I have a problem with my Mac 512k (european 230V). I got the mac with a defect analog board. Some caps where leaking. So I changed all electrolytic caps on the board. After the revision run the Mac well. After 1-2 hours running i saw that the Q2 (BU 406) was running hot. The top case above startet already to melt. After that I read in Macintosh Repair & Upgrade Secrets, that the Flyback might be drawing to much power. I replaced the flyback with an Mac SE 30 Flyback (very good condition) and put a new BU 406 on the board. I also made the heavy duty power supply upgrade according to the book (CR 1, CR 5, CR 20, CR 21). After the upgrade powers the mac 512k on without problems, but the BU 406 is getting hot again. So my question. Is there any other problem on my board? I changed the Flyback, so I would take it out of the equation. Could it be, that a resistor or any other part is the reason for the BU 406 getting instantly hot? Has anyone a Mac 512k? Would be at least interesting to know how warm the BU 406 gets during normal use.
Macintosh 512k analogboard is getting hot
- Thread starter Mac512k
- Start date
I've got an unmodified international 512K and haven't noticed any overheating issues like you mention - mind you, I haven't run it for hours on end. If I get time over the weekend I'll crack it open and leave it running for a bit to see if Q2 gets overly hot. Will dig out my contactless thermometer so I don't burn my finger! 
Sitting here with my 512K and it’s been powered on for 15 minutes now and Q2 is still cool enough to touch. My thermometer says it’s 33C.
As mentioned this is completely stock. Haven’t even recapped it as there’s no need currently. Let me know if you need anything else.
As mentioned this is completely stock. Haven’t even recapped it as there’s no need currently. Let me know if you need anything else.