Author Topic: tv repair help (Read 20757 times)

snipersquad100 · « **Reply #25 on:** October 23, 2013, 03:10:36 pm »

pon in faulty state is 0v. voltage accross e&c of pc9502 in faulty state is 20.6vac
the 375 net is 336.5v

tom66 · « **Reply #26 on:** October 23, 2013, 03:16:29 pm »

You using VAC or VDC? You should use VDC.
The PON signal going high should cause the C-E voltage to drop very low, under a volt, so the reading doesn't make much sense...
Note E&C of PC9502 are on primary side not secondary side.

snipersquad100 · « **Reply #27 on:** October 23, 2013, 03:31:21 pm »

the part is this way up in the tv I measured the left side. Its 0.1 dc and the right side is 0.6dc

wraper · « **Reply #28 on:** October 23, 2013, 04:35:41 pm »

Quote from: snipersquad100 on October 23, 2013, 03:31:21 pm

the part is this way up in the tv I measured the left side. Its 0.1 dc and the right side is 0.6dc

Why the hell you are measuring voltage between primary and secondary. That can be dangerous BTW.

tom66 · « **Reply #29 on:** October 23, 2013, 04:35:54 pm »

Hah sorry for the confusion but the CATHODE pin is often called K to avoid confusion with the collector pin. So you need to test across the collector and emitter on the primary side. There is no electrical connection between the primary and secondary of a power supply like this.

snipersquad100 · « **Reply #30 on:** October 23, 2013, 04:41:46 pm »

that's my fault sorry across pins 3 and 4 of pc9502 is 0.09vdc

tom66 · « **Reply #31 on:** October 23, 2013, 05:08:58 pm »

Is that working or faulty?
If faulty, that indicates the opto is fine and the fault is somewhere on the transistor hanging off the PON line, I suspect.

snipersquad100 · « **Reply #32 on:** October 23, 2013, 05:13:35 pm »

that's when it was working. That noise I can here is coming from Lf9002 according to the mrs.

tom66 · « **Reply #33 on:** October 23, 2013, 06:03:49 pm »

OK, that's good. Just wait for it to fail to make sure it's not the opto. Looks like it's somewhere around the area switching the Vcc, so should be easy enough to trace down (hah, famous last words...)

snipersquad100 · « **Reply #34 on:** October 23, 2013, 07:58:37 pm »

the voltage across pins 3 and 4 of pc9502 when faulty is 0.1vdc. so what do you think it is?

tom66 · « **Reply #35 on:** October 23, 2013, 08:24:26 pm »

The opto is fine, then. There are a few things that may be pulling down the PON signal.

The voltage across C9511 should not exceed 11V, what does it measure? (I'm basing this on the MAB100 zener diode being 10V rated.)

Q9503 can cause PON to be pulled low, caused by voltage at end of one end R9519 (relative to 450V capacitor negative lead) being lower than approx 0.7V. I'm hoping R9519 is through hole.

snipersquad100 · « **Reply #36 on:** October 23, 2013, 09:54:54 pm »

c9511 is 10v. r9519 is smd I cant get a ohm reading across it but I can with another 474 smd resister, could it be cos its in circuit?

tom66 · « **Reply #37 on:** October 23, 2013, 10:43:54 pm »

You should still be able to measure a resistance, even if it is in circuit. It could be cracked/damaged maybe? And that could cause your intermittent issue.

snipersquad100 · « **Reply #38 on:** October 23, 2013, 10:54:35 pm »

I pull it out tomorrow, im off to bed. thanks mate for you help.

wraper · « **Reply #39 on:** October 24, 2013, 07:49:22 am »

I doubt that there are any cracked parts. I there would be such, board should react to bending and defect should be stable enough without it. I say again, check the capacitors. It is very common for them to cause intermittent issues when they are almost dead. When device fails to start but works normally if it managed to do it, 90% that this is faulty electrolytic capacitor. And problem becomes worse with time until device stops to work completely.

fluxcapacitor · « **Reply #40 on:** October 24, 2013, 08:56:24 am »

This post might help.

http://www.justanswer.com/tv-repair/7kz6q-jvc-lt-42x579-trying-trouble-shoot.html

As already suggested its usually,but not always the caps,and they are cheap enough to replace anyway,and saves doing it at at later point.Good luck with it.

tom66 · « **Reply #41 on:** October 24, 2013, 09:57:24 am »

Bad caps are very unlikely on this actually-made-by-JVC TV because it uses entirely high quality capacitors: Rubycon mostly with a few Nichicon. Yes while even good capacitors fail their failure rate is so low it's NOT a good idea to shot-gun replace them on the board, you'll just waste time. Out of nearly 60 (hobby) TV repairs I've had maybe 6 or 7 bad capacitor replacement jobs... It's a common suggestion on the internet "have you replaced the caps?" but it's nearly irrelevant if you aren't talking about a Samsung or LG made in 2007~2008.

Bad capacitors also cause odd symptoms. A bad startup capacitor could cause this problem (by checking the voltages across them that has been mostly ruled out) whereas a bad output capacitor would tend to cause low output voltages rising after warming up, flickering backlight, distorted audio, glitches on display, etc.

The particular fault could be caused by a leaky transistor, intermittent resistor (SMD resistors can become intermittent) or some other problem along the PON circuit.

fluxcapacitor · « **Reply #42 on:** October 24, 2013, 10:37:11 am »

Yes,the capacitors should be good ,i thought i might get shot down for suggesting replacing them.If i have them in stock i replace them anyway and test the old ones,any any that test good i reuse.

wraper · « **Reply #43 on:** October 24, 2013, 10:58:49 am »

I replaced not so small amount of faulty "good brand" capacitors in SMPS. Being Nippon chemi-con, Rubicon or whatever does not guarantee them to be fail proof. They still remain the most unreliable components, they just don't fail in tons like crap ones. I didn't suggest to replace big ones on secondary side BTW, that is the place where crap ones fail usually. What I see from those symptoms is bad capacitor on PWM controller power rail (or something like that) and protection kicking in. And do you really think that "intermittent resistor" is more possible that faulty capacitor. What fascinates me that you just throw away the whole idea of faulty capacitor just because it is JVC, Badcaps don't write about that, Rubycon... That can be fast and dirty repair but can became a real PITA for OP with such suggestions. OP doesn't seem to be very familiar with electronics and I believe suggestions must be that he should do easiest things first before digging deeper. I'm sorry If I hurt your feelings but that's what I think.

snipersquad100 · « **Reply #44 on:** October 24, 2013, 02:24:50 pm »

ok I pulled out R9519 and its 470k dead. Ive changed the caps but to no success. This Lf9002 is making a loud buzzing noise, its only an duel coil or inductor im not 100% sure. I also changed ic9501 but still nothing. I would like to change that Lf9002 before I take this to the tip but I cant find the part anywhere. Any more ideas before it goes to the tip lol. ive danted with it.

snipersquad100 · « **Reply #45 on:** October 24, 2013, 02:27:36 pm »

this is the part where the buzzing is coming from.

wraper · « **Reply #46 on:** October 24, 2013, 02:47:06 pm »

Quote from: snipersquad100 on October 24, 2013, 02:24:50 pm

ok I pulled out R9519 and its 470k dead.

Did replacing R9519 change anything? As I read circuit PFC won't start with it being open. That buzzing coil is just mains filter. You can also try to unsolder collector of Q9503 and swith on, then measure 375V rail to see if PFC works.

snipersquad100 · « **Reply #47 on:** October 24, 2013, 03:01:25 pm »

I didn't replace R9519 it measured 470k so I put it back in. Whats pcf mean? i'll pull up that collector now. the 375v rail has got 335v has it goto be 375?

snipersquad100 · « **Reply #48 on:** October 24, 2013, 03:12:51 pm »

I cant lift that leg with out braking it, it's a tiny smd one with no number on it so I don't know witch one is the collector anyway.

wraper · « **Reply #49 on:** October 24, 2013, 03:13:13 pm »

That 470Kkdead looked as dead for me, not native english speaker

. OK, if that resistor is ok no need to unsolder that transistor. Just measure voltage Between GND1 and collector of Q9503, collector of Q9502, emitter of Q9507 and pin 8 of IC9502. All in working state, no need to measure faulty.


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Author Topic: tv repair help (Read 20757 times)

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