Hi everyone! I hope you're all having a great MARCHintosh so far!
I've been working on repairing a Macintosh LC with accompanying monitor that I purchased here in Korea not too long ago that was sold as "for junk" and in non-working state. Both visually looked very clean and not all that yellowed, and the LC's logic board looked very clean too, so I took a gamble on it, even though the asking price was a bit high (par for the course here where I live, sadly). The LC itself is back to life with the exception of sound, which I'm pretty sure is due to the sound chip having gone bad. Hopefully I'll somewhat soon be able to try to fix that last remaining item thanks to a kind soul who may be able to send me a replacement chip. Fingers crossed!
But, onto my main question, and this is related to the Monitor. I purchased the capacitor replacement kit from Console5 and, even though my particular monitor model was ever so slightly different (M1296G vs M1296Z), internally these are identical. I have replaced all capacitors on the main logic board, but have not yet replaced those on the neck board.
After re-capping and doing an initial smoke test, I heard a high-pitched noise, and the monitor's power light did not turn on. I tried to trace down where the noise was coming from, and I'm fairly certain it's coming from T901. I used a sensitive microphone to help pinpoint the origin of the sound — it's not coming from the flyback transformer or tube or so, those are on the other side of the board compared the source of this particular sound I'm referring to.
I'm attaching a (wobbly, apologies) video that captures the sound I'm referring to, alongside with what to my ears sounds like the expected/correct high voltage sound — though please correct me if I'm wrong about that.
I don't know if that component itself is the problem though, or if it's merely a symptom, as when I check for voltages on the test points, none are getting anything remotely close to good readings, only something around or just under 1v. At the same time, it does sound like high voltage is working, or at least I hear the usual high voltage CRT monitor sound when powering on the monitor.
I suspect that there's one or more resistors that might have gone bad, and maybe other components too. I just feel like I'm kind of poking in the dark here as none of the test points measure correctly, and I am not sure where I can and should measure before those test points to find where the likely culprit(s) are. I have gone in and measured various resistors, but without really knowing where to look, I kind of feel like just blindly going around the board is probably not the most productive way of trying to figure this out.
There was some damage caused by leakage in the usual spot, though all traces still check out fine. I did thoroughly clean the whole board, that area in particular, and measured the various components around there that aren't replaced by the kit to see if they still measure OK.
I did find that R534 and R525 were seemingly not measuring correctly. so I have already tried replacing these to see if that made any difference., I did not have 100% exact matching resistors, but they were close enough at least to run a quick test. That made no difference to the results of measuring voltages at all the test points, sadly.
Of course I'll be replacing them with correct resistors, but I need to order those and don't want to do that before knowing which other components I'll be needing to bring this one back alive — if at all possible, of course.
If you have any suggestions as to where I can/should measure or check, please do let me know. It'd be great if I could bring this monitor back alive and use it with the LC.
Thanks so much in advance!
I've been working on repairing a Macintosh LC with accompanying monitor that I purchased here in Korea not too long ago that was sold as "for junk" and in non-working state. Both visually looked very clean and not all that yellowed, and the LC's logic board looked very clean too, so I took a gamble on it, even though the asking price was a bit high (par for the course here where I live, sadly). The LC itself is back to life with the exception of sound, which I'm pretty sure is due to the sound chip having gone bad. Hopefully I'll somewhat soon be able to try to fix that last remaining item thanks to a kind soul who may be able to send me a replacement chip. Fingers crossed!
But, onto my main question, and this is related to the Monitor. I purchased the capacitor replacement kit from Console5 and, even though my particular monitor model was ever so slightly different (M1296G vs M1296Z), internally these are identical. I have replaced all capacitors on the main logic board, but have not yet replaced those on the neck board.
After re-capping and doing an initial smoke test, I heard a high-pitched noise, and the monitor's power light did not turn on. I tried to trace down where the noise was coming from, and I'm fairly certain it's coming from T901. I used a sensitive microphone to help pinpoint the origin of the sound — it's not coming from the flyback transformer or tube or so, those are on the other side of the board compared the source of this particular sound I'm referring to.
I'm attaching a (wobbly, apologies) video that captures the sound I'm referring to, alongside with what to my ears sounds like the expected/correct high voltage sound — though please correct me if I'm wrong about that.
I don't know if that component itself is the problem though, or if it's merely a symptom, as when I check for voltages on the test points, none are getting anything remotely close to good readings, only something around or just under 1v. At the same time, it does sound like high voltage is working, or at least I hear the usual high voltage CRT monitor sound when powering on the monitor.
I suspect that there's one or more resistors that might have gone bad, and maybe other components too. I just feel like I'm kind of poking in the dark here as none of the test points measure correctly, and I am not sure where I can and should measure before those test points to find where the likely culprit(s) are. I have gone in and measured various resistors, but without really knowing where to look, I kind of feel like just blindly going around the board is probably not the most productive way of trying to figure this out.
There was some damage caused by leakage in the usual spot, though all traces still check out fine. I did thoroughly clean the whole board, that area in particular, and measured the various components around there that aren't replaced by the kit to see if they still measure OK.
I did find that R534 and R525 were seemingly not measuring correctly. so I have already tried replacing these to see if that made any difference., I did not have 100% exact matching resistors, but they were close enough at least to run a quick test. That made no difference to the results of measuring voltages at all the test points, sadly.
Of course I'll be replacing them with correct resistors, but I need to order those and don't want to do that before knowing which other components I'll be needing to bring this one back alive — if at all possible, of course.
If you have any suggestions as to where I can/should measure or check, please do let me know. It'd be great if I could bring this monitor back alive and use it with the LC.
Thanks so much in advance!
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