Hitachi 55HTD52 Sound, but no picture

[Dennis H]

Hello, I am hoping You all might be able to help steer me in the right direction with this old Boat anchor of a TV. First a little background:

We bought the TV new in late 2005 and it has been hanging in the same spot on the wall ever since working fine until a couple of months ago when upon turning the TV on one day, it never showed a picture (sound was ok and it seemed as though all the commands etc worked even though I got absolutely noting on the screen). I did not notice any pops, noises, or other prior to the issue, and it had worked fine the night before. Although the TV is plugged into large surge protector, I recognize that probably is not a guarantee of keeping the spikes away.

Ok, sooo..... me being a little slow to get started and of course that beast weighing about 140 pounds (what 65 kg or so?)...it stayed on the wall for a few months until my neighbor helped me take it down.

I removed the rear sheet metal cover and have the TV sitting upright in the foam shipping blocks it came in. This seems to allow me enough access to everything to work on it.

Ok, so first things first, Blew the dust off and looked and smelled for anything out of the ordinary...no luck there. I used my old Simpson Ohm-Volt multimeter to see if the main switch and fuse were ok. Seemed good. plugged in..got 120V ish (line voltage) coming from the pwb to the main board. I expected that since the sound works, so far so good.

Ok, I managed to get some diagrams and pinout voltages etc for this model and started checking the out puts.

So as you may expect, I got no output Vs or Va voltage (on this model it is plug CN64 and should have been around 64v and 82 volts).

So, I'm not a EE, but am an ME (but man EE classes were not my favorite), and I'm thinking , ok, no Vs and Va must mean a bad power supply so I disconnect everything and start looking closely at the board, but nothing jumps out. Then, reading about some similar trouble shooting (maybe on this form) I noticed some discussion about logic boards and circuit protection--specifically suggesting that a fault in the X, Y, or buffer boards could or should ultimately signal the logic board to go into protection mode basically telling the main board to shut down Vs and Va. Ok...how the heck do you check that... well, more internet searching led to other trouble shooting discussions on the same TV.. Short story, you unplug the main output to the X sus board (Cn64) (which feed the Y also) and also unplug CN 63 and 68. They have you connect a jumper that simulates the logic boards output back to the main board (when working correctly) and tells the main to provide Vs and Va. Low and behold... I have Vs and Va, so I think the main board is ok now.

Onward....Seems like mostly people just swap the boards on these, which, as I have read, sometimes works, sometimes not with all kinds of bad results.

So, how can I try to narrow it further, Xsus, or Ysus, or maybe the buffer boards (upper and or lower)?

Here is where we get to where I am not sure if I was just lucky or if my thoughts are/were correct.

The idea was, remove the faulty board which would (hopefully) let the logic board "clear" the error history, and put out a Vs and Va.

At first, I tried disconnecting the Y from the X which did nothing. Next I removed the upper and lower buffer boards and Y board., more so for inspection, but this allowed me to learn some stuff in the end, at least I think I did .

Long story short again, I plugged the Y board back in but left off both buffer boards. Interestingly, when I powered up, I got my 64 and 82 volts. I was pretty excited actually. I though maybe I was getting somewhere.

So I thought I would try the same thing with one of the buffer boards plugged in to see if I could trace it back to one of those boards. Well, I didn't get anything when I plugged the upper board back in. So I removed it and tried to verify my previous success, ie: Y board only with Vs and Va. but the first try, got nothing...uh oh ..... stay cool....ok think..I powered all the way down, unplug as well as the main power button then power back up and low and behold, I had my Vs and Va. All is good.........but it disappeared after several seconds. Darn it! Tis made me wonder if there was also an issue with the Y board.

So at this point, I think that:
1) Either one or both buffer boards are toast

2) The Y board has issues as well

3) Main board ok

4) X board ok

It seems these are the common boards that fail, sometimes together- probably one fails and takes the other out.

I guess my question to the experts here is (excusing my babble) am I going about this in a reasonable way (makes sense to me...but lol).
And is there a way to further trouble shoot the Y and buffer boards down tot he component level. I was hoping that if it was an MOSFET or something I can replace, I would like to do that. I suspect that is not reasonale for a buffer chip though.

I don't see any holes in the Mosfets but it seems (from reading a little) that they may not show any external damage when they have failed.

So can I check them with out removing them from the board?

Thanks for any words of wisdom!!

[tom66]

Re: Hitachi 55HTD52 Sound, but no picture

A very common fault on this model is for some capacitors on the power supply to fail.
Apparently this causes unstable Vs which damages the buffer boards.

Can you post some pictures of this chassis -- inside of the TV and one of each major board.

[Dennis H]

Re: Hitachi 55HTD52 Sound, but no picture

Yes, Here are some pictures, overall looking at the back.
The Y board is on the Left,
Main Pwr in the middle (has the two larger CAPS on it)
Logic board is smaller and to the left of Main board
Xsus is to the far right

The upper and lower buffer boards mount to the far LEFT outside of the Y sus board (they are in a seperate close up)

Vs and Va go from the Main power board over to the X sus board which then send them over to the Y sus board.

Both the X and Y board's have a separate flat cable going back to the logic board (the white flat cables in the pics --about 1 inch wide). There are also the same size flat cables coming back from the upper and lower bus boards to the logic board. There is a smaller plug of blue wires going from the Logic board back to the main pwr board.

So, It's funny you mention the CAPS on the main board....I wondered if they were suspect or not. The picture may not show it very well, but they do not look like other healthy CAPS to me... the top is either flat or ever so slightly domed. I would have thought they should look slightly indented like the rest of the CAPS.

Your comments on a potential theory to my failure, makes sense to me, especially of you think these CAPS look jacked up.

So right now, I am getting the 64 and 84 volts all the way over into the Y sus board ( had to make sure i had everything unplugged and waited a few minutes) It's now been sitting running, holding voltage for maybe 20 minutes. This is without the two buffer boards in.

Can I check those CAPS on the pwr board to rule them out with my meter, it will let me charge and then watch the decay 9not sure thats the right terminology)

[tom66]

Re: Hitachi 55HTD52 Sound, but no picture

Those are most likely the main PFC capacitors.
Their failure would not damage the buffer boards.

This is an older chassis, then again I have very little Hitachi experience, having only worked on a 42" plasma, which was internally an LG (after they closed down their factory and switched to re-badging TVs.) I don't see many of them, I guess they're pretty reliable...

I'm doubting your buffers are bad now: The failure I'm aware of only affects their newer sets (one of the last they made), so I'd rule them out at the moment. I'm more thinking of a video board problem. Let's rule that out. Turn off all the lights in the room. An older plasma like this should have a distinct, faint glow visible from the screen. Do you see any glow?

[Dennis H]

Re: Hitachi 55HTD52 Sound, but no picture

Those buffer chips confuse me, I see what looks like a molded indention in one corner (I assume this is the spot they would burn out and show a failure??) but then they all seem to have an almost irregular kind of circular mark in another corner, again, not sure if this shows up in the photo's.

Changing the CAPS would be pretty easy, but I suspect I won't be able to change out the buffer chips if they are toasted, right? On the other hand, if it is possible, I think I found a source for the correct part number...

[Dennis H]

Re: Hitachi 55HTD52 Sound, but no picture

I'll check the screen in a couple of hours when it's good and dark to make sure, but generally speaking, I don't think I'm getting any glow

Although, right now, without the buffer's in, I shouldn't get any should I?

[tom66]

Re: Hitachi 55HTD52 Sound, but no picture

The indentations are used to align the chips on the board when the robot pick and place machine puts each part on the board using the component imaging camera...

A burned buffer IC looks like this:
http://img16.*************/img16/1374/img1809vs.jpg

You need buffer boards installed for the plasma panel to glow.

[Dennis H]

Re: Hitachi 55HTD52 Sound, but no picture

Ok, chips haven't failed like that, at least not yet.

So, I powered it all down, unplugged and re installed the buffer boards and seated everything carefully. Powered it back up and I still show my Vs and Va out the main and all the way over to the plug on the Y sus board. ...but no picture, and no glow.

And, The heat sinks on the X sus board all have some degree of warmth to them and the main board heat sinks are nice and warm. The Y board heat sinks are the least warm, and at least one does not seem to have any warmth at all. Mind you I still show Vs and Va getting to the input plug on the Ysus board at the correct voltages (within a volt or two).

[tom66]

Re: Hitachi 55HTD52 Sound, but no picture

What multimeter do you have?
Try measuring on VDC the output of the Y-SUS relative to the chassis.
Do the same for the Z-SUS.

I do not know if this will work with all meters, but many will read a voltage due to the sustaining process.

[Dennis H]

Re: Hitachi 55HTD52 Sound, but no picture

The meter is a vintage Simpson 260series 7P. It's old but seems to work fairly well.

Ok, I dis connected the plug between the two buffer boards and we're back to showing Vs and Va.

I get the same voltage number whether I ground on the chassis or the gnd pins at the appropriate plug.

so current status;

all boards plugged in with the exception of jumper plug between buffer boards.

In this state, I still have my sound (always had sound), no screen glow, Do have correct Vs and Va on X sus and Y sys input plug (sorry, The Hitachi's seem to use X and Y instead of Y and Z like some others).

It seems as though having the buffer boards dis connected from each other is keeping it from going into a protective state, but as soon as I try it with then plugged together, she goes down hard.

hmmmmm time for more looking and thinking

[tom66]

Re: Hitachi 55HTD52 Sound, but no picture

It seems as though having the buffer boards dis connected from each other is keeping it from going into a protective state, but as soon as I try it with then plugged together, she goes down hard.

Hmm. Maybe it is a buffer fault.

An analog meter should work fine for the tests.

[Dennis H]

Re: Hitachi 55HTD52 Sound, but no picture

I checked both buffer boards (out of the TV) with the meter to try and see if I could find any issues (my logic being that with 6 buffer chips on each board, I should be able to get the same resistance from the corresponding pin points).




I did find one chip that did not respond like the rest.


There are 3 output plugs on each buffer board, and two chips going to each output.

The orientation on the boards is the same for all 12 chips so I found that if I placed my black probe at the lower pin for each chips output section and then slowly walked the red probe to the upper pin for each chip I saw a resistance that seemed to be more or less consistent.. The reading you see on the meter is the odd reading and it jumped up and down as I moved from one pin to the next where as the rest were more up around 70 to 100K.

This is where me not being real familiar with these circuits hurts me as while checking this way makes sense on the surface to me, it may not actually be worth anything due to the circuit design or the component.. but if nothing else, I'm hope you guys can straighten me out

[Dennis H]

Re: Hitachi 55HTD52 Sound, but no picture

Oh and is that a burned spot I see on the back side of the board, last picture almost directly up from the 2008 date. Its right under a chip and it looks like one of the pin holes may be burned... what do you think?

[tom66]

Re: Hitachi 55HTD52 Sound, but no picture

I have a feeling you should try testing across those blue caps.

[Dennis H]

Re: Hitachi 55HTD52 Sound, but no picture

yes, did that too, three of them show about 200ohms in both directions...the others are open one way and about 800-1000 ohms in the other direction... So I assume at least the three are bad..

Any change I can just replace these guys and solve the mystery?

[ben7]

Re: Hitachi 55HTD52 Sound, but no picture

Any change I can just replace these guys and solve the mystery?

Very slim chance. Film capacitors like those are quite tough!

[tom66]

Re: Hitachi 55HTD52 Sound, but no picture

Film caps usually fail open circuit, but what I was getting at is that's a convenient way to check if the buffer is shorted, which, in this case, it would appear so.

[Dennis H]

Re: Hitachi 55HTD52 Sound, but no picture

Tom, I was thinking about it,the three blue caps that show low resistance are all on the lower sdr and are all the lower cap of the three pairs that go to the three outputs. Looks like they are all on a group ground, so I thought maybe if one was jacked it could cause my readings for the other two to show the same?? maybe, maybe not?? The thinking a little further, the buffer chip (ic) that is showing the screwy non-uniform (Different from the other 11) is the lower chip of the middle pair...so I was wondering if it were shorted, could it cause the readings I saw on the three blue chips....

Kind of the same thought Tom had I think.

Looks like buffer boards are in short supply, I'm tempted to have a go at replacing that chip, but my new question is, what sorts of thinks should I consider or examine up stream of the bad chips that may have caused the chip failure?

In a twisted sort of way, I'm having a little fun working through this.

[tom66]

Re: Hitachi 55HTD52 Sound, but no picture

Yes, I agree.

Usually on these buffers only one fails. However, the failures usually only occur when the sustain board driving them has a problem. Usually, you can operate a set with just the upper or lower buffer installed if one is bad. I can't remember; did you try this?

[Dennis H]

Re: Hitachi 55HTD52 Sound, but no picture

I've tried to indicate which component's had what readings to support the thoughts that IC M810 is bad..., C878 is dead short, and C888,890,892 (blue caps) are showing low resistance both ways.

Think we are getting somewhere