Pioneer PDP-502MXE 50" 720p plasma

[tom66]

Just won this plasma on eBay. It's an older Pioneer (1280x768), no HDMI, but got component and 2xVGA.

Fault: LED blinks once, no picture.

I will open it up soon, post pics and start diagnosis. I do not have a remote. I will be careful to avoid the trap switch being an issue, although I suspect this *may* be the problem.

Due to lack of HDMI (only VGA and component for HD) I'm probably not going to keep it, although it would make an awesome dorm room TV... If I can fit it in!

[vinceroger69]

Re: Pioneer PDP-502MXE 50" 720p plasma

what is the trap switch purpose i have never heard about this?

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

what is the trap switch purpose i have never heard about this?

Pioneers have a trap switch. If you open the TV up with power applied, the switch will trigger and it will go into lock-out mode. Due to some copy protection thing.

[vinceroger69]

Re: Pioneer PDP-502MXE 50" 720p plasma

ah i get you know i have just found the reset procedure on google

1. Press the “display” button then release the “display” button.
2. Wait between 3 and 7 seconds
3. Press and release the “<”, “^”, “<”, “>”, and “power” buttons in sequence.

Panel will now turn on in “service mode”.
4. Press “muting” button 3, 4 or 5 times depending on model you are working on.
Until the display shows the “initialize” page.
5. Press and hold the “display” button until the error indicator (red LED) on
either the panel or the media receiver goes out.
6. Exit service mode by pressing the “power” button on the remote.
i would never of thought of checking something like this myself. have you got the set yet?

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

ah i get you know i have just found the reset procedure on google

1. Press the “display” button then release the “display” button.
2. Wait between 3 and 7 seconds
3. Press and release the “<”, “^”, “<”, “>”, and “power” buttons in sequence.

Panel will now turn on in “service mode”.
4. Press “muting” button 3, 4 or 5 times depending on model you are working on.
Until the display shows the “initialize” page.
5. Press and hold the “display” button until the error indicator (red LED) on
either the panel or the media receiver goes out.
6. Exit service mode by pressing the “power” button on the remote.
i would never of thought of checking something like this myself. have you got the set yet?

Yeah, I've got it... it's friggin' massive! Gonna be a two person job to get it in the shed.

[vinceroger69]

Re: Pioneer PDP-502MXE 50" 720p plasma

keep us updated on how it goes hope its a quick easy fix for you i have been looking on ebay my self no much going cheap at the minute lcd/plasma wise.

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

I had to go all the way to Swindon to get it, and it cost me £48.00. Not bad I think, if you are patient you will get a good bargain.

Okay... got it in the shed & took it apart.

No trap switch - this model is too old for that! As it has no HDMI etc no need to keep any of that silly stuff secret.

First impressions VERY nice. It is completely chock full of stuff. Barely any space in it! PSU has all Nichicon and Chemicon caps. Sustain boards have Nichicon, Chemicon and Elna caps. There's a few Panasonic caps on some other boards too. On this plasma the Y drive is on the other side of the screen, where the X drive would normally be, but it's just convention to put it on the left, not a requirement of the panel layout.

The Vs bus alone has 3000uF capacitance! It's HUGE, compared to a 42" Samsung I serviced with -just- 150uF!

Also, it's got a Pioneer panel, with Pioneer drive logic, but the PSU looks to be OEM of some kind, I can't tell who makes it. Pioneer have used hybrids on this design which I -don't- like, but at least the devices aren't impossible to remove.

So, symptom is: Plug it in. Power LED comes on red. Press power button, LED goes green, one relay click, then ~5 seconds later another click, and the LED goes red again.

Initial checks showed a good STBY+5V at exactly 5.000V according to my meter (±0.7%). STBY+12V however measured a high +14.5V. However, I don't think this is the problem, it is probably high because it is not under much load.

When power button is pressed the "POWER" signal goes from ~14V to 0V and that's when the first click is heard from the relay. After about 5 seconds, the POWER signal rises back to 14V and the relay clicks back out.

So, I checked to see if any DC bus was appearing... nothing, nip, zilch, nada. None of the main -8V, +8V, +12V or +14V supplies are firing up, they're stuck in millivolt amounts. Vs and Vda (Va on Samsung/LG) are both millivolt too...

Checked the main PFC caps (3x270uF 420V Nichicons)... aha, a clue... nothing on them. Checked the pre-charge resistors (2.2 ohm 8W, 3 in series) and I think one is open circuit, because they all show as O.L. I'll pull the board and check.

According to the owner, he took it to a TV repair shop and they kept it for 2 months unable to repair it, so he took it back and put it on eBay, and yet I think I may have found the fault with 10 minutes of troubleshooting with a meter??

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

Yep, as expected (very common failure) one of the inrush limit resistors is o/c. I have a 3.3R ohm 25W power resistor knocking around, I'll see if I can use that to test it, then I'll order the right replacement.

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

Hmm... the mystery deepens...

I found my 4.7 ohm (not 3.3 ohm) 25W resistor for a temporary fix and installed it.

However upon powering it up there was a crackle/bang and some smoke from the resistor, it is now o/c as well as one other resistor in the chain.

I checked further down the line, and it appears as if all the power MOSFETs for the SMPS are shorted... what could cause this...? One is shorted gate source and drain source, the other two are both shorted drain source.

This PSU uses a very odd flyback design for all the outputs. That means a single transistor for each one. I call this odd because flybacks are generally difficult to design for output powers in excess of around 40W, and 100W is a generally accepted limit.

It uses 2SK2847 FETs by Toshiba.

I will pull all the fets and test them. The PFC fets are fine.

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

Okay, I figured out the topology of the power supply means that one shorted fet will make all three appear shorted. The only failed fet is the one that is shorted to both gate-source, gate-drain and drain-source, the others are fine. Amazingly the control logic appears to have survived this gate-drain surge - I can only guess because of the 2.2 x 3 ohm input resistors will have limited the current before they failed completely.

So, I guess this is how it took out the test resistor - because there was a dead short on the rails. Amazing it didn't blow the fuse!

I'll replace this and the resistors, and see if it works. Wish me luck!

[vinceroger69]

Re: Pioneer PDP-502MXE 50" 720p plasma

good luck hope its a easy fix have you got the parts already as pity its a bank holiday and may have to wait for parts? just noticed you posted pics will have a look.

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

No components here to fix it unfortunately, I'll get them from Farnell. Sourcing the 2.2 ohm resistor is a pain; I may just find it on eBay.

[Th3_uN1Qu3]

Re: Pioneer PDP-502MXE 50" 720p plasma

So, I guess this is how it took out the test resistor - because there was a dead short on the rails. Amazing it didn't blow the fuse!

Simple Ohm's Law there - this is a big set with high consumption so it's going to have a big fuse. The component with the highest resistance at that current fails first under a current surge - and in your case this happened to be one of those resistors, not the fuse.

[cashkennedy]

Re: Pioneer PDP-502MXE 50" 720p plasma

If your going to go to college for EE i think your gonna know more then the teachers. lol Not sure what you plan to study though.

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

Simple Ohm's Law there - this is a big set with high consumption so it's going to have a big fuse. The component with the highest resistance at that current fails first under a current surge - and in your case this happened to be one of those resistors, not the fuse.

Yeah. It's got a 10A HRC fuse. I've never seen a HRC fuse in a consumer appliance. Also, the fuse is 400V rated. Unusual. Not 250V as would be normally expected.

This thing is about 8-10 years old from what I can find on the 'net so it probably cost around £5,000-£10,000 back then. For the price, it is a very, very well built. It's surprising one of the FETs would short, but it does provide Vs, which is the heaviest bus on the TV, drawing close to 400W for full white. The TV is rated 470W input max.

I tore apart one of the ceramic power resistors and got to the resistance wire. Found a clear break in it with burn marks on the substrate/core. In fact there were two breaks in the wire around the same area, I guess it's the weakest part of the wire. No other signs of damage elsewhere in the wire.

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

If your going to go to college for EE i think your gonna know more then the teachers. lol Not sure what you plan to study though.

I'm studying Electronics Engineering, in general I am interested in power electronics (SMPS design and semiconductors) and analog electronics. Digital electronics ain't my thing, although I can do that on a hobbyist level, once it gets above 10 MHz I get squeemish!

[Th3_uN1Qu3]

Re: Pioneer PDP-502MXE 50" 720p plasma

Digital electronics ain't my thing, although I can do that on a hobbyist level, once it gets above 10 MHz I get squeemish!

High frequency analog electronics is even more fun. Pirate radio! But agreed, RF is really funky stuff. RF biasing of transistors still seems like magic to me, even though i've learned how to do it myself i'm still amazed it actually works.

Having a transistor amplify a signal, with nothing else but a coil of 4 turns of wire between base and emitter (basically a dead short at DC, so from a DC point of view that transistor is completely off and should pass no current), is like voodoo.

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

High frequency analog electronics is even more fun. Pirate radio! But agreed, RF is really funky stuff. RF biasing of transistors still seems like magic to me, even though i've learned how to do it myself i'm still amazed it actually works.

It's a little known fact that RF engineers are actually wizards, they cast spells to make sure the circuits work. Seriously, it ain't easy! For a project (paid work), I now have to layout a 2.4 GHz radio... so I'm following the app note layout to the letter and I'm not going to change a thing!

Having a transistor amplify a signal, with nothing else but a coil of 4 turns of wire between base and emitter (basically a dead short at DC, so from a DC point of view that transistor is completely off and should pass no current), is like voodoo.

Even cheap made in China FM radios make me go "wow". It's incredible how it is all implemented.

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

I found the datasheet for the resistors.



They are BGR7 resistors, 7W power ceramic cased wirewound devices.

I need to find equivalents, I can only find 5W, but even if the lower power dissipation was not an issue, the lead spacing is wrong. I'm wondering if I can bodge in an axial lead 7W resistor, as I see quite a lot of those...

[tom66]

Re: Pioneer PDP-502MXE 50" 720p plasma

Okay, I'm using this fet:

http://uk.farnell.com/jsp/search/pro...sp?sku=1664089

They used a 1.1 ohm 900V fet (2SK2847) in the original PSU, and the gate charge is nearly the same, so I think this is an acceptable substitution.

And these resistors (I'm replacing all three to be sure):

http://uk.farnell.com/jsp/search/pro...sp?sku=1174355