Samsung UE46EH6030 - Blowing fuse and mosfet

[budm]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

So it does come up from 8V to 14V.

"PFC main cap voltage now moves up and down between 100 and 130V." Do you mean the DCV between the two legs of the main filter cap is that low?
Normal DCV on the main filter cap when PFC is not on should be around 330VDC.

[tn245]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

Yes, it comes up to 14V.

Yes DCV between the two legs of the main filter cap is moving up and down between 100 and 130V.

[budm]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

Yes, it comes up to 14V.

Yes DCV between the two legs of the main filter cap is moving up and down between 100 and 130V.

There is no way you can have DCV between the two legs of the main filter cap to be that low when AC input in your country is 230VAC, especially in standby without having TV turned on, your filter cap has to be real bad.

[tn245]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

There is no way you can have DCV between the two legs of the main filter cap to be that low when AC input in your country is 230VAC, especially in standby without having TV turned on, your filter cap has to be real bad.

It's not in standby. In standby the main cap is steady at 330V. I have been talking about when the power supply is fully on (with series lamp) and connected to backlight LED strings.

[tn245]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

So to sum up:

Main filter cap:

• In standby: 330VDC
• PSU turned on, J824 removed (FSFR deactivated): 390VDC
• PSU on, J824 in place: 260VDC (fluctuating slightly)
• PSU on, J824 in place + QM801 forced on: 100 to 130VDC up and down.

[dick_barton]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

If you short the emitter/collector and the voltages all come up correctly then I would be tempted to replace QM801 and the ICM803

Edit
The reference voltage of 2.5V or greater must be reached before the TL431 allows current to flow via RM802/RM803 switching on the transistor.

[budm]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

All this time with lamp in series, that mean you are not getting anything close to 230V feeding the TV, as the circuit try to draw more current to start run the less AC will be fed to the TV. You are using less than 100W lamp aren't you. I can tell by your DC on the cap? At 260V (only about 180VAC to run the TV, AND EVEN LESS AT 100 to 130VDC ON THE CAP) that TL431 is not going to turn on to BIAS on that transistor which we already proof by using the resistor, it is used for LOW Voltage protection.
You have to disconnect ALL the loads and use 100W lamp may work.

[tn245]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

Yes, I switched to 60W as it was suggested a few posts back. Back to 100W now.

Without loads connected, bulb flashes about every 3 seconds each time a little dimmer until staying off entirely after maybe four flashes. During this time main cap is building up to 390V with each flash until is sticks around 390 though not steady. PSU makes a soft tick sound in time with the flashes and keeps on doing it.

Standby 5VA is steady at 5.2V, but all other output voltages only pulse on briefly on each tick. Looks like SMPS is attempting to start every few seconds. PS_ON/OFF pin is low at 0.8V and pulses high with each tick.

This is with 100W lamp in series and nothing connected to the psu board.

[dick_barton]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

What is the voltage at Vref while this is all happening and is it also pulsing. If it is then it's probably switching the transistor QM801 on and off. => 2.5V then Qm801 ON, <2.5V then QM801 Off

[dick_barton]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

Having a re-read of your post you say that if you disconnect a link which powers the FSFR IC then the PFC voltage is correct so something in that circuit is affecting this voltage.
Have you checked CM813 coupled to the transformer. I recall reading that on some power supplies (not this one) the coupling capacitors cause problems.

[tn245]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

Voltage at Vref is pulsing, but so is voltage at emitter of QM801.

Basically the 15V Vcc supply for both the PFC and FSFR SMPS ics is pulsing. This is due to PS_ON/OFF on cold side being low and pulsing.

Looks to me like the backlight driver (SLC3011M) is shutting down the power supply and trying to restart it. It doesn't do this when backlight LEDs are connected so maybe this is just what it does when it detects LED strings are open?

[tn245]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

I have checked CM813. Pulled it out and tested and it measured fine.

All this time I am wondering if the PSU is fixed and it's just the bulb that is choking it and stopping it from starting properly. Without backlights connected when it's ticking/restarting the bulb goes dim once the main cap reaches 390V which would indicate no shorts in primary right? If LEDs are connected they are flashing and the bulb is glowing bright, but that I guess is because the main cap is struggling to reach correct PFC voltage while FSFR is trying to start.

Is it time to take a chance without the bulb?

[PowerAmpFreak]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

I have been working with quite a large number of Samsung PSU's.
I think you are on the right track here, in order to achieve proper supply to FSFR the LLC controller, the PFC voltage has to be at its correct level.
When LLC starts, the PFC tries to cope with the additional load, which makes bulb steal away voltage from the PFC.
I think you have to test this supply without the bulb now.

[dick_barton]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

There has been this problem before where the bulb in circuit has stopped the set from coming on.
In this instance without the PFC coming up to full voltage it appears to be affecting the 15V supply being fully switched on due to low Vref which is derived by a resistor chain from the PFC voltage.

[tn245]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

I have been working with quite a large number of Samsung PSU's.
I think you are on the right track here, in order to achieve proper supply to FSFR the LLC controller, the PFC voltage has to be at its correct level.
When LLC starts, the PFC tries to cope with the additional load, which makes bulb steal away voltage from the PFC.
I think you have to test this supply without the bulb now.

Yup! Took out the bulb and TV is working. Thanks PowerAmpFreak.

So in the end it was fixed by changing the mosfet, PFC ic, FSFR1700 and transistor QM801. Also changed the standby ic D2011K but I don't think it was bad.

It was only the bulb that was stopping it from starting up.

[tn245]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

Thanks for the help budm, dick_barton and others.

[dick_barton]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

Glad you got there in the end.

[budm]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

100W lamp in place is barely enough for this TV, as I indicated, 100W may work, no way using 60W. If you actually check the current draw during startup, i will be quite high for the TV power supply. I use 100W when working on 20" monitor so for TV you need more than that, especially with load. You can tell if the lamp is too little by monitoring the dcV on the filter cap, you gave me the clue when you said you have only 100 something Volt on the filter cap.
BTW, where did using 60W come from any way?

[tn245]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

I started with 100W. In post #34 it was suggested it was too high and 60W was more suitable.

Got there in the end yes. In fact got there in the beginning but only realised I was there in the end. Anyway I learned a bunch of stuff on the way so thanks.

[budm]

Re: Samsung UE46EH6030 - Blowing fuse and mosfet

BTW, 60W LAMP 230V the max current draw is about 0.26A if the load (TV) is shorted.
If you want to collect some DATA of the power supply board current draw with load and without load you can hook up you meter ACA mode and put meter in series with the AC power supply cord or when the main AC fuse is, then you can see the peak current (if meter has peak hold) draw at startup, at running mode, standby mode with difference backlights level.