Samsung PN42C430A1D turns on but no picture

[neilc6]

This plasma turns on and off with chimes but there is no picture. Checked Vs and Va on the power supply and they were about 10V. No short detected at the supply input to the Xmain board (found repair kit for this problem). Appears that PSON is not coming from the logic control board. 5.3V is present at the supply to the control boards Not sure if I should try to trace it back to the main board or jumper PSON high. Will continue investigating.

[neilc6]

Re: Samsung PN42C430A1D turns on but no picture

Further measurements indicate the TV is powering up, but VSON isn't staying in the on state. In the off state, PSON is 3.3V and VSON 0V. When turned on, PSON goes low, VSON is at 3.3V, VS=212V, VA=54V but after the startup chime, VSON goes low and VS and VA voltages start dropping. I unplugged the connector to the Ymain board and it exhibits the same behavior. Not sure if the power supply is detecting a fault or if there is an issue with the PSON signal.

[neilc6]

Re: Samsung PN42C430A1D turns on but no picture

Tried to do a test by jumpering pins 3-4 on the header connector of the logic board and disconnecting the cable to the main board but VSON still didn't come on. Looking at a schematic for another plasma power supply, VSON should switch a transistor pulling the leg of an optoisolator to gnd. VSON is not shorted so I believe the issue is with the logic control board. Luckily used boards are plentiful on ebay and only around $5 so worth a gamble.

[neilc6]

Re: Samsung PN42C430A1D turns on but no picture

Thinking about this some more, there are ribbon cables coming from the Xmain and Ymain boards going to the logic control board. Error signals on these lines could cause VSON to shut down. Will need to do some more probing.

[neilc6]

Re: Samsung PN42C430A1D turns on but no picture

Bumping this thread. Any input here?

[dick_barton]

Re: Samsung PN42C430A1D turns on but no picture

I don't know if this is similar to your set. May be of assistance to you.

[freakaftr8]

Re: Samsung PN42C430A1D turns on but no picture

Try disconnecting the flat white ribbon cable that connects from the logic board to the Ysustain. It's your voltages come up then it's most certainly a problem with the Ysustain

[neilc6]

Re: Samsung PN42C430A1D turns on but no picture

Try disconnecting the flat white ribbon cable that connects from the logic board to the Ysustain. It's your voltages come up then it's most certainly a problem with the Ysustain

Disconnected the ribbon cable from the Ysus and the voltages stay up.

Vsc and Ve measure ok on the Ysus. Pulled out Ysus and inspected. No cold solder joints on coils and parts attached to heatsink not shorted. Shopjimmy repair kit for this board replaces all the FETs and Diodes attached to the heatsink.

[freakaftr8]

Re: Samsung PN42C430A1D turns on but no picture

I would try disconnecting the buffer boards from the Y main and power up to see if voltages stay up if so then you have buffer board failure and Y main is probably ok

[neilc6]

Re: Samsung PN42C430A1D turns on but no picture

I would try disconnecting the buffer boards from the Y main and power up to see if voltages stay up if so then you have buffer board failure and Y main is probably ok

Disconnected the Y buffer and voltages stay up. Does this confirm the buffer is bad. Could it be the panel??

[freakaftr8]

Re: Samsung PN42C430A1D turns on but no picture

No its most likely the buffer board. This TV looks like it most likely has just one buffer board that spans from the top to the bottom so you would have to find a replacement.

[neilc6]

Re: Samsung PN42C430A1D turns on but no picture

No its most likely the buffer board. This TV looks like it most likely has just one buffer board that spans from the top to the bottom so you would have to find a replacement.

I ordered a used one on ebay for $15. Worth a gamble since this model is a newer and lighter plasma.

Thanks for the feedback since I could have potentially replaced the logic, xmain and ymain boards.

[tvtimmy]

Re: Samsung PN42C430A1D turns on but no picture

Let us know if it worked. I think it will.

[neilc6]

Re: Samsung PN42C430A1D turns on but no picture

Got a replacement board and I think the new board caused a short in the Y-main. PS clicks and no more chime so it is worse. Old board put back in has the same new symptoms. Think I'll scrap the tv for the power supply and main boards.