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Also, I agree, an oscilloscope would be useful at this point. Perhaps I'll look into getting one. But I think the 100 watt lightbulb in the post-recap +B circuit overloaded the PSU or something else, and caused damage. That's why I somewhat suspect burnt resistors, diodes, and transistors as they may have had their power rating exceeded by the bulb's current draw. I tried running with a much smaller 15 watt bulb in place of the +B fuse but the set wouldn't power up this way. Only a feeble whine. After I removed the bulb, that's when +B started floating around low. Quote:
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Couldn't you use the 90% alcohol they sell at drug stores? Yes, but all that'd brought it back from the dead was a complete and utter recap. Despite this I couldn't save the floppy drive & ye olde spinny hard drive soon died from goopy head bumpers. Also this was one of the cheapo, "pizza box" form factor Macs. They weren't the early compact ones with a 9" CRT built-in, you had to source your own monitor for these.
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An oscilloscope yes, but also a an isolation transformer. That will greatly reduce the chance of a fatal accident if you touch the wrong thing
this is just about the cheapest scope you could get any use out of. You still can't do high voltage without differential probes, but you would need to buy those separately with more expensive scopes as well also, get yourself one of these types of devices to do a quick check on diodes and transistors. It's not completely foolproof, but I find they generally don't lie, and they will almost certainly tell you if a transistor is still showing as one or not. Capacitance is also fairly accurate up to a certain point. I think they start to get so-so around 2200uf and up I'm not specifically endorsing either of these two devices or sellers; there are many versions of them on amazon and ebay, and they are all pretty much the same thing AFAIK. Just read feedback and stuff and find a good deal on a good one |
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Can't power on the set yet so here are pictures of the mainboard I took today. Feel free to pour over them, I cannot see anything wrong myself.
To get the full-resolution photos please download from imgbb. Note: C605 appears bridged in the first photo, but it is not. When doing the first solder reflow, I noticed C751 was bridged. I don't know how long it was bridged for. Since then, C751 has been replaced but to no improvement. The horizontal driver section may've been pooched by the C751 short, now that I think of it. Should check waveforms.
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#4
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1) that resistor on the back of the PCB is somewhat sus. i've had issues with those plastic package resistors before. maybe it's fine, but could be worth testing them if there are any others on the front side. the one bodged onto the back is unlikely to make a huge difference anyway, but if there's one, many there's others 2) there's one spot towards the bottom that i don't understand. it looks like missing solder on a connector or something, but perhaps that is supposed to be that way? this: |
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At that time I wasn't interested in lugging the brutes around and they were looking to retire, I remember hauling a few of those big 30+ inch CRT's to the bench but never got into the RPTV's. I miss the days of the EZ triplers and sagging 3A3 heaters that took out the flyback.
Getting back to the Panasonic I see so many suspect connections I don't know where to start but D551 anode is just as good as any. First soldering takes a lot more than globbing it on the connections and hoping it conducts, they need to be heated until the solder flows. Those connections on the flyback are not up to par by any means. I see the majority of solder connections have not been touched and they are all suspect until addressed. Soldering is a skill that comes with years of practice, not something you can learn from a book. Honestly I think you bit off more than you can chew with this one. Originally Posted by luRaichu Can't power on the set yet so here are pictures of the mainboard I took today. Feel free to pour over them, I cannot see anything wrong myself. And this is what separates the experienced. just a quick glance I see a halo around the anode of D551, the posts around the DY terminals esp #3 don't look very good. TPB4 looks to be shorting across to the adjacent trace for TPB3 just above R603. All of the connections around the flyback pins need to be reflowed and when I say this I mean heated until the entire solder connection melts and flows around the pin, simply touching the glob is not going to cut it and with all that has been done so far I wouldn't be surprised to find blown semiconductors. You're going to need a lot more luck to get this one working right again. Last edited by ARC Tech-109; 05-13-2024 at 11:06 AM. Reason: Autopost keeps timing out |
Audiokarma |
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As an ASC we had to have a test jig, so I didn't do much lugging. I also cheated a bit - if we had a big tube Sony that was dead, I'd just grab the chassis even though I didn't have any test jig adapters for them and just use a scrapped yoke and HV probe. I kept a bunch of yokes on the shelf for that reason. When I got the power and HV repaired as indicated by the HV probe, I'd just return the chassis. John |
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Also, I guess it wouldn't hurt to work on the flyback's pads a bit more, and the other things you'd mentioned too...
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