Panasonic CT-1310M keeps blowing horizontal output transistor

[luRaichu]

Originally Posted by vol.2

There are some low cost scope options for someone on a budget that will at least give you some feedback. For around $100 you can get a little handheld battery powered one that will be high enough to capture the bandwidth of a crystal.

Yeah, I don't exactly feel like blowing a hundie just to debunk ONE crystal, especially when a replacement crystal probably costs less than the oscilloscope itself!

I measured various PSU voltages, just to be sure:
19.77v line = 18.77v
12.10v(A) line = 12.40v
12.10v(B) line = 12.36v
12.09v(A) line = 12.39v
160v line = 155v
11.60v line = 9.80v (measured from C559 instead of L351 because I didn't bother playing this game of Where's Waldo long enough)

[vol.2]

Originally Posted by luRaichu

Yeah, I don't exactly feel like blowing a hundie just to debunk ONE crystal, especially when a replacement crystal probably costs less than the oscilloscope itself!

I measured various PSU voltages, just to be sure:
19.77v line = 18.77v
12.10v(A) line = 12.40v
12.10v(B) line = 12.36v
12.09v(A) line = 12.39v
160v line = 155v
11.60v line = 9.80v (measured from C559 instead of L351 because I didn't bother playing this game of Where's Waldo long enough)

Looks good enough to me. As I mentioned earlier, you could also trace the voltages around the board. If there's a break in the PCB somewhere, that's usually a good way to find it because voltages are stable and predictable. Also, since you don't have a scope, you won't be able to check the various waveform that the Sam's calls out. Which, incidentally, is also a good reason to have at least a basic scope. You can look at all of those little black windows in the Sam's to make sure they look right.

If you plan on doing this kind of thing any more than this one set, a scope is a pretty core tool in electronics troubleshooting

[luRaichu]

Originally Posted by vol.2

As I mentioned earlier, you could also trace the voltages around the board. If there's a break in the PCB somewhere, that's usually a good way to find it

I'd likely need a fuller picture of the Sams' for that. Right now, I only have about a dozen pages out of 30. And I seriously doubt the board is broken, as the picture was perfect pre-recap. If it were fractured, how the flinkerjub would I begin repairing such a fault?

Originally Posted by vol.2

Also, since you don't have a scope, you won't be able to check the various waveform that the Sam's calls out. Which, incidentally, is also a good reason to have at least a basic scope. You can look at all of those little black windows in the Sam's to make sure they look right.

And I sure wonder how'd you go about fixing a bad waveform. Actually, I think it might be worth it to buy the full Sams' for this TV, considering all the problems we're wading through.

Originally Posted by vol.2

If you plan on doing this kind of thing any more than this one set, a scope is a pretty core tool in electronics troubleshooting

This is a one-time ordeal. I hope.

About the H disable circuit - I'm seriously stumped as to why it's being activated. Hopefully our lord and savior Sams' shall yield thy answers...

[vol.2]

Originally Posted by luRaichu

I seriously doubt the board is broken, as the picture was perfect pre-recap.

You clearly had issues or you wouldn't have been recapping anything. But even so, problems can get worse or become less intermittent when you work on thing or have it on for longer. Just moving stuff around and (more importantly) heating things up has a tendency to make problems come out.

If it were fractured, how the flinkerjub would I begin repairing such a fault?

You would bridge over the traces with wire, or solder bodge wires to restore continuity to the broken trace(s).

I'm not suggesting that it's the most likely problem, but it's a possible problem that should be fairly easy to check out with a multimeter.

And I sure wonder how'd you go about fixing a bad waveform. Actually, I think it might be worth it to buy the full Sams' for this TV, considering all the problems we're wading through.

You would take the bad waveform as evidence that the circuit is pooched in that particular area of the board and start testing components connected to it. Some people are good enough to know what is likely wrong just from that, but I would have to just test stuff mostly. If the waveform originates from an IC and not a group of discrete components, it might be a sign of a bad IC, and it is usually possible to lift things out of the circuit and test the output of the IC removed from any possible shorts or loads and see if it's good or not.

About the H disable circuit - I'm seriously stumped as to why it's being activated. Hopefully our lord and savior Sams' shall yield thy answers...

I wouldn't know. Hopefully one of these other oldbies can't point you right. My level of troubleshooting is "okay," and I can generally figure stuff out if it's right in front of my face and I'm working on it.

[luRaichu]

Originally Posted by vol.2

You clearly had issues or you wouldn't have been recapping

I recapped because HOTs kept blowing out. Did you see this?

[luRaichu]

I read about H osc. disabling circuits in other Panasonic TVs. It pumps up H frequency to eliminate X-Ray risk if HV is found to be above spec. Which might explain why the picture is so bright & shrinks sometimes. But most other sets from other brands simply shut down if HV is too high.
I can't test the HV without a high voltage meter though.

[luRaichu]

Originally Posted by zeno

133 volts may be OK but you need to see if it changes. Use a variac
or go from zero brightness to full brite. It must stay the same.

Well I did some testing tonight and found the +B voltage floating around. It was up to 125v with a dark picture but lowers to 120v when bright. +B control resistor DOESN'T work sometimes. Sometimes it goes back to 130v and that's when the H osc. disable circuit gets triggered. I think the low voltage regulator is crapping out! https://youtu.be/OqzFIbvbYJQ

The lack of color & white horizontal dots seriously concern me. Honestly, I'm almost at my wits end with all these failures!
Considering just sending this set off to Multi Media Medic in Maryland.

[vol.2]

Originally Posted by luRaichu

Considering just sending this set off to Multi Media Medic in Maryland.

If I was seeing fluctuating voltages in the B+, I'd probably suspect one of the transistors of being flaky. Sometimes they only behave poorly when under load, and they test okay when you take them out. Usually, that will come out when you use a curve tracer, but not always. And they are pretty expensive

Interesting. I live in Maryland but I didn't know about that guy. I used to always go to a dude in Silver Spring called Danco, but he's semi retired now and he won't always take stuff in if he doesn't want to. Last thing I brought to him he sat on for six months and then said he didn't want to do it lol

[luRaichu]

Does anybody know why the color is gone & how to fix? You can kind of see it but just barely.

[luRaichu]

In an attempt to cripple the H disabling circuit I left R539 open, and switched the set on. I've never seen the HOT blow out quicker!
I give up.

[luRaichu]

Originally Posted by vol.2

Interesting. I live in Maryland but I didn't know about that guy.

Well I tried calling this Multi Media Medic man today and he didn't pick up. Left him a voicemail but I doubt I'll get anything back.

Please, enlighten me to any other repair shops or techs in Maryland or Virginia. I cannot bring myself to work on this set anymore. If anything, I can sell it for parts on eBay or something...

[zeno]

MUSTS HAVES !
Power supply must be 130 VDC under both zero beam current or max
( full normal brite ) beam current. & varying line voltage. If not suspect
Q801.

Too bright. REPLACE C559 no matter what, its very common on ALL
brands of TV's, Its in the top ten TV problems. Lots of different symptoms too !

G2 must be about @ 300 VDC too high = too bright.

CRT cathodes need to be @100 VDC. Too low too bright & visa versa.

Blows HOT. Be sure its running cool. If not it WILL give up soon.

NOTES : The FBT's in this era of Pannys / Quasars were trouble. Usually
windings shorted & it cooked, crackled, smoked then blew the HOT.
It ended the TV often. On yours it MAY be it has a bad triple / divider
section.
Last keep in mind to do things right you need: a variac / isolation transformer(S). quality meter & good 100 + Mhz scope with 1 KV probes. Anything less is pushing it. Just think of the $ in blown parts you will save
if you do more sets.

73 Zeno
LFOD !

[luRaichu]

Originally Posted by zeno

Too bright. REPLACE C559 no matter what, its very common on ALL
brands of TV's, Its in the top ten TV problems. Lots of different symptoms too !

I've already done a near-full recap.