Question about Planar PDP-42BK 42 in. Plasma HDTV

1 Answer

Planar PDP-42BK PDP42BK blowing PSU fuse repeatedly - 2 bad 5W Rs

Okay, when I got the unit, it had the classic symptom of going on standby shortly after power-up and flashing the Green LED on the PSU board.

Full disclosure:

I bought the panel non-working from a local university without testing it, etc. When I tried to power it up at home, I got the green light, click from relay and nothing. No test screen. Using the symptoms I had, I checked FixYa to see the common C16, C19, C97 capacitor combo listed. I didn't open the set to see if the capacitors were bad. I just ordered new ones.

When those arrived, it was then that I opened the back and checked everything. To my amazement, the capacitors looked fine.

Powering the system on with the back taken off, I noticed the green LED on the PSU for the first time. It appeared to have a sequence of five short flashes, a long gap/flash where it stayed on and then three short flashes with another long gap/flash. I was unsure whether I counted the flashes right so I turned off the main power and turned it back on and maybe hit the soft power on button. I forget. In any event, I heard a fizzle and everything went dead. No lights (No music? Just anger! But I digress...) on the PSU and nothing at all. I unhooked everything and tested the 8A fuse at F1. It was blown so I decided to pull and test the capacitors.

When I pulled and tested each one with my meter, they were well within specification for capacitance. I don't have an ESR meter, but I do have access to one at work. My meter's capacitance test only charges with about 3VDC, for the record, so I don't know about leakage at the voltages seen inside the set.

I also looked at C103 for issues. It looked like there was crusty stuff on one lead that wasn't flux residue. I removed it and it also tested fine. Luckily, I had a replacement for that part on-hand.

I installed the new C16, C19, C97 and C103. Figuring the fuse was worth a look, I pulled it and saw it had a snap-together case. Opening the case, I saw the wire had melted and there was a little bit of black residue, but not what I see from really bad shorts. I soldered a 6.5A glass fuse to the posts of the original fuse and installed it. I figured it would just melt if the circuit was otherwise good.

I installed the power board and hooked everything back up. I plugged it in and hit the main power switch. It was fine with a green light on the PSU board until the relay clicked and the fuse blew quite energetically.

I started testing after the relay and found that R177 and R2 are both open while R3 measures 4.7ohm like it should. With R2 and R3 being in series, I believe it was a matter of R2 being weakest link.

So there are three things for the FixYa crowd to figure out:

1. Why does the relay turn on without the soft-switch being pressed?
2. Why would the lack of the resistors cause the fuse to blow?
3. Why did the resistors blow in the first place?

I have the power board schematic in front of me, but I seem to be missing something. If you want to take a crack at this and need a copy of the schematic, I can upload it and provide a link.

If you need more details or want me to do any tests, I can.

Posted by on

  • derek512 Jan 11, 2009

    I have gone further in my search for a solution. I replaced the blown power resistors in order to get the unit to start up again for a moment. I used a single Radio Shack supplied 10ohm 10W wirewound resistor in place of R2 and R3, which are in series. When I hit Main Power, the resistor started glowing orange at the very center and smoking. Soon, the breaker tripped.

    I searched the board and found that Q5 and Q6 are near dead-short across them. They are blown and that's what's not working. I'm planning to order new ones.

    I wish I could tell if the monitor works before I do the repair. I still wonder what is causing them to go bad in the first place. I did see that the PFC IC is different from what is called for in the schematic. I doubt that has anything to do with it, however.

  • Xennon Jan 29, 2009

    Im having the same symptoms as you are with your board. I havent divedin as of yet but would appreciate a copy of the schematic if possible.I'll keep you posted as to how i get on.





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  • Planar Master
  • 29,394 Answers

You must replace the drivers, the output/chopper transistors and use the correct type of R2/3 resistors otherwise you have a fire waiting to start.

Posted on Feb 26, 2017


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Posted on Jan 02, 2017


SOURCE: planar PDP42BK no picture

Check the 15v line that runs through all the boards, left, right and top.. If that has no power, then look on the ysus board (left one) there is a flyback reg (5pin) standard to-220 case surrouded by caps, it does dc to ac conversion, if you dont have the 15v output then the chip is bad. I just did 2 of these that had the same problem.

Posted on Nov 09, 2008

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