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SE/30 screen very dim

JC8080

Well-known member
I finally got a working logic board for my SE/30 (thanks @mg.man), so now it's time to tackle the rest of the gremlins. I bought this machine a couple years ago with a badly damaged logic board and it's been collecting dust since then. When I first got it it would power on to the checkerboard screen, and I don't remember the screen being dim at the time, but I don't remember for sure. When I turn the brightness knob on the front all the way up I can barely see the image. I tried turning up the brightness adjustment on the analog board, when I turned it all the way up the screen didn't get any brighter, though the white lines did appear on the otherwise dim image. The same white slightly diagonal lines you would normally see if you turned the brightness knob up too far.

I do have a dead Classic II that I can rob the CRT and/or flyback from if need be, but I would rather not just start throwing parts at it. Could this potentially be an analog board issue?

Thanks
 

bdurbrow

Well-known member
If you are getting any image from the logic board whatsoever, then the issue is definitely on the analog board. There’s a 7400-series chip (the schematic is a little bit smudged, and I can’t quite make out which one) that is acting as a buffer & inverter for the video signal; this will have the effect of bringing the signal up to proper voltage levels, even if the logic board was outputting something less than ideal.

In general, the first thing to try is replacing the capacitors; as they will eventually fail just due to age. Beyond that, you get into actual troubleshooting, which requires that the machine be powered up while measurements are taken. This section of the machine is particularly hazardous because of the CRT’s high voltage circuitry. Also, some specialized test equipment will be needed; as well as a working understanding of CRT drive circuits.

Consequently, if you don’t want to just throw parts at the problem and see which one fixes it; I’m afraid you’re going to have to take it to somebody who knows what they’re doing and has the proper resources.

Based on your description, I don’t think that the CRT is at fault here; at least not due to being worn out (it’s possible that there’s something wrong with the gun or anode, but it wouldn’t be my first guess).
 

JC8080

Well-known member
Thanks for the thoughts. Recapping the analog board was on my to-do list anyways just because of age, so I will probably do that and see if there is any change. Fortunately I think I have enough spare parts around, including a spare SE/30 analog board, so I can definitely get it up and running one way or the other!
 

superjer2000

Well-known member
I had an SE30 with a very dim image. I recapped the analog board and replaced the power supply, but that didn’t fix it. What did, was a transplanted good CRT from a Mac Plus.
 
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