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Problem with the analog board in a Mac512ke

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Hi, I'm a vintage macs loving and I'm very proud of fix a lot of 8 different classic macs (reading the great books of Larry Pina!!!). I have skills in soldering and I'm learning about electronics by practice. Until now, I have a high degree of success!! until now. I'm the owner of a 512Ke that shows a lot of tiny vertical lines at startup. There's sound, no friendly bong, just something like "grrrrr" no matter.


I try to fix it and I saw my first surprise. It has a macsnap 3 memory and scsi expansión cards. The scsi card was free inside the box, no attached to the roms socket.I atached the scsi card, and resolder the yoke conector J1.


No success, same result. I'm think in a memory or ROM error, so I think that it would be a great idea to swap the logical board with the logic board of a mac Plus. I have a 220 V macPlus and my 512ke it's a 120 V, but I think that probably it works. I'm seeking in the internet and i didn't see nothing to not to do it.


Well, I changed the logical motherboard and turn it on. The fuse blow up. I was worried because I don't know why..After check out the motherboard, and saw no damages (at least at first sight), I thoght that I must changed the power supply and connect the 220 cable, not the 120 one (I have it together..) so I replace the 2,5 A fuse with the one that I have 5 A, thinking that everything it would be ok... mistake...


When I powered it on, a Little burn was in the neighborhood of the Q10. 4 or 5 resistor burned and the q10 literally annihilate .. jejeje


It was a very, very dumb mistake, I know..


Anyway, I would like to question you about this things..


- Is there any problem trying to do what I've done, swapping the logical boards??

- If no, what do you think about the first fuse crash?? Changing the voltage sources?? other reason??

- What do you think about the second problem?? Caused by the first one?? the same reason of the first crash??


Now, I'm going to try to fix this little disaster, and I trying to think about the components that I need to change, in order not to continue breaking my little boy..


I think to change these components:


R60 1k

R44 100

R45 1K

R46 22 1W

R47 1.5

R48 100

R49 1.5


Q9E 2N3906 o ECG159 o 2761604 o 2N4403 o 276-2023 (T-PNP, 1A,. 6W, TO92)

C39 470 mfd 10V 85C

U3 4N35 ECG3041 (IC, 6-p, optoisolator, 2500V)




Do you think that I have to change another components?? The bridge diodes??


Thank you very much for your patience, and I would be very appreciatte your help


By the way, when I'll fix the issue I'l need your help with the macsnap and the vertical bars!!!


Thx, Jorge

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swapping both cards are ok, and there is no reason it will not work... done it a thousand times, the Analog Board is the same or very similar between the 512 and Plus.


I will try the 512Ke Logic board in the Plus to double check you work.


A couple of pictures will be fine also.


A memory error will show a sad mac with error codes.


All in all, i think you have an Analog Board trouble.


A question, how was powered the 120 V Analog board in the first place ?

Edited by bibilit
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Hi, thank you for your fast response, I test several times to power on the 512 changing the SIMMS in the macSnap, try to reinsert the ROM chips, I think that I startup the mac at least 4 or 5 times with no issue. My first problem was when I swap the logic boards. As soon as I get home attach some pictures

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