Toshiba 37AV502R BAD Psu?

[tom66]

Re: Toshiba 37AV502R BAD Psu?

Bad startup cap, is it the same logo as the others? Startup caps seem to go bad quite often though not seen it yet in a Toshiba.

[IamCanadian]

Re: Toshiba 37AV502R BAD Psu?

Just pulling it out, same brand, I will post a pic after of the cap, top looks great.
Just wanted to see how long it will go, Been on solid with a 720p signal for close to an hr, But that is only because it is maintaining the high temp now, once it cools down I am sure it will mess up again so replacing it shortly. I will post value and voltage and board component number for others to find if they run across this problem.

Huge props to you tom66!

It is a 50v 22uF KY series, C207 on board.

[IamCanadian]

Re: Toshiba 37AV502R BAD Psu?

Update,
Replacing that cap made the power supply stable under all loads, However I did also have to reflow the main board to make the tv function reliably. been on for 16 hrs now with not a single hickup.

[tom66]

Re: Toshiba 37AV502R BAD Psu?

Glad to hear you fixed it.

[IamCanadian]

Re: Toshiba 37AV502R BAD Psu?

Thanks again tom66 You really helped speed up this process, I never would have even looked at that small cap, I think a high resistance joint on the mainboard caused that cap to fail drawing too much current and overworking that cap.

[tom66]

Re: Toshiba 37AV502R BAD Psu?

That cap usually wears out on its own but it is under higher stress when the power supply is at -low- load, i.e. in standby.

[budm]

Re: Toshiba 37AV502R BAD Psu?

Hair dryer is your friend for troubleshooting bad cap problem.

[tom66]

Re: Toshiba 37AV502R BAD Psu?

Yes, it can be very handy. I got this Samsung to power up (with bad caps) by heating them with a hairdryer.
http://www.youtube.com/watch?v=Ggn_ggaPvc4&t=2m35s

[budm]

Re: Toshiba 37AV502R BAD Psu?

I used to have the WHAH brand heat blower in the 70's that I have used for troubleshooting, iy has small nozzle attachment for localizing the heat. I do not know what I did to it. Now I use one of those cheapadjust able soldering iron set it to low and heat individual cap without heating the whole for pinpointing the bad cap, no power apply to the board of course.

[IamCanadian]

Re: Toshiba 37AV502R BAD Psu?

Found a Panasonic Plasma 42" Viera from 2010 for $100.00 with blinking red led, May try that one next.

[tom66]

Re: Toshiba 37AV502R BAD Psu?

Heh, Panasonics are tricky to repair, but very, very nice TVs when working. Ask owner to tell you how many times it blinks.

[keats11]

Re: Toshiba 37AV502R BAD Psu?

I have this same TV, same symptoms -- cycles on and off one it warms up nicely. Tried adding another cap tho this cap in parallel, but that didnt do anything. Is this a high ESR cap? If I pull another cap from a old power board (for another TV), should I pull the black or the brown caps to substitue for this cap?

[tom66]

Re: Toshiba 37AV502R BAD Psu?

Ideally, you'd use a new cap. The failure is generally due to leakage current; putting one in parallel will only make the problem worse. Sometimes the capacitance just falls so parallel ones will work. YMMV.

[keats11]

Re: Toshiba 37AV502R BAD Psu?

I have caps sitting around, should I worry about the ESR value for the caps? I don't think I have any low ESR caps sitting around. What does this cap do? I am going to try and replace this with another cap, since you mentioned leakage.

[tom66]

Re: Toshiba 37AV502R BAD Psu?

ESR isn't critical, and capacitance should be at least as much as was originally there. Larger capacitance will mean the TV takes longer to start from plugging in.

[keats11]

Re: Toshiba 37AV502R BAD Psu?

I tried replacing this cap but the problem persists. The user above also reports the same issue, but then he stated he had to reflow the board to get it working. I am thinking the issue is something else at this point. Looks like what is happening is that as soon as the backlights come on, the 24 volts drop and the power supply shuts down, then the voltage comes back up and triggers the back light on and the process repeats. I am wondering if this could be a problem in the inverter board rather than the PSU? But then that doesn't explain why the above user got it working.

[tom66]

Re: Toshiba 37AV502R BAD Psu?

Maybe it's an entirely different problem. The reflowing did seem odd to me. Can you get hold of some 1157 car rear light bulbs? Two in series can make a good load for 24V.

[keats11]

Re: Toshiba 37AV502R BAD Psu?

Yeah, I can try that. So, with two 1157 bulbs in series, you expect the same load as the inverter boards? Thst is a good test, I will have to perform that tonight. Right now I am at work. What is so special about the 1157 bulbs?

[tom66]

Re: Toshiba 37AV502R BAD Psu?

It will not be the same as an inverter (which draws close to 180W), but it should be enough load to evaluate the PSU's performance.

[IamCanadian]

Re: Toshiba 37AV502R BAD Psu?

I did a reflow on the main board. Because the tv would freeze, audio would lock up and video would skip, to me this indicates a bad solder joint just like what happens to a PS3 or xbox 360 with lead free solder. But your issue is different from mine.