Tuesday, May 17, 2022

Repairing Two Sad-Looking Apple IIc

I got a lot of 2 broken Apple IIc for cheap (the lot was almost 1/2 the usual price of a single Apple IIc in untested state), it was unclear from the listing if it included 1 or 2 computers. First, one arrived. Then, to my surprise, the other arrived a few weeks later.

The first Apple IIc to arrive. No, it did not cost me $4.95. It was quite dirty.
The second Apple IIc. No, it also did not cost me $2.99.

Both computers were very dirty, yellowed, and had missing keys. 

Disgusting dirty machine.

Cleaning

I gave them a superficial cleaning, so I could touch them without gloves...

 Notice the glass cleaner, IPA, Q-tips, paint brush, tooth brush, and microfiber cloth I used for the superficial cleaning. I also used a magic eraser to remove tough spots. But now I can touch it.

Keyboards

Three keys are missing in the 1st computer ("9", "S", and "Caps Lock"), while the second one is missing  "Caps Lock". I downloaded a design from Thingiverse and 3D printed replacement keys for the "9" and "S". I started designing a replacement for "Caps Lock", that uses different switches, but I have not finished yet. I printed the keys with both a filament and a resin 3D printer. The resin keys turned out better, as expected, but even the PLA plastic keys are very usable (I printed the keys on a 45 degree angle to maximize the resolution). I applied a spray primer and spray painted the keys gray, still, the color is not a good match.

Trying a 3D printed key (this one was printed with a filament printer).



Removed keys, and rotting rubber membrane.

I deep cleaned the keyboard by removing and cleaning all keys, and I discarded a rotting rubber membrane.


Keyboard switches ready for lubrication.

These keyboards use Apple hairpin switches... The Alps keyboard used in later revisions of the Apple IIc is one of the best keyboards I've ever used, but this earlier one is pretty horrible. Even worse, the keys have dirt or corrosion and stick frequently. I used first WD40 (some water may have gotten inside during cleaning) and then DeOxit on the key switches to improve their action.

Retrobrighting

It is April, and I am finally starting to get a few hours of direct sunlight in my north-facing back yard. This is the start of the retrobrighting season. After cleaning the cases, I retrobrighted them and the keys. 

Retrobrighting the two Apple IIc. I disassembled one of them but not the other. I am also retrobrigthting  two mice (one beige and one platinum).


Some time later, halfway though the process, and the difference is clear. An Apple IIc external drive is also getting the retrobrighting treatment it had been waiting for since the end of Summer.

To retrobright the keys, I put them in a closed container with liquid 3% hydrogen peroxide, and shuffled them around every 30m.

My technique for the cases is to brush thick cream bleach (peroxide) then spray 3% hydrogen peroxide (often reused from other applications), or just water, to melt the brush lines and achieve a consistent coating. I achieve better results with this technique than with plastic wrap to keep the cream bleach from drying, but I need to monitor the process every 30m, reorienting the parts, and spraying more liquid as needed.

Repair

When I tried to start the 1st computer, I got the following screen:


This does not look right.

Using an oscilloscope I looked for problems in the clock and reset lines of the CPU. I also looked for suspicious signals in the address and data lines, but all looked normal.

Since I have 2 computers, I systematically swapped socketed chips with the other computer, until I found the broken chip: It is the ROM (issue 256). This is an easy fix: I burned a 27C512 Eprom with 2 concatenated copies of the latest version for this motherboard (issue 0), and modified the board by cutting a trace and bridging a jumper, as described in bigmessowires.com.

Then I serviced the 5 1/4 floppy-drive: I cleaned the head with IPA on a cotton swab, then cleaned the rest of the drive and lubricated the drive mechanism.

The 1st computer is fixed and I was able to play a couple games.

It is working now. It is shown with the drive that is missing the latch spring. Also, note the two resin printed keys.


I started the 2nd computer, but it shows some garbage on the screen, and fails to fully boot. The garbage consists of scattered "!". This seems to be a RAM problem, the "!" (hex #21) differs only on bit-0 from space " " (hex #20), so it is probably a fault in a chip responsible for bit-0.

Some garbage on the screen that points to a bad RAM chip.  I am still using the same keyboard, parts get mixed up when working on more than one machine.

Looking at the Apple IIc schematics it is either chip UF19, or, less likely, UF11 (Apple identifies chips by their coordinates on the board, chip F19 is the one on coordinates F-19, bottom right corner).

Socketed and replaced RAM chips.

I desoldered both chips, installed sockets, and found that UF19 was indeed the culprit.  I replaced the bad chip with a compatible 4146 64k x 1bit DRAM chip. There is very little space between some of the RAM chips and the floppy drive, and I was afraid that UF11 would not fit with the socket, luckily it did fit thanks to some empty space in the drive mechanism. Later, I added some insulation tape over the chip as a precaution against shorts with the drive.

I also serviced the drive of the 2nd computer. This one is missing a spring in the drive closure mechanism, I tried replacing the spring with one from a ball point pen, but It was not strong enough. The drive still works fine, but the latch needs to be pulled to close it. I'll fix it once I find the right spring.

Both computers are now in working order, and (mostly) repaired. To fully finish the repair, I need to find original replacement keys, and a spring for the drive.

It is alive!

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