hitachi display question

[awyatt2]

if the zsus ribbons are removed from the display can you check the display for a short with a meter? anyone know the answer, and if so is it the two outer connectors(far each side wide).

[tom66]

Re: hitachi display question

No, I don't think so. There are too many connections to check anyway (Y buffer connections, for example.)

However, you will be able to see a picture if the Z-sus is faulty, but it will be dim, deep-purple ish and slow to change.

[awyatt2]

Re: hitachi display question

thanks tom, i cant find any info on it the digital board seems to be where it is but 150.00 for a board and if it turns out to be the display i would be sunk. i have followed the service manual to the point where it seems to leave you in midair. i cant even find a schematic to try and turn on the backlights. has to be a way to light it, something cuts the danged thing on,probally a transistor on the zsus. how does the digital board determine the short anyway. the voltage out of the ps holds steady va and vcc when it get the 5.1 volt return signal from the digital and logic controller. i know the logic is good,however when all is hooked up i cant get the 5.1 needed on the return.

[tom66]

Re: hitachi display question

I've never heard of plasma panels shorting. Only driver boards.

The short circuit is detected by the PSU because the load is excessive and it goes into protection mode. Rarely is there a fault signal going to the main board.

[tom66]

Re: hitachi display question

I've never heard of plasma panels shorting. Only driver boards.

The short circuit is detected by the PSU because the load is excessive and it goes into protection mode. Rarely is there a fault signal going to the main board.

[awyatt2]

Re: hitachi display question

tom, would you spend the money on the digital board and take the chance? serouisly. there are a couple on ebay but i am afraid of them, you usually get what you pay for and they probally aren't working anyway. tried to find a local trade for some of the good parts i have here on hand, seems no one local ever has what you need until you don't need it anymore. good case of murphys law. thanks dewey

[tom66]

Re: hitachi display question

tom, would you spend the money on the digital board and take the chance? serouisly. there are a couple on ebay but i am afraid of them, you usually get what you pay for and they probally aren't working anyway. tried to find a local trade for some of the good parts i have here on hand, seems no one local ever has what you need until you don't need it anymore. good case of murphys law. thanks dewey

What is the model of the TV? I would get the scope out and check, but I'm guessing you don't have one...

[awyatt2]

Re: hitachi display question

yes i do a 150 meg 2430a tektronix. but where are you going to start the va and vs wont hold like it is. i am wary of putting voltage thru the pins to keep it running while the rest of the set is powered on. the return signal is lost somewhere in the digital board. i have checked every component on it i could by meter, vom, esr, diode tester, transistor tester. could even be a failed processor it seems to be running pretty hot but i dont have anything to compare too

[awyatt2]

Re: hitachi display question

the model is p50h140

[tom66]

Re: hitachi display question

the model is p50h140

No info on that do you have a link to a product page?

[tom66]

Re: hitachi display question

yes i do a 150 meg 2430a tektronix. but where are you going to start the va and vs wont hold like it is. i am wary of putting voltage thru the pins to keep it running while the rest of the set is powered on. the return signal is lost somewhere in the digital board. i have checked every component on it i could by meter, vom, esr, diode tester, transistor tester. could even be a failed processor it seems to be running pretty hot but i dont have anything to compare too

Check crystal for the MCU.

Check waveforms stay, however briefly... if they appear almost zero all the time then there is a short!

[cadiman]

Re: hitachi display question

Your panel is fine. P50H401 is what you have.

The fault chart will normally get you pointed to the correct board that needs replaced.

I have only had two tvs that gave a dim picture with a faulty Z board. (L/G only so far) Mostly no picture will be the issue as with the failed y and/or buffers.

If this tv had a failed y or z or buffer board you would not get audio and the tv will shut down after about 2 seconds.

There are a few boards that tie into the power supply.

There should be a small board about 6" square just to the right of the mainboard.

Behind the mainboard there should be a timing or control board that feeds the y,z and x driver boards. (rare to fail)

I have never had an issue with the x (lower boards) on these tvs but I would not rule them out.

Again, the number one failure on these sets is the y buffers then the y drive board and the power supply.

What kills these tvs is people messing with them which makes it hard to repair by the time we get them.

[awyatt2]

Re: hitachi display question

the y drive checks out according to the flowchart and vom test, so does the z, power supply if i furnish the 5.1 volts needed stays up. it does shut down because of no video input. i cant tell which output i'm on now i hit the wrong button and changed it from tuner. when the thing was on tuner it would stay up. there is no square board near the mainboard except the logic and it is brand new, and tested in another set.in the morning the y and z and power supply will be too, i am afraid to try the main in a working tv i do not own. the tuner section plugs into the main. the va and vs will not come up on this set but it is not like a short it is simply not getting the needed 5.1 volts thru the logic or main. the short is somewhere on the main i think. i would hate to spend 150 on a main and still not be the problem.

[awyatt2]

Re: hitachi display question

need the value of r114 and r116 on the power supply now. would like to have a schematic on it if anyone has one.model # of ps is MPF7718 L / PCPF0164 / HA0192

[cadiman]

Re: hitachi display question

Are you feeding a video signal to this tv with audio?

It seems to be turning off or going into standby more than going into protect mode.

I wish i could help more

[awyatt2]

Re: hitachi display question

i feed it thru a dvd video and audio until i accidently got it off on input it was working off the channel tuner. you dont happen to have the skis on the ps, i could sure use them since the resistors toasted

[cadiman]

Re: hitachi display question

I don`t have any info on this tv. If there are issues with the power supply it can take out other boards and often will with this model.

[awyatt2]

Re: hitachi display question

went thru the service manual and according to it the absu-l board is defective. fairly cheap fix if that is what it is. still dont understand how address buffer holds down backlights. gonna give it a try anyway

[cadiman]

Re: hitachi display question

Remember, not backlights but whole plasma panel. The boards that power up the panel won`t fire up the panel if there is a fault.

Backlights are what lcd panels use to backlight the lcd screen.

Since you have audio I think you are close to a repair since these tvs normally are just dead or go into protect mode right away.

[bportner]

Re: hitachi display question

I ran into a little problem here with my 715t2454-2 board, T904 (the small vertical transformer) looking from the backside of the board on the bottom side with the 6 pins the third one in from the left side lost its connection surface on the board so it cannot be soldered on, can anybody tell me what i am missing in the schematics? the board was a chirper so i replaced the 3 caps and the 1 the q901 and d927 because it sounded like the chirp was coming from there but turns out it was the transformer so when i removed the old solder to give it a fresh connection the doughnut came off..... and help would be appreciated i would like to jump the lead and get the little bugger going