Black screen Samsung syncmaster 203B

[yzy]

Re: Black screen Samsung syncmaster 203B

OK I have a list of 6 photos to test the MOSFETs. Use diode check mode, probe each pair of pins, and swap probes around so you check each pair in both directions. Do this for both MOSFETs.

You can also check the driver IC, ceramic capacitors, and transformers following the other photos. You shouldn't need to test both ways for these tests. Do the transformers with resistance test.

Write down the results and post them here. Hopefully it is easy to follow.

Hi,
I'm also struggling with my ip43130a. I had replaced four bulged caps. Diodes and fuses seem to be ok. But tests on MOSFETs come with somehow different results (test 5):

test 1 - 477 / 1960
test 2 - 1997 / ol
test 3 - 711 / 1824
test 4 - 484 / ol
test 5 - ol / ol
test 6 - 689 / ol
test 7 - 232 / 1386
test 8 - 475 / 1963
test 9 - 0.8 ohm
test 10 - 1356 ohm

So does the abundance of two-directional reads suggest that my multimeter is broken or rather mosfet's? Also, what about double ol in test 5?

Also, my largest cap C105 is 100uF (not 150uF) ... is it ok?



regards,
yzy

[yzy]

Re: Black screen Samsung syncmaster 203B

as a side note, an assembled display now works (i did not touch mosfets), but I can hear some constant high freq noise (ca 14kHz).
Any idea how to eliminate that?

[lgcyber]

Re: Black screen Samsung syncmaster 203B

This thread is very helpful because I had some insights on how to trace errors like this. Nice job AGENT44!

[Agent24]

Re: Black screen Samsung syncmaster 203B

So does the abundance of two-directional reads suggest that my multimeter is broken or rather mosfet's? Also, what about double ol in test 5?

Also, my largest cap C105 is 100uF (not 150uF) ... is it ok?

as a side note, an assembled display now works (i did not touch mosfets), but I can hear some constant high freq noise (ca 14kHz).
Any idea how to eliminate that?

Every multimeter is different and not all the MOSFETs will be exactly the same so getting slightly different readings is not a cause for concern. In any case your monitor works now so the MOSFETs are likely just fine. If they were bad it wouldn't work at all.

C105 is which capacitor? There is no schematic here so I don't know where that capacitor is.

The high frequency noise is probably just vibration of the inverter transformers and unlikely to be a problem. Unless it's annoying I wouldn't worry about it.

But you should probably check that the transformers and driver MOSFETs all have good solder joints. Because of the heat produced in inverter circuits, these components often get bad solder joints after a couple of years, and it can cause the MOSFETs to blow if the joints are bad enough.

[yzy]

Re: Black screen Samsung syncmaster 203B

Thanks for explaination :-)

C105 is which capacitor? There is no schematic here so I don't know where that capacitor is.

in the first post of this thread there are pictures attached, C105 is the huge one, close to the power cord plug.

The high frequency noise is probably just vibration of the inverter transformers and unlikely to be a problem. Unless it's annoying I wouldn't worry about it.

I don't hear it anymore (probably I've become deaf on this particular frequency after a couple of days.

But you should probably check that the transformers and driver MOSFETs all have good solder joints. Because of the heat produced in inverter circuits, these components often get bad solder joints after a couple of years, and it can cause the MOSFETs to blow if the joints are bad enough.

thanks for this useful advice, I'll try to resolder them in few days.

[Agent24]

Re: Black screen Samsung syncmaster 203B

in the first post of this thread there are pictures attached, C105 is the huge one, close to the power cord plug.

Ah, OK. If it's only 100uF and it's marked 150uF, that's out of spec even for a +/-20% tolerance part. Unless your capacitance meter is wrong, it should read no less than 120uF.

This may or may not be an issue to the circuit operation, but if the capacitance has dropped that far it might be on the way out and worth replacing. If you can get a new one cheap enough. Sometimes those HV capacitors are quite expensive.

If you do replace it, make sure you discharge it first!

[yzy]

Re: Black screen Samsung syncmaster 203B

Ah, OK. If it's only 100uF and it's marked 150uF, that's out of spec even for a +/-20% tolerance part. Unless your capacitance meter is wrong, it should read no less than 120uF.

This may or may not be an issue to the circuit operation, but if the capacitance has dropped that far it might be on the way out and worth replacing. If you can get a new one cheap enough. Sometimes those HV capacitors are quite expensive.

If you do replace it, make sure you discharge it first!

perhaps I've expressed myself not in a clear manner.
I've seen (in this and other threads) that other people have in this place cap 150uF.
I do not have 150uF-marked cap that holds just 100uF.
I have there 100uF-marked cap and I did not measure its capacity.
That cap was out there by manufacturer (my guess); so my question should be:
is this really possible that some batches of displays had 100uF cap C105 instead of 150uF? (if not - does it mean that sb had changed in in the past and put there wrong cap which I should replace with 150uF).

[Agent24]

Re: Black screen Samsung syncmaster 203B

Oh right, yeah I was confused somehow.

Well, in that case, if it came from the factory like that then I imagine it would be just fine to leave it there, assuming the capacitor is in good conditon.

I imagine they just used whatever they had on hand at the time, probably one production run they had 150uF ones already or they were cheaper from the supplier that day.

Likely anything 100uF and up would be fine then, but beyond 150uF would be a waste of money though.

[Dragunov]

Re: Black screen Samsung syncmaster 203B

Thx guys f301 helped me to!