After a long work-related forced break I'm working on the Sharp MZ-731 again.
I removed the rust from the oscillator's bottom.

There's a little bit left inside the little recess for one pin. I used a fibre glass cleaning pen for it and I can't get into the little hole. I think it may be okay this way. I don't want to use any strong chemicals - don't want to risk damaging it.

So it'll go in the machine like that. Shouldn't spread from there within a lifetime, I hope.

I've also tested the 74LS10 IC that was also very rusty.

It seems to work just fine. All inputs and output work as expected, all triple input NANDs perform their NANDy function.

Didn't test input sensitivity (just 0V and 5V) but output is at about ON=4.5V and OFF=0.2V, which should be very much in spec.

The chip has a date code of 8342, which means it's 1.5y older than me.

Nice to be able to keep it original as much as possible.

Fingers crossed that it stays that way.

Show thread

I've removed all the rust from the CPU board (as well as I could). The board looks a lot less terrible now. Of course, there's still a lot of work ahead of me restoring the machine, but most of the rust was very superficial and hadn't yet started eating away at the copper or solder joints, yet. No idea if it ever would have - I'm no chemist and don't really understand how rust and other oxides actually spread.

But it's a lot more fun to look at the board now.

Show thread

Making pickled switches, pots and jacks 😋

They are from the Sharp and entirely rusted over. Couldn't even move the switch no matter how hard I tried.

Now I put them all in a jar with concentrated white vinegar. Chances are this will ruin at least the pot, but really I have nothing to lose here.

I'm now actuating the mixture every couple minutes. Will rinse with IPA (the non-potable kind) when the rust is gone and hope some contact cleaner will bring the stuff back to life.

Desoldered the Sharp MZ-731's oscillator. It doesn't look too good. Entire bottom side is covered in flash rust (I think), as do the ground and Φ pins.

Also, the pins are sealed with rubber, I think, and it's missing on the ground pin. Is that by design? The XO of that old PC mainboard doesn't have a seal there either, but instead case seals it off.

Maybe this one here does something similar, just less visibly.

Putting it into the breadboard for testing now.

Fingers crossed!

Doing some preparation for the Sharp MZ-731 tests. I've never tested a crystal oscillator before, and that 17.7MHz XO on the Sharp's mainboard is one of the hard-and-likely-annoying to replace parts.

So before testing it, I figured I better do a test run. Here's a 14.3MHz XO from a dead PC mainboard.

Turns out it was good I did this dry run, because now I know oscillators actually survive blasting 30V at there output instead of 5V at their power supply pin.

Alrighty, ordered a Chip Quik desoldering kit (thanks @krnlg and @zwangseinweisung!).

Apparently shipping from the UK to Germany will take between two and three weeks (oh boy). But that at least means I will actually have the time to get that pigsty of a workbench in order just in time.

Show thread

I figured it probably makes more sense desoldering the CRTC in the electronics lab at work.

I have a basic desoldering equipment at home that is fine for THT, but not for this, even with the large pin pitch.

In the lab I have access to an SMD rework station, but I've never actually done this.

So, what are your recommendations? Should I first add a bunch of fresh solder and flux to all the pins?

Put Kapton tape all over the plastic (top and bottom?) and surrounding PCB?

Show thread

Are there any federation relays focusing on , and that could help our tiny little instance focusing on exactly those topics get connected better with the rest of the world?

Some more rather well-known stuff. An 800XE, and a TI-99/4A.

Also the only compatible machine I own, a Sony Hit Bit HB-75P.. There's a spring in a little plastic bag included that I honestly don't know yet, what it is for.

Show thread

Okay, this one is for @Tijn

Sharp MZ-731. I think this computer was originally meant for small businesses mostly. It's graphics capabilities are essentially non-existent: It doesn't have any graphics video modes, just text modes, but surprisingly 512 characters to choose from.

The 731 is the second highest model from the range. It featured a built-in tape recorder and plotter.

There's a 780 model, which has all that and more.

Show thread

Okay, some 8-bit consoles up next.

First is a Master System II. This one I worked on before I knew the benefits of replacing capacitors or any other form of preventive maintenance.

So all I ever did to it was a) clean it, b) add composite video and mono audio output and c) ruin the case (somewhat).

Show thread

I got a 1541-II floppy drive with it, that looks similarly clean. Only cleaned the heads, lubricated moving parts and replaced the caps on that one.

This machine has been super reliable. People tend to dislike the newer model C for its edged looks, but I think it's timeless.

For convenience I got an SD2IEC for it. Some people install them irreversibly in their sixty-fours, I prefer to keep my machines such that I can revert everything.

Show thread

I think the issue is a shorted RAM chip so I bought a large batch of compatible chips a while ago. I haven't gotten around to testing them or fixing the memory expansion, but that's a project for the nearer future and I'm looking forward to boosting this thing to a whole whopping megabyte of RAM.

Show thread

Other than that I only did some maintenance - replacing caps, cleaning the disk drive and all that.

And I wanted to try newer versions of Amiga Workbench than the version 1.3 I got with it. Newer versions of Workbench need newer versions of the Kickstart ROM though and not all software is compatible with all ROM versions.

Going from what I learned while working on the ST, I made a circuit board that allows switching between multiple ROM versions.

Show thread

Well, more tomorrow, this is taking more time than I thought 😅

Amstrad CPC464, branded as "Schneider" for the German market. As you can see, apparently Germans don't like colors. I've always envied the colorful keyboard of the original.

My CPC actually always worked, but the metal plate holding the keyboard together had started rusting despite being painted.

Getting the remaining paint and all the rust off was painful, because there are little plastic guides for the keys molded onto the metal base.

Show thread

I guess I'm gonna talk a bit about the vintage computers I have accumulated over the years, what I have and haven't (yet) done to them, and maybe some extra info?

We'll see what sticks.

DOS Game Club Mastodon is the fediverse home of DOS Game Club. People here are all in one way or another involved with retro computing or retro gaming. Run by people of the DOS Game Club podcast.