Sadly, often a shorted / failing flyback.
How does C1 or the top-most pin on J1 look? Any darkened / burned-looking areas?Mac Plus.. ticking analog board
- Thread starter Michelangelo
- Start date
How does C1 or the top-most pin on J1 look? Any darkened / burned-looking areas?
@Michelangelo
Nice find!
The BU406 is right between T1 & T2, so I suspect it was either a voltage spike or a bad T1 or T2 which brought down the 406.
Nice find!
The BU406 is right between T1 & T2, so I suspect it was either a voltage spike or a bad T1 or T2 which brought down the 406.
Damn, it sounds like I will probably fry the replacement once installed ... worth trying regardless since I don't have many options.
Question: I have somewhere a spare analog board from a MacSe (not sure if SE30).. is the flyback compatible with the Mac Plus board ? Or maybe the size was a tad different.. not sure.
If the issue is the main transformer.. well, the MacSE has a completely different power supply, cannot transplant anything from that one to the Plus...
Bottom line.. what is the best plan.. for sure I will go on with step 1
1) Replace the busted Q3, turn on the machine and hope the best.
2) Transplant also the flyback from a donor board.. with the risk to fry that as well.
3) Find a MacPlus in better conditions hahah : P
Question: I have somewhere a spare analog board from a MacSe (not sure if SE30).. is the flyback compatible with the Mac Plus board ? Or maybe the size was a tad different.. not sure.
If the issue is the main transformer.. well, the MacSE has a completely different power supply, cannot transplant anything from that one to the Plus...
Bottom line.. what is the best plan.. for sure I will go on with step 1
1) Replace the busted Q3, turn on the machine and hope the best.
2) Transplant also the flyback from a donor board.. with the risk to fry that as well.
3) Find a MacPlus in better conditions hahah : P
Yes, flybacks from an SE or SE/30 are compatible with the analog boards for the Macintosh Plus and below. Here’s a photo of the flyback in one of my Mac Plus analog boards used in a Mac512…
So long as you bought two pieces of that BU406 transistor, I would suggest you go the easy route and install it and flip on power and see what happens. If nothing bad happens then you’re in the clear. But if something bad happens to it, then you should replace the flyback and that 406 component again.
So long as you bought two pieces of that BU406 transistor, I would suggest you go the easy route and install it and flip on power and see what happens. If nothing bad happens then you’re in the clear. But if something bad happens to it, then you should replace the flyback and that 406 component again.
Will do. And let you know if the living room catches fire : )
Behind the vinyl mask there are some markings around the main transformer, but tracks on the main board are just fine. Same around the flyback, not a trace of burning on the board.
Another question.. are out there modern replacement for the main transformer ?
Behind the vinyl mask there are some markings around the main transformer, but tracks on the main board are just fine. Same around the flyback, not a trace of burning on the board.
Another question.. are out there modern replacement for the main transformer ?
I think only the flyback could be in question. I've honestly never seen any report in all these years about the main transformer going bad. I wouldn't worry about it at this time.
Hello people.
Time to pause this project. I replaced the transistor and the flyback transformer and still nothing.. chirp chirp chirp. I checked all the documentation, scrolls and papers, tested the components and didn't find any other issue on the board. At this point I will wait to bump into another MacPlus and comparing the two, and maybe transplant T1 since there's no much more I can replace here.
In the meantime I want to thank all of you for your support, messages and for sharing your knowledge ... and the sacred scrolls : )
Time to pause this project. I replaced the transistor and the flyback transformer and still nothing.. chirp chirp chirp. I checked all the documentation, scrolls and papers, tested the components and didn't find any other issue on the board. At this point I will wait to bump into another MacPlus and comparing the two, and maybe transplant T1 since there's no much more I can replace here.
In the meantime I want to thank all of you for your support, messages and for sharing your knowledge ... and the sacred scrolls : )
Sorry to hear it... that's frustrating to be sure. Keep faith as this is a fixable problem.
I went back through the thread and didn't notice if this was stated clearly: did you replace the electrolytic capacitors on the analog board? It could be something as simple as that.
Did you replace U3?
Also, had you at any point adjusted the voltage regulator? I have found that sometimes after replacing components the machine will start crowbarring I need to re-adjust voltage down.
Yes. U3 brand new. Adjusted voltage from min to max with no results. Capacitors are looking very healthy, but I might have a go in a few weeks, when I find again the will to tackle this specific board hehe. If I have time I will "brute force it" and replace everything just to have the satisfaction to win this battle : )
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That sounds like a lot of work!
Your knowledge will be very helpful for others facing the same issue.
Has anyone ever thought about combining all known issues and solutions with pre-Intel Macs? I've thought about it and I find it would be a super helpful document.
Maybe even a full recap section and a common mod section?
Please don’t forget to check the hidden fuse in the harness:
Hello. Thanks for the tip but I checked continuity on all the connectors : )