AKAI PDP4273M Help Needed

[n7qpp]

This uses the LG PDP42X3 panel. A co-worker gave it to me with the issue of no picture but has sound. I found a blown fuse on the YSUS and ordered a replacement IPM. When I removed the old IPM I could see it was blown. So after the new IPM was installed I still have no picture. I tested all the voltages from the PS and they are all good as well as the voltages at the fuses on both the Y and Z sus broad. Also tried disconnecting the Z then the Y make no difference. I am looking of any additional ideas or tests i can run.

THANKS Joe

[capkid]

Re: AKAI PDP4273M Help Needed

Did you check the Vscan (VSC) and -Vy voltages on the Y-Sus? There should be a cap and resistor at the bottom of the board to check each of these voltages, respectively.

Edit: The appropriate voltages should be listed on the panel label.

[n7qpp]

Re: AKAI PDP4273M Help Needed

VSC on one side of cap C51 is 137v on the other leg 17.4
-Vy at one side of R36 is 16.4 on the other leg it is 17.7

Attached is a picture of the voltage tag on the panel

[capkid]

Re: AKAI PDP4273M Help Needed

Try reading across the resistor and cap (negative probe on one leg and the positive probe on the other leg). -200V is the expected -Vy, and 120V is the expected VSC.

[n7qpp]

Re: AKAI PDP4273M Help Needed

I have UL a couple of picture of the broad with a close-up where the readings were take

[n7qpp]

Re: AKAI PDP4273M Help Needed

okay the VSC shows 119.8v
-VY is jumping around between 1.5 - 3.5v

[capkid]

Re: AKAI PDP4273M Help Needed

Ok, so your -Vy is no good. It looks like your Y-Sus is still defective.

[n7qpp]

Re: AKAI PDP4273M Help Needed

Is there a schematic around that I could use to figure out what might be the bad part(s) in this power chain?

[capkid]

Re: AKAI PDP4273M Help Needed

You can try searching Tom's database: http://www.toms-service-manuals.com/

I'm not sure how detailed the manuals will be for this TV. You may also want to look at manuals for similar LG-based TVs. Check the list of TVs at the bottom of this page: http://www.shopjimmy.com/lg-6871qyh053b-ysus.htm

[n7qpp]

Re: AKAI PDP4273M Help Needed

Thank you for the help. It was worth the cost of the IPM to see if i could fix it. But if I can not locate the problem for the low Vy . I will just trash the set.

Again THANKS

[n7qpp]

Re: AKAI PDP4273M Help Needed

anyone else on the forum have any additional thoughts (not ready to give up yet).....

[tom66]

Re: AKAI PDP4273M Help Needed

Try measuring -Vy without Y-buffer, you may have defective Y-buffer.

[n7qpp]

Re: AKAI PDP4273M Help Needed

Okay removed the y-buffer and it made no change in the -Vy voltage. However I did some other checking when I remove the ribbon cable that leads to the 6871qch977b board the -Vy voltage is normal. I also tested removing the cables on the 997b to see if made a difference it did not. Only removing the ribbon cable between the y-sun and ctrl broad makes a difference.

[capkid]

Re: AKAI PDP4273M Help Needed

Okay removed the y-buffer and it made no change in the -Vy voltage. However I did some other checking when I remove the ribbon cable that leads to the 6871qch977b board the -Vy voltage is normal. I also tested removing the cables on the 997b to see if made a difference it did not. Only removing the ribbon cable between the y-sun and ctrl broad makes a difference.

Interesting. I wonder if the logic board (6871QCH977b) is bad if all your other voltages remain stable.

[n7qpp]

Re: AKAI PDP4273M Help Needed

does the logic board have control over the -Vy voltage or circuit?

[capkid]

Re: AKAI PDP4273M Help Needed

does the logic board have control over the -Vy voltage or circuit?

I know that for one of the 50" LG plasmas, a bad oscillator on the control board can cause a "no picture" issue. I don't want to lead you down a wrong path on this one, and I know Tom is more experienced with apparent control board issues, but here's a pic.

[n7qpp]

Re: AKAI PDP4273M Help Needed

Anyone know the function and meaning of the LED's on 6871QCH977b

[n7qpp]

Re: AKAI PDP4273M Help Needed

One last shot before I trash it. The -Vy is not correct not even close. Any direction on how to track down the cause of this ie other test point etc.

[capkid]

Re: AKAI PDP4273M Help Needed

You mentioned that the Y-Sustain's -Vy returns to normal when it's disconnected from the control board, correct? You may just have to try replacing the control board. It should be fairly cheap - less than $20.

[n7qpp]

Re: AKAI PDP4273M Help Needed

What puzzles me is I get three green lights on the control broad. You would think if it had a problem I would not get the 3 green.