applications. As I said in an earier post, opamps usually don't run hot, or even warm. If a new 4016 doesn't fix your problem, you might replace those opamps and see how it works. Does the unit keep track of time and date? If yes, then you may have a Y2K issue with the date display, but I doubt that could be causing your operational problem. Worst case, the date would be wrong, probably jumping back somewhere in the 1900's. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... Once again, thanks for your reply. I have no idea how long it has been dead. My brother in law got it for free (!) at a garage sale this summer, and was told that it was working. I was messing around with it again tonite, and I noticed a gross error. Remember I said I pulled a 4066 out because the voltage readings were way off from the schem? Well, it wasn't a 4066, it was a 4016, and (this is the embarrassing part) I had put it in backwards when I reinstalled it. Anyway, the good news is that (now that it is in the right way) the opamps are running at a normal temperature (slightly warm). I'm wondering though, if that part isn't screwed (the 4016) because when I say the voltages are off, I mean the wrong polarity as well as the wrong voltage. Maybe I'll pop a new one in and see what happens. Here's another thought: this thing was designed in the 70's, so maybe the CPU has a Y2K problem. I found a site that mentioned that the time was an issue because of this for this unit, but it didn't describe the symptoms I've got. "Tweetldee" wrote in message ... Yeah, your scope connection will be with the ground connection of the probe going to power supply return (most likely connected to the case, but not always) and the probe tip to the circuit point you're monitoring. if you saw no ripple there, then the PS is probably OK. How long has this unit been out of commission? Is it possible that it a lightening strike or power surge may have caused its demise? If so, then it's possible that most, if not all, of the semiconductors in the unit are bad. If the sensors are outside, and close to a power line or phone line, then it's possible that may have been the cause of failure. It's going to be a bit difficult to diagnose it without a schematic to reference, but if you can adequately describe the circuits and their symptoms, then we may be able to get it going again. I searched all the usual places for freebie downloads, but no joy. + Cheers!!!!!!!!!!!!! -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... The PS voltages were the 1st thing I checked. They were pretty saggy, so I replaced the main filter caps. That helped, but didn't fix the problem, so I moved on to the regulators, and found that the -15v regulator was out of commission, so I replaced it. This improved matters somewhat, but there were still problems, so I kept poking, and found a shorted PNP on the CPU board, which I replaced. I have a scope, but am kind of new to it. I basically attached the ground clip to the case and probed the regulator's output, which showed no ripple (which seemed a little unrealistic to me). Is this the proper method for checking for ripple? As for the tarnish issue, I'm just going to check for continuity from the IC's pins to the connections on the solder side of the board. Thanks again, and keep those suggestions comin' "Tweetldee" wrote in message ... You don't need to worry about the tarnish on the soldered component leads.. just the socketed components, such as ICs and transistors. If there are any connectors that appear to be tarnished, then you should clean those as well. BTW, have you checked the power supply output(s) with your multimeter? If the supply voltages aren't correct, then you can't expect the rest of the circuit to operate properly. How abot ripple on the PS lines? If there's a lot of ripple, then there will be all sorts of chaos in the circuit. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! "tempus fugit" wrote in message ... Thanks again. Unforunately, I don't think I can scan the schem (it's huge for one thing). As for the voltages, they don't match up with what's indicated on the schem in a lot of places (even when I had most of it working), so I don't know which to trust. I'll try removing the tarnish and checking for continuity though. Thanks "Tweetldee" wrote in message ... "tempus fugit" wrote in message ... Thanks tweet. The black stuff is actually on quite a few of the components - diode leads, resistors, ICs, etc. I never really looked too close at it, but it almost looks like black paint. The opamps are HOT. They start out cold, and after about 2 minutes are too hot to touch. I have the original schematic, as well as the manual, but have noticed some errors on the schem (or the circuit board, I don't know which). One thing that I have noticed on a lot of components (mostly xsistors) is odd voltage readings. There might be 5v on one side of a bias resistor, and 0.3v on the other (xsistor) side, but the xsistor checks out OK with a diode test (i.e., not leaky or shorted). Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Undoubtedly, the "black stuff" that you see on the leads is tarnish. It's not dangerous to the components, but if it's interfering with mating of component contacts, it will certainly prevent the circuit from operating correctly. This could be the problem with the opamps. There's something seriously out of whack if the opamps are too hot to touch.. Don't allow it to run for more than just a few seconds until you get it fixed.. the opamps will be destroyed, if they are not defective already. I can't tell a thing from your voltage measurements without seeing the schematic along with the voltages. It certainly would be a big help if you could scan the schematic and post it somewhere. Without it, it's pretty much a waste of time here. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
#17
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need help repairing old Heathkit weather computer
tempus fugit wrote:
The PS voltages were the 1st thing I checked. They should be _first_! :-) They were pretty saggy, so I replaced the main filter caps. That helped, but didn't fix the problem, so I moved on to the regulators, and found that the -15v regulator was out of commission, so I replaced it. This improved matters somewhat, but there were still problems, so I kept poking, and found a shorted PNP on the CPU board, which I replaced. I have a scope, but am kind of new to it. I basically attached the ground clip to the case and probed the regulator's output, which showed no ripple (which seemed a little unrealistic to me). Not unrealistic at all, if the lowest point of voltage in the ripple at the input to the regulator is above what the regulator wants to see as minimum, you won't see any on the regulator output at all. This can be the case even when there's several volts of ripple on the input side. |
#18
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need help repairing old Heathkit weather computer
tempus fugit wrote:
Once again, thanks for your reply. I have no idea how long it has been dead. My brother in law got it for free (!) at a garage sale this summer, and was told that it was working. I was messing around with it again tonite, and I noticed a gross error. Remember I said I pulled a 4066 out because the voltage readings were way off from the schem? Well, it wasn't a 4066, it was a 4016, Pretty near the same part (different spec for "on" resistance is most of it as I recall). and (this is the embarrassing part) I had put it in backwards when I reinstalled it. Ouch. I hate it when that happens... :-) Anyway, the good news is that (now that it is in the right way) It still not be any good, though. Reverse power to a CMOS part like that can result in fairly high current, since the power pins are then looking at what amounts to a forward-biased diode. That thing may be cooked. But they're cheap. the opamps are running at a normal temperature (slightly warm). I'm wondering though, if that part isn't screwed (the 4016) because when I say the voltages are off, I mean the wrong polarity as well as the wrong voltage. Maybe I'll pop a new one in and see what happens. There ya go. Here's another thought: this thing was designed in the 70's, so maybe the CPU has a Y2K problem. I found a site that mentioned that the time was an issue because of this for this unit, but it didn't describe the symptoms I've got. What would that thing do with a date? |
#19
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need help repairing old Heathkit weather computer
Hey Tweetldee;
I don't know if I mentioned in my OP, but the 1st thing that was wrong was a defective -15v regulator. I'm wondering if all the ICs that needed +/-15v got damaged (these would be the 4016, 324, and a couple 1458s). The voltages around these seem OK though, and there are no direct shorts. Maybe I'll try replacing them and see what happens. They're cheap, so it will only end up costing a couple bucks. "Tweetldee" wrote in message ... "tempus fugit" wrote in message ... Hey all; I'm working on repairing a Heath weather computer. Initially, none of the funcitons really worked (temp, pressure, clock, etc.) I got it to the point last night where everything was working except the clock, which kept time, but I couldn't actually set it. So, I (stupidly?) poked around a little more to try to get the clock going. I noticed a 4066 with some black stuff on the pins, and some weird voltages around it, so I pulled it out, fired the unit up, and checked the voltages again. They were still weird, but when I put it back in and turned it on again, the pressure and temperature stayed at 0. I was messing around with it again tonite, and the pressure and temperature readings were more normal, but I noticed a couple of opamps (in different locations) that were hot to the touch. There were no shorts in either of them, and the voltages around them pretty much matched the schematic. I now get bad readings in the temperature (-40) and pressure (0). I'm guessing the opamps are at least part of the problem. Any idea why they are getting so hot? Any other suggestions? Thanks From your description, I'd guess that your problem is intermittent, and may be easily repairable. When you say that there is "black stuff" on the pins of the 4066, is it just tarnish or something else? If it's tarnish, then that could be the majority of your problems. I assume that the ICs are socketed. If so, you can use any of a few methods to clean the tarnish off the pins. The quickest is Tarn-X, but you have to rinse them very well afterwards with clean water. Don't leave *any* Tarn-X residue on the pins, since it is corrosive. Another cleaning method is with a rubber pencil eraser. Be careful with this, since it is easy to bend/break the pins. What condition are the IC sockets in? They may need to be cleaned or replaced if they are in bad condition. How hot are the opamps? Are they just warm or really hot? If they're just warm, it may be normal, depending on the circuit. Opamps usually are low-level components... that is, they don't handle any appreciable power, and usually run pretty cool. Is the schematic of the unit available on the web anywhere, or can you post it to the binaries NG? Might help with some suggestions to help you. -- Tweetldee Tweetldee at att dot net (Just subsitute the appropriate characters in the address) Never take a laxative and a sleeping pill at the same time!! |
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need help repairing old Heathkit weather computer
tempus fugit wrote:
Hey Tweetldee; I don't know if I mentioned in my OP, but the 1st thing that was wrong was a defective -15v regulator. I'm wondering if all the ICs that needed +/-15v got damaged (these would be the 4016, 324, and a couple 1458s). The voltages around these seem OK though, and there are no direct shorts. Maybe I'll try replacing them and see what happens. They're cheap, so it will only end up costing a couple bucks. Those 40xx CMOS parts don't do real well with over-voltage on the supply lines... See if any of them are at all warm to the touch -- if so, then _those_ are the ones that need to be replaced. |
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