Samsung SyncMaster T24B350

[lotas]

Re: Samsung SyncMaster T24B350

Yes, in this video he replaced the LDO with 3.3v (sot-23) on a board with a regulator.

[lotas]

Re: Samsung SyncMaster T24B350

Thanks.. I can't understand Hindi, but I think my board checks out except for the Memory Chips VCC.

I found this video of a board with very similar problem to mine. But I'm not sure how he fixed it.

https://www.youtube.com/watch?v=iJQIbeiXhsg

My transistor (NPN I believe is getting 0.39 V on top pin, then 0.823 V (same as VCC on memory) on bottom right, and about 0 V on bottom left. I don't know why it's not getting 5 V on top pin??

This is not a transistor, it's an LDO at 3.3v.

[jason123]

Re: Samsung SyncMaster T24B350

Ok.. Quick Update. All videos, though not in english, implied the little transistor gets +5.2 V from the board and generates the Mem_VCC. However, upon running continuity check the MEM_VCC comes from Standby Voltage from the PS board!!!! I was not providing that, I was simply providing +5V, +11.9V, and GND.

Now with +5, STB(+5) and 11.9V with GND, the little transistor is getting 5V, but still the bottom right (Mem_VCC) is only coming to +.9 V. I don't know how that 3.3 is supposed to be generated. Looks like one trace goes to CPU, and others go to resistors (voltage dividers? - 22k and 10k = ~3.4 V Checks out)

[lotas]

Re: Samsung SyncMaster T24B350

It's something like this (with a fixed output voltage of 3.3v).

[jason123]

Re: Samsung SyncMaster T24B350

This is not a transistor, it's an LDO at 3.3v.

Thanks I searched for that marking and came up with NPN.

Any idea what part number that is? it does seem that the regulator is bad, correct?

[lotas]

Re: Samsung SyncMaster T24B350

You can use:
S-1206B33-MT1G,
TS9011SCX,
MCP1700T3302E...

Yes, and you can solder some kind of 1117 33 to check on short wires.

[jason123]

Re: Samsung SyncMaster T24B350

Thank you.. On order

[jason123]

Re: Samsung SyncMaster T24B350

You can use:
S-1206B33-MT1G,
TS9011SCX,
MCP1700T3302E...

Yes, and you can solder some kind of 1117 33 to check on short wires.

Sorry, I didn't understand: Yes, and you can solder some kind of 1117 33 to check on short wires.
Do you mean I use high output current device to test and see how much the 3.3 V node is drawing??

[lotas]

Re: Samsung SyncMaster T24B350

Do you mean I use high output current device to test and see how much the 3.3 V node is drawing??

I meant to find the most popular regulator (1117 33), it also has a fixed voltage of 3.3v, solder three wires to the legs and solder the other ends to the board, instead of the original one.

[jason123]

Re: Samsung SyncMaster T24B350

Prepping the board - removed the regulator, and it looks like the 3.3 pin was barely hanging in there. But I measured the impedance between GND and 3.3 V node, and it's only ~30 Ohm.. is that right? I guess 3.3/30 is about 110 mA, but it seems very low.

[lotas]

Re: Samsung SyncMaster T24B350

Usually, like in such Samsung boards, because of this capacitor that you changed in the power supply, the motherboard also suffers, namely this regulator for 3.3v and micom Weltrend wt61p805, but I don’t see it on your board, maybe it’s located on another sides.

I just found a photo of your board, there’s nothing on the back side, you need to supply somewhere 2v from the laboratory power supply to this 3.3v point and observe what can heat up by increasing the current on the power supply and find the culprit who drains this power, this can maybe a ceramic capacitor, spi flash, eeprom,...

[jason123]

Re: Samsung SyncMaster T24B350

I did comnect the on-board 3.3v to this node while regulator still on. No damage or overheating

[lotas]

Re: Samsung SyncMaster T24B350

But 30 Ohm is a low resistance for such a regulator, which drains the power supply.

[jason123]

Re: Samsung SyncMaster T24B350

Not sure if we can assume with power (3.3 V present) that 30 Ohm will result in 110 mA usage and that's 0.363 W for standby usage? (in addition to PS standby current?)

Anyway, LDOs are on order. and I don't know where the leakage is to get the 30 ohm. I see quite few ceramic caps, and one can be semi shorted, but not sure how to detect as ESR doesn't seem to catch them all.

[lotas]

Re: Samsung SyncMaster T24B350

But only when applying an external power supply and increasing the current, try to carefully lift the legs of the spi flash (1,2) and eeprom (8) to eliminate them.

[jason123]

Re: Samsung SyncMaster T24B350

Final Update: Ok, got the regulator, put it onboard, and voila, 3.3 is present. However, board still not turning on, and SOT23 is warmer than I'd like to see. Lifted the pins as in #35, no luck, still 31.5 Ohm across 3.3 and GND. Removed all caps on the line that I could see. Still 31.5 Ohm. Removed both memory chips on board - still no change.. at this point, board is throw away, so I removed the Big BGA / Processor and there it is. Must have had shorted pins or internal chip issue ... impedance now is 684 kOhm across the LDO (3.3 and GND) and the board is a designated as donor board

That's a wrap up.. thanks for the help.