Toshiba power supply 37LX96 repair

[MtnFrost]

Hi All, and hello!

I got a toshiba 37LX96 very cheap because the owners claimed it was good as long as it was kept plugged in, but if you unplugged it, they had to wait 3-4 days before they could plug it back in and have it work.

Starting from scratch, plugging it in revealed the three yellow flashes. So I replaced the three ICs normally associated with this issue - strz4479, strw6765, and srx2039. Visually checked the caps, nothing visibly bad.

Now plugging it back in and nothing flashes - the relays on the power board are cycling, click-click, click-click.

I want to repair this board, but I have not been able to find schematics and the only service manual I could find and download for this set was a zipped collection of broken html pages and DWF files.

I find the relays don't click if I unplug PB809B. I am not reading the 30v or 24v pins. The 5v pins reads correct.

Help? Thanks

[budm]

Re: Toshiba power supply 37LX96 repair

Here is the SCH for the power supply board.
BTW, there are two relays, which one is clicking? the 5V Relay or the 12V relay?

[MtnFrost]

Re: Toshiba power supply 37LX96 repair

Thank you Bud for the SCH! I believe it's the 5V relay, though to be honest the two are so close to each other I'm having a hard time definitively telling which is clicking. I've included a pic of the board, front and back, for reference.

[MtnFrost]

Re: Toshiba power supply 37LX96 repair

Okay, definitely the 5V relay. I was able to visually confirm it.

Just a note on my background with electronics - I was a collector of pinball machines for several years, and that required I learn how to use a multimeter, solder and desolder, and learn core concepts of electronics to repair and troubleshoot the early solid state boards.

In short, I know I can repair this board, but greatly appreciate all help.

[budm]

Re: Toshiba power supply 37LX96 repair

You may want to read this:
https://www.badcaps.net/forum/showth...oshiba+42HL196
His board has intermittent 5V that some times it will work OK with resistor load.
You can try loading your board and see what happen.

[MtnFrost]

Re: Toshiba power supply 37LX96 repair

I read through the link - am I reading it right that there never was a solution?

[budm]

Re: Toshiba power supply 37LX96 repair

I did not hear back from the OP. the problem is that some time his 5VSTBY power supply will go dead and then comes back again just long enough to probe for more but then it dies again, he may have bad connection some where. So we need to use resistor on the 5VSTBY by itself without any other board connected, then we can try force on after that to find out if the PFC, the 12V are working or not. The main key is to get the 5VSTBY to work first.

[MtnFrost]

Re: Toshiba power supply 37LX96 repair

So I'm going to be using a resistor to connect the 5VSTBY to ground, right? I seem to remember someone posting a link to their test setup somewhere here.

Found the link - this setup?

https://www.badcaps.net/forum/showth...196#post507565

I take I don't need to hook up a 12v bulb for our testing purposes.

[MtnFrost]

Re: Toshiba power supply 37LX96 repair

So I connected two 1K resistors from the power and power sig to ground, just to see what we'd get without any other board connected. Sure enough, the 5V relay is clicking on and off.

[MtnFrost]

Re: Toshiba power supply 37LX96 repair

So using my limited understanding of all things circuit board related, the clicking of the 5V relay is the relay closing, and then opening. So the driver circuit closes the relay, but the load side of the relay cannot sustain that closing, and the relay goes back to it's initial state. And then the driver circuit closes the relay again, and we keep repeating the process.

So the driver circuit is good, but the load side is not. Do I have that right? Thanks!

[MtnFrost]

Re: Toshiba power supply 37LX96 repair

So I connected two 1K resistors from the power and power sig to ground, just to see what we'd get without any other board connected. Sure enough, the 5V relay is clicking on and off.

Checking voltage at C840, I'm getting 160-166 V DC. This seems to be in keeping with what we'd expect, based off that troubleshooting link posted further up. I'm also not getting 5V DC at the 5V-1 post at P809B - it fluctuates between nothing and .8 V, timed to the relay clicking.

[budm]

Re: Toshiba power supply 37LX96 repair

OK, no need to have the force on resistors connected yet, since 5VSTBY is always running, we need to put the resistor load to see if it can handle the current draw, 10 Ohms 5W will draw 0.5A, 5 Ohms will draw 1A.

[MtnFrost]

Re: Toshiba power supply 37LX96 repair

Okay, I'll remove them and put 10 Ohms 5W resistor on the 5V1 and GND. Thank you for the help. Have to run out to get one. Will report back. Thank you.

[CapLeaker]

Re: Toshiba power supply 37LX96 repair

In the schematic there was a note on one page that the 5v rail only supported 250ma

[MtnFrost]

Re: Toshiba power supply 37LX96 repair

As it happens Radio Shack has nothing I need, so I have to wait until tomorrow to find a local electronic store. Let me know if you think I should get a different rated resistor for the load test. $#$ radio shack....

[budm]

Re: Toshiba power supply 37LX96 repair

In the schematic there was a note on one page that the 5v rail only supported 250ma

Good catch, use 20 Ohms 2W.
You can use 60W 120v Incandescent lamp which will have enough cold resistance close to 20 Ohms.

[sammons]

Toshiba 55UX600 75017826 power supply DPS-255GP

Hi,
Toshiba 55UX600 power supply DPS-255GP 75017826
We have a good looking 55 here that needs a power supply. I would like to repair this one but as far as I can tell, there is no manual available. PS has no STY BY voltage and is dead. Anyone willing to try there hand on the repair ? I would be glad to pay. Looking for diagram . Power supply is available in India but I can't find anyone who will ship.
Please contact me at
sammonselectronics@lycos.com

David

[MtnFrost]

Re: Toshiba power supply 37LX96 repair

Sorry bud for the delay - I am working with one of those online electricians to troubleshoot the board and accidentally blew out Q840 and a resistor. Had to wait forever since I have no local electronic parts supplier locally. After replacing those, we're back to square one, where the 5V relay is power cycling.

[CapLeaker]

Re: Toshiba power supply 37LX96 repair

... and you still not having 5V-1 on PB809B under load? What happens to the 5V-1 when nothing is connected to it? Does it come up, or is it still gone?

[MtnFrost]

Re: Toshiba power supply 37LX96 repair

Still gone. I've gotten some sample readings around the board as we've been working through. I'll share them here. These are taken with 1K resistors from power and sig_power to ground on a workbench, out of the tv. When plugged in, after replacing Q840, the board takes about 10 seconds after the relay engages before the relay begins cycling.

Q840 pin 2 using pin 3 as hot ground: 21 VDC, cycling to 10 VDC with relay
Cathode of D842 - fluctuates between 167 and 162 VDC
Pin 5 of Q840 - fluctuates between 160-96 VDC
Cathode of D823 - fluctuates between 167-164 VDC
Q820 Pin 7 - fluctuates between 9.6 and .4 VDC
Fuse F820 is getting 167-164 VDC, again fluctuates with the relay
D825, D8273, D8274, D826 and R8217 are all confirmed good (tested out of circuit)

With unit unplugged, Q820 resistance for:
Pin 1 & 2 = 296 K
Pin 1 & 3 = 292 K
Pin 2 & 3 = 4.1 ohm

Plugged in, Q820:
Pin 4 and 5 - no measurable voltage
Pin 6 cycles between 2.2 - .5 VDC
Pin 7 cycles between 7.8 - .5 VDC

There is 22V at the collector of Q822
Testing between ground and 5V1 on P809B I get no measurable voltage.