Macintosh Plus - CRT goes to black 10 minutes after cold boot ... help!


#1

This Mac Plus boots off cold and after about ten minutes the screen goes dead, it used to be fine if I gave it a tap on the side of the housing but today it just refused to come back on unless I let it cool back down, then the cycle repeats. Removing the cover and bending the board back and tapping it in a few spots gets it back for a moment but then goes back to black. any ideas would be appreciated!

You can see the fault here:


Macintosh Plus with Weird CRT startup
#2

Cold solder joint would be my first guess. Around the solder connections to the flyback transformer is a common point of failure and close to where you’re bending and tapping in the video. Around the connectors to the yoke and the neck connector are also relatively common problem places.

Power off and leave off for a while, discharge the CRT and reflow or replace the solder connecting the flyback transformer to the analog board. Only if you’re comfortable with electronics and high voltages that is.


#3

Hi there sorry to ask but could you u point out which one is the flyback transformer and the connectors to the yoke and the neck connector are😄I’m pretty green when it comes to Mac anatomy


#4

I have to say if you can’t identify the parts visually then you really should not be working near the high voltage present with a CRT for your own safety.


#5

Okay got it off and a better picture results! And I’m still breathing - if I have googled correctly the flyback transformer is the big barrel shaped thing connected to the suction cup


#6

I hear you Geoff and thanks for the concern but then again how is anyone supposed to learn without learning? I have exercised due care and discharged the crt prior to this.


#7

Now this is very strange … what’s that hole? I’ve seen other reference pictures and it’s is soldered over …


#8

Bingo. The “Suction Cup” is the Anode Cap, connected via its cable to the Flyback Transformer.

The Yoke and Neck connectors are simply where the multi-coloured cables coming off the CRT connect to on the Analog Board. The Yoke being the copper windings around the CRT, the Neck being the very end of the glass tube. Trace those back to the Analog Board and you have the connectors you’re looking for.

At a guess, the board was designed to take more than one type of Flyback Transformer and so it had holes for the different types and lead spacings. Yours happens to be soldered into the furthest point, but they’re still on the same track. I remember mine having this hole in the board too. It’s meant to be that way.


#9

Thank you iMic this has nailed it: my Mac has been going now for half an hour with no issues!

I reflowed (melted and let cool the solder) the potential dry joints on the circuit board connected to the flyback, yoke and Neck cables I’ll indicate in pictures (first one was the flyback in the above photo)
Next was the neck connectors


#10


#11

Last was the yoke connectors