Sanyo DP37647 no backlight

[ishfish]

Hey all, I've got a Sanyo DP37647 with no backlight at all. LCD is working, just no backlight. I thought I was probably looking at a bad inverter board as I've done a few easy fixes with that before, but after reading a different thread about this and testing a little on the inverter board, I started to wonder if I was wrong.

The first thing I did was test power to the inverter board from the power supply and I'm getting about 16V. My understanding is it should be 24V and that's where it ends for me.

I don't know what else to test or what might be causing that. All components on all of my boards look okay, nothing looks burnt/blown out. The power boards are running close to $100 and my customer wants to know if there's any chance of me just fixing his old board (so do I) as a cheaper option if that is indeed the issue.

Any guidance or help is greatly appreciated. Thanks!

[johnboy1313]

Re: Sanyo DP37647 no backlight

I can get you the service manual if you get me the chassis number off the tag on the bag. i.e DP37647-01, -02, -03, etc...

[ishfish]

Re: Sanyo DP37647 no backlight

Looks like -00?

[tom66]

Re: Sanyo DP37647 no backlight

http://www.toms-service-manuals.com/...&Search=Submit

[budm]

Re: Sanyo DP37647 no backlight

Upload good clear picture of the boards, closed up picture of the inverter boards, especially around the connectors so we can see if there are any voltage labeling on them. We are looking for BL_ON (INV_ON or ON/OFF) signal, 24V pins on the inverter board,

[ishfish]

Re: Sanyo DP37647 no backlight

I've attached an overview picture, the power board, connectors to the inverter, the inverter board, and the connectors from the power board. The 24V lines coming off of the power board are what I'm testing ~16V.

[tom66]

Re: Sanyo DP37647 no backlight

16V way too low. Check your multimeter is accurate by testing a fresh 1.5V battery.

[ishfish]

Re: Sanyo DP37647 no backlight

Just tested my multimeter on 3 1.5V batteries and a 3.7V phone battery. It's reading correctly on all of them.

The 16V reading had led me to suspect the power board in the first place, but I don't know enough about it to track down what might be wrong.

[Shane711]

Re: Sanyo DP37647 no backlight

I have a Sanyo DP37647 and I am having this exact problem. I am getting 5v on the standby, 8v on the 12v and 17v on the 24v. A wierd thing is when I have the main board disconnected I get 23.6v on the 24v and 11.6v on the 12v. Seems to me there might be a short on the main board but if not I guess it could be a bad cap on the Power board. Any ideas?

[budm]

Re: Sanyo DP37647 no backlight

What is the DCV measured between the two legs for the main DC filter cap when the TV is ON?

[Shane711]

Re: Sanyo DP37647 no backlight

With everything plugged in I am getting 140v on, 146v off. With the main board disconnected I am getting 186v on. I am guessing this is way too low.

[budm]

Re: Sanyo DP37647 no backlight

AC 120VAC feeding the TV then you should have about 165~170VDC (120VAC x 1.414 = 169VDC), if you are only getting 146VDC (TV OFF) on the two legs of the main filter cap, I would say you probably have bad filter cap, since when TV is off you will have minimum load on that filter cap.
Any good clear pictures of YOUR board?

[Shane711]

Re: Sanyo DP37647 no backlight

OK, I took the power board and resoldered some connections, didn't see any broken spots. Used a different meter and got 211v on the cap. Might have been the use of a different(Better) meter. Still getting the voltage drop with the main board connected. Everything on the power board seems perfect. There is like 165v DC leaving the rectifier. I had another TV with the same problem and I changed all the caps and that fixed it so I think I will try that. I will start with the main cap.

On the main board I was testing the power fail circuit. The voltages looked good except for D1621 which is suppose to read 33v but is 5.75v. Not sure if this means a main board failure.

[budm]

Re: Sanyo DP37647 no backlight

So now with all the boards connected, you are still getting steady 165VDC between the 2 legs of the main filter cap, right? So when the power switch is activate do you get >360VDC? If not, then the PFC Voltage booster circuit is not working. You do have PS-ON control signal form the main board feeding the power supply board, right?

[Shane711]

Re: Sanyo DP37647 no backlight

167.7v with the power off, I press power and it goes down to 163.00 and the backlights flash. I found 4 weak caps on the PS and changed them, not making any difference. I also changed out the main cap with one closer to the value of 150uf. Also it seems that at one time there was an arch from the PS to the frame, I included a picture. Sounds like it could be the PFC Voltage booster circuit as you describe, but I am not sure just what that is.

[budm]

Re: Sanyo DP37647 no backlight

167.7v with the power off, I press power and it goes down to 163.00 and the backlights flash. I found 4 weak caps on the PS and changed them, not making any difference. I also changed out the main cap with one closer to the value of 150uf. Also it seems that at one time there was an arch from the PS to the frame, I included a picture. Sounds like it could be the PFC Voltage booster circuit as you describe, but I am not sure just what that is.

So you are not getting boosted PFC Voltage.
Need the pictures that show the whole bottom side of the power supply board so we can try to identify the PFC section.

[Shane711]

Re: Sanyo DP37647 no backlight

OK, there is a IC that I suspect, ICE 1PCS02. The weirdest thing is when I have it on and I am probing this IC it was cause the backlights to blink rapidly so it would seem this IC is at fault.

[budm]

Re: Sanyo DP37647 no backlight

ICE 1PCS02;' Are you talking IC800 DIP-8 through hole mounting IC?
That is the PFC Controller IC. Are you getting steady DCV at the VCC pin and Gnd pin?

[Shane711]

Re: Sanyo DP37647 no backlight

Yes, IC800 DIP-8 as you stated. I am getting a steady voltage at all the pins. I would think I would not get a reading at the ground pin but I do. Most of the voltages are around 33v. I am not at my shop now so I don't know the exact readings.

[budm]

Re: Sanyo DP37647 no backlight

Yes, IC800 DIP-8 as you stated. I am getting a steady voltage at all the pins. I would think I would not get a reading at the ground pin but I do. Most of the voltages are around 33v. I am not at my shop now so I don't know the exact readings.

You have to measure the DCV between the VCC pin and the Ground pin. Do not use the chassis as the GND ref. point for the meter because you are making Voltage measurement in the primary side of the circuit, not on the cold side (Isolated) of the circuit.

"I would think I would not get a reading at the ground pin but I do. Most of the voltages are around 33v" That must be an error in measurement method.