SE/30 screen dims to black

[mooseman]

So I'm trying to get an old SE/30 running and I'm having strange trouble with the CRT.  When the computer first turns on, the screen is super bright and washed out.  Then after about a minute it dims to normal, but it continues dimming to the point where after about three minutes it's completely black.

Figured it was likely a bad analog board, so I swapped in a new one.  Same problem.

Anyone seen this before and have any suggestions?  I don't think this could be caused by the motherboard.  I did not replace the little board at the back end of the CRT:  could that be it, or is the CRT just toast?

Any help appreciated - thanks!

 

[rsolberg]

I think you're on the right track- it sounds like the issue is on the CRT socket board to me since it behaves the same with two analogue boards. "The Dead Mac Scrolls" mentions these symptoms, but without the fade to black on page 169. Remedy is to replace the transistor at Q1 on the socket board, a 2N 3904.

 

[mooseman]

Well shoot, that's easier than sourcing a new board.  Thanks.

If anyone has any other ideas, keep 'em coming.

 

[bigmessowires]

I have Larry Pina's "Macintosh Repair and Upgrade Secrets", which I think is an earlier version of the Dead Mac Scrolls. It says:

If you've got severe display distortion, wavy lines, if everything is getting darker and darker, T1 has shorted, and high current is being drawn through Q3 (international Q2). In that case, Q3 will have to be changed along with T1, even if by some miracle Q3 still tests good.

(Lots of additional text omitted)

But both of those components are on the analog board, not the CRT socket board. I actually don't see anything in the book that even mentions the CRT socket board. Hmmm.

This post describes some similar symptoms, but they were never really resolved: https://68kmla.org/forums/index.php?/topic/24660-finally-a-macintosh-se-with-troubles/

This may also be relevant: https://68kmla.org/forums/index.php?/topic/27017-newbie-could-use-some-help-with-half-dead-se30/

 

[mooseman]

Well, problem found.  One of the pins at the back of the CRT yoke is broken.  I missed this when I was looking at it.

The pin came off with the yoke connector.  It's busted off a millimeter or two into the glass:  I can press it into place, but obviously it's not making a good connection.

Suggestions for fixing this?  Use some flux and hope it wicks the solder down into the hole, or try something like conductive epoxy?

 

[mooseman]

Crap:

 

[mooseman]

Okay, from doing a search it looks like folks have fixed this sort of thing with conductive epoxy.  I think I've got some lying around from a repair a few years back:  will try it and report back.

 

[bibilit]

Good luck, don't Try to heat the pin or you will end up with a brocken CRT.

 

[bigmessowires]

Nice detective work! It may be simpler to substitute a CRT from an otherwise broken compact Mac, if the conductive epoxy doesn't work out.

 

[mooseman]

Woohoo - it's fixed!

I ended up getting a single-use tube of silver conductive epoxy from Amazon.  Cleaned out the hole a bit and glued the pin in place.  Everything is working now.

Thanks for the help, guys.