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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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LCD Monitor problem
I picked up a used Micron AP150T at our town's recycling center. It cost
me nothing, so there is no loss if I can't figure out what's wrong. When I hook it up to a computer, all works just fine. Then the picture starts tearing horizontally after a few moments of on time. When I hit the Function key, the function block pops up and looks perfectly fine while the picture behind it is tearing. So I assume that the sync signal from the computer is somehow being lost. It does the same with two different computers, so the computer output is not the problem; the computer outputs are fine with other monitors. Any ideas? Is there a know problem with this unit syncing to the VGA signal? Al |
#2
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LCD Monitor problem
On Sunday 04 May 2008 19:21, Al wrote:
I picked up a used Micron AP150T at our town's recycling center. It cost me nothing, so there is no loss if I can't figure out what's wrong. When I hook it up to a computer, all works just fine. Then the picture starts tearing horizontally after a few moments of on time. When I hit the Function key, the function block pops up and looks perfectly fine while the picture behind it is tearing. So I assume that the sync signal from the computer is somehow being lost. It does the same with two different computers, so the computer output is not the problem; the computer outputs are fine with other monitors. Any ideas? Is there a know problem with this unit syncing to the VGA signal? Al Does it always happen after the same time period? Also when you don't allow time to cool down? Perhaps it's simply a connection somewhere which gets interrupted when the monitor warms up. Do you have a scope? If so, you could track the input sync signals in the circuit, and find out where it gets mixed up. If all VGA signal enters the ADC correctly, then the fault will be a bit more difficult to find... |
#3
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LCD Monitor problem
"Al" wrote in message news:jgmTj.13391$qW.835@trnddc06... I picked up a used Micron AP150T at our town's recycling center. It cost me nothing, so there is no loss if I can't figure out what's wrong. When I hook it up to a computer, all works just fine. Then the picture starts tearing horizontally after a few moments of on time. When I hit the Function key, the function block pops up and looks perfectly fine while the picture behind it is tearing. So I assume that the sync signal from the computer is somehow being lost. It does the same with two different computers, so the computer output is not the problem; the computer outputs are fine with other monitors. Any ideas? Is there a know problem with this unit syncing to the VGA signal? Al Bad electrolytic capacitors are fairly common and can cause any number of strange symptoms. That's where I'd look first, the surface mount sort used in flat panels tend to be especially troublesome. |
#4
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LCD Monitor problem
On Sun, 04 May 2008 20:09:03 +0200, Wiebe Cazemier wrote:
On Sunday 04 May 2008 19:21, Al wrote: I picked up a used Micron AP150T at our town's recycling center. It cost me nothing, so there is no loss if I can't figure out what's wrong. snip Does it always happen after the same time period? Also when you don't allow time to cool down? Perhaps it's simply a connection somewhere which gets interrupted when the monitor warms up. Do you have a scope? If so, you could track the input sync signals in the circuit, and find out where it gets mixed up. If all VGA signal enters the ADC correctly, then the fault will be a bit more difficult to find... OK, I'll do the check with the 'scope. And the time of the start of the tearing does vary with the interval between startups; something must be temperature sensitive. Al |
#5
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LCD Monitor problem
On Sunday 04 May 2008 23:27, Al wrote:
OK, I'll do the check with the 'scope. And the time of the start of the tearing does vary with the interval between startups; something must be temperature sensitive. That does not rule out capacitor based problems. I've repaired several mainboards which had leaky capacitors, which worked fine as soon as they were warm. It's the opposite to what you're experiencing, but it illustrates that caps are temperature senstive. |
#6
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LCD Monitor problem
On May 4, 3:42*pm, Wiebe Cazemier wrote:
On Sunday 04 May 2008 23:27, Al wrote: OK, I'll do the check with the 'scope. And the time of the start of the tearing does vary with the interval between startups; something must be temperature sensitive. That does not rule out capacitor based problems. I've repaired several mainboards which had leaky capacitors, which worked fine as soon as they were warm. It's the opposite to what you're experiencing, but it illustrates that caps are temperature senstive. If this is a crt monitor, there could be a high-voltage arc that is not high enough to be seen or heard, but is generating "noise" that is being picked up by some other circuit. A scope would be invaluable. |
#7
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LCD Monitor problem
"Wiebe Cazemier" wrote in message b.home.nl... On Sunday 04 May 2008 23:27, Al wrote: OK, I'll do the check with the 'scope. And the time of the start of the tearing does vary with the interval between startups; something must be temperature sensitive. That does not rule out capacitor based problems. I've repaired several mainboards which had leaky capacitors, which worked fine as soon as they were warm. It's the opposite to what you're experiencing, but it illustrates that caps are temperature senstive. Capacitors are very temperature sensitive, more so than any other part I can think of, aside from those meant to react to temperature. |
#8
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LCD Monitor problem
On Monday 05 May 2008 03:00, hr(bob) wrote:
If this is a crt monitor, there could be a high-voltage arc that is not high enough to be seen or heard, but is generating "noise" that is being picked up by some other circuit. A scope would be invaluable. Judging by the subject, I would say it is not a CRT |
#9
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LCD Monitor problem
On Sun, 04 May 2008 19:49:14 GMT, "James Sweet"
wrote: "Al" wrote in message news:jgmTj.13391$qW.835@trnddc06... I picked up a used Micron AP150T at our town's recycling center. It cost me nothing, so there is no loss if I can't figure out what's wrong. When I hook it up to a computer, all works just fine. Then the picture starts tearing horizontally after a few moments of on time. When I hit the Function key, the function block pops up and looks perfectly fine while the picture behind it is tearing. So I assume that the sync signal from the computer is somehow being lost. It does the same with two different computers, so the computer output is not the problem; the computer outputs are fine with other monitors. Any ideas? Is there a know problem with this unit syncing to the VGA signal? Al Bad electrolytic capacitors are fairly common and can cause any number of strange symptoms. That's where I'd look first, the surface mount sort used in flat panels tend to be especially troublesome. I second this. About 90% of the bad LCD monitors I see can be fixed with new caps. Don't forget about the surface mount electrolytics on the main board. I just fixed a Viewsonic that needed to have every single cap on the main board replaced. Andy Cuffe |
#10
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LCD Monitor problem
On Mon, 05 May 2008 11:23:13 -0500, Andy Cuffe wrote:
On Sun, 04 May 2008 19:49:14 GMT, "James Sweet" wrote: "Al" wrote in message news:jgmTj.13391$qW.835@trnddc06... I picked up a used Micron AP150T at our town's recycling center. It cost me nothing, so there is no loss if I can't figure out what's wrong. When I hook it up to a computer, all works just fine. Then the picture starts tearing horizontally after a few moments of on time. When I hit the Function key, the function block pops up and looks perfectly fine while the picture behind it is tearing. So I assume that the sync signal from the computer is somehow being lost. It does the same with two different computers, so the computer output is not the problem; the computer outputs are fine with other monitors. Any ideas? Is there a know problem with this unit syncing to the VGA signal? Al Bad electrolytic capacitors are fairly common and can cause any number of strange symptoms. That's where I'd look first, the surface mount sort used in flat panels tend to be especially troublesome. I second this. About 90% of the bad LCD monitors I see can be fixed with new caps. Don't forget about the surface mount electrolytics on the main board. I just fixed a Viewsonic that needed to have every single cap on the main board replaced. Andy Cuffe The display generated internally is just fine. Only the externally input display tears. So it can't be "every single cap." I imagine it is something in the sync input. I'll be checking it out. And like I said, it is a "saved" monitor. If a quick fix won't do it, back to the dump. Al Al |
#11
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LCD Monitor problem
The display generated internally is just fine. Only the externally input display tears. So it can't be "every single cap." I imagine it is something in the sync input. I'll be checking it out. And like I said, it is a "saved" monitor. If a quick fix won't do it, back to the dump. Al Sure it could, may only be one or two that are bad enough to cause a malfunction, but it's worth checking the rest. Usually when one of these surface mount capacitors is bad, the rest are nearly shot too. I usually replace them all, then the thing is good for years. In a pinch, one can check the ESR of all of them and replace those that check bad. There's usually only a dozen or so. |
#12
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LCD Monitor problem
"James Sweet" wrote in message news:w2ITj.5088$ch1.1375@trndny09... The display generated internally is just fine. Only the externally input display tears. So it can't be "every single cap." I imagine it is something in the sync input. I'll be checking it out. And like I said, it is a "saved" monitor. If a quick fix won't do it, back to the dump. Al Sure it could, may only be one or two that are bad enough to cause a malfunction, but it's worth checking the rest. Usually when one of these surface mount capacitors is bad, the rest are nearly shot too. I usually replace them all, then the thing is good for years. In a pinch, one can check the ESR of all of them and replace those that check bad. There's usually only a dozen or so. Agreed, but be aware that the ESR values of surface mount electros tends to be somewhat higher than those of a similar value in 'conventional' leaded format, so a cap that you are expecting to read say 1 ohm, may correctly read several ohms in surface mount. Arfa |
#13
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LCD Monitor problem
James Sweet wrote:
Usually when one of these surface mount capacitors is bad, the rest are nearly shot too. I usually replace them all, then the thing is good for years. I'd be interested to know what makes you so sure that the caps you bought for replacement are of superior longevity compared to those the manufacturer did put in :-). Regards, H. |
#14
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LCD Monitor problem
On Tuesday 06 May 2008 11:05, Heinz Schmitz wrote:
I'd be interested to know what makes you so sure that the caps you bought for replacement are of superior longevity compared to those the manufacturer did put in :-). Regards, H. Well, I guess by now that is over, but in the past, the market was flooded with bad electrolytes. Some manufacturer copied a formula from another manufacturer, but it contained a deliberate mistake to foul anyone who might want to steal it. The result was that a lot of electronic equipment contained these bad caps. Mainboard from around 2000 are very suspect for example. The most likely cause form any mainboard from that period which has become unstable, is the caps. But the problem wasn't limited to computers. Even airplane electronics contained them... |
#15
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LCD Monitor problem
On Mon, 05 May 2008 17:57:38 GMT, Al wrote:
The display generated internally is just fine. Only the externally input display tears. So it can't be "every single cap." I imagine it is something in the sync input. I'll be checking it out. And like I said, it is a "saved" monitor. If a quick fix won't do it, back to the dump. Al Al It's not unusual for bad caps to only affect the video from the computer, leaving the OSD looking fine. Andy Cuffe |
#16
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LCD Monitor problem
"Heinz Schmitz" wrote in message ... James Sweet wrote: Usually when one of these surface mount capacitors is bad, the rest are nearly shot too. I usually replace them all, then the thing is good for years. I'd be interested to know what makes you so sure that the caps you bought for replacement are of superior longevity compared to those the manufacturer did put in :-). Regards, H. Well for starters they don't have several years of use on them. All else being equal, they're probably not. I hate surface mount lytics. |
#17
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LCD Monitor problem
"James Sweet" wrote in message news:3P%Tj.19807$aA1.15676@trnddc05... "Heinz Schmitz" wrote in message ... James Sweet wrote: Usually when one of these surface mount capacitors is bad, the rest are nearly shot too. I usually replace them all, then the thing is good for years. I'd be interested to know what makes you so sure that the caps you bought for replacement are of superior longevity compared to those the manufacturer did put in :-). Regards, H. Well for starters they don't have several years of use on them. All else being equal, they're probably not. I hate surface mount lytics. I replace them with regular through hole caps. It usually works without any problems. Just bend over the leads and solder them to the lands on the board. The biggest reason I do this is I can`t get smd stuff locally but can get almost any value through hole cap. Mike |
#18
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LCD Monitor problem
"Michael Kennedy" wrote in message ... "James Sweet" wrote in message news:3P%Tj.19807$aA1.15676@trnddc05... "Heinz Schmitz" wrote in message ... James Sweet wrote: Usually when one of these surface mount capacitors is bad, the rest are nearly shot too. I usually replace them all, then the thing is good for years. I'd be interested to know what makes you so sure that the caps you bought for replacement are of superior longevity compared to those the manufacturer did put in :-). Regards, H. Well for starters they don't have several years of use on them. All else being equal, they're probably not. I hate surface mount lytics. I replace them with regular through hole caps. It usually works without any problems. Just bend over the leads and solder them to the lands on the board. The biggest reason I do this is I can`t get smd stuff locally but can get almost any value through hole cap. Mike That's interesting. On some Sony servo boards fitted to many of their CD players a few years back, there were three sm electros along one edge of the board, which used to go faulty, and occasionally leak. This gave the symptom of either totally refusing to play, or very poor playability. If you tried to sub regular electros for them, the board would never work again, even if it worked, allbeit poorly, before. However, fit the correct sm types, and it would immediately work again to full original spec. Arfa |
#19
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LCD Monitor problem
That's interesting. On some Sony servo boards fitted to many of their CD players a few years back, there were three sm electros along one edge of the board, which used to go faulty, and occasionally leak. This gave the symptom of either totally refusing to play, or very poor playability. If you tried to sub regular electros for them, the board would never work again, even if it worked, allbeit poorly, before. However, fit the correct sm types, and it would immediately work again to full original spec. Arfa Sony has a history of building things which are very particular about the components used. I've had issues with some of the TVs not working with subs that were fine in everything else. |
#20
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LCD Monitor problem
"Arfa Daily" wrote in message ... "Michael Kennedy" wrote in message ... "James Sweet" wrote in message news:3P%Tj.19807$aA1.15676@trnddc05... "Heinz Schmitz" wrote in message ... James Sweet wrote: Usually when one of these surface mount capacitors is bad, the rest are nearly shot too. I usually replace them all, then the thing is good for years. I'd be interested to know what makes you so sure that the caps you bought for replacement are of superior longevity compared to those the manufacturer did put in :-). Regards, H. Well for starters they don't have several years of use on them. All else being equal, they're probably not. I hate surface mount lytics. I replace them with regular through hole caps. It usually works without any problems. Just bend over the leads and solder them to the lands on the board. The biggest reason I do this is I can`t get smd stuff locally but can get almost any value through hole cap. Mike That's interesting. On some Sony servo boards fitted to many of their CD players a few years back, there were three sm electros along one edge of the board, which used to go faulty, and occasionally leak. This gave the symptom of either totally refusing to play, or very poor playability. If you tried to sub regular electros for them, the board would never work again, even if it worked, allbeit poorly, before. However, fit the correct sm types, and it would immediately work again to full original spec. Arfa Well I haven`t worked on nearly as much equipment as you have so, I`m sure that there are plenty of things that you know that I dont. ;-) I am just a novice and just mess around with stuff of mine that breaks or stuff I get for free. Mike |
#21
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LCD Monitor problem
"Michael Kennedy" wrote in message ... "Arfa Daily" wrote in message ... "Michael Kennedy" wrote in message ... "James Sweet" wrote in message news:3P%Tj.19807$aA1.15676@trnddc05... "Heinz Schmitz" wrote in message ... James Sweet wrote: Usually when one of these surface mount capacitors is bad, the rest are nearly shot too. I usually replace them all, then the thing is good for years. I'd be interested to know what makes you so sure that the caps you bought for replacement are of superior longevity compared to those the manufacturer did put in :-). Regards, H. Well for starters they don't have several years of use on them. All else being equal, they're probably not. I hate surface mount lytics. I replace them with regular through hole caps. It usually works without any problems. Just bend over the leads and solder them to the lands on the board. The biggest reason I do this is I can`t get smd stuff locally but can get almost any value through hole cap. Mike That's interesting. On some Sony servo boards fitted to many of their CD players a few years back, there were three sm electros along one edge of the board, which used to go faulty, and occasionally leak. This gave the symptom of either totally refusing to play, or very poor playability. If you tried to sub regular electros for them, the board would never work again, even if it worked, allbeit poorly, before. However, fit the correct sm types, and it would immediately work again to full original spec. Arfa Well I haven`t worked on nearly as much equipment as you have so, I`m sure that there are plenty of things that you know that I dont. ;-) I am just a novice and just mess around with stuff of mine that breaks or stuff I get for free. Mike Well, if ever you get one of those Sony players - and there was lots of 'em that used variations of the same board, mounted directly to the underside of the deck - if it 'feels' like you've got a bad laser, look to see if it's got those three caps along the edge of the board. If it has, you better start looking for a supplier ... !! I never have figured out why 'standard' electros won't work in that position. Like you, I have subbed leaded for sm's in other places, without problem. About the only difference that I've found is that the leaded types tend to have a lower ESR than the sm's, which under normal circumstances, you'd say was a good thing. Arfa |
#22
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LCD Monitor problem
On Friday 09 May 2008 10:07, Arfa Daily wrote:
Well, if ever you get one of those Sony players - and there was lots of 'em that used variations of the same board, mounted directly to the underside of the deck - if it 'feels' like you've got a bad laser, look to see if it's got those three caps along the edge of the board. If it has, you better start looking for a supplier ... !! I never have figured out why 'standard' electros won't work in that position. Like you, I have subbed leaded for sm's in other places, without problem. About the only difference that I've found is that the leaded types tend to have a lower ESR than the sm's, which under normal circumstances, you'd say was a good thing. Arfa Doesn't it have to do with higher stray inductance (more inductance, less high-frequency shunt capability)? SMD parts are usually the only usable kind of part in sensitive equipment, like PWM amplifiers. |
#23
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LCD Monitor problem
"Wiebe Cazemier" wrote in message .home.nl... On Friday 09 May 2008 10:07, Arfa Daily wrote: Well, if ever you get one of those Sony players - and there was lots of 'em that used variations of the same board, mounted directly to the underside of the deck - if it 'feels' like you've got a bad laser, look to see if it's got those three caps along the edge of the board. If it has, you better start looking for a supplier ... !! I never have figured out why 'standard' electros won't work in that position. Like you, I have subbed leaded for sm's in other places, without problem. About the only difference that I've found is that the leaded types tend to have a lower ESR than the sm's, which under normal circumstances, you'd say was a good thing. Arfa Doesn't it have to do with higher stray inductance (more inductance, less high-frequency shunt capability)? SMD parts are usually the only usable kind of part in sensitive equipment, like PWM amplifiers. That's certainly a possibility. The servo data strippers and loops, are quite sensitive bits of circuitry in CD players, and these caps are glued straight on the end of pins on the servo processor chip, so they may well be decouplers or timing caps. Arfa |
#24
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LCD Monitor problem
On Friday 09 May 2008 16:42, Arfa Daily wrote:
That's certainly a possibility. The servo data strippers and loops, are quite sensitive bits of circuitry in CD players, and these caps are glued straight on the end of pins on the servo processor chip, so they may well be decouplers or timing caps. Arfa I would hope that all timing is done with a clock pulse, based on a crystal. Caps used for timings yield very unstable circuits, at least where high frequencies are concerned, such as FM transmitters. |
#25
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LCD Monitor problem
"Wiebe Cazemier" wrote in message b.home.nl... On Friday 09 May 2008 16:42, Arfa Daily wrote: That's certainly a possibility. The servo data strippers and loops, are quite sensitive bits of circuitry in CD players, and these caps are glued straight on the end of pins on the servo processor chip, so they may well be decouplers or timing caps. Arfa I would hope that all timing is done with a clock pulse, based on a crystal. Caps used for timings yield very unstable circuits, at least where high frequencies are concerned, such as FM transmitters. Yes, but this is not an FM transmitter ... The servo processor chips used in CD players are a hybrid mix of digital and analogue circuitry. There are analogue servo loops to control focus, tracking, disc rotational speed and laser output power, as well as accurately defined reference voltages for such things as the data slicer, and temperature tracking and compensation. In common with most hybrid loops, although they may be controlled digitally, with a clock derived from a crystal source as you surmise (and hope!), they will still have analogue filtering in the loop feedback, formed from C and R. If the time constant of these is not correct within a relatively small range - as may be the case if the filter capacitor is no longer to spec - then failure of the servo loop to lock reliably, is the likely outcome. Arfa |
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