Just reread the description of the fault on your site - I'd gotten the impression it was always squashed like that the first time I looked at it. If it's intermittent (i.e., you can hit it and it pops back), it's probably just a bad solder joint. Resolder Q1 and Q2, and nearby components, as well as the yoke connector. If it starts out bad and gets better as it heats up, or starts good and gets worse as it heats up, and hitting it doesn't affect it, then, it's definitely one of those caps. -Ian On Thu, Apr 28, 2016 at 8:12 AM, william degnan via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
thanks. b
On Thu, Apr 28, 2016 at 8:09 AM, Ian Primus via vcf-midatlantic < vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
Kind of covered - in my class on CRT monitor repair, I mentioned vertical problems like this, and in my old Mac class, I went over some of the basics there, but, didn't specifically get to this as it relates to Macs. It's hard to cram that much information into a one hour class - I had to move rather quickly.
The 128 uses a pair of discrete transistors for it's vertical driver. One of the caps in that circuit has failed/is failing. I'm guessing it's C6. Failing that, it's either C5 or C11. While you're in there, be sure to resolder the yoke connector, it's a very common point for cold solder joints (will cause total loss of deflection)
-Ian
On Thu, Apr 28, 2016 at 7:57 AM, william degnan via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
I am thinking about working to repair the display on my '84 MAC, occasionally the horizontal is "squashed" although for now it recovers. Was this covered in any VCF E classes this or last year?
http://vintagecomputer.net/browse_thread.cfm?id=95
I assume there are a few places on the web that describe MAC repairs like these, but any comments as to what to target are welcome and will save me some time.
b
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