Sansui LCD does not power on

[vusi]

Hi friends

i have been fixing a Sansui LCD TV (model SV3220) that did not not power on, first i repaired the power supply(200-P00-HM150h): checked the FETs, caps, transistors, diodes, resistors, and all the transformers, was a bit of a job, i replaced on cap that feed the inverter transformer. i can measure 5v stb on one of the supply rails, and the FET that drive the inverter transfomers read 141v on the drain, and i can find 22v in one of the lines, to me it looks like all is fine. but if i put it back to the set it does not work can it be the main board how do i establish if it is the main board, please help.

[CapLeaker]

Re: Sansui LCD does not power on

can you make a hi res picture of the power supply and the main board? This one is to small, I can't see anything. Also on the power supply make another picture of the pin outs that go to the main board.

To test the power supply, you know already that the standby voltage 5V is already there. Now we have to figure out the rest. If you unhook the main board from the power supply and force the power supply on with some jumper resistors (1k ohm), and another jumper from BLON to 5V, should power up all of the power supply.

[vusi]

Re: Sansui LCD does not power on

Thanks CapLeaker . please see from the pics, the problem is i cant figure out from the pins how to force this power supply on because i cant see any power on or relay on please check the pin outs

[ReeceyBurger123]

Re: Sansui LCD does not power on

Firstly replace all the caps on the psu as they are the type to go bad with out bulging and can cause the psu not to start, I worked in one of these Ipos150s with the same symptoms repaired it by replacing every cap on the psu with high quality panasonics try that first.

[ReeceyBurger123]

Re: Sansui LCD does not power on

Note the primary cap will look bulged but its just the top casing thats domed the cap probably isnt, its the same on all these models.

[vusi]

Re: Sansui LCD does not power on

what do you say about the 141v on the drain of the 2mosfet feeding the two inverters and the 22v to feed the audio and video circuits? Those must appear on the pin outs when the main board is activated, do i miss a point now i have a headache my friends

[vusi]

Re: Sansui LCD does not power on

Primary Cap is ok and it has the correct voltage across it and it holds the voltage proof for not being leaky

[ReeceyBurger123]

Re: Sansui LCD does not power on

Im saying replace the all the other smaller capacitors on the board as some of them may be bad and will cause the psu not to start.
From my photo you can see that on the board I worled on I replaced all the capacitors.

[CapLeaker]

Re: Sansui LCD does not power on

I see now that you power supply has the inverter for the back lights on board. Thus there is no BLON pin. The 5VSB should always have 5v, regardless if power supply on or off. The STB pin should be the same as PSON. So if you jumper 5VSB to STB with a 1k ohm resistor, the power supply should turn on all the rest of the voltages on that connector.

[budm]

Re: Sansui LCD does not power on

I see now that you power supply has the inverter for the back lights on board. Thus there is no BLON pin. The 5VSB should always have 5v, regardless if power supply on or off. The STB pin should be the same as PSON. So if you jumper 5VSB to STB with a 1k ohm resistor, the power supply should turn on all the rest of the voltages on that connector.

It still needs BL_ON signal, PS_ON on turns on the PFC and the rest of the power supply to run the inverter circuits but the inverter circuit still needs to be turned on, this BL_ON signal is on the connector to the left of the big connector with pin labeled as BK_ON for BacKlights ON.
https://www.badcaps.net/forum/attach...3&d=1420747563
Common failure on this board is the failed 10uF 450VDC caps next to the inverter transformer.

BTW: "and the FET that drive the inverter transfomers read 141v on the drain" What did you use as the GND ref for the meter probe, the chassis? If that is the case, the measurement is invalid.
The DCV on the main filter cap should be around 330VDC and it should jump up to >360VDC when the power switch is activated and the main board sends the PS_ON (stby in this case) to turn on the PFC Voltage booster circuit which the Inverter drive section needs to run.
When making measurement in the primary side of the board you MUST use the Negative leg of the main filter cap as the GND ref point for you meter.

[vusi]

Re: Sansui LCD does not power on

Thanks for the advice and i really appreciate, i just want to mention that i did try to force the power supply on by putting a jumper between the 5stb and the
Stb pin but there was no success. today i will start all over again. i will change the caps and replace with a very reliable brand, can anyone make a suggestion for a reliable brand. what must i use as reference when testing the drain of the mosfets inorder to get a reliable reading?

[selldoor]

Re: Sansui LCD does not power on

Thanks for the advice and i really appreciate, i just want to mention that i did try to force the power supply on by putting a jumper between the 5stb and the
Stb pin but there was no success. today i will start all over again. i will change the caps and replace with a very reliable brand, can anyone make a suggestion for a reliable brand. what must i use as reference when testing the drain of the mosfets inorder to get a reliable reading?

It will depend on what you can get where you live?
If possible panasonic FR FM and FC series or Nichicon and Rubycon equivalents. Check the physical size to make sure they will fit. Probably best not not buy from ebay - many fakes about.

[budm]

Re: Sansui LCD does not power on

"i did try to force the power supply on by putting a jumper between the 5stb and the
Stb pin but there was no success" Did you remove the wire going back to the main board first? If it is still connected then the main board will keep that line low and you can also damage the switched transistor on the main board.

[vusi]

Re: Sansui LCD does not power on

"Did you remove the wire going back to the main board first? If it is still connected then the main board will keep that line low and you can also damage the switched transistor on the main board."

yes i did remove the main-board connectors when i tried to force the power supply on, right now i am waiting for the new caps i ordered and will go over the whole process again, i hope for the best now.
what can i use as reference to test the drain voltage of the mosfets? i heard that if i use the chassis as reference it will be unreliable.

[Ltank]

Re: Sansui LCD does not power on

I worked on a different Sanusi Tv yesterday. They are difficult to find boards bit the P.S. looks exactly like it's from a Sanyo Tv

[budm]

Re: Sansui LCD does not power on

OK, you need to get the PFC Voltage booster circuit to work first, so with force on applied, you must verify that you do have >360VDC RIGHT AT THE TWO LEGS OF THE MAIN FILTER CAP. The inverter circuits needs that Voltage to run, this MEGMMET POWER supply is known for having two bad 10uF 459VDC caps in the inverter section.