LCD Power Supply

[karyoker]

uploaded jpg

 

[jetstream]

now i cant upload

Sorry, I have been a pain in the ?????

 

[karyoker]

**broken link removed**

 

[jetstream]

karyoker, here is a an edited ver. of your picks,( no offense ), do you know what is the voltage at pin 7 Should be? because I still don't have any voltage, and do you know if I can bye a schematic for this board anywhere.
THANKS again for all the help, sincerely and greatly appreciated.
https://www.electro-tech-online.com/attachments/bottom-of-polaroid-psb-jpg.31773/

 

[techy_not]

I have been having the same issue. My tv is dead no red light or blue light. I have done some light troubleshooting because of my lack of tools. I am not a techy...lol...
i can tell that the ac power gets to the ac side of the transformers but i get no dc voltage on the other end ot he transformer. All 3 of them. Any ideas?

 

[karyoker]

karyoker, here is a an edited ver. of your picks,( no offense ), do you know what is the voltage at pin 7 Should be?

Pin 7? Without a partial trace of a schematic i have no idea..

 

[techy_not]

I can definitley tell you that i think pin 7 is the load that is used to switch on the Tv. I dont know much about power supplies but just like a switch mode power supply in a computer there is always an extra wire that is used just for turning on the power supply. The voltage for pin 7 is meant to be 0.

 

[karyoker]

That voltage is 3.5 to 5 volts. 5 volts standby is routed to the main board and is indicated by the red LED. Pushing the on button keys the mico processor which sends the ON voltage to the power supply.

 

[techy_not]

okay thanks for the clarification. Would you know any reasons why none of the transformers send out any dc output although they receive the correct ac input.? I would hate to think all the transformers on the board are burnt. what do you think

 

[blueroomelectronics]

I have been having the same issue. My tv is dead no red light or blue light. I have done some light troubleshooting because of my lack of tools. I am not a techy...lol...
i can tell that the ac power gets to the ac side of the transformers but i get no dc voltage on the other end ot he transformer. All 3 of them. Any ideas?

You're going to need a multimeter, plus fixing TVs while unfamiliar with working with HV can get you dead.

PS transformers don't output DC only AC.

 

[techy_not]

I am bit familiar with electronics just didnt have access to tools. i am heading out to get a miltimeter. Its also an Lcd tv and the power board is isolated so i dont intend on getting killed just yet. Thanks for the tip thought.. i will post my finding once i get back with the multimeter.

 

[techy_not]

so this is what i found.
When i removed the dc side of the transformer from the board. IT does have power so i am assuming something on the dc side is shorting somewhere. there are some transistors i think i will test them in a bit

 

[jetstream]

techy_not, THANKS for getting in on the conversation, please keep us up on your progress.

 

[jetstream]

That voltage is 3.5 to 5 volts. 5 volts standby is routed to the main board and is indicated by the red LED. Pushing the on button keys the mico processor which sends the ON voltage to the power supply.

Does that mean the problem could be in the control panel, and not in the PSB?
In the factory service manual trouble shooting charts, they don't mention the PSB at all.

 

[techy_not]

karyoker, purpulhaze - any progress to report?

I have the same ps as chriss123, and same symptoms: no led at all. Our power supplies have 7-pin and 10-pin connecters, not the two 10s.

I have 24vdc on pins 4, 5, and 6 of the 7-pin, but 0v on pin 7, which appears to be the STB. Which would account for the no red led. I have 0v on all of the "hot" pins on the 10-pin, the one that feeds the lcd panel.

There is no visible bulging or leakage on any of the caps, and I don't have an ESR meter.

Anyway, karyoker, purpulhaze, any progress to report? Good news on your efforts, I hope?

Thanks,
Keith

Did you test the voltages on the board while all the connections were connected to the tv or did you test them with just the ac power cord connected to the psb.

 

[techy_not]

JUST TO LET EVERYONE KNOW
I called Polaroid today and they are selling the control box for $225 which includes everything in the grey housing. tuners, main board, power supply board. However if you tell them you are going to install it yourself they are selling it for $122 which is not a bad price to pay. So if you are in desperate need just give them a call. As for me i will buy it someday but i figure if i found out what was wrong i could help some others as well.

 

[jetstream]

THANKS techy_not for all your efforts, keep us posted please.

 

[techy_not]

So far i have tested all the capacitors, diodes , transformers and resistors. They all checked out okay. I think the problem maybe a transistor or one of the Ics'. What i have gotten so far is that all the transformers are converting to a lower ac voltage properly when the output pins of the transformers are disconnected fromt the board. Once re connected something gets shorted somewhere and there is no power comming out.
Any ideas on what i should be checking?

 

[rfxcasey]

Not to sound like a smart guy, but have you checked for physical shorts whether it be solder joints, the board or componet making contact with something? I have seen cases where solder has heated up enough to reflow and then create a bridge where one shouldn't be. Just some ideas, never underestimate the obvious. Also there should be some shunt or overvoltage circuitry in there. Make sure it is working correctly and not jumping the gun so to speak. Maybe a weak relay but I am just throwing that one out there.

 

[techy_not]

lol..Thank you but yes i have checked these as well.