68kMLA Classic Interface
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| Click here to select a new forum. | | 128k/512k/Plus analog board voltage adjustment | Posted by: apm on 2017-01-21 16:27:20
I recapped the analog board on my 128k last week. Everything is running fine, but I am curious about the voltage adjustment. Since there's only one adjustment that affects all voltages, getting 5V set exactly to 5.00V on this Mac leaves 12V and -12V at 12.3V and -12.4V, respectively. The Mac works, but will that create problems later on?
Also, a data point on analog board testing. After recapping, I first tried to power it up without a logic board, since I didn't want to risk damaging the 128k logic board if something went wrong. I was disappointed to be greeted with the "flup-flup-flup" noise. Double-checking my work found nothing amiss.
Some posters here said that the original Mac analog board needs a logic board attached to function correctly, while others suggested the opposite. I can confirm that in my case, a logic board *was* needed. Attaching a Plus logic board (and later the original), everything powered up fine. Without it, even with a dummy load (47 ohms on 12V or 22 ohms on 5V), flup-flup-flup.
Finally, I discovered a new failure point I haven't seen before: the fuse clip. My machine sometimes didn't want to power up, and the problem seemed to be fixed by jiggling the mains cord around. Turns out one end of the fuse clip is broken and not springy anymore. I wouldn't have spotted it without a meter. Perhaps one more thing to check on a dead machine.
| Posted by: unity on 2017-01-21 16:54:12
Its fine. Set 5 to 4.9 if you want to balance things out a little.
Yes on the flup-flup, your results are on par.
I have never seen a bad fuse clip, but I am sure anything is possible. At least you figured it out!
| Posted by: Compgeke on 2017-01-21 16:56:38
12.3 and -12.4 aren't going to really make any problems. If really worried do like unity said and drop 5 to 4.9. Anything more than +/-.4 I'd be worried about.
| Posted by: bibilit on 2017-01-21 23:30:23
Turns out one end of the fuse clip is broken and not springy anymore I have seen a couple lately.
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