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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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An Update on my 2465B scope
Here is a copy of an email I sent out:
I have removed the cover from the scope to check out U800. With the unit lying on its left side so the front is to the left and the back is the right and I'm facing the bottom, the IC (U800) was on the bottom of the board on the Y axis and about the middle of the X axis. I turned the scope on and waited for about the 3 min before the screen shuts off and as usual, the same results; no picture after the 3 min. So I did some fiddling around and found that the 'beam find' still works because it puts a line about 2 divisions across nice and dark with a few dots around it most likely being the digital read outs of the amplitude and time base that are normally shown on the screen. I shut it off to see how hot the IC gets and it did not feel that hot at all, it actually felt like it was running pretty cool. It was only one for about 4min total though. I turned the scope back on and still no picture which is a bit unusual, usually I get something for about 10-30 seconds, but not a major problem. I sprayed the chip with some freeze spray and still no picture, I shut it off and back on, but still nothing. I sprayed it again, but still nothing when I turned it back on. I believe I repeated this about 4-5 times and only got the picture to come on once for about 30 seconds. The IC was pretty cool the entire time from the spray. I noticed that after I turned it back on and needed to push the 'trig a/b' button because of the error I get at turn on (not a big deal to me right now), that the controls all work fine. You are able to switch between AC and DC coupling, change channels, etc... Basically the entire logic of the scope works fine and there is a glow on the screen like some sort of picture is present. It's almost like there is a bright line off to the side reflecting onto the screen, but you can't position it onto the screen so it just glows on the side. I found a site that sells Tek parts located in Canada, but they are currently sold out. I'm sure I can find someone that may sell this part. But right now my problem is, I'm not sure if that's the actual problem or not. I don't have a service manual for this scope nor do I know what signals I should get in/out of this chip. Do you have anymore input? The site I saw with the part I have (Maxim 155-0241-02) is: http://www.sphere.bc.ca/test/tek-parts/tekparts3.html Thanks |
#2
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"Peter" wrote in message news:JOyed.304002$D%.257789@attbi_s51... Here is a copy of an email I sent out: I have removed the cover from the scope to check out U800. With the unit lying on its left side so the front is to the left and the back is the right and I'm facing the bottom, the IC (U800) was on the bottom of the board on the Y axis and about the middle of the X axis. I turned the scope on and waited for about the 3 min before the screen shuts off and as usual, the same results; no picture after the 3 min. So I did some fiddling around and found that the 'beam find' still works because it puts a line about 2 divisions across nice and dark with a few dots around it most likely being the digital read outs of the amplitude and time base that are normally shown on the screen. I shut it off to see how hot the IC gets and it did not feel that hot at all, it actually felt like it was running pretty cool. It was only one for about 4min total though. I turned the scope back on and still no picture which is a bit unusual, usually I get something for about 10-30 seconds, but not a major problem. I sprayed the chip with some freeze spray and still no picture, I shut it off and back on, but still nothing. I sprayed it again, but still nothing when I turned it back on. I believe I repeated this about 4-5 times and only got the picture to come on once for about 30 seconds. The IC was pretty cool the entire time from the spray. I noticed that after I turned it back on and needed to push the 'trig a/b' button because of the error I get at turn on (not a big deal to me right now), that the controls all work fine. You are able to switch between AC and DC coupling, change channels, etc... Basically the entire logic of the scope works fine and there is a glow on the screen like some sort of picture is present. It's almost like there is a bright line off to the side reflecting onto the screen, but you can't position it onto the screen so it just glows on the side. I found a site that sells Tek parts located in Canada, but they are currently sold out. I'm sure I can find someone that may sell this part. But right now my problem is, I'm not sure if that's the actual problem or not. I don't have a service manual for this scope nor do I know what signals I should get in/out of this chip. Do you have anymore input? The site I saw with the part I have (Maxim 155-0241-02) is: http://www.sphere.bc.ca/test/tek-parts/tekparts3.html Thanks Peter Having just gone through this exact fault finding procedure today, here's what to check: U735 (14 pin DIL package located to the left of U800) pin 3 should have a ramp waveform between -1.3V and +1.3V on it, the ramp should be linear and there is a delay between each ramp determined by the timebase holdoff /delay settings. If this is OK, check the 2 outputs of U800 (pin 9 and the RHS of R804 which connects to the - Y plate of the tube), these should be ramps similar to the signal on U735 pin 3, but going between +28V and +46V, the ramp on pin 9 is + going and the ramp on R804 is negative going (the inverse of the pin 9 signal). In my case, the signal on U735 was correct, but the 2 outputs from U800 were correct for a few seconds then become very low in amplitude and distorted. Check also for +87V on pin 7 of U800. U800 on my scope ran only slightly warm but is almost certainly faulty. I earthed the scope (the one displaying the waveforms!) and the meter to pin 7 of J119, the empty 14 pin DIL socket just above the pushrod for the power switch, which is the PSU diagnostic socket. Martin -- martindot herewhybrowat herentlworlddot herecom |
#3
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U800 is a well known failure int Tek scopes. It is a custom IC made by a Tek
group later sold to Maxim IIRC. Maxim stoped making the custom Tek IC sometime ago. Tek has no repair stock. You need to find a donner scope or check on the Tekscopes Yahoo group. Hugh "Peter" wrote in message news:JOyed.304002$D%.257789@attbi_s51... Here is a copy of an email I sent out: I have removed the cover from the scope to check out U800. With the unit lying on its left side so the front is to the left and the back is the right and I'm facing the bottom, the IC (U800) was on the bottom of the board on the Y axis and about the middle of the X axis. I turned the scope on and waited for about the 3 min before the screen shuts off and as usual, the same results; no picture after the 3 min. So I did some fiddling around and found that the 'beam find' still works because it puts a line about 2 divisions across nice and dark with a few dots around it most likely being the digital read outs of the amplitude and time base that are normally shown on the screen. I shut it off to see how hot the IC gets and it did not feel that hot at all, it actually felt like it was running pretty cool. It was only one for about 4min total though. I turned the scope back on and still no picture which is a bit unusual, usually I get something for about 10-30 seconds, but not a major problem. I sprayed the chip with some freeze spray and still no picture, I shut it off and back on, but still nothing. I sprayed it again, but still nothing when I turned it back on. I believe I repeated this about 4-5 times and only got the picture to come on once for about 30 seconds. The IC was pretty cool the entire time from the spray. I noticed that after I turned it back on and needed to push the 'trig a/b' button because of the error I get at turn on (not a big deal to me right now), that the controls all work fine. You are able to switch between AC and DC coupling, change channels, etc... Basically the entire logic of the scope works fine and there is a glow on the screen like some sort of picture is present. It's almost like there is a bright line off to the side reflecting onto the screen, but you can't position it onto the screen so it just glows on the side. I found a site that sells Tek parts located in Canada, but they are currently sold out. I'm sure I can find someone that may sell this part. But right now my problem is, I'm not sure if that's the actual problem or not. I don't have a service manual for this scope nor do I know what signals I should get in/out of this chip. Do you have anymore input? The site I saw with the part I have (Maxim 155-0241-02) is: http://www.sphere.bc.ca/test/tek-parts/tekparts3.html Thanks |
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