Sanyo DP42740 no power

[triplefour]

got my first plasma TV to attempt a repair on today.
a friend of mine said if i can fix it we'll sell it and split the money.
the people he got it from gave this story as to why its broken:
"we were watching it, during a lightning storm, when it suddenly turned off and wouldn't turn back on again. nothing else in the house was affected. we were not hit by the lightning or anything"

at any rate, i plugged it in and i do not get a standby light or anything and pushing the power does nothing.
it has a million screws in the back for some reason. but i took them all out and got some pictures of the boards.

i know that plasmas are much different from the LCD's so i dont really know what im looking at here.

where should i start? on the LCD boards there is usually one big capacitor on the power board. the main filter cap. but on this board there are 4 big capacitors.

is working on a plasma TV any more dangerous than LCD or LED tvs?

[martino]

Re: Sanyo DP42740 no power

No standby light would put the powersupply at first suspect I'd say.
Is there a legend printed at the connector that goes to the mainboard?
Assuming you already checked the fuses F201,F202,F204?
First we need to figure out if you get the standby voltage.I'm trying to find a schematic..
Working on plasma's is not more dangerous then a lcd tv,yes,there is the VA and VS voltage of 200+dc volt etc,but 1000volt plus on a lcd tv for inverter doesnt feel nice either
Bigger caps on power supply you have to watch for,they hold a good charge for awhile after unplugging,best to drain them with a heavy resistor before poking around on that board(been there,done that,trust me,doesnt feel nice at all)

[martino]

Re: Sanyo DP42740 no power

"borrowed" a picture from the psu

http://www.toms-service-manuals.com/...h=Submit+Query

There ya go for schematics,thank tom66 for his amazing database.super handy

[triplefour]

Re: Sanyo DP42740 no power

yeah thats what mine looks like...

[triplefour]

Re: Sanyo DP42740 no power

awesome. i guess i better go thru everything in this service manual and then report back. thanks!

[johnboy1313]

Re: Sanyo DP42740 no power

Set your meter to the highest DC volts setting and check across the leads on one of the big 450V caps at the top of the PSU, with the set plugged in. Red on one leg, black on the other. Report back.

[selldoor]

Re: Sanyo DP42740 no power

A good in focus straight on picture of the front and back of the power supply might help.
Not able to see much at all on the one you posted.

[martino]

Re: Sanyo DP42740 no power

The big main caps are probably not active till the psu gets forced on. Might not see a voltage on those in standby.

[johnboy1313]

Re: Sanyo DP42740 no power

If the set is in standby, he should still see roughly 170V, if not roughly 400V. I had the same set with the same symptoms. My PSU was stuck ON.

https://www.badcaps.net/forum/showthread.php?t=28850

[triplefour]

Re: Sanyo DP42740 no power

i get no volts at the big caps (well the 2 i can test without turning over the board anyway)
and i only get 84v AC from the plug... shouldnt it be 120?

[triplefour]

Re: Sanyo DP42740 no power

at the very beginning of the service manual it says
"An isolation transformer must be connected in the power
line between the receiver and the AC line before any service
is performed on the receiver"

is this really true? what is an isolation transformer anyway?

[budm]

Re: Sanyo DP42740 no power

It is for safety when you are probing around the Primary (Deadly) side of the circuit, you should have 120VAC right at the AC connector on the board. Is your meter's battery OK?
Example of Isolation transformer:
https://cdn.badcaps-static.com/pdfs/...4cc7e77847.pdf

[triplefour]

Re: Sanyo DP42740 no power

i dont think my meters battery is bad. i can test double A batteries and i get the same readings as with my analog meter...

[triplefour]

Re: Sanyo DP42740 no power

selldoor, in post 3 there is a clear picture of the power board (from the front anyway)
ill try to take a good one of the back.

[triplefour]

Re: Sanyo DP42740 no power

ok heres the pictures of the back. the board is pretty big so i couldnt take a detailed picture of the whole thing so i did it in sections as well.

[triplefour]

Re: Sanyo DP42740 no power

ok i re-tested the AC volts and i do get 120 now. i dunno what that 84v was about but its 120 now... how do i test for 5v standby? i get no volts across the capacitors. no volts across any of the fuses either. what should i use for ground ref to test the volts at the connectors? and how do i tell which one is standby? theres no legend anywhere!

[budm]

Re: Sanyo DP42740 no power

So you do not have aboyt 165~170VDC measured right at the two legs of the main filter caps (100uF 450VDC)?
All three fuses show <1 Ohms? measure them with TV unplugged.

[triplefour]

Re: Sanyo DP42740 no power

yes the fuses are not open. and with the tv plugged in i get 0v on the filter caps (the 2 i can measure without flipping the board over that is)

[budm]

Re: Sanyo DP42740 no power

OK, I will have to trace out the connections from each leg of the AC inlet all the way to the two inner legs of the bridge rectifier. That will take awhile. I did not download all the pictures of the bottom side of the board yet, hopefully they are clear enough for me to trace out the connections.

[budm]

Re: Sanyo DP42740 no power

OK, luckily shopjimmy has good pictures of the top and the bottom side of the board.
http://www.shopjimmy.com/sanyo-n0ae5...ply-board.htm#
You can test the board by itself to see if you are getting the DC Voltage on the filter cap CE203 which is the filter cap for the standby power supply, measure right at the two legs of the cap.