Toshiba 37AV502R PSU

[CapLeaker]

Re: Toshiba 37AV502R PSU

Thanks for the explanation!

[budm]

Re: Toshiba 37AV502R PSU

Pin 3 of the IC is the Over voltage sensing pin, the bad diode has small leakage current and cause the IC to trip.
That is why when d200 is removed, the circuit works fine (but without OV protection).

[CapLeaker]

Re: Toshiba 37AV502R PSU

Thanks for the follow up, glad to hear that it just the bad diode, it took me a long time to narrow it down to that D200.

what does that D200 actually do in that circuit? If you don't mind explaining...

[bryanhill7]

Re: Toshiba 37AV502R PSU

In talks with guy on craigslist to get 4- 40" inch Proscan's for $10 each. All bad boards of some sort. Wife gonna kill me.

[budm]

Re: Toshiba 37AV502R PSU

Thanks for the follow up, glad to hear that it just the bad diode, it took me a long time to narrow it down to that D200.

[CapLeaker]

Re: Toshiba 37AV502R PSU

Glad you got her going!

[bryanhill7]

Re: Toshiba 37AV502R PSU

Got the diode replaced. Thanks for all you help. I did not know my multi-meter could be setup to show the amp draw and that idea really helped identify the psu as the problem. Thanks again everyone.

[bryanhill7]

Re: Toshiba 37AV502R PSU

scouring some computer psu's and motherboards looking for a good diode to use.

[budm]

Re: Toshiba 37AV502R PSU

I put in the SMD 1N914, you can use axial small signal diode, just bend the legs.

[bryanhill7]

Re: Toshiba 37AV502R PSU

Nice. Removed D200 and it started right up. Guess I need to order a diode?

[budm]

Re: Toshiba 37AV502R PSU

OK, remove smd Diode D200 and see if the 5V will be stable, if it does you can use 1N914/ or 1n4148.
It uses the same standby circuit as used in the 32" version.
http://s807.photobucket.com/user/bud...?sort=3&page=1

[bryanhill7]

Re: Toshiba 37AV502R PSU

Initial load is 1020mah. From previous testing I know that I can only pull ~800+mah before the ps starts dropping out. Another clue that the ps is bad.

Once it is done with the initial load it sits around 140mah and with hdmi content playing it goes close to 200mah. Interesting stuff.

[budm]

Re: Toshiba 37AV502R PSU

Put your meter in DCA mode and hook it up in series with the 5V wire feeding the main board so we can see how much current the main board is drawing, at least we know that the main board is OK.
I will see if I have the diagram for this power supply.

[CapLeaker]

Re: Toshiba 37AV502R PSU

Any way to hook up the main board to the TV power supply and watch the 5v rail with an oscilloscope? How much current is the board drawing on the computer power supply?

[bryanhill7]

Re: Toshiba 37AV502R PSU

HA HA. I hooked up a computer PSU and drove the board with that. Its working. Deff a bad psu on the tv.

[CapLeaker]

Re: Toshiba 37AV502R PSU

I guess something must be turning on and off on the main board to cause that swing that bad. So by rights, sumtin must get warm or even hot on the main board, if left on for a period of time.
If you would have a CC and CV power supply you could hook the main board up to that and "play" with it. See what gets hot if you try to give it lets say 1A @5V.

[bryanhill7]

Re: Toshiba 37AV502R PSU

Replaced C207 and no luck. 5v is still swinging up and down when plugged into the tv but stable not plugged into anything. I soldered the 5v to the pwr on so I would know as soon as its plugged in that it will always be giving power to the main board but the voltage is only 1.8v. My guess is that the mainboard is requiring more power than the ps can give.

[bryanhill7]

Re: Toshiba 37AV502R PSU

I ordered a variety of caps and they should be here Wednesday. I'm so tempted to hijack the 5v with a computer PSU and attempt to see if that is the problem with the tv psu.

[budm]

Re: Toshiba 37AV502R PSU

Ok. Just so were clear.
C207 is on the primary side (HOT).
My C207 cap is a KY 50v 22uf (so i dont know how 160+v could be possible to begin with)

To further complicate things I have made things worse. Earlier I removed C207 and was troubleshooting with the only cap I had around that could replace it with a 200v 1800uf but it did not help and made things worse. I put the original back in and now the green power light flashes at a faster rate instead of the steady slow before.

That is start up cap, you cannot use 1800uf, it is way too much, and as I indicate, you cannot us the chassis as the GND ref for your meter.

[budm]

Re: Toshiba 37AV502R PSU

I do not know the current rating spec of this 5VSTBY, so it can be that the main board is drawing too much and causes the 5vstby to drop, or the power supply just cannot handle it.
You can try heating up the area for the 5Vstby section with hair dryer to see if it becomes steady, or try changing that C207.