My Mac Plus powered up on brightest settings and when I dimmed using the toggle it doesn't dim and it flickers.
I think it needs a recap and I don't wish to recap the whole board. Anyone knows which caps do I change for the brightness control on the analog board?
At last I found someone describing what seems to me a common fault - I have several Mac Plus machines doing this.
With the brightness (contrast) knob under the screen turned to maximum, the display is good, no flickering. With the brightness turned to anything other than maximum, the screen flickers, and when turned to minimum, the display is not as dark as it should be.
The cut-off control next to focus on the analog board is working normally. Adjusting that can give a bright or dark display but does not allow the other control to brighten or darken the display sufficiently, and the flickering remains.
This is not to be confused with intermittent flickering caused by a worn potentiometer or bad video connection etc. This is a regular brightness-pulsing effect that might be caused by mains frequency interacting with display frequency, as though there was a ground problem or something.
On some machines, as the analog board warms up, things become better - the brightness control will darken the display more and the flickering goes away.
What is likely to be the cause?
I tried replacing the 10uF 100V electrolytic capacitor connected with the brightness control; no change. Have checked all resistors in-circuit and couldn’t see any obvious anomalies.
As this is common to four machines I have here, I’m thinking it must be a common fault, yet I cannot find anything by searching.
Thanks for your time reading
