68kMLA Classic Interface
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| Click here to select a new forum. | | Classic Mac II Power supply issue | Posted by: pme on 2020-05-09 08:22:19
Hi,
I have purchase an old classic mac
I have recap logic and analogic (ref 820-0525) boards, replaced IRF BC40, TDA4605 and CNY17 (opto), diode dp3, dp4, rework connectors solder, but +5v still weak (start at 4.65v) cold boot doesn't work.
If i use a hair dryer a little on analogic board, +5v increase till 5.1v (keep stable) and boot is ok.
Any advice to find the issue ? I'm out of idea.
Thanks in advance
| Posted by: dochilli on 2020-05-09 08:34:41
Turning pp1 a little bit could be a solution, but measure the 12V while you turn pp1. Check the voltages for the next minutes, if they are stable.
Sometimes the potentiometer needs some turns and works again afterwards.
| Posted by: pme on 2020-05-09 11:38:11
I've already tried PP1 but not solve the issue PP1 at max give 4.81v
| Posted by: OsvaL on 2020-06-19 11:28:53
Did you solve this issue? I have the exactly same problem with my Macintosh Classic. It will only boot when I use a hair dryer to heat the analog board (already recapped). When I test the rails from the hard drive power supply I get a steady 12V and 5V respectively without using the hair dryer. When using the 12V goes up to 12.3V
If I turn the potentiometer a little bit the voltage increase up to 13V but it doesn't fix the problem. Only the hair dryer does it.
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