42" Plasma Toshiba model:42DPC85

[LongJohns]

Chassis TAC515

Gentlemen,

Ok, I have a Toshiba plasma 42" model: 42DPC85 that will not turn on, the front panel LED blinks red.

Would appreciate any help with getting this unit going again. I have done TV repair in the past, now I am talking 25+ years ago and all this new stuff is, well new to me, so that makes me a newbie again.

When the unit is plugged in, a relay cycles on, panel LED is a constant red and then the relay turns off shortly after and the LED now blinks.

I do have a copy of the schematic, but unfortunatly it does not show the power supply, so at a bit of a lost right now on where to start.

Please see attached pictures of the supply that is in this unit (pictures are counter clockwise direction starting in the lower right).

Thanks.

[tom66]

Re: 42" Plasma Toshiba model:42DPC85

Okay - on this TV you have two sustain boards (for driving the plasma panel), the Y sus and the Z sus. Y sus is on the left of the panel, Z sus on the right, when looking from the back.

Try unplugging the Y sus and seeing if the set will power on. If it will, this board is shorted. (You won't get a picture.)

If not, try plugging in the Y sus again and unplugging the Z sus. If it will power on, this board is shorted. (With an unplugged Z sus you will get a faint/dim/smudgy picture.)

If neither of these tests work you may have the all too common LG plasma AC detect issue which is relatively easy to fix...

[LongJohns]

Re: 42" Plasma Toshiba model:42DPC85

Okay - on this TV you have two sustain boards (for driving the plasma panel), the Y sus and the Z sus. Y sus is on the left of the panel, Z sus on the right, when looking from the back.

Try unplugging the Y sus and seeing if the set will power on. If it will, this board is shorted. (You won't get a picture.)

If not, try plugging in the Y sus again and unplugging the Z sus. If it will power on, this board is shorted. (With an unplugged Z sus you will get a faint/dim/smudgy picture.)

If neither of these tests work you may have the all too common LG plasma AC detect issue which is relatively easy to fix...

Thank you for the reply, I was doing some tests this morning and started unplugging various boards with no change in the result (which would have included the Y sus and Z sus boards - thanks for pointing those out as they don't seem to be labelled in the SM location pages).

I was also measuinr ghte voltages and the AC Detect line out of the PS has 3.45VDC on it and after reading your post confirms that this may be too low. Am I correct in assuming it should be 5VDC?

I tried a search on here for tghe "LG plasma AC detect" issue and didn't really come up with anything, so is it possible for you to steer me to a thread or are willing to step this out for me? Or perhapes you know where I can find a schematic for this PS.


Tim

BTW: included an overall picture just in case.

[tom66]

Re: 42" Plasma Toshiba model:42DPC85

3.45V does sound low, but the problem on the LG TVs (and your TV is basically an LG with a Toshiba video board and badge, although the PSU is higher quality than found in LG TVs, with decent caps) is when they turn on the AC detect tends to drop to zero, from about 5V; this causes the TV to go into some protection mode. I've not entirely determined what causes it to drop to zero, but bridging it has never caused issues, apart from the loud crackle that comes from the speakers when it is unplugged while it is running (turning to standby doesn't make a sound, nor does unplugging during standby.)

See these threads for some hints, but your PSU is different so I can't guarantee it will work.

https://www.badcaps.net/forum/showpo...2&postcount=15
https://www.badcaps.net/forum/showpo...2&postcount=17
https://www.badcaps.net/forum/showpo...4&postcount=18

BTW, I am aware of another issue regarding this Toshiba model; the "Seine" board. I believe it handles HDMI and the cable card slot, and a lot of people have managed to get their TV to power up with this board unplugged.

[LongJohns]

Re: 42" Plasma Toshiba model:42DPC85

Thanks again for the quick reply.

I was reading up and did run across others talking about the "Seine" board - now I just went to try unplugging what I am thinking is this board (the HMDI input) and with the board unplugged the unit does nothing when plugged in. It would seem that the power signal passes though this board. Would have to figure out what to jumper.

I have pulled the PS out and will look over it the next few days and will report back on what I find (or lack of) as the problem seems to come from here. The AC detect line reads 3.44 VDC with no other conenctions to the PS.

All I can say is, I sure liked the 'old' days - when you got a factory service manual they were almost like a phone book with timing charts, waveforms and complete circuit description to go along with the schematics. What I have for this set is only a fraction of the size and is missing the PS diagram (obviously built by a 3rd party) - just so disappointed.

Anyways, thanks for hte suggestion and links about the opto-couplers.

[LongJohns]

Re: 42" Plasma Toshiba model:42DPC85

Just to update.

Looks like the PS is ok - the 12v line is being dragged down by the 'input module' where the HMDI cable plugs into the unit.

The unfortunate part with this you simply couldn't unplug the harness to check as the 5VDC power signal also runs through this harness. I had to isolate each of the power feed lines through a couple of boards from the PS to find the problem child.

Now the question comes along if I want to replace this board at $100.

tom66 - thanks for the help you provided, got me at least going in the right direction. Cheers