Sanyo DP42740 - Powers On, No Video - Missing 15/25v

[grimacelord]

TV original came to me with no power, no LED, no sign of life whatsoever. I took some initial voltage measurements and found the SN board had multiple shorted components on the board and I found a replacement cheap enough so I replaced the SN board. I also bought and installed a repair kit for the main power supply board. Now, the TV shows some signs of life, but it still isn't there yet. I scoured through all of the threads here about this model, but haven't found anything similar to this particular problem. Here is what it is doing now:

When I plug in the TV to power, I hear the relay click and a few seconds later, click once more. I can press the power button and the relay will click again and the LED turns green and remains on. There is no video on the display or even a slight glow. Just totally black.

Taking measurements of the various voltages, I find that all of them are present except for 24/15V measured at J1624 on the analog control/power board (which is where I assume I should be taking all of the voltage measurements anyway because I can't find printed values for the voltages or test points on the main power board. The analog control board/power board is the only one with printed values at the various jumper pin sites.)

The two main 450V 100uF filter caps marked as CE202 and CE201 both measure at 167.4V across their legs while the TV is powered on. All 3 fuses are not open.

My specific chassis model is DP42740-05 J4HGE. I cannot find a service manual specific to this chassis model, so I am using one I found for DP42740-00 J4HE which is a bit different that mine.

Not really sure where to go from here. Was hoping someone could help. Thanks guys. Attached pics

[grimacelord]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

Update: I believe the digital main board is at fault, but I cannot find a 1LG4B10Y06900 J4HGE board ANYWHERE. I have found several of other model boards including a 1LG4B10Y06900 J4HG (no "E") but I have no idea if they are compatible or interchangeable.

[budm]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

"The two main 450V 100uF filter caps marked as CE202 and CE201 both measure at 167.4V across their legs while the TV is powered on. " The power supply board has PFC Voltage booster circuit so if the PS-ON is present then the DC Voltage on the filter should be around 380 ~ 400VDC range if the PFC circuit is working, at this point it is not working.

[R_J]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

I agree, pfc is not working, Did you find and bad parts on the power supply board or just install the parts from the kit? If any parts were bad that might give a clue to what else is bad

[grimacelord]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

"The two main 450V 100uF filter caps marked as CE202 and CE201 both measure at 167.4V across their legs while the TV is powered on. " The power supply board has PFC Voltage booster circuit so if the PS-ON is present then the DC Voltage on the filter should be around 380 ~ 400VDC range if the PFC circuit is working, at this point it is not working.

Wow. I must be tired. I even remember thinking that yesterday! That the PFC circuit wasn't working. I somehow totally forgot about it and even missed it as I typed out this thread. Ugh.

So, any idea on where I can start poking and prodding around to find the cause?

I agree, pfc is not working, Did you find and bad parts on the power supply board or just install the parts from the kit? If any parts were bad that might give a clue to what else is bad

I installed everything from the kit except for the 3 fuses as the original 3 fuses were just fine. The parts I replaced were:

Q211
Q206
Q505
Q507
U203
U204
U208
U202
UN301
UN302
UN303
D201
D202
D203
D209
F100

EDIT: Here is the closest service manual I can find for my model: on page 12 it begins listing the part numbers and component values for the various components.

[R_J]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

I would start by rechecking the parts you replaced, If the original fuses were ok its likely the power supply components were ok.
Do you have vcc voltage on pin 12 of u204 when tv power is on (not in standby) Due to the fine pin pitch of the ic, find a place away from the ic to measure the voltage

[grimacelord]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

I would start by rechecking the parts you replaced, If the original fuses were ok its likely the power supply components were ok.

Well, it was only after I replaced those components did I start to get a bit of life out of the TV. Prior to installing the components, I got no relay clicks, no LED, nothing. After, I now get relay clicks, green LED, all voltages except for the 24/15v one I mentioned.

I tried finding a service manual for the Darfon B159-001 power supply and wasn't able to find one. I was, however, able to find one for the Darfon B159-201 and there is a section there on the PFC circuit.



page 4 shows the PFC circuit, but the model may be too different to really get any helpful information out of it. I thought I would post it anyway to see if you guys thought it would be helpful

[R_J]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

Ok, you likely had no standby voltage at the start, installing the parts in that circuit restored the standby voltage, I believe that schematic is very close but the part locations are different.
You can see from the schematic, the standby circuit supplies VDD1 (D305), check if that voltage is ok, the opto will turn on Q409 and Q315 will supply the VCC_P for the pfc circuit when you have F15V_ON

[Unspun01]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

In your first picture, there appears to be a discoloring of the PCB near capacitors CE316 and CE317 (possibly from the 8-pin SOIC component U203 directly on the underside of the board). Did you replace U203? or is it original? Perhaps this component is burned?

Several models of Sanyo 42" and 47" LCD mainboard has issues with a 8-pin SOIC regulator used in 13V audio amplifier circuit. This plasma does not use same mainboard, but I would check IC6720 on the mainboard near where the 4-wire audio plug is. It could be pulling voltage down.

[grimacelord]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

... VDD1 (D305), check if that voltage is ok, the opto will turn on Q409 and Q315 will supply the VCC_P for the pfc circuit when you have F15V_ON

The problem is D305 is located on the bottom side of the power board. Do I need to have all of the boards and cables connected to test D305?

[grimacelord]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

Do you have vcc voltage on pin 12 of u204 when tv power is on (not in standby) Due to the fine pin pitch of the ic, find a place away from the ic to measure the voltage

I will test this in the morning and let you know.

[grimacelord]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

In your first picture, there appears to be a discoloring of the PCB near capacitors CE316 and CE317 (possibly from the 8-pin SOIC component U203 directly on the underside of the board). Did you replace U203? or is it original? Perhaps this component is burned?

Several models of Sanyo 42" and 47" LCD mainboard has issues with a 8-pin SOIC regulator used in 13V audio amplifier circuit. This plasma does not use same mainboard, but I would check IC6720 on the mainboard near where the 4-wire audio plug is. It could be pulling voltage down.

U203 was replaced as part of the power board repair kit. I will check IC6720 in the morning as well. I will have to grab a datasheet on it and see what the pins are. Thanks for the advice. I'll update in the morning.

[R_J]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

To check the D305 output, check across CE316 capacitor. (top of board)

[grimacelord]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

Ok, you likely had no standby voltage at the start, installing the parts in that circuit restored the standby voltage, I believe that schematic is very close but the part locations are different.
You can see from the schematic, the standby circuit supplies VDD1 (D305), check if that voltage is ok, the opto will turn on Q409 and Q315 will supply the VCC_P for the pfc circuit when you have F15V_ON

Sorry it took me awhile to respond. Got busy with other things.

Voltage on D305 is 17.82 DCV. I took the measurement with only main logic board connected to power supply as the service manual instructs for troubleshooting the power supply.

[grimacelord]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

Several models of Sanyo 42" and 47" LCD mainboard has issues with a 8-pin SOIC regulator used in 13V audio amplifier circuit. This plasma does not use same mainboard, but I would check IC6720 on the mainboard near where the 4-wire audio plug is. It could be pulling voltage down.

I replaced the regulator and no effect. Unit will respond to power button press, green light, relays click, no image/glow, no sound, and two main filter caps still not boosting at 167.8 DCV

[R_J]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

That diode supplies the VDD1 voltage, On page #1 of the schematic you see its source, on page #3, Vdd1 is the supply to switch Q409 that supplies regulator transistor Q315 which supplies VCC_P.
{part on board}
You need to follow that same circuit on the board itself, After D305 the voltage goes through two 10Ω resistors in parallel, then to RJ15 (0Ω) - RJ25 - RJ27 - Q407 {Q409?} then to Q305 {Q315?} I believe Q305 could be the regulator transistor that supplies the VCC_P to the PFC ic U204
Check if you have voltage on {Q407} E & C

[grimacelord]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

That diode supplies the VDD1 voltage, On page #1 of the schematic you see its source, on page #3, Vdd1 is the supply to switch Q409 that supplies regulator transistor Q315 which supplies VCC_P.
{part on board}
You need to follow that same circuit on the board itself, After D305 the voltage goes through two 10Ω resistors in parallel, then to RJ15 (0Ω) - RJ25 - RJ27 - Q407 {Q409?} then to Q305 {Q315?} I believe Q305 could be the regulator transistor that supplies the VCC_P to the PFC ic U204
Check if you have voltage on {Q407} E & C

Thanks for the reply. I disconnected all boards from the power supply except for the main logic board and of course the power cable. Flipping the power board over and testing these components, I'm getting a different voltage than I was before.

Following the circuit from D305, I now get 8.03DCV on each component along the circuit. 8.03DCV from D305, the 10 ohm resistors in parallel, RJ15, RJ26, RJ27, and both E and C of Q407.

Weird because I was getting 17.82DCV at the diode earlier.

The two 10 ohm resistors both read 5.5 ohms, I thought I'd add.

[grimacelord]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

Here is the circuit. Best photo I could come up with at the moment.

[R_J]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

What ground are you using to measure that voltage? It could be that the supply is in standby and you need the F15v_on signal to fully turn on that section.
When all the boards were connected did you ever check if there was any Vs or Va voltage?

as for the resistors, two 10Ω in parallel = 5Ω, so they are good,

[grimacelord]

Re: Sanyo DP42740 - Powers On, No Video - Missing 15/25v

What ground are you using to measure that voltage? It could be that the supply is in standby and you need the F15v_on signal to fully turn on that section.
When all the boards were connected did you ever check if there was any Vs or Va voltage?

as for the resistors, two 10Ω in parallel = 5Ω, so they are good,

Whoops. That's what threw off the voltage. I went back and remeasured this time using a leg of one of the heatsinks for the mosfets as ground and got 16.5DCV. I checked all down the circuit at each component and got 16.5DCV. After about 3 minutes of being plugged in and on, I check again to double check my readings and now its 18.10 consistently down each component. I power off the TV, unplug, wait a minute or two, and the whole process repeats. Starts at 16.5DCV and after a couple minutes, it boots to 18.10dcv.

Q407 E & C gets the same. 16.5DCV initially and then 18.10 when it boosts up after a couple minutes.

As far as Vsus and Va goes, I am not sure where to measure it since there is no printed values or test points on the board.
If you could tell me where to measure it, I'll gladly take a measurement.

Also some additional info that might be helpful, with TV plugged in and powered on, pin 1 of P2 that goes to the SN board measures at 72.5DCV. pin 1 of p11 that goes to SS board reads 1DCV. Definitely something wrong but I don't know what it means. Plasmas are kinda confusing to me.

Anyway, thank you so much for your help and patience so far. I'll keep at it as long as you (or someone else) is willing to.