Thursday, January 12, 2017

Apple Macintosh Classic II - Part 1

Any of my regular readers (I know you're out there, I can hear you breathing) will realise that I have a bit of a bias towards certain early 90's home computers. Specifically, the Commodore Amiga. Any Amiga is a computer worth saving, whether it's painted in bright red gloss paint or destroyed by battery acid, twice. I've done my utmost over the years to save and release into the wild any Amiga that I can a) afford and b) repair. So far, I've managed to fix anything that I've come across including the capacitors on my Amiga A1200 which actually started out as an exercise in trying to make the case white again.

But now, I have turned to the 'dark side'. I have bought an Apple Macintosh. An Apple Macintosh Classic II to be more precise. This particular model replaced the Mac SE/30 and was, rather bizarrely, less powerful than the SE/30, had no expansion slot, used a 16-bit data bus with a 32 bit CPU, could only address 10Mb of RAM and had only single channel sound. Who said Commodore had exclusive rights to ridiculous management decisions?

Anyway, this Mac was bought from a very nice chap in Worcester and it also came with two Apple Stylewriter printers (one still boxed!). The Mac itself suffers from the classic issue of vertical lines on the display. I am hoping that this will be down to leaky capacitors (sound familiar?) and will be a relatively straightforward fix. Worst case would be that the rechargeable battery has leaked over the motherboard (also sounds familiar).

The first nice surprise was to find out that the printers are basically re-badged Canon (BJC-200?) and you can still get ink cartridges too! Also, because of the Canon technology, when the ink is replaced, so is the print head, so even with the age of these things they should still work perfectly, if a bit slow by today's standards.

First, a few pics of the unit:

In all his glory
That doesn't look like System 7 to me...
The vertical stripes are, as I said, a classic sign of leaking/broken capacitors. I might be able to cure this just by cleaning the main board but it may be that the caps will be too far gone and need replacement.
Danger! Danger! High voltage!
Taking the back off and this looks pretty clean inside. There's no issues with the CRT otherwise we wouldn't see the vertical stripes. There is some damage to bottom corner of the case but it is very minor although I did also notice that one side of the case doesn't fit correctly. I suspect that this poor Mac has been dropped at some point in it's history.

The business end of the high voltage
Under that insulation cap is the main anode (not cathode like I said before) for the tube. That is something that I DON'T want to touch. It's very well insulated though, as is all of the HV stuff so I should be relatively safe playing with the insides. Notice that it's disconnected from the mains while the cover is off. Mains will NOT be applied unless the cover is on. To quote from Ghostbusters: "I don't want my face burned off.."

Hard disk with floppy drive underneath (still containing a floppy disk!)
There is a hard disk here which, if it's the original should be either 40Mb or 80Mb. Yes, megabytes.

The main board
After a bit of cable disconnecting and a little persuasion, the main board came out and, on first sight, doesn't look too bad. There is a battery that hasn't leaked (phew!) but I haven't checked it yet to see if there is any sign of life. I doubt there will be but these batteries are easily available from ebay etc.

Extra memory - cool
The main board has two 30pin SIMMs installed. I think that they are 2Mb each taking this Mac to 6Mb. I'm not sure though and need to check. If I'm really lucky they will be 4Mb each taking it to the maximum 10Mb (Nope - they're 1Mb each making a total of 4Mb. Oh well.).

A closer look at the main board shows that the capacitors in this are bad, with a capital "fetch me the PCB cleaner and a gallon of cotton buds..." as you can see below.

Even where there is no leakage, it's obvious from the corrosion on the capacitor's solder pads that something is very clearly wrong. They should be bright and shiny, even after 25 years but they are showing a lot of corrosion. I can try and clean the board but I suspect the caps have had it.

(Cue montage of me getting cotton buds - lots of them - and IPA and then spending over an hour cleaning, wiping, sweating, more cleaning etc)

Alas, I was correct. Cleaning the board made no difference. Virtually no difference. Those vertical lines that you can see in the first picture are actually quite bright but this only happened one time out of about seven. All the other times the lines were still there but the stripes were much dimmer. Now, after cleaning the board, the stripes are bright every time. Is that good? Maybe, maybe not.

New capacitors are on the way from RS Components and should be here Friday. Until then, he will just have to sit on my desk and look cool..

No comments: