HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

[ngc1068]

Hi,

I have a 50" HP CPTOH-0603 Plasma TV that recently failed.

The kids told me it wasn't working this week, and they had no info about what happened. I've had the TV since new.

I uploaded a video of what its doing to this URL, warning its about 21MBytes.

http://www.modschat.com/HP_plasma.MOV

The unit will power on, and stay on indefinitely, and power off both from the remote, and the local panel, but the display shows nothing but a flickering screen with snow. I couldn't tell if there's any audio.

The HP splash icon and none of the on-screen menus or graphics are visible.

When the unit is powered on, you can see a single bright blue LED through the rear panel grill.

Please, if anyone has advice, it would be appreciated greatly!

[tw2005]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Sounds like faulty ybuffers but I can't download the video. try posting some still shots using the 'go advanced" "manage attachments" buttons and upload.

Sometimes it's just one board shorting and drags the volatges down. I have had a coloured mess with a 42" V6 SD plasma some time ago and it had all snow and colored mess randomly jumping around.

Bottom ybuffer had failed, I disconnected the lower board from the Ysus and the interconnecting cable between the upper and lower buffer boards and that resulted in a perfect top half being produced.

Not entirely sure about this model if you can do that but i suspect your buffers may be the ones people talk about SMD FETS shorting on the buffer boards themselves.

A quick search of your model showed me it is LG based.

[capkid]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

It appears that you have a faulty Y-Sustain. One or more of your IPMs under the large heat sinks is probably bad. You may also have a bad Y-buffer based on the faint vertical stripe that's visible when the screen flickers. You'll have to remove the back cover to investigate further.

[ngc1068]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Thank you both for the assistance.
Should I just buy replacement boards (can you give a recommended supplier?) or is there testing I should do, to further narrow down the failure?

Thanks, in advance!

[capkid]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

I'd do some testing first before spending money. Start with tw2005's simple Y-buffer test. The Y-buffers are two narrow boards that run vertically along the left side of the panel if you're looking at the TV from the back; they're connected to the Y-Sustain, which is the bigger circuit board just to the right of the Y-buffers.

Make sure you unplug the TV before connecting or disconnecting circuit boards. Allow at least 5 mins. to elapse after unplugging the TV before reconnecting a board. Do you access to a multimeter? You may not need one if the first test reveals the root cause of the issue. Post pics of the circuit board layout if you're unsure so we can guide you.

[ngc1068]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Here are some still images of it. The display alternates between dark and flickers briefly (fractions of a second) to these patterns.

[tom66]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

I would say ER IPM + Y-buffer.

[capkid]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Let us know what you see onscreen after you remove the back cover and disconnect the lower Y-buffer.

[ngc1068]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Disconnected and removed the lower buffer, it showed 110ohms, approximately, both directions. No visible damage or discoloration. I would assume its bad?

Disconnected and removed the upper buffer, it showed infinite one way, and around 2.4MegOhm the other way. I would assume its ok?

Put the upper back in, powered up and I now get the flickering only on the top half. The HP startup logo is recognizable, but just barely.

[capkid]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

So, it does appear that at least your lower Y-buffer is bad. It's common for one of the fets to fail on the Y-buffer. You can either replace the buffer or replace the bad fet. You'll have to remove one of the fets to find the bad one, since they're in parallel. Also, check your buffer chips closely for small pinholes or burns.

For the flickering, check voltages on the Y-Sus to see if they fluctuate with the flickering. There should be -Vy and VSC (VSCAN) test points on the Y-Sus. Also, check the Y-Sus fuses, but I suspect they're intact.

[ngc1068]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Vsc TP is steady 119.65VDC

-Vy TP is erratic, seems to start at around 199VDC, and will exponentially decay towards 0V, it may get down to fractions of a V before starting ober at 199VDC. It may reset back to 199 at any point in the decay...Seems random. Faint audible clicking noise from YSUS too, same freq approx as the screen flickers.

[capkid]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Ok. I'd say that the Y-Sus is bad. As one other check, confirm that your Z-Sus voltages are ok. Assuming that only your Y-Sus is faulty, you have a few choices from least reliable to most reliable. Coincidentally, the options are listed from least difficult to most difficult.

(1) Replace the Y-Sus with a used one.
(2) Replace the IPMs on the Y-Sus.
(3) Recommended for longevity, but relatively expensive: Replace the IPMs on both the Y-Sus and Z-Sus.

Here's a video on IPM replacement: http://m.youtube.com/watch?v=Y8MNQYXw8E0

Edit: Check your PSU output VS and VA voltages to eliminate any likelihood that the PSU is faulty - very doubtful.

[ngc1068]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Is there a guide on how to check that Z-sus voltages are ok?

[capkid]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Is there a guide on how to check that Z-sus voltages are ok?

Check Zbias voltage across the R111 resistor on the Z-Sus - it should be somewhere around 100V. The panel label should have the exact spec.

[ngc1068]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Its holding 111.4VDC

[capkid]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Its holding 111.4VDC

Ok, it's probably supposed to be 110V, which isn't far off. It seems to be working fine. The Y-Sus and lower Y-buffer appear to be the sole culprits.

[ngc1068]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

If it was your TV, and you had the money to spare, would it be worth repairing?

[capkid]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Good question. I might spend $100 to replace the Y-Sus IPMs and buffer fet for now. New TVs are very inexpensive now, so I wouldn't put much money into it.

[ngc1068]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Upon removing and inspecting, it definitely looks like some heat on Y-SUS around the upper IPM, clear residue and discoloration, around the ER_LOW pin area and the C5, C6, C24 area.

Not clear to me how to remove the IPM heatsinks, do you have to unsolder the IPM from the rear and get it off the board to remove the sink? There are screws that are holding the sink on that appear otherwise inaccessible.

[capkid]

Re: HP 50" Plasma TV, Model: CPTOH-0603... plz, need help troubleshooting

Upon removing and inspecting, it definitely looks like some heat on Y-SUS around the upper IPM, clear residue and discoloration, around the ER_LOW pin area and the C5, C6, C24 area.

Not clear to me how to remove the IPM heatsinks, do you have to unsolder the IPM from the rear and get it off the board to remove the sink? There are screws that are holding the sink on that appear otherwise inaccessible.

The video link I provided earlier shows how to replace the IPMs. It's not an easy procedure without the proper equipment, and you have to be careful not to damage the traces and rings on the circuit board: http://m.youtube.com/watch?v=Y8MNQYXw8E0

Edit: If you decide to just replace the Y-Sus as a whole, it looks like you have a few substitutes available: http://www.shopjimmy.com/lg-ebr30597501-ysus.htm