Pioneer KRP-500A strange fault - misfiring

[Z704T]

Hello everyone,

been reading the forum for a while now and seeing some really ingenious repairs described by Tom and the other members, I decided to register and kindly ask if anyone might have an idea what could be the cause of my 9G Pioneer plasma misfiring randomly or at least whether it's software / voltage or hardware related..

So I bought a used KRP-500A (besides the 500M the last and best of KURO) with very little - just about under 11k hours - use on the panel and ofcourse in a blacked out room its blacks were bleeding red which was to be expected and only confirmed for me the panel hadn't been tweaked before. Tried voltage adjusting it first from the SM to get the blacks close to stock, but after some testing, I decided (per recommendation of AVS and AV forum members) to just reset it. Did a safe reset first (backed up eeprom) to make sure I didn't ruin anything and was amazed how the black level really dropped to practically 0 immediately. Tried displaying various test "masks" from the service menu and after just a few minor adjustment of x_sus, y_sus and fsad (couple of ticks to compensate for the aging), the TV seemed to pass every test with flying colors. So I adjusted eeprom (confirmed reset, no turning back now) and the TV was ready for calibration. It went like I dream, everything spot on the mark.
But only after a couple of days did I notice strange sparkles appearing randomly on close-to-black content. Put on a test pattern with levels 0 - 15% IRE, and found out that the TV actually only misfires on content that is about 3 - 5% IRE (very dark grey), where individual pixels seem to light up (sparkle /flash white or greenish) wherever on the screen these shades are being displayed. Mind you this is practicaly only noticable in a pitch black room and only when a movie / content is showing this exact range of tones. Everything blacker or lighter than that - no problem whatsoever. Now I've talked to many who have reset their KRPs and noone seems to have this problem but me so they suspect the cause is a failing component (PSU?). As there is no voltage adjustment in the SM that would only control the voltage values near black, and as the TV misfires most when started from cold and then when it warms up, the sparklies become practically unnoticable, I might have to agree..
What do you guys think? The TV is currently at my local repair shop where they replaced an IC regulator in the media box (the TV wouldn't restart when warm, but that was an easy fix and is in no way connected to the misfiring), but the repairman doesn't have a clue what the cause of misfiring could be.. Says the fault is so bizzare he's never seen it before. I'm not an electrician, just love the TV to bits so would really apreciate any suggestions as to what should be looked into, as spares are hard to find and I can't just tell them to go swapping out board after board..

Sorry for such a lengthy post, just wanted to give you as clear a description of (my) fault as I can.


Best regards

[tom66]

Re: Pioneer KRP-500A strange fault - misfiring

Here is the problem.

You should not have reset your set. Unfortunately the advice is faulty. It works on sets with a few thousand hours of life on them, but after that the drift is big.

Hopefully you can restore the backup.

Then you need to tweak it carefully: VPNRST is the biggest factor affecting black/red levels, YNOFSAD1,3,4 also affect it.

Resetting it throws the control board out of sync with panel aging, causing various issues to creep up.

This isn't an issue with the PSU...it's just maldischarge caused by a reset.

[Z704T]

Re: Pioneer KRP-500A strange fault - misfiring

Well yes, I understood the risks of resetting, but people who have reset many KRPs, some with a lot more (20+k) hours on the counter, told me they never once had a problem with misfires on a KRP, only on LX5090s, so I went ahead. I do not think there is a way to undo it, as I've already completed the write to eeprom, just wish I'd noticed this issue when it was still in safe mode..
I know how to modify the voltages on a non-reset panel, but is there a way to fix this maldischarge via voltage adjustments on a panel, that's been reset?
The only way to keep black levels stock(ish) on these old sets seems to be to keep resetting them every couple hundred hours or so, because with voltage adjustments only you run out of headroom sooner or later..

[tom66]

Re: Pioneer KRP-500A strange fault - misfiring

Well yes, I understood the risks of resetting, but people who have reset many KRPs, some with a lot more (20+k) hours on the counter, told me they never once had a problem with misfires on a KRP, only on LX5090s, so I went ahead. I do not think there is a way to undo it, as I've already completed the write to eeprom, just wish I'd noticed this issue when it was still in safe mode..
I know how to modify the voltages on a non-reset panel, but is there a way to fix this maldischarge via voltage adjustments on a panel, that's been reset?
The only way to keep black levels stock(ish) on these old sets seems to be to keep resetting them every couple hundred hours or so, because with voltage adjustments only you run out of headroom sooner or later..

All resetting does is reset the internal timers which adjust the various voltages as the panel ages; for some reason Pioneer got the adjustments wrong (possibly in a rush to get 9G sets out there). It may also affect phosphor gain, but I am not certain.

It is possible to adjust the voltages to compensate for this, but it requires you to follow the full set up process detailed in the service manual and it requires the details printed on the sticker inside the unit, on the back of the plasma panel.

[Z704T]

Re: Pioneer KRP-500A strange fault - misfiring

Yes I know they got it wrong with the aging compensations, that's what left many users struggling in the long run with these marvelous TVs... There should have been a firmware fix but there clearly isn't one that I'd know of.

So you're saying there is a way to "tune" even a reset panel step by step, so that all the voltages are pretty much in line with what they should be? Have you ever done this before? And could you describe where exactly that sticker should be located?

Really thankful for your input, Tom.

[tom66]

Re: Pioneer KRP-500A strange fault - misfiring

Yes I know they got it wrong with the aging compensations, that's what left many users struggling in the long run with these marvelous TVs... There should have been a firmware fix but there clearly isn't one that I'd know of.

So you're saying there is a way to "tune" even a reset panel step by step, so that all the voltages are pretty much in line with what they should be? Have you ever done this before? And could you describe where exactly that sticker should be located?

Really thankful for your input, Tom.

I've not done it before...both LX5090s I've had were not reset units.

The service manual for the PDP-LX5090 has all the details if I recall, including the location of the sticker (it's just where the panel part number and serial number are located). It's a roughly 30-step process involving several flowcharts and looking at different test patterns.

[Z704T]

Re: Pioneer KRP-500A strange fault - misfiring

Okay, so you're pretty certain this isn't hardware related.. it just doesn't make complete sense to me that when warm, it mal-discharges much less. Will anyway try and do the full setup at home and if I have any success, will let you know.

Thank you once more for your replies!

[tom66]

Re: Pioneer KRP-500A strange fault - misfiring

Okay, so you're pretty certain this isn't hardware related.. it just doesn't make complete sense to me that when warm, it mal-discharges much less. Will anyway try and do the full setup at home and if I have any success, will let you know.

Thank you once more for your replies!

Plasma panels (the actual glass panel with gas in it) are temperature sensitive devices. The TV handles the compensation with panel temperature; you adjust the base point only.

The base adjustments should be done at room temperature (i.e. 23 +/- 5C) once the set has warmed up (normal TV should do; sometimes the manual specifies 100% or 50% white, so check.)