The Archimedes is back on the bench

Now I have an oscilloscope, I thought it was time to break out the Archimedes. So far it has resisted my attempts to diagnose exactly what is wrong with it but I will persevere.

Why must you vex me so?

Symptoms are the same whether I use a Gotek or a real drive.
When you try and access the drive you get a “Drive empty” error. The disk drive motor does not spin.

I have:
Replaced the drive cable, making sure I use one with pin 1 cut for the Goteks. (It doesn’t make life easier with the pin order being reversed on the A440)
Tried two different Goteks (They power up and respond. I have rebuilt the config to have the right settings for the Archimedes as well)
Checked voltages (5v and 12v are fine at the cable)
Replaced a mess of logic in and around the FDD controller. ICs 29,30,38,46.
Traced all the connections from the 34 pin FDD connector to the next chip / resistor array.
Reset the Config. (Hold down Delete when booting the Archimedes. You also need to do this if the CMOS battery ever gets disconnected)
Replaced the WD1772 with another one from ExxosUK (Who is probably as close to a reliable source as I could find)

I’m hitting a strange issue when I connect my ‘scope to the system and try measuring the drive signals, where rather than reading, then throwing an error, the system just locks up instead. I need to learn more about using my oscilloscope.

Meanwhile I have done a couple of other projects.

I got offered, and accepted a huge CRT TV. This thing took three of us to lift it. It’s a “29 inch” model and is obviously a late model system, with both SVideo and Component inputs. Unfortunately on inspection, I noticed a very bulgy capacitor, so that’s staying off until I can replace it.

It was very dusty inside too.
Bulgy cap is bulgy.

I finally got around to making a Apple IIgs to SCART adapter cable so I could use my IIgs with my Commodore 1081 monitor. It’s pretty simple. 2 resistors and everything else is just connect the pin to the connector. Here is the guide I used. The SCART connector I got from a cable I had surplus. I’d purchased an RGB cable for my Sega Megadrive II, but despite me choosing the right item on the order, I was shipped a cable for the Megadrive 1. Thankfully they let me keep the incorrect cable and shipped me the right replacement. I kept the incorrect cable around “just in case” and just desoldered the cable and used the connector when I went to make this new cable.

The CRT turns the harsh lines into softer blurs, and what looked like odd dark blue and white bars on LCD came through as a light blue shade on the CRT.

On an LCD, that background is harsh stripes.

As is often the case, the cable flopped around loose in the 15 pin shell. 3D printer to the rescue! I have even redesigned the OpenSCAD file I sue to generate these cable glands to be parametrised, so I can easily update it to match new cable hoods and cable thicknesses as needed. If there’s any interest I can stick it up on GitHub, but it’s a really simple design.

This took 2 minutes an 40 seconds to run. Most systems can do it in well under a minute.

Finally I got the piece I needed to fix my Creativision keyboard adapter, and got it working. This allowed me to type in a piece of software developed by Noel’s Retro Lab, used to benchmark BASIC on 8 bit systems. We managed to turn in a truly abysmal speed, making the BASIC on the Creativision among the slowest so far, and slower than even notoriously slow systems like the ZX81. Our shame is also our pride.

I’ve also done some maintenance, in the form of swapping out the regulators, and an old capacitor. I am still seeing some issues with it so I need to get to the bottom of that. I need to heatsink the graphics processor in it next, as they are notorious for running excessively hot.





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