So I'm trying to troubleshoot a few monitors and am having various issues. I wouldn't consider myself a noob when it comes to monitors, I've done capkits, flybacks, and tube swaps successfully so I'm not afraid of testing/replacing anything. I tried to be as methodical as possible so here's what I've got.
1. WG 19K7901 with tube1
2. WG 4900 with tube2 (don't know the exact model, had to use Bob Roberts monitor ID page)
3. WG 13K7886
With monitor 1 the picture is clear and the colors are normal but it is shrunk to the middle third of the screen. Playing with all the size/pos pots changed nothing. I haven't replaced any capacitors yet, but more on that in a sec.
Monitor 2 has a deep blue/purple tint to it and none of the RGB pots on the neckboard change anything. This board looks like it was recapped.
Monitor 3 looks fine for the most part except it's kind of dim. When I up the gain pot or fiddle with the RGB pots, I can get it a little brighter, but then the colors smear pretty bad. This has not been re-capped from what I can see. Will a cap kit likely fix this?
Now back to 1 and 2. I swapped chassis to see if I could eliminate any problems. When I put the 4900 on the first tube, the picture is still shrunk and now the picture is only tinted blue. Again, none of the size/pos pots change the picture. I'm thinking bad tube? Other issue is that none (except green) of the color pots on the neck board change the picture at all, it's as if they don't exist. I checked the solder joints on the neckboard and everything looks fine. Looking at the main chassis I only see a bad joint on a tiny ceramic capacitor, but I doubt this will affect the neckboard. So any suggestions on this chassis? Also does the tube sound bad? I don't really know what to look for on the yoke or tube itself to see if anything is bad. How do I know if the yoke impedance is compatible with this chassis?
I put the chassis from monitor 1 (7901) on the second tube to see if anything else could be eliminated. This time the picture is still purple/blue but the picture is now full size. Again, none of the rgb pots on the neckboard affect the picture. Another bad tube?
I didn't think tubes went bad all that often, but I don't see what else could be the problem. Any ideas on any of the three monitors? Sorry for the essay, but there was a lot of troubleshooting going on.
Thanks,
Scott