Pioneer PDP-503cmx won't power on

[theojt]

Background: Set was purchased new circa 2002 has been working normally until a few weeks ago. Went out suddenly but no popping sound. There was a Red blink code but it displayed only once and I didn't catch it.

Set will go to Standby when plugged in.

There are no signs of overheated components that i can see (at least on the top side of the board). No bulged capacitors. I realize there can still be bad caps or shorted components.

Power on occurs and I sometimes see a brief full screen white flash (scrambled with noise), then immediate power down of the power supply.

If I pull the Y Sustain connector, the set will stay powered up. I replaced the Y Sustain board but that did not fix it.

I checked PS voltages - all low voltage test points (+5v, +6.5V, +12, +13.5, +15, and -9) look ok. The 12V reads 11.75 and that's the biggest variance. VSUS reads 224V, VADR is 61.5V but i didn't see any values in the manual for these.

What I did find however, is that all test points on the Power Supply that are labeled 0V are reading -52V. So I'm thinking something is shorted in the power supply.

Do I have a correct understanding? If it's the Power Supply, what short would cause a zero voltage point to go negative? Any ideas what components to look at first? If it's not the PS, what else could it be?

TIA!

[kgavionics]

Re: Pioneer PDP-503cmx won't power on

hi
Must be a problem with the PS if your ground is -52V.
can you please share a picture of the power supply?

[theojt]

Re: Pioneer PDP-503cmx won't power on

Hi-res Power Supply photo attached.

[dick_barton]

Re: Pioneer PDP-503cmx won't power on

background:
I checked ps voltages - all low voltage test points (+5v, +6.5v, +12, +13.5, +15, and -9) look ok. The 12v reads 11.75 and that's the biggest variance. Vsus reads 224v, vadr is 61.5v but i didn't see any values in the manual for these.

What i did find however, is that all test points on the power supply that are labeled 0v are reading -52v. So i'm thinking something is shorted in the power supply.
Tia!

vadr = 60v
vsus = 225v

[tom66]

Re: Pioneer PDP-503cmx won't power on

You might be using the wrong ground. Use the chassis of the TV as your ground. If you use neutral or something else it could explain the strange readings.

[theojt]

Re: Pioneer PDP-503cmx won't power on

I should have been clearer on that Tom....I am reading -52V between chassis ground and the 0V test point on the board.

I assume this is the 0V reference for the digital circuits? I'm sure it's isolated from chassis ground but should read very close to the same (i.e. 0.0 VDC).

[tom66]

Re: Pioneer PDP-503cmx won't power on

Is it on the HOT / LIVE / PRIMARY side? If so it's probably Mains referenced and not important. I'd say if the chassis is grounded you haven't got an issue there

[theojt]

Re: Pioneer PDP-503cmx won't power on

Yes, I found a schematic for a newer version of the board and those "0V" measurement points are just that. They should read 0V but they are NOT ground references.

Nonetheless, those points read -52v instead of 0v. I've no idea why and the schematic I have is not correct for this board (can't seem to find the correct one either). I may take a chance and just order a PS board but it's one of the more expensive boards for this set so I'm hesitant to order without better info.

[tom66]

Re: Pioneer PDP-503cmx won't power on

FWIW it doesn't look like a power board fault.
Service manual:

Have a look at page 147 onwards.

There may be a way to get power down info via RS232 or otherwise, which might give you a clue as to the cause of the fault.

For RS232, you would use a USB to RS232 cable (available on eBay for a few dollars shipped) or an older PC with an RS232 port, then a program like PuTTY or Teraterm.

You might need an escape code sequence to send commands. I don't know what it is for this panel, but it's likely to be the same as the 9Gs, and that's (hex digits) \x01 followed by \x00. You will need to enter these into your chosen terminal as hex bytes e.g. by copy and paste or by using a hex entry of some kind...

[theojt]

Re: Pioneer PDP-503cmx won't power on

Yep, I'm already on the RS232 interface thing. I have everything I need except for a F-F adapter and then I should be able to give it a shot.

Let me give you the complete background as I'm confused by the Power Supply. As noted prior, all the voltages seem to be okay except for that -52 on the 0V measurement points. If I plug in P2 and P3 the set will Power Down (protection condition).

The manual states that that "Shut Down" and "Power Down" are two different failure modes:

Shut Down - Green LED flashes failure code when the microprocessor detects an issue.

Power Down - Red LED flashes failure code. This is a dangerous state and the PS is turned off by the protection circuit.

Mine is definately a Power Down failure. I started my troubleshooting journey thinking that since the power supply voltages mostly looked okay, then it must be in the Y drive board since unplugging the Y drive connector (P3) allowed the power supply to stay energized.

So I replaced the Y drive board and it was no better. I then disconnected the y drive from the upper and lower scan boards and tested those across all pins, checking for shorts to ground - and I found none. I think I can also eliminate the Y drive since for a brief moment when the set powers up cold, I do get a full screen display of white-ish background with noise in it. I am assuming that if the Y drive was shot or if the scan boards were shorted, or if the PDP panel itself was bad, then I would never see even that brief display.

That led me back to thinking it might be the Power Supply. If the 0V measurements are biased down at -52V, my thought was that maybe the OVP protection circuit was (fooled into) thinking that there was an over-voltage condition and it had to shut down the PS. Additionally, I saw that there is a "390V adjustment" pot on the PS board. Coincidentally, the points where I measure it, the 300+ voltage measures around 343.5V - or about 47-50v low. Could a short on the PS board pull the 0V reference down -52v, and also pull down the the 390v supply???

Feel free to tell me I'm not thinking correctly or just being stupid. The other possibilities could be the Resonance board, microprocessor board (unlikely), or possibly the audio/fan driver board. Its probably something pretty obvious to someone familiar with plasma set repairs but that's definitely not me.

I'll try to get a connector to get some TTY readings and maybe that will indicate something.

Thanks very much for your input!

[tom66]

Re: Pioneer PDP-503cmx won't power on

So I replaced the Y drive board and it was no better. I then disconnected the y drive from the upper and lower scan boards and tested those across all pins, checking for shorts to ground - and I found none. I think I can also eliminate the Y drive since for a brief moment when the set powers up cold, I do get a full screen display of white-ish background with noise in it. I am assuming that if the Y drive was shot or if the scan boards were shorted, or if the PDP panel itself was bad, then I would never see even that brief display.

Not really true unfortunately. There are a great many Y-drive faults that can cause malformed display images. If you look in detail at that manual at how a PDP is driven, even an older model like this has a fairly complex drive waveform. Any fault in that wave can cause picture distortion. You are probably on the right track when you say the PDP is okay. It is very rare for one of these old panels to fail, and as far as I know it's pretty much unheard of for a PDP to fail anyway except through physical cracking or damage to the connectors on the display.

That led me back to thinking it might be the Power Supply. If the 0V measurements are biased down at -52V, my thought was that maybe the OVP protection circuit was (fooled into) thinking that there was an over-voltage condition and it had to shut down the PS. Additionally, I saw that there is a "390V adjustment" pot on the PS board. Coincidentally, the points where I measure it, the 300+ voltage measures around 343.5V - or about 47-50v low. Could a short on the PS board pull the 0V reference down -52v, and also pull down the the 390v supply???

I'm assuming you're powering the TV with 115V.

If you have 230V then you would expect about 340V when the TV is off, because the power factor correction circuit is off. This circuit ensures the input power to the TV is proportional to the input voltage...it's a bit complicated but it comes down to not distorting the mains grid too badly with lots of power being drawn at the peaks. So in standby, the PFC is off because it's not needed (TV is not drawing much power, a watt or less) and you get a lower voltage across those caps. When things like the Vsus is on, and when the panel turns on, the PFC will turn on to start correcting input current, and this will boost the voltage on the caps up to around 380 to 420V. That is probably what the 390V adjust is for.

It is a bit odd that you are only seeing 340V here. I don't think it's anything to do with your -52V readings. If you had something shorted on the power board, on the primary, it would be blowing fuses almost always. And I can't think of a fault like that which could cause that odd reading. It might be because the TV is under less load or because it's at 115V it's dropping the bulk voltage, I'm not sure.

[dskall]

Re: Pioneer PDP-503cmx won't power on

You may have feedback resistors out of tolerance giving you low pfc voltage.
BTW congrats tom66. Hope you continue to contribute.

[theojt]

Re: Pioneer PDP-503cmx won't power on

Got back around to looking at this set. Replaced the power supply (found one on eBay for $18) and it no longer goes into Power Down mode (protection). Now I get an ugly looking raster display - See attached picture. Is the panel shot or is this some kind of issue with the buffer?

Still not getting any blink codes at all (just solid Red LED in Standby and solid Green LED when turned On) and I was not able to successfully read anything via RS232 with my cobbled together USB>RS232 cable and adapters. There was no signal present on any connector when I took this picture.

[freakaftr8]

Re: Pioneer PDP-503cmx won't power on

Those destincive "lines" in the screen worry me to thinking buffer board fault. Is this the panel that has the drive cables fused to the buffer boards?

What is your y scan reading? Is Vsus coreect? How about Vadr?

[theojt]

Re: Pioneer PDP-503cmx won't power on

Not sure, I'm going to dig into it tomorrow. The buffer boards sit under part of the frame, I'll have some disassembly to do to get at them. Between the Y drive board and the buffer boards there are two semi-flex cables that are more like sets of bent wires. No idea what's beyond that yet. Will post back.

[theojt]

Re: Pioneer PDP-503cmx won't power on

After I removed the frame and gained access to the buffer boards, I can confirm that the buffers are indeed bonded to the panel.

The set is buzzing pretty loud when the raster is on the display so I didn't leave it on for long - I turned the set on, quickly took 2-3 measurements and then turned it off again.

Here's what I got:
SUSoutA = -9.0
SUS_U = 91.0
SUS_D = 1.3
PSUS = -35
SUSoutB = 1.4
SUS_U = 93.0
SUS_D = 1.1

Y-board connector measurements:
+15V = 15.0
+13.5 = 13.7
-9V = -9.0
YDRIVE_PD = 5.0
YDC_DC_PD = 0
VOFS_ADJ = 2.4
VSUS = 202.0

Measured at Power Supply:
VSUS = 202.0
VADR = 61.0

This is a replacement power supply and the VSUS is low - it should be around 224v. This is supposed to be a software-controlled voltage regulator that produces VSUS, so I don't think there are any adjustment points but I'll have to go back through the manual again to be sure.

[freakaftr8]

Re: Pioneer PDP-503cmx won't power on

I have worked on a bunch of those horrible Chinese power supplies and they are a pain in the ars to figure out lots of bad SMD soldering around output mosfets. Smd resistors fall off the board!!

Isn't that power supply an AXY-1059? I have like 3 spare sit around my house set or bad only checking them out tonight but I believe there is some kind of adjustment.

When you purchased this power supply were you assured that it did work correctly? This power supply is also used in the 43" version and I'm wondering if VSUS is set low because of a smaller panel if it was in fact for the 43" version

[theojt]

Re: Pioneer PDP-503cmx won't power on

Hi,
Could have been for a 43in, I bought by board number not TV model. The one I replaced was a AXY-1053, that was the original board. Pioneeer changed alopt of them for AXY-1059 and then later I believe an AXY-1064 or something like that. I get back to looking the board over in a little while.

Thanks for your input.

[theojt]

Re: Pioneer PDP-503cmx won't power on

I've reviewed the docs - they say that the voltage regulation never needs adjusted since it loads from a stored memory value. Since I had my A board replaced, could this where the incorrect low voltage is coming from? I know that at least some of the memory was cleared in the repair process - maybe this wiped out the original value. Not sire how I would 'put it back' in that case.

I also found a VSUS adjustment on the PS board - not sure if I should mess with it or not?

[freakaftr8]

Re: Pioneer PDP-503cmx won't power on

Well if your VSUS is reading 202 but your panel requires 224 id give it a shot. This is mostg likely a source of the issue.

Pioneer is finicky with voltage settings. A little too low and the whole screen gets blotchy. I've dealt w this first hand. I had a Pioneer that had over 70000 hours on it and had to crank up VSUS just a bit to fix the panel blob issue.

Pioneer has a service menu and I'd have to look it up but I believe the setting are user serviceable there.