G05-801 Random Brightness

Lamonsoff

Well-known member

Donor 2020, 2024
Joined
Mar 27, 2020
Messages
1,103
Reaction score
1,234
Location
Okotoks, AB
I have this G05-801 whose image will vary in brightness all by itself. The issue is contained to the deflection board. I swapped in a known good deflection board to confirm and the image is stable. The image is good at startup and will slowly get brighter, then have bursts of dimness, then almost no image until you turn up the pots. I found a bad diode in the X section, but that is unrelated. I've replaced both the brightness and contrast pots as well as Q504 in the Z section. Gone through every resistor, diode and capacitor and all are within spec. Thinking this may be coming down to the neon lamps. It's hard to capture on video, but I'll try to again later. Anyone care to give a guess?

EDIT - After reading a few more threads, the neon bulbs are likely not the cause of my problems…
 
Last edited:
And did that fix it?

Never underestimate the power of dirty connections. Especially the tube sockets on these. If the heater voltage is varying, the brightness will fluctuate.

Clean and DeOxit all connectors, including the CRT connector and pins. Even if that doesn't fix every problem, you always want to start there before going deeper.
 
Unfortunately no. I replaced the yoke and the connector below it as they were nice and brown from heat.
 
Though you've gone through all the "R, C and D", maybe take a look again at the transistors in the combo Spot-Killer / Zamp circuit. In particular Q503. :unsure:
If the issue is time/heat related, consider investing in some cold spray.

Make sure the +90V is DC and stable.
 
Q503 and Q506 were both replaced with MPSA05's. But I will go back and check the 90v you mentioned.
 
I finally figured it out.

I thought it was the deflection board, so I threw mine in and let it run. 30 min in, no picture, but no spot killer. So I swapped all my 801 components in, and it still flickered. So it's then either wiring or the tube. While running I lightly tapped the tube neck with a screwdriver and it flickered. So it's the tube. Put the rejuvenator on it and it's initially fine. Check the setup again, but on test this time a dim short light comes on. I tried cleaning it, the short comes back. Hit the short button. Still there. Hit it with a full rejuv, still there, then a second rejuv and the short light goes out. Been running perfectly now for an hour.
 
Last edited:
Back
Top Bottom