Screen Cuts Out on my Macintosh Plus.

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Screen Cuts Out on my Macintosh Plus.

Just as the title says. The screen goes black after about 5 to 10 minutes of use. Hitting it on the side with the analog board will bring it back for a few seconds at best but with diminishing returns every time.

The good news is that the computer boots and loads an operating system. SCSI port works. Mouse works, The new floppy drive reads disks and ejects without a problem. All keys on the keyboard work, and I've tested several keyboards on this machine. But the screen still cuts out.

So far, I've recapped the entire motherboard, reflowed all the solder joints (as well as on the motherboard connector for good measure), and replaced the flyback transformer, with no success. Any ideas?

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Since it happens after the

Since it happens after the machine warms up, and that some percussive maintenance gets it working again briefly, suggests a connection issue on the analog board. You mentioned you reflowed the solder joints, did you do so on the analog board or just the motherboard? Cold/cracked joints on the analog board are a very common problem on the 128K/512K/Plus. Barring that, I'd look at the components themselves for cracked/broken leads.

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Dr. Webster wrote:Since it
Dr. Webster wrote:

Since it happens after the machine warms up, and that some percussive maintenance gets it working again briefly, suggests a connection issue on the analog board. You mentioned you reflowed the solder joints, did you do so on the analog board or just the motherboard? Cold/cracked joints on the analog board are a very common problem on the 128K/512K/Plus. Barring that, I'd look at the components

 

This advice seems spot on.  The analog boards were notorious for cracked solder joints and even leads and traces on the boards.  Heat causes expansion which causes connection failures.  Even if it looks good cold it may not once it gets warm.

 

 

CVT
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This problem is on the

This problem is on the monitor part of the Mac and it is probably the most common CRT problem that I deal with. Of the 6 CRT monitors that I currently own, 3 had it at one point or another. Unfortunately it's always something different: sometimes it’s a bad solder joint, but it could also be a bad cable connection somewhere.

 

What you have to do is disassemble it and carefully poke around while it is on to localize it. You can use a hot air gun on a particular area to make it happen faster than it does or a freeze spray to reverse the effect once it happens. In both cases the strategy is to localize the cause to a very small area.

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Yup!  Cracked joints....  Or

Yup!  Cracked joints....  Or so I'm guessing.  I've reflowed these connections at least five times, but ended up desoldering and resoldering the connector to the motherboard and it seems to be holding.  Fingers crossed.

 

Thanks all!!  :-)

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