Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

[djh2]

Hi, I've had this broken set for a while now and have narrowed the issue down to the power supply board.

The TV indicator light turns orange when plugged in, and changes to Blue when you press the power button. However, there is no screen response which I believe is due to the lack of 12V/24V power sources.

I have taken some measurements and testing on components based on other posts here, but I'm just looking for some advice now based on what I've come up with.

Here are the test voltages on the connectors, in both states:

After plugging unit in, indicator light turns on, Orange
1 - GND : Unused 
2 - GND : 0.00
3 - GND : 0.00
4 - GND : 0.00
5 - 24V : 0.00
6 - 24V : 0.00
7 - 24V : 0.00
8 - 24V : Unused

1 - GND : Unused
2 - GND : Unused
3 - 24V : 0.00
4 - 24V : 0.00

1 - 12V : 0.00
2 - GND : Unused
3 - GND : Unused
4 - GND : Unused
5 - GND : Unused
6 - 5V   : 0.00 
7 - 5VSTB? : 0.00
8 - 5VSTB : 5.07
9 - STB  : 0.14
10- 5V   : 0.00
11- 5V   : 0.00
12- GND  : 0.00
13- GND  : 0.00

Big Cap Voltage: 162V (Should be OK)

After pressing Power Button, indicator light turns Blue
1 - GND : Unused 
2 - GND : 0.00
3 - GND : 0.00
4 - GND : 0.00
5 - 24V : 0.00
6 - 24V : 0.00
7 - 24V : 0.00
8 - 24V : Unused

1 - GND : Unused
2 - GND : Unused
3 - 24V : 0.00
4 - 24V : 0.00

1 - 12V : Reads 0.10 max then decreases to 0.00 over 2-3 seconds.
2 - GND : Unused
3 - GND : Unused
4 - GND : Unused
5 - GND : Unused
6 - 5V   : 5.06 
7 - 5VSTB? : 5.06
8 - 5VSTB : 5.07
9 - STB  : 4.00
10- 5V   : 5.06
11- 5V   : 5.06
12- GND  : 0.00
13- GND  : 0.00

Big Cap Voltage 278 (Not high enough, should be 380-400 VDC)

I see that the large capacitor (with RoHS sticker in picture) is not getting the correct voltage at the "ON" state. I'm not sure what this relates to, because unlike most my other TV projects, I haven't found a whole lot of information on this power supply and my background is not as strong once you get to these more complicated (to me) fixes.

I did not change any capacitors yet, although I have read that the Cold side caps are susceptible to having issues especially when they are CapXon brand. Nothing looks visibly buldged, but I'm aware of the quality issues with the brand. I've got another project with parts to order from Digi Key, so if you have any suggestions for specific things to test and replace, I can add to the order.

Thanks for your help!

[CapLeaker]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

No high voltage from the PFC = no 12 and 24v.
Btw a new PSU from SJ is $40. Unless you are fixing it for educational purposes, it isnt worth it.
Are there any capacitors underneath that big heat sink on the left?

[ReeceyBurger123]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

I had this on this Psu the 24v output diode was shorted. Do you have a DMM and know how to check for S/C ?

[jetadm123]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

The STB pin is the PS_ON, which from your readings is getting 4V from the main board when you push the power button. For this power supply, you can disconnect the right side connectors and just leave it connected to the mains. If you get 12V and 24V output, then your problem lies elsewhere. Photos of the entire back side of how all the boards are connected would be helpful.

[djh2]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

CapLeaker: There is a 10uf 50V capacitor under the perforated metal heat sink on the left. This is repairing for educational purposes

ReeceyBurger123: Thanks for the tip, I checked D4 D5 and D6, which are 3-leg diodes. FCH20A10 is D4 and from the datasheet, looks like pin 2 is the shared leg of the diode. Regardless, each of these appear to have a measurable, low resistance between the legs which I understand means they are shorted (as diodes should read ~infinity). Testing on diode mode, the meter gives a beep then starts increasing, which to me also signals a problem for the diodes. D16, a small cylindrical one on the Hot side beeps as continuous.

For example D5 readings, diode mode:
1-2: 595
2-1: 188
Similar behavior for 2-3 3-2


jetadm123: I attached a (bad quality) photo of the back of the unit. The main board is along the bottom, looks like LCD inverter on the left, and T-Con on the top

[jetadm123]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

A shorted inverter is common on this model, which could be giving you the readings on the diodes you're measuring. Another quick test you can run is to disconnect the two plugs from the inverter. If the the 12V and 24V comes up, then you have verified the inverter is bad.

[dabone]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

I've got one of these,power button responds, turns on the +24 and +12 voltages with the inverter attached. 4 Volts appears on the STB, but never any backlights.

I had a couple of dead 1000uf caps on the psu I replaced. (c10 and c16)
I also replaced the 1000uf caps at c14 and c15 also, since I had extras.

So to recap, I have voltages, but no happiness.

Comments? Suggestions?

Thanks.

[budm]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

So you have 24V for running the inverter board, but do you have BL-ON and Dim control signals to turn on the Inverter?
How about pictures of YOUR board? I assume you already tested all the fuses on the inverter board.
Is it one the troublesome SAMSUNG Inverter board?
Toshiba/RCA/Samsung LJ97-02098B (INV40N14B) Backlight Inverter
http://www.shopjimmy.com/toshiba-rca...t-inverter.htm

[dabone]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

It's that inverter board.

And I thought I had checked the fuses, but checking again today, f102 is open.


No stock on boards, do you think I should just get this and install it?
I've currently got $25 in the tv, and my labor is free.

http://www.shopjimmy.com/samsung-lj9...repair-kit.htm

Or there is a used one available for $23.00

[jetadm123]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

Well, it depends on your soldering skills. There's a lot of fine pitch soldering involved. If the warranty is good for the used board, you might be better off spending the additional $8.00.

[dabone]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

Well I got the rebuild kit, I figured that the used board would need it eventually also. As for skills, I've got em, and the hot air rework station. .

So for my TV, it took 2 caps in the PSU, and the rebuild kit on the inverter board. It's up and running, and I'll leave it on all day tomorrow when I'm back in my shop to test some more.

Later,
dabone

[dabone]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

Well crap, It worked for about 2 hours, and now I've lost backlight again.
Now the fuses are stable, but when the inverter board is connected I lose my +24v.

Grrrr.

Later,
dabone

[budm]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

Well crap, It worked for about 2 hours, and now I've lost backlight again.
Now the fuses are stable, but when the inverter board is connected I lose my +24v.

Grrrr.

Later,
dabone

It sounds like the inverter board failed caused the over current draw so the the 24V power supply goes into shutdown mode, the 24V power supply has problem and cannot handle the load.

[dabone]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

I ended up buying a substitute board off ebay straight from china.




It plugged straight in, but the mounting is the strangest thing, It came with 4 stand offs that have magnets on the bottom. So, I wouldn't want to ever ship this thing.

But it works just fine. And the board only cost $16.00 + shipping.

You know that the original boards are crap when someone took the time to make a drop in sub.

Later,
dabone

[djh2]

Re: Westinghouse VR-4085DF / MLT668TL-V Power supply troubleshooting

OP here just closing the loop. I decided the electronics debugging was over my head on this board and ended up buying a replacement. That fixed it! Thanks for your help though, and it looks like dabone got some help here too.