Samsung SyncMaster 204b

[PlainBill]

Re: Samsung SyncMaster 204b

IC 304 with tab at top:

tab = 1.81V
left pin = 0V
stub = 1.81V
right pin = 3.23V

That's correct for a 1.8 volt LDO regulator.

The symptoms indicate the processor is shutting down. The power supplies appear to be good. The two possibilities are that a power regulator is shutting down, or a processor is sensing problems. I've been able to identify major parts of the circuit.

The area circled in red in the upper left corner is the main regulator. It is a type known as a bucking regulator, this puts a high stress on the caps. One option would be to replace the three caps (2 ea 100uF 25V, 1 ea 100uF, 16V) inside the circle. I don't have high hopes for that.

The area circled in green is the switch for the LCD panel itself. There is no reason to believe that is causing any problem.

There are two areas circled in umber, one on the left side, one on the far right. By the voltages, these are LDO regulators, and are very unlikely to be responsible.

The area on the left circled in yellow represents a mystery. It is clearly a bucking regulator, but there is no identifiable regulator. I suspect it is the 8 pin IC, but the part number is not identifiable. Again, you could try replacing the caps, but I can't offer much hope that would help.

On the right I have circled some pads in gold. That is the area I would expect to find the cable going to the front panel. Which presents a minor mystery - where is the cable to the front panel?

The chip circled in black is the prime suspect. It is the control processor, and because of the white label, is loaded with a custom program for this monitor. And if it can be positively identified as bad, it is pure 'unobtanium'.

PlainBill

[john98103]

Re: Samsung SyncMaster 204b

A quick update: first of all THANKS for all the effort in helping try to pinpoint the problem.

I located another identical monitor which had a bad power supply and swaped signal cards; my monitor works fine now. I was going to log all the correct voltages throughout the good board and then compare with the non-working board but my desire to use the working monitor overrode my curiosity and I failed to follow through.

[kking85743]

Re: Samsung SyncMaster 204b

For those who have replaced all the capacitors, but still have trouble with the back light (like me), look for a green resistor-like thing with a f### along side it. These are wire fuses, sometimes called pickle fuses (because they are green?). Unsolder one end and test for continuity. Mine was blown, and a quick trip to an electronics supply store fixed me up. Mine was a 3A unit, yours may be a different value (it was printed on the fuse). Hope that helps!

[PlainBill]

Re: Samsung SyncMaster 204b

For those who have replaced all the capacitors, but still have trouble with the back light (like me), look for a green resistor-like thing with a f### along side it. These are wire fuses, sometimes called pickle fuses (because they are green?). Unsolder one end and test for continuity. Mine was blown, and a quick trip to an electronics supply store fixed me up. Mine was a 3A unit, yours may be a different value (it was printed on the fuse). Hope that helps!

Not 'pickle fuse', 'Pico fuse'. The name chosen by the manufacturer.

Other than that, your suggestion is sound.

PlainBill