WG 6100 brightness issues

komodo

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Donor 2019, 2021
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Fixed a WG 6100 for a Tempest. Monitor works fine. After about 5 minutes of use, the brightness begins to increase and you see trace lines for the different vectors. Turning down the brightness control fixes the problem for about 30 seconds and the brightness continues to increase until I am at the point where the brightness pot is turned down almost completely.

Rather than burn the tube, I power down the machine and attempt to find the problem. Some issues with the HV cage were that the 3 pin connector on the side of the HV cage had been removed and the wires had been soldered from the neckboard to the HV cage. I fixed that back to the original setup. The pins on the focus/brightness block were loose and I fixed those by tightening them down and testing for fit. Several caps were bad (high ESR) and I replaced those as well. I am pretty sure it is somewhere in the Z-circuit and I am thinking a bad transistor or one of the Zeners.

As I am a little short on time, I was wondering if anyone had experienced this issue before and could point me in the direction I need to pursue. I won't be able to get back to it till later tonight and after I have had a chance to look at the schematic. It is the P316 HV board.

Yes, I googled this site for answers but found none. I was quite surprised at the lack of hits that came up for the 6100. Maybe my search-fu is off.

Thanks
 
Some more info. The neckboard does not have the brightness pot so that is not an issue. I did find a post by Jasonlee where the solution was to solder the pins to the flyback block. Is that the way they are supposed to be? Soldered to the focus block?
 
Well, I pulled the HV cage again, and upgraded caps C901 and C902 to 220 uf versions per the FAQ. (Not sure how I missed this the first time) and then I pulled and replaced ZD902. Retested monitor and all is well. I highly suspect that ZD902 was bad. Will test the old zener later. I have 2 other monitors to fix tonight. Will continue to do a burn-in test just in case I didn't fix it.
 
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