Samsung LN32A450C1D Red light

[CraigR]

Re: Samsung LN32A450C1D Red light

OK, with negative still on negative of the big cap then positive on pin 15 of ICM801 the meter just bounces around the mV range.

[mmartell]

Re: Samsung LN32A450C1D Red light

Sorry for being lazy and not reading this in its entirety but I did hear you say QB802 solder joints look good. I thought the same looking at mine but it fixed mine and others.

https://www.badcaps.net/forum/showth...t=16718&page=2

[tom66]

Re: Samsung LN32A450C1D Red light

QB802 could cause that issue with low Vcc. I'd check as mmartell suggests

[CraigR]

Re: Samsung LN32A450C1D Red light

I just went an touched up everything on a heatsink and anything that even looked like it might need it.

[mmartell]

Re: Samsung LN32A450C1D Red light

QB802 has no heatsink and probably doesn't look like it needs it.

[CraigR]

Re: Samsung LN32A450C1D Red light

My bad was looking at QM802. Removed QB802 tested and reinstalled and same thing.

[CraigR]

Re: Samsung LN32A450C1D Red light

Well took a chance and got a main board from Jimmy and that did not do it so must be in the power board.

[CraigR]

Re: Samsung LN32A450C1D Red light

Anybody have any other suggestions?

[CraigR]

Re: Samsung LN32A450C1D Red light

Well I replace the IC801 chip and that did not help either.

[budm]

Re: Samsung LN32A450C1D Red light

"OK, with negative still on negative of the big cap then positive on pin 15 of ICM801 the meter just bounces around the mV range." This does not make sense to me because this out put at the Emitter of QB802 is the M_VCC which is fed into the VCC pin 8 of the PFC Controller IC and also to the VCC pin 15 of the PWM IC. You have indicated that the boosted voltage on the big cap is around 380VDC. I cannot see why you only have mV range but the PFC is working. Something is not being measured correctly.
So lets verify the voltages at the Collector, Base, and Emitter of QB802?

[CraigR]

Re: Samsung LN32A450C1D Red light

Am I reading the pins correctly as in this pic?

[budm]

Re: Samsung LN32A450C1D Red light

That is correct, so per SCH, pin 15 is the VCC pin. you should be able to read low resistance (<1 Ohm) between pin 15 and the Emitter pin of the QB802.
QB802 is setup as a simple 15V linear regulator.

[CraigR]

Re: Samsung LN32A450C1D Red light

I checked pin 15 again with a different meter and it reads 15V then drops to almost nothing then back to 15V again just keeps doing that never a steady constant reading.

[CraigR]

Re: Samsung LN32A450C1D Red light

on QB802 left leg goes from -53V to -41V back and forth center leg -32V to -29V and right leg -56V to -41V that's with negative lead on chassis ground.

[budm]

Re: Samsung LN32A450C1D Red light

You are measuring the voltage on the primary circuit, so the negative leg of the main filter cap will be your ground ref point, not the chassis.

[CraigR]

Re: Samsung LN32A450C1D Red light

Ok then the outside legs start at 15V then drop to zero and repeat and the center leg is 39V and drops to 26V and repeats.

[budm]

Re: Samsung LN32A450C1D Red light

OK, that 39V reading does not look right, we need to find which pin is Base, Collector, and Emitter. Need picture of this transistor. I expect one pin will have 15.6V, another pin will be 15V, and another pin will be about 20V.
Not only that, since you are indicated that the pin15 of the ICM801 was reading in mV, it cannot be since one of the leg of that transistor is connected directly to the IC VCC pin. You need to check the resistance between the VCC pin and one of the leg of the transistor to see which one will show < 1 Ohm. I think we are having error in measurement here.

[CraigR]

Re: Samsung LN32A450C1D Red light

As good as I can get.

[budm]

Re: Samsung LN32A450C1D Red light

OK, the left pin is the base, the center/tab is Collector, the right pin is the Emitter.
So you have indicated that the two outside pin has 15V then drop down and the Collector pin (middle pin) varies its voltage. There is small electrolytics cap connected to the Collector pin, so check that.
Also you should see the voltage at the VCC pins of the PFC IC and the SMPS IC VCC pin voltage go up and down, same for the DC voltage on the main cap, it should be going up and down also.

[CraigR]

Re: Samsung LN32A450C1D Red light

One of the first things I did was to pull the caps out and check with my ESR70 meter and were all good. less than 10% off and low esr.