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Discussion Starter #1
This video projection unit will not vertical sync. I have physically removed and inspected all the PCB’s including the sync generator board and found nothing out of the ordinary. I have also switched the two input modules and fed a know good video signal into all inputs without any improvement. The vertical will not lock on manual or auto, the picture will either roll from top to bottom or vice versa. When in auto mode, the sync locks at 45hz and I am unable to change it. Since everything else has failed, I believe the problem is most likely an IC on the Sync generator PCB. Does anyone have an idea on how I should proceed or have a schematic of this board to assist in locating the culprit?
 

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Tucker,


Try connecting the H and V sync cables with a T connector, then connect this T connector to the H sync input of the projector.
 

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I have tried to combine sync signals on RGB with no luck. I have also applied S video from a DVD player and composite video from DSS with no improvement. It appears to be boiling down to the Sync Gen PCB. I have even performed a system reset with no resulting change.
 

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Hi Tucker,


On the vert defl & H reg board, there are 2 circuits that could affect this. The V hold and the vertical waveform circuit. The v hold is fed a 0 - 10 v dc signal to base of Q9, and the the vert 1 is sent a sawtooth to the autolock circuit involving IC1C and IC2B. This in turn feeds IC7, which also is fed the collector output from vhold of Q9. All this crap then goes to drive IC3, which is a TDA1170. Sawtooth goes into pin 8, output of IC 7 goes to pin 9 and IC1D feeds pin 7 - this is a feedback loop off output of IC3, which first goes through IC10to drive the V drive and IC1B input for size regulation. Good luck pal, there's a lot of crap in that circuit to diagnose, which is why I usually resort to board swapping to fix the problem in a matter of minutes instead of days.
 

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Discussion Starter #5
Thank you for your advice... it was right on target. I had received advice from another source indicating I had a problem on the Sync Gen. board, so I wasn't even looking in the right direction. After reviewing your post and comparing it to the correct PCB, I did some basic probing and found D26 open. I replaced the diode, re-inserted the PCB, turned the unit on, and what do you know, a rock solid picture. I can't thank you enough for your advice and saving me $150 on a new PCB, and then I would have ordered the wrong one... Have a cold one on me! I will continue to monitor the forum and try to repay the favor.


Best Regards,

Tucker
 

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Good for you, Tucker!!

Glad I could help - yea, that waveform board is rarely the culprit in symptoms like you were experiencing. Glad you're back up and running again.
 
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