TNPA4250 Board Repair

[tom66]

Re: TNPA4250 Board Repair

I think the 55V line is ERC midpoint, i.e. connected to the blue poly caps on the right of the board (load of 2.2uF ones next to each other IIRC.)

If so it should measure about 1/2 of Vsus in operation and hardly vary from this. 55V is much too low, it indicates the ER path is not working. This can be for a number of reasons, it could be the SUS path is malfunctioning or the ER path is malfunctioning (or both) or something common to them.

[canadaboy25]

Re: TNPA4250 Board Repair

So it has something to do with this M81707FP High Voltage Half Bridge Divider?

[canadaboy25]

Re: TNPA4250 Board Repair

Well I pulled the scope out and tested all of the pins of the chip.

I attached a pinout of the chip and all of the attached waveforms have the name of the pin they correspond to on them.

From what I can tell pins HIN and LIN don't seem right to me because it's just a bit of low-voltage noise.

[hennes]

Re: TNPA4250 Board Repair

...your Hin Lin looks like open loop.

You have good connection to the control board ??

[tom66]

Re: TNPA4250 Board Repair

Yes, it looks like there is a problem with signals reaching that IC.

[canadaboy25]

Re: TNPA4250 Board Repair

Well I drew some signal paths on the image attached. I'm assuming this is how the signals are supposed to run?

If so the only thing on this board that can be damaged are the resistor networks or the Octal Bus Buffer 74VHC244? Otherwise it would have to be on the D board. At least that is my understanding.

[hennes]

Re: TNPA4250 Board Repair

...follow these signals to the control board.
Maybe they are switched of because of the sos signal.

On other TV s ,this signal source keeps working unless control board is bad...

[tom66]

Re: TNPA4250 Board Repair

The buffer IC, or control board, could be bad if the signals are missing elsewhere along that chain. Also note the buffer IC is tristate and disabled by the "MAIN STOP circuit" - at least for one half. Worth checking the voltage at that point.

[canadaboy25]

Re: TNPA4250 Board Repair

Sorry for not posting for a long time, have been busy with other stuff.

I got around to testing the board and there is a signal at the one side of the buffer but no signal at the other. There is also 5 volts at the corresponding control pin.

I have attached a picture of this.

[canadaboy25]

Re: TNPA4250 Board Repair

Well I tested it again and now there is no signal, just some high frequency static.