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OK, here's a strange one. My Macintosh Portable works fine when powered up but after about 10 minutes of use if I shutdown then it "twitches in its sleep". The sound crackles and the display randomly displays things. Pressing the spacebar wakes the machine and it's happy again. This happens...

D-oh! Oh well. :-) One bodge wire doesn't look too bad.

So, I've created the CUPL file, burned the GAL and done the patch wire.. The IDC connectors and ribbon cable arrived but I made the mistake of modifying the male IDC connector before trying to put it on the cable. It wouldn't clamp and broke and that was the only one I didn't get multiple of...

Yeah, A20's pretty important.. it's the one which enables everything. I'm just seeing if I can write the code in CUPL using WinCUPL and running the simulator to test the logic. For this CUPL isn't that brain twisting. I've started doing the simulator test, only done two lines so far...

Oh bother! Just checking the GAL programming next to the schematic and discovered a major error. A20 isn't actually connected to the GAL at all! It seems that when I moved from the 20V10 to the 16V8 I missed one wire in the schematic, Oh well, it'll just mean lifting pin 1 of the GAL and...

The "Freerouting" auto routing work-around works fine. It needs a bit of time and sometimes it gets stuck. Just moving a component by a 0.1mm in the design and suddenly it works again.

I didn't see that they did it in different heights. There was no choice in any of the retail supply sites I could find. Only RS Components had it as far as I could see. As for the pins, they are very fine, 0.49mm so it's not really feasible to modify them after manufacture. (They are metal...

Yeah, it's "Sod's Law". Still, I'm wondering about a 50-way female IDC connector + ribbon cable from the M/B socket connecting to a male connector with one side broken away (on the PCB side). That would be a quick and cheap solution to all the problems and there should be space for the memory...

Well, I managed to remove the base of the socket and the PLCC adapter sits nicely. I then did a test fit in the machine and... the board fouls the next socket along by about 0.25mm! :-( I have no idea why Winslow made the adapter so high, it could have easily been half the height. *sigh*

I've made up the board but haven't programmed the GAL yet. I should have clipped out the base of the PLCC socket. Not only would it have made soldering a darned sight easier but it would have allowed the adapter to settle about a mm lower, up to its skirt. Oh well, too late now. So, the jobs...

PCBway have a 10 minute review policy and then 24 hour turnaround for 2 layer boards. 4 layer boards take about a week apparently.

The new PCBs have arrived. I'm not sure when I'll get the time to make one up though.

Technically, having a complete ground plain on both sides of the board with the active traces on top dampens noise. To be honest I only did it as a "I wonder what would happen if" experiment. I never contemplated actually doing it.

I never understand why Apple didn't fit a zener diode and fuse to stop this causing damage... Or design a proper failsafe power sub-system.

Looking at PCBway, 4 layer boards are about 5 times the price of 2 layer and have a lead time of a week rather than 24 hours. I did try my board routed on a 4 layer board but Freerouting didn't do a very good job especially as it didn't seem to understand a ground plane.

There's enough clearance as long as I don't try to insert a PDS card. I don't have one for the slot anyway. The board itself has a cut-out for the connector space. the issue is the lack of clearance between the socket end and the PLCC socket. That can be fixed in one way or another.

I de-soldered the "Dunkirk" chip today and replaced it with a socket. Now I have an issue of mechanical interference between the chip socket and the RAM board socket I'm going to have to look into. I had sanded the socket down a bit because I thought that this may be an issue but it's not...

I'll repeat what everyone else has said, replace the capacitors. On the Portable they are guaranteed to be bad and cause all sorts of problems. It's possible that they killed the voltage regulator at some point, though I've had more issues with Q10, Q11 and Q12.

Well, the PCB design is off to PCBWayyyy... (Sorry, I've been watching far too many "Retro Recipes" videos on YouTube.) Hopefully this will be what it looks like (tall, red capacitors replaced by yellow blobs).

That's a mighty tower you have there! Is that a TRS-80 CoCo?