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Old 4th Aug 2011, 6:48 pm   #35
TriMan66
Pentode
 
Join Date: Jun 2009
Location: Royston
Posts: 116
Default Re: Help with a HMV TV

Hello all,
Thanks to everyone who has contributed. I have appreciated the feedback. I was reading back through all the comments to find the problem.
I re-baked the LOPT. I tried yet another set of EHT valves with no change.
Then I finally found the issue. A dry joint on one of the high meg resistors in the boost section driving the picture tube.
I also increased smooting on the boost volts to reduce the ripple.
Now, I have 550V on start up and within 10 minute its settles to 630V. It is very pleasing to turn on the set and be greeted by a full screen picture which is bright and with good contrast.
On this last point, I added a 6.8M resister from pin 3 of the picture tube to gound. I did this since I noticed the contrast got significanlty better each time I used my DMM to measure the pin 3 volts.
I am using direct video input to the video amplifier and the contrast is used to drive the RF section which I am bypassing and so the contrast controls have no effect.
The next issue to move onto is that the vertical hold keeps losing lock. Hopefully not as difficult as the boost volts.

regards
Craig
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