Hitachi 55HDX99 Plasma Powers on but no picture

[canadaboy25]

Hey guys, I recently acquired a Hitachi 55HDX99 plasma TV that doesn't work. The TV powers on and eventually goes into standby which is indicated by the blue power led changing to orange. If I plug a VCR into it to keep it awake, I can feed an audio source in and it will play the sound no problem. The volume controls on the TV work as well so it is obviously just a display problem.

I found the Hitachi service manual online which is also hosted on tom66's manual archive. Compared to the Panasonic service manual I had for the last plasma I worked on, this one is underwhelming to say the least. The troubleshooting section is basically non existent and there are no schematics or board views for the board that powers the panel itself.

There were some DC voltages listed so I started checking those. Picture of the voltages is attached. The voltages on CN63 were all fine but none of the voltages on CN64 were present. These are the high voltages for running the display which would make sense considering the symptom. I also posted a picture of this connector.

I would normally give it a go at diagnosing it based on the schematics but considering there are none I'm sort of stuck. I'm hoping someone with more experience working on plasma TV's can help me out.

If anyone wants and pictures of anything specific I'll post them.

Thanks

[Unspun01]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

Hey Saskabush - These Hitachis are great TVs, but I've repaired a few that had buffer board issues.

Check the square QFP ICs on the upper and lower buffer boards that are driven from the Y-Sustain. They are the thin boards (connected to the panel), leftmost as viewed from rear. Be very careful to not rip or tear the ribbon cables since these are not repairable.

One or more of those ICs may have developed a short and bringing down the set.

It may be visibly damaged (as in there is a hole or burn mark on the top) or there may be signs of heating. If visually ok, you will want to check for shorts with your multimeter between each "pin" on the ribbon cable connectors and the floating ground.

If you replace the IC, always replace the clear silicone over the pins to prevent high-voltage arcs or shorts due to close proximity of pins and future dust accumulation.

The ICs are a pain to remove and replace. I don't know why manufacturers make these ICs with such a tight pin spacing. I mean, they're about an inch square behind a screen that's literally hundreds and hundreds of square inches... These chips could be made a wee bit bigger for ease of repair.

[canadaboy25]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

Hey Saskabush - These Hitachis are great TVs, but I've repaired a few that had buffer board issues.

Check the square QFP ICs on the upper and lower buffer boards that are driven from the Y-Sustain. They are the thin boards (connected to the panel), leftmost as viewed from rear. Be very careful to not rip or tear the ribbon cables since these are not repairable.

One or more of those ICs may have developed a short and bringing down the set.

It may be visibly damaged (as in there is a hole or burn mark on the top) or there may be signs of heating. If visually ok, you will want to check for shorts with your multimeter between each "pin" on the ribbon cable connectors and the floating ground.

If you replace the IC, always replace the clear silicone over the pins to prevent high-voltage arcs or shorts due to close proximity of pins and future dust accumulation.

The ICs are a pain to remove and replace. I don't know why manufacturers make these ICs with such a tight pin spacing. I mean, they're about an inch square behind a screen that's literally hundreds and hundreds of square inches... These chips could be made a wee bit bigger for ease of repair.

All the chips look fine on visual inspection. I disconnected the power connector going to power supply that powers the panel and checked the voltages again. There was still nothing at all on any of the pins. If the chips are shorted they shouldn't be able to drag the supply down with it unplugged. I don't know if the controller senses that there is a fault and shuts the high voltage side down. Do you know if the main power supply board runs independently and should always be producing voltages or if portions can be individually controlled by the main board?

[R_J]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

Usually on the hitachi power supplies you need to load the Vs with an incandescent light bulb otherwise it wil go into over voltage shutdown when testing by itself. You can also check the voltage when first powered on, they should come up and then drop off, the Vs shuts down at 100 volts. If the power supply shuts down you need to remove a/c power from the tv to reset it.

You may need to check the buffer board/ic's with your meter and check for a short, You can operate the tv for a short test without the upper connected to the y-sus
If the buffer boards have small blue ceramic capacitors on them (likely 6) check the resistance across each of them

[canadaboy25]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

Usually on the hitachi power supplies you need to load the Vs with an incandescent light bulb otherwise it wil go into over voltage shutdown when testing by itself. You can also check the voltage when first powered on, they should come up and then drop off, the Vs shuts down at 100 volts

You may need to check the buffer board/ic's with your meter and check for a short, You can operate the tv for a short test without the upper connected to the y-sus
If the buffer boards have small blue ceramic capacitors on them (likely 6) check the resistance across each of them

I disconnected the two buffer boards from the y-sus board and powered it on for a second. After it booted up I got the 5, 60, and 80 volt rails that were missing before.

Each buffer board does have 6 blue caps on it but I will have to disconnect the ribbons from the boards and remove them to access the bottom side. I'm also not sure how I would go about testing the IC's on the board.

I've attached pictures of the buffer boards.

[R_J]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

a good buffer line would measure about .6xx - .7xx on the meter, a shorted pin indicates the bad buffer line (ic) and that ic would be bad

It's usually the upper board that fails so you could connect the lower buffer and see if you get a picture on the lower half of the screen. If you do, don't leave it on very long, just a few minutes should be ok

[canadaboy25]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

a good buffer line would measure about .6xx - .7xx on the meter, a shorted pin indicates the bad buffer line (ic) and that ic would be bad

It's usually the upper board that fails so you could connect the lower buffer and see if you get a picture on the lower half of the screen. If you do, don't leave it on very long, just a few minutes should be ok

I plugged in the bottom board and did get a picture on the bottom half. It was just a blank blue screen from my VCR. Impressive diagnosis on your part. There is some light blue speckled artifacting which I hope is just due to having half the thing apart?

I'll have to wait until after the weekend to test the upper buffer board. Thanks for all the help so far.

[R_J]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

Yes I believe you will get some speckling with just one board, I think it is usually the top ic on the upper buffer that goes bad also, but could be anyone of them.

[canadaboy25]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

Well I did the tests and they all test 0.7v except for the chip second from the top. A couple of the pins tested 0.7v but some were 0.1v some were shorted and some didn't show anything. So it looks like that chip is dead. Found some on fleabay that I'll try and order.

[Unspun01]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

Yes, sounds like at least one buffer IC is bad. You can usually tell if it's just one by following the traces between pins and ICs. I've only ever had one bad at a time.

Removal is difficult without damaging the traces because you want to make sure you don't peel or rip off traces that are still stuck.

Apply heat from heat gun or hot air rework station. About 300-350 is good for helping remove the silicone.

Then you want to use lots of Flux and flood all the pins with lead solder using a soldering iron. Like flood flood. This will allow the solder to have lower overall melting point than lead-free.

Then use heat gun or hot air rework station at 400C, you can go up to 450C if you have to but not recommended because it can warp or damage board.

There is a solder pad beneath chip that requires lots of heat to melt solder.

Another alternative is to use X-acto blade or dremel tool to cut all pins and cut away top of IC to make removal easier in pieces but I have not used that method.

With IC removed you want to remove all silicone residue and have nice round bumps of lead solder on all pins with no bridges under magnifying lens.

You can reinstall board into TV to test if you like - it will work now that the bad IC is removed except the area of the screen driven by that IC will be black.

Before putting new IC in place make sure you also have a small amount of LEAD solder on the main pad under IC but remove any excess otherwise new IC will float on it and never be able to solder all the pins. If you have too much and try to push down, it could squeeze out and bridge to other pins.

Carefully align new IC and use lots of FLUX and hot air rework station at 400C to install chip. Check for bridges and shorts before any testing.

If you have any black lines after testing you might have pins that are not soldered correctly.

I cannot stress the importance of good soldering here and a good magnifying lens or microscope.

What is the part number of your buffer IC?

[R_J]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

I think you would be better off sending the board away for repair, they have been doing it longer, have the equipment and usually will warranty the repair. If you try and repair it first, those repair companies will not accept it.

[canadaboy25]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

It is the bottom half of the top connector which is testing as bad and those traces all lead to the chip second from the top. Interestingly, it is the same chips as the one with the silicone removed from around it on the picture R_J posted.

Those are all good tips for soldering the chip. I have the liquid flux and hot air station. I have replaced chips of a similar size and pin density on my laptop successfully so I have a bit of experience.

The chip is an SN755866.

This TV isn't really worth it for me to pay someone else to do it since it is just an old power hungry plasma. I'm pretty confident in my ability to solder the chip so I'd like to do the repair myself.

[R_J]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

It's not so much the ic's pins, but it's 1/4 inch heatsink pad. I would carefully cut the pins on the old ic then unsolder it from the heatsink pad, then deal with removing the left over pins from the traces.
The picture I use was from the internet, One of the boards I have had the first ic bad. Others I have seen have had more than one ic bad.

[canadaboy25]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

It's not so much the ic's pins, but it's 1/4 inch heatsink pad. I would carefully cut the pins on the old ic then unsolder it from the heatsink pad, then deal with removing the left over pins from the traces.

That's my plan for removing it. Cut the legs and desolder them with an iron so when I am removing the chip with hot air I have no chance of pulling pin pads.

That's the hope anyway.

[canadaboy25]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

I got the chip removed from the board. I first peeled all of the silicone off then used a thin knife to cut all of the pins. I flooded solder over all the pads to remove the pins and then went back with solder wick to remove any solder that might be bridging from the chip to the pads.

After I did that on all 4 sides, I got some old heatsinks that had large enough fin spacing to go over top of the connectors and protect them from the heat. I used the hot air at 400C and unsurprisingly it was taking forever. I had a pair of tweezers resting under the edge of the chip so that the weight was providing some upwards pressure on it since there were no pins to be worried about ripping off. After a while I nudged the heat up to 420C and the chip popped off.

I then cleaned the flux up and put the board in the TV. It turned on and the display has the pattern shown in the pictures I've attached. I'm surprised that is how the display is set up. I was expecting to have one thin black bar at the top, not the black stripes that it has. Doesn't matter though because the other chips obviously aren't shorted as it is now working.

Guess I'll order a couple chips in case I stuff one up and wait a month for them to come from china...

Thanks to everyone who has helped me get this far.

[Unspun01]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

Great job. Very clean. It's like you're following in the exact footsteps of my Hitachi plasma repairs.

In my case i only needed to go to 400C because i also had a lower pre-heater. In your case going higher to 420C was probably necessary if you didn't use a lower pre-heater.

And yes, by reconnecting without that IC in place and getting an image, you have confirmed that IC alone was your issue - everything else looks like it's working.

That's even the same IC that I had to replace - 2nd from the top.

Best of luck with the rest of your repair.

[canadaboy25]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

Great job. Very clean. It's like you're following in the exact footsteps of my Hitachi plasma repairs.

In my case i only needed to go to 400C because i also had a lower pre-heater. In your case going higher to 420C was probably necessary if you didn't use a lower pre-heater.

And yes, by reconnecting without that IC in place and getting an image, you have confirmed that IC alone was your issue - everything else looks like it's working.

That's even the same IC that I had to replace - 2nd from the top.

Best of luck with the rest of your repair.

Thanks for the kind words.

I ordered 4 chips and they should be here midway through April. This way I will have extras if I happen to mess one up or another chip dies in the future. Do these chips get hot when in use and shorten their lifespan? If so I could probably put some fans in the back to help move some air.

Also, is it common for these plasma's to make slight crunching noises while moving them? It's not very loud but it sound almost like pieces of glass sliding along each other which is a bit unsettling. I thought the panel might have been broken when I got it but obviously it's not. Maybe just how these things are?

[canadaboy25]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

The replacement chips showed up so I soldered one on and measured the connectors again. All tested well. I installed the board back in the TV and its working.

Just have to get some silicone to put back on the chip.

Thanks to everyone who helped me get it fixed.

[Unspun01]

Re: Hitachi 55HDX99 Plasma Powers on but no picture

Just have to get some silicone to put back on the chip.

Thanks to everyone who helped me get it fixed.

Don't operate the TV for more than a few minutes without that silicone. There's high voltage between those pins and easy to arc across fine pin pitch and short out again. The silicone is protection against dust or lint that can short out under high voltage.

Ensure you put silicone across and between pins to complete your repair. Use fine tip nozzle for clean application.

Don't cover the top of the chip if possible because it can trap heat and lead to re-failure.

Permatex RTV is a good product and easy to install. Clear or grey is ok. Even the copper one (despite it's copper color, it contains no copper and is a good electrical insulator as well)