Sanyo DP32642 No Power

[killian6pk]

I picked up a very clean 32 inch Sanyo tv at the electronic recycle bin. There is no power after the main fuse. I changed the caps including the main filter cap. The main fuse was blown when I first checked out the power board. I replaced it and it is not blowing when I plug it in. I checked to see if I had power at the main filter cap and had none. I also do not have any power at the plug from the power board to the green main board.

Any ideas where I might check to see if anything else might have gotten fried.
By the way I did a search on this model and only found a couple of threads, neither seemed relevant. I have attached photos of the front and back of the power board.

Thanks for the help.

[tom66]

Re: Sanyo DP32642 No Power

Test across the inner two pins of the bridge, on AC volts you should see approx 120V.
Test across the outer two pins of the bridge, on DC volts you should see approx 160V.

[killian6pk]

Re: Sanyo DP32642 No Power

Tom thanks for the fast response. I checked both as you asked and neither set of legs showed a reading. So I guess that means I need to replace the bridge rectifier?

[tom66]

Re: Sanyo DP32642 No Power

No, it means that AC voltage isn't reaching the bridge (you did test 120V on AC right?) which means that a fuse or other component along the way is failed -- just trace the middle two pins from the bridge, checking resistance as you go, and you should find what's open. Typical failures are the NTC and fuse, but you ruled out the fuse. Rare failures are the filter coils / line filters.

[killian6pk]

Re: Sanyo DP32642 No Power

Thanks I will check those.

[tom66]

Re: Sanyo DP32642 No Power

Also, check you get 120VAC at the AC input pins. May have a fuse in the plug? (Rare in US equipment I believe, but legally required in UK equipment.)

[killian6pk]

Re: Sanyo DP32642 No Power

Ok I will check the plug also.

As you suggested I followed the traces from the two middle ac pins of the bridge rectifier. One pin traces to one side of the main ceramic fuse. The other side traces to one pin where the AC cord connects to the circuit board. There were no breaks in the continuity all the way to those points. You mentioned something about the NTC. I don't know what that is.

If I accomplished what you wanted, there does not seem to be a problem up to the B.R. Any other suggestions?

[budm]

Re: Sanyo DP32642 No Power

The NTC is for the inrush current limiter (its resistance is about 2~5 Ohms range), it is connected to one of the bridge AC in. So you should check and see if you do get the continuity all the way to the AC plug. BTW what resistance do you read on the continuity test? We need to get 120VAC at the two pins of the bridge.

[killian6pk]

Re: Sanyo DP32642 No Power

Bud
I did get continuity all the way to one pin of the power plug on the board.
The NTC read 1.7 ohms. Measured with one probe on each leg.

From one of the AC pins of the Bridge it was between 1.7 and 2.3 ohms at every solder connection on the trace.

From the other AC pin of the Bridge it was between 0.2 and 0.7 ohms at every solder connection on the trace. In other words at each solder point the resistance reading was a little different. Don't know if that is normal or not.

If you look at the picture of the top of the power board next to the NTC (gray colored not green as they usually are) (bottom right corner of picture) there is what appears to be one of two small transformers. One of the traces is connected to one side of the transformer and it read 1.7 ohms. On the other trace it read 0.2 ohms. There again not sure if this is correct or not.

[tom66]

Re: Sanyo DP32642 No Power

So, you have 120V AC in at the pins from the plug, and at the socket? Because there is no other way the voltage could get lost.

[killian6pk]

Re: Sanyo DP32642 No Power

The pins where the AC line connects to the board show 124v and the fuse shows 124v and I rechecked the 2 AC pins of the Bridge Rectifier and they read 0.45v.

I also checked the AC plug and could see no fuse in it or where it plugs into on the board.

Bud mentioned the In Rush Current Limiter NTC. I'm not sure what voltage it should read, but it also read 0.45v. Maybe that part could be bad. I am not sure what its part number is so I could not look up a spec sheet on it.
It has 3 printed lines
5 (This could also be an S maybe a logo sort of looks like a 3D 5 or S)
1.5 D215
C X
any ideas

[budm]

Re: Sanyo DP32642 No Power

Please check the AC voltage a each pair of the test points from 1 ~5 to see where you lost the 120vac.

[killian6pk]

Re: Sanyo DP32642 No Power

I've discovered why I don't have power to the bridge currently. I was measuring the fuse with one lead on each end. It was showing the 124 volts. But when I checked the fuse (with no power on) on the ohms setting it was showing open. I believe that I was checking the fuse incorrectly when actually it had blown again. I started checking the N-Channel fets on the heat sinks to see if one of them could be blown and causing the fuse to blow. I found two that were bad. I have ordered them.

Bud I will check the test points you circled and get back to you.

Bud as I guessed none of the test points read more than 0.6mv due to the bad fuse. I don't want to put another fuse in until I replace the fets that are bad. Hopefully those are the only two problems on the board and it will work properly when those are replaced.

On the other tv's I've fixed the culprit was either one or two 1N5406 600v 3amp Rectifier Diodes and a fuse on each set. I am hoping that the fets are all that is wrong. I tested several of these high voltage diodes on this board by pulling one leg and they were good.

[tom66]

Re: Sanyo DP32642 No Power

If the FETs have failed, also recommend replacing their respective driver resistors and the driver IC. Can you highlight which FETs died? Also check the bridge for shorts -- a shorted bridge may make two FETs in series (for example) look shorted.

[killian6pk]

Re: Sanyo DP32642 No Power

Ok will do. I pulled each of the fets and checked them out of circuit so nothing would influence my readings. I will get the pictured with the fets marked back to you ASAP.

[killian6pk]

Re: Sanyo DP32642 No Power

Tom
I marked in red the two fets that failed.

Could you mark which are the driver resistors and the driver IC.

Thanks

[killian6pk]

Re: Sanyo DP32642 No Power

Sorry forgot to attach the photo.

[tom66]

Re: Sanyo DP32642 No Power

How did you determine those to be failed? Very odd for two FETs on different parts of a circuit board to be bad. If the two in a pair were bad, I'd not have much difficulty accepting it...

[killian6pk]

Re: Sanyo DP32642 No Power

I checked the Fets out of circuit with my auto ranging DMM set to diode.
Fet 1
Pin 1-2 Pin 1-3 Pin 2-3 (Black probe on first pin red on second)
OF OF .389v

OF OF OF (Red probe on first pin black on second)

Fet 2

Pin 1-2 Pin 1-3 Pin 2-3 (Same as above for probes)
.001v .001v .000v

.001v .001v .000v

Also checked ohms

On Fet 1 all pins read OF

On Fet 2
1-2 1-3 2-3

1.6ohms 1.4 .2

Also checked bridge rectifier in circuit (Let me know if you think this one is good or bad)

Ohms Test
Pin 1-2 1-3 1-4 2-3 2-4 3-4
.708mohm .769m .764m 1.74m .754m .711m

Diode Test

1-2 1-3 1-4 2-3 2-4 3-4 (Black on 1st pin red on 2nd)
.470v .478v .470v OF .482v .475v

2-1 3-1 4-1 3-2 4-2 4-3 (Red on 1st pin black on 2nd)
OF OF OF OF OF OF

Let me know if I did this correctly. Sorry the layout stinks. Hope you can read it.
Thanks

[tom66]

Re: Sanyo DP32642 No Power

FET 2 is definitely bad, but FET 1 looks OK to me. I would replace FET 2 and if it has a partner (like one next to it) then I would also replace that. On the bottom of the board you will have some SMD resistors and a small chip to drive the FET, those should also be replaced.

mohm on bridge = 2000 kohm? It looks OK.