68kMLA Classic Interface

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SE/30 recap issues

Posted by: likanen on 2020-04-13 01:28:24 Hi, I recapped recently obtained SE/30 with simasimac issue. Only mouse cursor and the horizontal black stripes. After recapping nothing actually changed, so I took out the multimeter checked the connections and found that my C1 is shorted to ground on - and + gives resistance of 100 Ohms (?). Other than that and C6 not connected to UB11 pin 7 (which I think can be easily jumped) I didn't find anything wrong with the connections. My question is where I should start looking for fixing the C1. Cheers, Harri

Posted by: likanen on 2020-04-13 09:38:20 Spent couple of hours cleaning the board even more, adding jump wire for C6, found that trace between circled leg and and its other end is broken, jumped it. Anyways, no change in out come except some attempts to play something from audio but it also fainted away after few resets. I also realised I get sad Mac if I press the programmers button.

Posted by: Bolle on 2020-04-13 09:54:03 You likely have a broken address line either going into or coming out of one of the four muxers UA8 to UD8. One of the chips itself could also be bad.

Posted by: likanen on 2020-04-13 10:01:34 Thanks! Is there a chart where each should be connected or how should I test the lines? I tried searching the forums earlier but I couldn't find a chart.

Posted by: Bolle on 2020-04-13 10:47:22 Schematics are available here: https://museo.freaknet.org/gallery/apple/stuff/mac/andreas.kann/schemat.html Start by checking address lines between the CPU (or the ROM slot to make things easier) and the muxes. Then go for the actual VRAM address lines between muxes and the two VRAM chips.

Posted by: likanen on 2020-04-14 10:26:55 Thank you @Bolle, I found UC8 pin 13 not connected. After fixing the A(11) connection the picture looks good (I guess I could have taken A(11) closer to UC8  :lol: ). The programmers button still produces same error code (0000000F,00000013), I've lost whatever sound I had (some beeping), and no ? floppy. Further guidance is appreciated.

Posted by: likanen on 2020-04-18 09:55:53 Finally, I can report a success (I hate when people don't finish a topic they started, if it got resolved or not). Sound and ? floppy. The sound problems I was able to find a potential cause from here:  And it was indeed a broken data line to ASC (among many others 🙂 ). Funny that the trace looks fine (no black rot) but doesn't work between the UJ11 and the first test point. I even removed the (previously replaced) caps C9 & C10 to check the trace underneath. For me, the most surprising thing was, that once audio started to work, the ? floppy appeared as well.

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