Hitachi 55HDs69 plasma No VS,VA, bad buffer

[kerbsjacob]

Have a hitachi du2 chassis 55hds69 that will not command on PSU. Found a bad buffer board , it was shorted , disconnected it but still no vs or va attempt.

If I manually force vago and vego high, I get PSU voltages for a couple seconds before crowbar circuit trips and shorts to ground va and vs. PSU then locks out.

There appear to be a vs and va feedback from digital board somehow that are needed for PSU to stay on.

How do I determine if PSU is good? Va seems low, 45v, can only keep on for couple seconds. How can I force PSU to stay on in this set? Is the feedback loop or va and vs set point closed by the digital board?

Ihave service manual for set, but no info on panel itself or sustain boards. I want to force error signal low to let set attempt to power vs and va. Anyone know the pin out for the comms with the digital or sustain boards on this set?

[freakaftr8]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

Disconnect all power connectors going to the main board from power supply with it unplugged. I know it sounds crazy but I've been through this before let it sit like that for 30 seconds then plug the connectors back in and then try to power it up.

there's something like residual voltage that feeds the mainboard from the power supply even when its unplugged for ever some capacitor holds a charge

[kca]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

Hello fa8 ~

Just picked up an old but beautiful Hitachi 55HDS69 and came across this post when initially researching. Have the same problem as described by kerbsjacob above. No picture, but sound works great. Blue LED light on the front. lower-right stays constant. No blinking.

Not getting any Vs or Va readings off the PSU, so I tried your suggestion above. Hopeful it would work and be this simple on my set, but to no avail.

I'm wondering if you had any further experience with these sets that gave you more insight into the heart of the problem(s). Do you think it is the PSU itself or something on the logic or main board that is prohibiting the voltages to come up properly?

I read a couple of posts that said it was safe to remove one buffer board at a time and test whether or not I get half a picture. Do you think this is a safe test to perform on these particular Hitachi models? I have worked on a couple of Hitachi P50H401's in the past where you could do that but only leave it on for a short while or risk it blowing out the IC's on the single, functioning buffer board.

Hoping you can help me get this 55" Hitachi up and running. Of course, anyone else reading this is perfectly welcome and encouraged to chip in as well.

Thanks ~

kca

[freakaftr8]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

Yes you can do the one buffer at a time on hatachi. Note that when you have only one buffer installed it'll have an interlaced picture.

You may have something else going on if you're not getting any power supply voltages with all boards disconnected though.

[kca]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

Thanks. I went ahead and disconnected the SDR boards, one at a time.

When I disconnected the UPPER SDR (only), there is no picture across the entire screen. It remains all black. Sound is there, but no picture at all.


When I disconnected the LOWER SDR (only), a picture appeared on the top half of the screen only. Sound remained present. At first, there were black, horizontal lines across this top-half image all the way from left to right. What you called interlaced.

After about 3 minutes, and a couple of channel changes, these black, horizontal lines disappeared. However, the entire time this top-half picture was (and still is) populated with sparkling blue dots that can be seen throughout this entire top-half image. The picture is watchable, but the blue dots are clearly visible and highly visible whenever the screen goes momentarily black upon a channel change.

Strange that the horizontal lines cleared up on their own. I've seen those lines many times when working on other sets, but never had that disappearing act happen before.


Given all of this, is it logical to assume that either the UPPER SDR need be replaced (and then the set will be fixed)? Or, is it possible that the Y-SUS is defective and prohibiting the UPPER SDR from working properly?

None of the IC chips on this UPPER SDR board seem to be visibly damaged, though one of them has a very small, hairline mark on it. None of these IC's are blown with a small, pinpoint hole or two visible, like the ones on the Hitachi P50H401's would usually show.


Additional Note: I just tested the voltages with the top-half of the screen still showing an image and I got the following:

Vs = 87.5
Va = 63.2
Vcc = 5.0

All three are in the correct range. Service manual reads 80+, 60+, and 5.1.

These values came off the PSU and carried over successfully to the X-SUS. I tried to measure them as they migrated back over to the Y-SUS connector, but there I could only get two 88.5 readings and a 5.0. The last two wires gave 0.0 readings, but I think that might likely due to the probe on my Digital Multi-Meter not making the proper contact despite my best attempts. Pressed down quite hard, but did not want to force down any harder and risk breaking the plastic of the connector itself.

Is there anything else I can / should test at this point in time? Feels like it's close to being fixed.

[freakaftr8]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

Sounds like your on the right track. These Hitachis burn out the lower board before the top goes short for some reason. Same with Fujitsu. The interlaced lines disappearing is most likely the sustain board resetting from a shorted lower.

Id perform an ohms test on the lower to confirm.

[kca]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

Thanks.

That makes sense with the Y-SUS resetting.

I'll perform that Ohms test on the lower SDR.

Would you say that because the Y-SUS was able to reset itself, that it is likely okay? Or, could it still be partially defective?

And, do you think these blue dots will clear up once I have replaced the lower SDR and therefore have two working SDR's in place? Or, on that front, are the blue dots showing up because the UPPER SDR is on its last legs and needs to be replaced along with a new lower?

[freakaftr8]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

Yes the blue dots will clear up after the lower SDR is straightened out. The Ysus is compensating for the data driving to upper only. It's supposed to supply dual duty cycles to both so only driving one, the YRR, YFR, (Samsung terminology) is off cycle. Nothing to worry about.

[kca]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

That’s great news! Thank you.

Would you just go ahead and track down a good quality LOWER SDR at this point in time if you were working on it? Seems like that’s the only thing that need be replaced.

[freakaftr8]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

Yes. But usually these are in China. Have you ever replaces one if these ICs yet on a buffer board?

[kca]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

I haven't tried to replace any IC's yet, on the buffer board or any chip elsewhere. Almost did. Watched a couple of detailed videos and with a heatgun and extreme patience it looked possible. I might try that on this lower buffer board in this 55HDS69 if I test it today and find with the Ohm test that there is only one clear IC chip that has failed. Maybe two.

I did find a pretty reliable way to test the Y-SUS board back when I was working on the 50" Hitachi models. It was to pull both SDR boards and then test each and every pin on the two Y-SUS connectors that go out to the SDR's. If and when there is a perfect voltage symmetry between the top connector and the bottom, then I figured that the entire Y-SUS was functioning properly. Does that make sense?

So, also going to try that today to help ensure that the Y-SUS is good and won't be the reason a new SDR board would blow.

[freakaftr8]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

IF it is operating your top SDR then there's no reason it should blow your bottom.

[kca]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

That's what I thought.

So, I pulled the lower SDR from the set and performed the Ohms test. Strange results. All six of the chips tested good. Got readings between 733 and 738 on all of them. Extremely consistent. Did the test up and down the board several times to make sure.

None of the IC's seem to be bad, and none of them are visually compromised in any way. Given these two factors, can this SDR board still be bad?


More info:
Tested all six of the blue parts (see Pic #3) by flipping the SDR board over and putting the DMM in the 200 Ohms range. Got exact readings of 13.2 on three of these, but nothing at all on the other three. Each 13.2 coupled with the no reading existed in the three pairs. So, when close to one another, one produced a reading and one did not. Is that normal / expected?

[freakaftr8]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

Would that be 13.2 Ω? I would compare this with the blue capacitors on the upper board to verify

[kca]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

Yes. that’s correct.

And, good call on comparing these cap readings to the working upper board. Will do that next.

[freakaftr8]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

If in fact you are getting low resistance readings along those caps, that may confirm a shorted VADR to ground. This in fact would cause a board shut down

[kca]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

UPDATE;

The upper SDR tests exactly the same on the IC's as the lower one did. Meaning, readings of about 735 on all six chips. So, all is good there.

Tested the six blue caps on the upper SDR as well and there were NO readings on any of the six.

So, the only three caps that gave off those 13.2 ohm readings were the three alternating ones on the LOWER SDR ONLY Please refer to the picture below. I have circled these three in yellow.

Re: your last reply, can you tell me what a VADR is? Never heard that term before. And, is it repairable on this lower SDR? I hope so, because I'm finding that they generally are running about $80 to $100, which is doable but a little steep.

[freakaftr8]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

VADR is Vscan for most Japanese made plasmas. Scan voltage. I remove one leg of each of those caps to see if the caps are shorted or if it's something in line with the I c's

[kca]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

Ahhhh .... that makes sense. Thanks.

I'm going to remove those cap legs and test, as you suggested. Before I do, I used the DMM to look for shorts in the pins. Found a couple.

#1 — On the main connector that comes in from the Y-SUS, I put the Black DMM probe on the last / bottom pin and ran the red probe down the length. The top half of the pins were fine, but ran into shorts (continuity / beeping) on all of the final 9 pins. Please see the photo below. Every pin that is inside the yellow rectangle registered the beeping.

#2 — Also found two, singular pins on the uppermost connector that holds the ribbon. Again, please see the photo below and look for the two red circles. These were the only two on this connector, and the other two connectors below it showed no signs of shorts.

Tested quite thoroughly. I'm convinced the shorts noted above are the only ones in play.

Do you think this means that the uppermost chip is damaged? Or, could the three blue caps that are demonstrating resistance be responsible for all of this trouble noted above?

I've never had a whole block of pins (in the yellow rectangle) register bad before on any of the SDR's I've worked on. Seems telltale in some manner.

[freakaftr8]

Re: Hitachi 55HDs69 plasma No VS,VA, bad buffer

What you're probably seeing is the IC damaged in some way which is registering against the blue cap. I like to do is remove the IC with heat ,.clean the pins and then power up and see if the rest of the IC's are OK if so you'll have a black spot in the screen at that point you can decide if you want to replace the IC or replace the board completely