CurtPalme.com Home Theater Forum

[Zolzar]

Quick question.
Which board in the PG series controls the B&W drive?

I think when I recapped my PG10 I may have made a mistake somewhere. I have absolutely no control over the blue tube and when I take the blue W over. 50% the cutoff kicks in and the tube flashes. I need to yank the board that controls these functions and go over them very carefully.

Thanks,

John

[gjaky]

The white balance adjustments are on both GAIN CTL and VIDEO OUT boards, and the driving signal coming from the WAVE board. your pots on the video out board may have been touched earlier and that's why the limiter kicks in.

[Zolzar]

Thanks you for the information. The part of my problem that doesn't make sense is the lack of control on the blue. Nothing happens at all with the blue white balance adjustment below %50. Even with W set to zero the output remains unchanged. I hope to go over the boards this weekend. It has to be something simple. Pot or cap issue. Time to dust off the service manual and try to make sense of the prints.

John

[gjaky]

I've seen similar, but there only one tube (maybe red was it?) responded to the B/W adjustments, brightness was also functionless, but fortunately I didn't have to go much into it.

The question is how far are you from the ideal B/W on the blue tube?

[Zolzar]

According to my readings on ColorHFCR I'm out 25% on blue. That's way too much for me unless I work the red and green drive around the blue. What do you think?

[gjaky]

Ok, but 25% what? Be specific, the whole blue channel is 25% bighter or darker? Or just either end, then which?

[Zolzar]

Sorry about that. 25% darker on 80IRE test pattern.

John

[gjaky]

Is this with the defocus?

[Zolzar]

Yes. With deferocus switch turned on.

[gjaky]

If you have an oscilloscope and don't fear to use it, then I think we can discuss this here openly, since Curt stopped offering repairs for the older PGs, and though still sell boards, but these two boards are individually trimmed for the machine, so better to fix it than buy a working one.
Let me know if you're ready.

[Zolzar]

I have a Fluke 123 scope. I don't have much experience with it but this looks like a great opportunity to learn. I also have the service manual if you need to reference anything.

John

[gjaky]

For the testing you will need three different kind of test patterns, 0IRE, stair pattern, 100IRE.
Leave your contrast /brightness settings on your default, check the signal with the o'scope on TP7005(red), TP7006 (green), TP7007 (blue) test points on GAIN CTL board (if you can't access these test points solder a flying wire on them to ensure comfortable connectivity to the scope probe). With the 0IRE pattern you should see the black level respect to ground and the blanking pulse (below black), write down these values on all three channels, switch to the 100IRE pattern, and write down the white levels to. Now on we will focus on only two channels either green or red, and blue; check the effect the brightness and contrast (min. to max.) menu controls on these channels, and compare the results.
This will be enough for the first step.

[Zolzar]

Yes! Blue control has been restored. I cut a NP from the blue blue section of the video out board and never replaced it when I recapped the machine! I distinctly remember falling short specifically on the NP caps and had to place a second Digikey order. This is the board I think I fell short on. Either way it's fixed.


gjaky,
Should we continue the testing or sit tight?


John

[gjaky]

Which cap was missing (position#)?

If all controls working asthey should, then I don't see much point in chasing a non existent problem,of course if you would like to know more about the signal chain we can go on...

[Zolzar]

I buttoned up the machine but I'm pretty sure it was C3437. 10uf-16v NP. Area 6-52, B5 on the print. If that was missing in the op-amp's follower (IC3402) it may have been causing an oscillation in the op-amp's output as W drive increased above 50. This would explain the flashing tube output.

What do you think?


John

[gjaky]

Yes, most likely that was it!