WG6100 oddity

mjenison

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Hi all,

The other day I pulled my spare WG6100 out of storage. It's been there so long I don't even remember where I got it from. I recall it had some issue where the HV seemed to drop out intermittently, with an audible "snap" and the picture pulsing inward.

I purchased a replacement HV unit from TwistedQuarter and installed it.

The monitor starts up, but during the first minute or so, it would pulse inwards 2 or 3 times like there was an issue with the HV. But after warmed up, it worked fine for hours with no visual issues.

The HV board looks to have been already recapped by someone. I decided to replace ZD902 and the b+ adjustment pot, but no change.

Upon further inspection, I found the following:
D901 had been replaced with a IN4005 (?)
C905 was completely missing

The diode at D901 is supposed to be a 13V 1W zener diode according the manual addendum. I found a NTE143 diode in my stash (at 13V 1W equivalent) and replaced it with that. I also installed the 33uf 160V capacitor at C905, and replaced Q903.

Upon power up, R912 smoked immediately.

Lacking any other obvious leads as to what the issue could be and following the advice of any FAQs I could find, I couldn't find any clear path forward. I replaced R912 and reinstalled the IN4005 at D901 and disconnected C905.

Monitor works again.

Any thoughts?
 
FAQ HV Board Notes.
On the HV circuit board there are two diodes D901 and D902, which the Atari TM-183 manual
does not identify. They are just referred to as "silicon diodes". Apparently the replacement for
these is NTE558 – a 1500V general-purpose silicon rectifier in a DO41 package. Also be careful
installing the zener diode ZD902. Apparently some people mistakenly install this at D902 instead
of ZD902. The monitor will not work if you make this mistake!
 
Ah, I see...Atari lists their items like this:

13V, 1W Zener Diode (ZD900, 901)...dropping the prefix on the subsequent devices...so that second one is ZD901.

I just saw 901 and assumed D901. Oops.

So while it appears IN4007 is supposed to be used for D901 instead, this IN4005 seems to be holding up ok.
 
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