magnavox plasma 42mf230a Power issues

[splatee]

First off sorry for double post. I was unable to start a thread earlier and posted in another thread that was related to my issue.

I picked up a magnavox plasma 42mf230a for free that randomly turns on by itself and off and then would just powers cycle and makes a click sound when powering on and off. The image looks great when it works. Sometimes it will work for 30 mins or longer and sometimes it's after just a minute.

I downloaded the service manual and checked voltages coming from the power supply and hey all seem to be within spec. I checked e power supply board for bulging caps and did not see any but went ahead and resoldered them in case of a cold solder joint. I also unplugged the "Y" board and "X" board and tv would still power up and down on its own. I even went as far as to unsolder the rfi sensor for the remote to make sure it was not picking up something. He tv did not come with a remote either so I can not go into the service menu.

Any other ideas? I'm pretty sure it is probably a cap issue on the power supply but don't want to randomly change them, there are a lot of them. On a side note all the boards and panel are labeled Samsung.

One other thing I have not looked at is the PDC board aka power down control board, wonder if that may be an issue?

Thank you
Last edited by splatee; Today at 10:28 AM..

[ReeceyBurger123]

Re: magnavox plasma 42mf230a Power issues

Images of the boards please ? Also maybe try heating the Psu with a hair dryer see if it goes off faster ?

[splatee]

Re: magnavox plasma 42mf230a Power issues

Here are some pics of power supply, and other boards

[splatee]

Re: magnavox plasma 42mf230a Power issues

Power supply

[splatee]

Re: magnavox plasma 42mf230a Power issues

Another of power supply

[splatee]

Re: magnavox plasma 42mf230a Power issues

Looks like i narrowed it down to the Power Down Control Board "PDC". Checking voltages on one of the capacitors it should be 300v but only reading 158v. From there it says to check an IC and a Diode. I have not checked those yet because i pulled the cap.

Also i had it completely disconnected from the main power supply board and it was still powering on.

Thank you

[ReeceyBurger123]

Re: magnavox plasma 42mf230a Power issues

Ahh right ok, have you an image of the cap please ?

[splatee]

Re: magnavox plasma 42mf230a Power issues

Image of board

[splatee]

Re: magnavox plasma 42mf230a Power issues

Capacitor

[splatee]

Re: magnavox plasma 42mf230a Power issues

Well still no luck. Changed the capacitor and still reading the wrong voltage. I went ahead and checked the fuses and diodes on the board and they are fine. The only other thing to check for per the service manual is an IC chip on that board. I went ahead and ordered one from Mouser.

The main number on the chip matches but when I googled it with the rest of the other numbers it did not come up. Hopefully it works if not I guess I will just dump the set.

[splatee]

Re: magnavox plasma 42mf230a Power issues

Tv is back up and working again. Replaced the IC chip that I ordered from Mouser.

Thank you

[splatee]

Re: magnavox plasma 42mf230a Power issues

Well I spoke to soon. It just started turning back on on its own. I am starting to wonder if it possibly be the EMI noise filter where the power cord plugs into? Also is it ok to use one that has a higher amperage rating? The one in it now is rated at 8 amps and I have a spare that is rated at 10 amps.

[R_J]

Re: magnavox plasma 42mf230a Power issues

If its turning on and off on its own, I would find the plug for the keyboard buttons and unplug it from the main board, many times the tack switches will cause these problems. the emi filter is more for stoping noise from the tv going back on the ac line then coming into the tv.
Try taping around on the power supplies ( or inspect the solder connections) and see if an intermitint connection might be causing the shutdown.

[ReeceyBurger123]

Re: magnavox plasma 42mf230a Power issues

Try heating board see if heating one makes it shut off faster.

[splatee]

Re: magnavox plasma 42mf230a Power issues

If its turning on and off on its own, I would find the plug for the keyboard buttons and unplug it from the main board, many times the tack switches will cause these problems. the emi filter is more for stoping noise from the tv going back on the ac line then coming into the tv.
Try taping around on the power supplies ( or inspect the solder connections) and see if an intermitint connection might be causing the shutdown.

Thanks for the response. I had the main power supply board disconnected from the Power Down Control board which I believe to have the problems with. With the main power supply unplugged I could here the relay click on the PDC board and the led on the front would turn blue. Now sometimes I would have trouble turning it back off when pressing the power switch, I would have to unplug it. I checked the tact switch on the keyboard and it seems ok, no sticking.

I had the tv plugged in for two days and there was no issue. Now today it has turned on by itself multiple times. I have it unplugged now.

[R_J]

Re: magnavox plasma 42mf230a Power issues

The tack switches can get a bit resistive, even if they check ok on a low ohm scale on a higher meg ohm scale the may read some resistance. and if they are part of a resistive ladder, a small change can cause an operation to activate, ie volume going up or down by itself, menu poping up for no reason, channels changing. tv turning on and off. You could put that same switch where it only did one function and it might be ok.

[splatee]

Re: magnavox plasma 42mf230a Power issues

I will swap the tact switches on the keyboard and see if there is a change. I may just order a PCD board as well. Because even after swapping the IC chip and capacitor on it I still am not reading the correct voltage at the capacitor. It should read 300vdc but I am getting around 153vdc. There may be some other component on the board that's bad.

[R_J]

Re: magnavox plasma 42mf230a Power issues

Are you talking about this board? because all you are going to get on c905 (with 120 volts ac input) is 160 volts dc, if you supply it with 240 volts ac (europe) then you will get around 300 vdc. thats the only reason for the high voltage rated capacitor
See that printing on the board near the 4 pin plug?
input: 100 ~ 240 50/60 Hz
All the board does is come up with + 5 volts standby, and supplies it to (I assume) the main board, the main board then tells the PS-ON pin to turn on the relay which takes the a/c input on cn901 and connects it to cn902 which supplies the main power supply board.

[splatee]

Re: magnavox plasma 42mf230a Power issues

Yes that is the board. Ok I was going by what the service manual said I should get at c905 it did not specify (Europe). I am going to open it back up again and check voltages again. Also pull the keyboard and swap the power tact button.

This is the flow chart I was using to trouble shoot.

[splatee]

Re: magnavox plasma 42mf230a Power issues

Just swapped the power tact button with the device button.

All voltages measured on the PDC board measure up are correct.

I guess wait and see what happens.