CurtPalme.com Home Theater Forum

[HD-DAVE]

Well, after three years of perfect operation post scan board replacement, this amazing first ever hd plasma set has died again. Wouldn't power up one day last week .... main front panel power led is always green but it's going into shutdown again. First thing I did was pull each of the Scan boards one by one to see if that was the cause but they are all good. In fact, I checked all the localized PD signals coming back to the main Power Supply and none of the "accessory boards" (as pioneer calls them) appear to be causing the PD. A bit scary as it points to the Power Supply itself which is unbelieveably complicated. So far the only anomoly I have found so far is the +12 Standby voltage is quite high at around 18 volts. Its generated from a simple half-wave rectifier affair so i should be able to figure that one out...The schematics I have from the service manual I found online are not very clear and the troubleshooting instructions are poorly translated from japanese but I will keep at it.

( no bad caps found so far...the quality of the caps in this set is really good).

Mac if you are listening, any suggestions ?

Thanks,
Dave

[macgyver655]

Can't give you anything specific to look at so you will have to hunt it down. That 12v supply is quite high. I do have a clear copy of the service manual with the PS schematics and PD trouble shooting guides if you want it.

[HogPilot]

[HD-DAVE]

Thanks, Mac (and Hogpilot for the interesting explanation of the green "phospor trails"). Mac thanks for the offer but I don't think i need a second copy of the service manual - mine is complete, its just that a few of the lines on the power supply schematic pages (four of them) are "faint" as that portion of the manual must have been scanned in to the electronic copy by Pioneer. I've been educating myself intensely on switch-mode power supply troubleshooting for the past day or so, having never seriously boned up on how they really work (instead relying on "fix by inspection" (or esr tester ) and more importantly what the most common failure modes are. Given the lack of a proper block diagram anywhere in the Pioneer service manual, last night I googled up the service manual for the second generation of this set (PDP-502) to gain insights into the first gen one - the manual I found has an excellent block diagram and descriptions/schematics of how all of the protection circuits work. I can do a backwards comparison to look for all the things in common inspite of there having been a lot of changes (introduction of LED fault code blinkers for example). On my set the secondary transformer for the 9 volt and 12 volt standby power supplies share the same switching input even though they have separate windings and given the 9 volt is ok, the finger might be pointing to the output side rectifier/filter circuits - I'll be checking the series output inductors tonight as I learned they can cause overvoltages if they fail...

[Nashou66]

This is a pretty good introduction to repairing SMPS.

http://www.repairfaq.org/sam/smpsfaq.htm

Athanasios

[macgyver655]

Do you not have page 83 in your manual? Diag of malfunctions when PD occurs.

Page 85, PD circuit block diagrams?

[HD-DAVE]

Hey Mac, after a few hours of poking around this sets "power supply from hell" watching what the opto-isolators are doing (they're used for power up sequencing, under/over voltage sensing, etc) I've made some minor progress: something on either the Y-Drive A or B could be pulling down the 150 Volt supply ("Vofs"). I say "could" because its not being detected via the PD circuits on either of these two boards but rather the undervoltage detection circuit for the 150V supply on the PS board itself is causing the PD...specifically Opto-isolator PC-10 (serv manual page 18 approx middle has the output side, page 19 top center has the diode emitter ) is getting activated.

When I disconnect the two four conductor cables (P5 and P8) that send Vsus (175V) and Vofs (150V) to the Y-Drive boards the 150V rail pops up to where it should be (145V)....with them plugged in it never gets beyond 90V before the set shuts down. When I disconnect one or the other it still does a PD so I am testing components on the YA and YB boards now. Unfortunately there is no full schematic for these boards but there is decent block diagram.

I think another useful step I will take is to put a dummy load on the 150V supply rail with the Y-Drive boards disconnected to see if it can provide the amperage spec'd on the schematic ( 0.046 Amps ... I can't believe its so small !).

...back to the test bench i go...

[HD-DAVE]

In case anyone wondered what ever happened with this, in the end I gave up in frustration trying to fix this sucker. It simply was a case of the power supply being too poorly documented in the service manuals for me to get further than I had in the last post. Entire sections of the PS relating to numerous daughter boards were missing, there was no annotation on the schematics as to what voltages should be present at various points, the language in the service manual was poorly translated, etc. Pioneer techs must have pulled their hair out providing warranty service on these back in the day!

I could have dropped $125 into it by getting an entire new power supply board but given that maybe had a 50% chance of this fixing the problem, and the weak picture quality the set had ( it was almost 16 years old after all ) I decided against it.

Sadly I dropped it off at the local e-waste collector on the weekend. I told the guys who worked there they would likely never see another one like it, ever ! They could not believe how heavy it was for a flatscreen. No wonder - the ,massive power supply board alone weighed 13 pounds....must have had 1000 discrete components on it.

Oh well, I got 4 years out of it for a $35 investment so I did well.

[Curt Palme]

And it wasn't even worth driving it to my place.. sad but true.

Nice to see though that others persevere for almost a year to the day on trying to repair stuff.

[Curt Palme]

And it wasn't even worth driving it to my place.. sad but true.

Nice to see though that others persevere for almost a year to the day on trying to repair stuff.

[macgyver655]

Why do you guys need schematics to repair stuff?

I only use them to talk you guys through stuff without my eyes and hands being there, lol.

[Jeremy112]

[andy2000]

I just picked up one of these for $25 from a thrift store. I haven't connected it to a signal yet, but it produced on screen display when I powered it up. I didn't see any obvious burn in on the "black" background to the OSD.

I could use a stand and remote if anyone has one. I also wouldn't turn down some spare scan boards since they seem to be high failure items.

[HD-DAVE]

Hey Andy,
You are too late on the Stand, sold that to a guy in Australia (he paid like $120 for shipping!). ...but I still have the remote for my PDP-501MX ... it is model CU-PD001 or something. Only has about 12 buttons. Check this link it is pictured on page 14 and get back to me and we can work something out.
Dave