DP40142 Power Supply

[RAMSELECTRONICS]

I have a board of power supply part number FSP140-4F01 for LCD TV model DP40142.

It has 5V, 12V, and 24V output. The issue is 12V and 24V is dead but 5V is working.

You can see schematic: See page 51



I replaced on U101 SSC9512S as new, also checked on 2 MOSFET Q101 and Q102 looks good. but I suspected the PC101 does not activated but the chip is good.

I have no luck also I unable to find the waveform for the SSC9512S.

need help. THANKS!!

[CapLeaker]

Re: DP40142 Power Supply

Did you "force" the PSU on with a couple of resistors or did you just put the PSU back into the TV and truned the TV on?

[RAMSELECTRONICS]

Re: DP40142 Power Supply

using TV power on.

[budm]

Re: DP40142 Power Supply

If PWR (PS-ON, >2.5VDC = ON) is not present then you will not have 12V/24V. So check and see if you do have PWR (PS-ON) connector P802 pin 13 signal from the main board.

[RAMSELECTRONICS]

Re: DP40142 Power Supply

ok

[RAMSELECTRONICS]

Re: DP40142 Power Supply

Ok, Will check it out.
THANKS!

[RAMSELECTRONICS]

Re: DP40142 Power Supply

I checked the voltmeter said 3.4V.

[budm]

Re: DP40142 Power Supply

Good, so now you will need to check the DCV in the 12V/24V power supply section, start by verifying that you do have VCC to run the SMPS IC U101, check the DCV between pin 2 (VCC) and PIN 4 (SGND).
What is the P/N as printed on top of that U101?

[RAMSELECTRONICS]

Re: DP40142 Power Supply

U101 I posted at the first. see scroll up there is p/n
it say SSC9512S

[RAMSELECTRONICS]

Re: DP40142 Power Supply

I check on pin 4 now

[budm]

Re: DP40142 Power Supply

I check on pin 4 now

DCV between pin 2 (VCC) and pin 4 (GND, PRIMARY SIDE circuit GND).

[RAMSELECTRONICS]

Re: DP40142 Power Supply

Here I use oscilloscope:

PIN 2:




PIN 4:

[budm]

Re: DP40142 Power Supply

You use the scope to directly measuring the Voltage on the HOT PRIMARY side of the circuit?
It looks to me you are using the chassis for your scope probe that is why you are seeing such a large AC signal.
To use the scope in the primary side, you MUST is Isolation transformer on the unit you are working on, the GND ref for the primary is the negative leg of the main filter cap, so DO NOT ATTACH THE SCOPE GND probe to anything in the primary side of the circuit!
Why don't you just use the DMM to measure the VCC of that IC?

[RAMSELECTRONICS]

Re: DP40142 Power Supply

Shoot. what's wrong my brain! I will use isolate transformer for the oscilloscope to use gnd and vcc. be back.

[budm]

Re: DP40142 Power Supply

Shoot. what's wrong my brain! I will use isolate transformer for the oscilloscope to use gnd and vcc. be back.

Not on the scope, you use it on the unit you are working on and you must make sure that it is true isolation transformer, the Neutral should not be tied to the ground prong of the AC outlet of the isolation transformer.

[CapLeaker]

Re: DP40142 Power Supply

Shoot. what's wrong my brain! I will use isolate transformer for the oscilloscope to use gnd and vcc. be back.

DON'T DO THAT!
That is backwards! You supposed to put the PSU on the isolation transformer. The scope supposed to be connected to your wall socket!

[RAMSELECTRONICS]

Re: DP40142 Power Supply

HA HA... no worries.. I checked with voltmeter VCC pin 2 and GND pin 4 DC is zero, AC is 3.33V.

BUT I look up the schematic the VCC where came from.. I could not find it ummm...

[RAMSELECTRONICS]

Re: DP40142 Power Supply

Ummm.. Look the schematic... you see U501 is A6069H is CLICK HERE

I checked voltmeter showing 14.4V out from the VCC pin 5 from U501.
So it connected to Q503 emitter and base showing 15V DC.
The collector is zero voltage.

seem like Q503 is bad? it is VERY small as SMD.

[RAMSELECTRONICS]

Re: DP40142 Power Supply

Do you guys think I should try replace with 2N3906?

I unable to read the label on the bad one as no label.

[budm]

Re: DP40142 Power Supply

Ummm.. Look the schematic... you see U501 is A6069H is CLICK HERE

I checked voltmeter showing 14.4V out from the VCC pin 5 from U501.
So it connected to Q503 emitter and base showing 15V DC.
The collector is zero voltage.

seem like Q503 is bad? it is VERY small as SMD.

Q503 PNP Transistor is not turned on.
The Voltage is generated from the AUX winding of the standby power supply transformer T501, the AC is then rectified by D505 and filtered by C509, it is then fed into linear regulator circuit consists of Q504 (NPN)/ZENER ZD503, the regulated output is on the Emitter of Q504 which is fed to Emitter of Q503 (PNP), for Q503 to be turned on, the Base Voltage will have to be 0.6~0.7V LOWER than the Voltage at the Emitter of Q503, this is done by turning on OPTO PC502, the PC 502 is turned on when Q203 is turned on by the PS_ON signal.
So you need to check the BASE Voltage OF Q503, it must be 0.6~0.7VDC less than the Emitter Voltage, if it is not then the opto or Q203 is not working.
Also the resistance between VCC (2) and GND (4) PIN of the IC to make sure it does not show low resistance.
BTW, you did change C509, right?