Panasonic CT-1310M keeps blowing horizontal output transistor

[luRaichu]

Originally Posted by ARC Tech-109

I then move on to capacitors. You said that you have replaced a majority of electrolytics, what did you use? This is very important as the vast majority of chinesiums are bad right out of the box.

I used mostly Würth Elektronik & a few Nichicon caps. I would never trust the cheaper brands like "Elite".

Originally Posted by ARC Tech-109

Have you gone over the top of the board and actually verified each capacitor is the proper value according to the schematic AND the polarity is correct?

I couldn't cross-reference with the Sams' as I don't have all pages; but I've checked and every new cap installed is the exact same capacitance, same voltage rating or higher as it's predeccessor. Polarity is easy because most if not all caps on the main board have their negative side facing right.

Originally Posted by ARC Tech-109

Okay so we "think" the electrolytics are good being name brand parts like Nichicon then I'd move into the various supply voltages following the schematic. With the horizontal transistor blown I'd remove it from the circuit and sub in a 40-watt incandescent lightbulb between the emitter & collector to load the main part of the power supply, no you won't have any sweep but this is not important at the moment... an oscilloscope however would be most helpful and the reason for this is even without the HOT in place there should still be drive available on the collector of Q501 unless the failsafe has an issue. Without horizontal pulses coming into the failsafe it shouldn't trigger a shutdown. How about voltages? We don't need exact numbers here, +/-5% is a good working margin.

As you might have seen, I measured and re-measured the PSU voltages prior to the +B regulator taking a nose dive. Everything seemed up to spec then.
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.

Originally Posted by ARC Tech-109

That being said what are the voltages going on the various circuitrace flags listed on the schematic? If they're within the spec tolerance how about at the various collectors of transistors or the VCC point of IC301?

Good call. I will check this.

Originally Posted by ARC Tech-109

I've been trying to follow along the schematic you posted the image of but the hosting site is a pain and I can't see the whole thing.

You can download them from the hosting site and magnify with your image viewer of choice. If not I can put the schematics up on the Internet Archive and you may see them better there.

Originally Posted by ARC Tech-109

Don't like the smell of flux? Sorry but it's a fact of electronics repair and you will have to deal with it. Personally I'd pull the board completely and do a de-flux using the fuel additive "Purex99" in the red bottle, that is 99% pure isopropyl alcohol and that will take ALL the flux off with a little scrubbing with an old toothbrush.

It's only the OLD flux that really smells like shit. I've always been fine with it though, but my neighbors sure aren't.
Couldn't you use the 90% alcohol they sell at drug stores?

Originally Posted by ARC Tech-109

I mean you fixed a McIntosh right?

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.

[vol.2]

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

[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.
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.

[vol.2]

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.

Doesn't appear to be broken to me. A couple of notes.

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:

[ARC Tech-109]

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.

[JohnCT]

Originally Posted by ARC Tech-109

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.

Man, triplers were great - they'd generally arc and burn through and people were so happy when the price to repair the TV was half of what they were afraid of what it would be because of the acrid smoke they'd belch..

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

[ARC Tech-109]

Originally Posted by JohnCT

Man, triplers were great - they'd generally arc and burn through and people were so happy when the price to repair the TV was half of what they were afraid of what it would be because of the acrid smoke they'd belch..

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

We didn't cheat so much, I was a 20-something who was bigger than his britches and would literally pick those big tube sets up solo and gracefully load them in the van, now at 55 I'm feeling every one of those on every bump I hit on the road... not so graceful today.

[luRaichu]

Originally Posted by ARC Tech-109

TPB4 looks to be shorting across to the adjacent trace for TPB3 just above R603.

No, it is not. See the 2nd pic.

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...