Viewsonic VG930M-3 - 2 seconds to black

[ChazzyD]

Hello everyone. I am a new troubleshooter and have fixed about 10 Viewsonic monitors all by replacing caps. This new monitor I have here to fix is a Viewsonic VG930M-3. It has the 2 seconds to black problem. I already replaced all the caps with Panasonic and Nichicon caps. I also replaced the large filter cap, still the same issue. I have determined that the three diodes on the power supply/Inverter board are passing electricity both ways and high values for passing voltage, so they are bad. I can also see a browning of the circuit board at the leads of one of them. Seems I have a shorted output transistor as well. I think I can identify and order one of those. I am getting 5V from the two red power supply pins, as I should. My problem is trying to order new diodes for this. How do I know what to order from Digikey? They have numbers on them but I have no idea what they mean. I can order caps on Digikey but diodes are a whole 'nother animal. Can anyone help me out? The screen looks fine for the two seconds it works, I would like to save it. Thank you.
Charles

[jetadm123]

Re: Viewsonic VG930M-3 - 2 seconds to black

If you can share those numbers, then maybe someone can help. It also wouldn't hurt to post a photo, so that we know what case style they are.

[budm]

Re: Viewsonic VG930M-3 - 2 seconds to black

We need to see the pictures of the board, the suspect bad Diodes, etc.

[ChazzyD]

Re: Viewsonic VG930M-3 - 2 seconds to black

The left most diode, I can't read any numbers as they are on the bottom. The right two have the same numbers, T9528 and B560 (maybe something before that, I can't see as it wraps around). I guess I would have to unsolder them to really get any good info off of them. They are D801, D805 and D807 on the board. The three diodes are just below the large caps at the top of the board. The left diode has browning of the board at the leads. Power Supply board PI-SB03 REV: D P/N BLM1700P60210-2. BTW: I'm getting 165V at the large cap. Thank you for your help! I'm a novice at this, but I did manage to fix our Magnavox 32 inch TV a month ago with a new T-con board and I have also fixed 4 Apple Time Capsules with P/S caps, as well as the Viewsonics, so I keep trying.
Charles

[budm]

Re: Viewsonic VG930M-3 - 2 seconds to black

That D801 is the inverter circuit power supply section, you do need to remove it to get the number, it is more likely to be high speed diode (SCHOTTKY) rated at about 5A 50~100V.
SB560?
Here is the spec:

[ChazzyD]

Re: Viewsonic VG930M-3 - 2 seconds to black

Thank you: The D801 is a 31GF4 and the middle and right ones, the D805 and D807 are an LT9528 SB560. How do I find these on Digi-key?
Charles

[budm]

Re: Viewsonic VG930M-3 - 2 seconds to black

31GF4:

Just type in "31GF4" in search box on Digikey. Same for the other Diode.

[ChazzyD]

Re: Viewsonic VG930M-3 - 2 seconds to black

Ok, I found them both. The only problem is the 31GF4 is a non stock item. Any another source/s?
Charles

[ChazzyD]

Re: Viewsonic VG930M-3 - 2 seconds to black

Check that, Now that they are removed from the circuit board, they are testing as perfectly good diodes. Power only the proper way and passing the voltage in a good range the correct way. I'm learning. OK what next? Take the transistor out and test it off the board? I'm beginning to think maybe I have a bad CCFL?
Charles

[ChazzyD]

Re: Viewsonic VG930M-3 - 2 seconds to black

I have now tested the transistor out of circuit and it is good. I also did the transformer test per the procedure in the sticky thread so, I'm thinking on to CCFL tests. Not sure yet how I'm going to proceed as I don't have a spare CCFL. I will have to make a test bulb from a household screw in CFL bulb, I guess.
Charles

[ChazzyD]

Re: Viewsonic VG930M-3 - 2 seconds to black

Just to follow up on this, I took the screen apart to inspect the CCFLs and the bottom tubes were definitely bad. Blacked and one broken at the end. I ordered up a set from CCFL warehouse. Thank you all for your help. Taking the screen apart is pretty fiddly, I wouldn't think you would want to pay someone to change these as I think it would be cost prohibitive labor wise. My time is free though so I will spend the time and fairly little money to save it.
Charles