Samsung SyncMaster T24B350

[jason123]

Hello there,
I had this TV for years plugged in connected to an old xBox. Went to turn it on today, and I noticed standby light is off, and not turning on.

Opened it to find the Corner Cap (for 5V standby I believe) is bulging and replaced it. Still no standby light. won't turn on

Measured voltages going to the main board, and with the connected to the main board in place, the 5V, PS_On, and 13 V pins were jumping all over the place. When I disconnect the cable to main board, the 5V reads 5.2V, the 13 V, reads 11.8V, and the PS_ON is 3.12 V and the backlight comes on.

I'm thinking main board is out to lunch but I figured I'd post this and see if anyone has experience with these as to common components that may go bad??
Thanks

[nomoresonys]

Re: Samsung SyncMaster T24B350

Maybe try unhook lvds cable at mainboard and retest those voltages, just to make sure it isn't the panel making them unstable.

[jason123]

Re: Samsung SyncMaster T24B350

Thank you. Done. No effect on these voltages. With LVDS disconnected, voltages all over the place still

[nomoresonys]

Re: Samsung SyncMaster T24B350

Maybe a bad voltage regulator on mainboard?

[Storyteller12]

Re: Samsung SyncMaster T24B350

I’ve seen a few like this were a bad diode on mainboard caused voltages to fluctuate. A lot of times it’s next to one of those 8 pin ic’s and the diode and ic will be bad.

[jason123]

Re: Samsung SyncMaster T24B350

So I took the main board and provided external +5 and +12 V and GND
Current draw was in the 200 mA range on the 12 V, and less than 50 mA on the +5.

Could it be the power board that's unable to provide enough juice?? I did replace all the caps on that board, but I'm not sure if it's some sense resistor or something not allowing it to provide all the muscle it needs?

[jason123]

Re: Samsung SyncMaster T24B350

I've seen a few like this were a bad diode on mainboard caused voltages to fluctuate. A lot of times it's next to one of those 8 pin ic's and the diode and ic will be bad.

Hi, after post #6, do you still think this would be the case? Thank you

[lotas]

Re: Samsung SyncMaster T24B350

If the power supply is unstable with large pulsations, the firmware in the spi flash could suffer.

[jason123]

Re: Samsung SyncMaster T24B350

Another experiment:

with everything connected, I forced the Power Supply to turn on by throwing a resistor between 5A (Standby - stable at 5.2 V) and PS_ON on the main board.

This did result in the Backlight being on, 5B pin @ 5.18 V, 13V Pin @11.80V all stable. No display on the screen however (Just bright backlight)
I also noticed the large cap voltage is still 157 VDC (was 161VDC before the forced PS_ON pulled high externally.

Should the large cap voltage go high to ~300 V or So?

[lotas]

Re: Samsung SyncMaster T24B350

There is no PFC (Power Factor Correction) in the power supply, the panel is small and the backlight is LED. If the backlight turns on without the motherboard and lights up without failure, then we can assume that the power supply is corrected.

[jason123]

Re: Samsung SyncMaster T24B350

I have a replacement main board on order. Fairly expensive board for such old TV, but I'd love to get it fixed - anyone has experience with this board?

[nomoresonys]

Re: Samsung SyncMaster T24B350

Probably the usual, poor solder ball connection of the bga after many many power thermal cycles, also the boards tend to warp over the years, making it still harder for those solderballs to keep connected.

[jason123]

Re: Samsung SyncMaster T24B350

Did a reflow on the processor - no luck. Touch up many solder joints, still. I noticed that the Flash chip (with sticker) is not getting power on pin 8. From datasheet, VCC is supposed to be in the ~3V range and I'm getting 0.8 V
Lifted the pin (to see if that chip is shorted) but pad was still 0.8V. Anyone with a schematic for this board? Thank you

[lotas]

Re: Samsung SyncMaster T24B350

Your power supply should be suitable not for 8 pin, but for 2 pin.

[jason123]

Re: Samsung SyncMaster T24B350

You're correct - Pin 2 of this IC is reading 0.8 V

This pin is tied to Pin 1 of the same IC. And that's connected to Pin 8 of the adjacent IC (ATMLH208) - I can't find a datasheet for that IC!

[lotas]

Re: Samsung SyncMaster T24B350

IC (ATMLH208) - I can't find a datasheet for that IC!

This is an EEPROM, the full name requires a second line.

[jason123]

Re: Samsung SyncMaster T24B350

ATMLH208
2GB 1
1H1109


Another note: This morning when I powered up the board (applying +5V and 11.8 V and GND), the voltage at the VCC pins were 0.448 V... then when the board warmed up, it went up to 0.823 V

I momentarily applied 3.3 V (from a switcher on the board) to the VCC pins of these Flash / mem.. and the voltage held (meaning, it's not really low impedance on these nodes, simply the source is not able to drive 3.3v?)

[nomoresonys]

Re: Samsung SyncMaster T24B350

Wonder if there's a bad capacitor in that area.

[lotas]

Re: Samsung SyncMaster T24B350

ATMLH208 2GB 1 - AT24C1024B

Here is a video of powering your board:
https://www.youtube.com/watch?v=Ly1UURZ2ml4

[jason123]

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??