Amiga 2000 (1987) – Part 2

  • by

It took me two years to find some time to disassemble the machine and then another year to start fixing it. Repairing the PSU with the blown EMI suppression capacitor was an easy task and that’s what we started with. Worse part was the instability – machine often crashed to a guru meditation error during certain tasks and sometimes a restart resulted in a “color screen” error.

David created and programmed a small device with eight differential inputs for voltage measurement (and logging) so we could check if the electrolytic capacitors did their job properly. To our surprise, they were fine. We also tried different programs to test memory and other hardware but the computer successfully passed all the tests.

Based on the Guru error codes, we found the root cause in the faulty EPROM chip (Kickstart 3.1). It started to lose data and reading of certain regions of the chip was sometimes affected. Thus, CPU executed faulty code (like a word or long word access on an odd address boundary).

The system is now running with Kickstart 1.3 and Workbench 1.3 and all original upgrades are inside except one. The Commodore A2630 accelerator card (25MHz 68030+98882, 2MB 32-bit RAM) crashes with dark blue and green screens and I’m afraid that there is a mechanical issue.

Next steps: Fix A2630 and reprogram the EPROM chip.

Backing Up DD Floppies

I was asked by my manager to download data from multiple boxes full of floppy disks he used in the early 90s. I’m used to people at work asking me for help with old UNIX systems, but reading 5.25-inch floppies is here for the first time. He used to be a musician when he lived in Israel and used his 386 PC as a sequencer with an E-mu Proteus/1 external wavetable synthesizer.

I picked my Vienna 286 computer to read the floppies. It’s quite a high spec machine with an 8MHz CPU, math coprocessor, Hercules-compatible Graphics and 1.5meg ISA RAM card… and it’s my only computer with a 5.25-inch drive. If you ask why I removed the CRT before I started copying the files, ugly mold smell goes from it every time it’s turned on and I hate it. I rather configured the machine to work in a headless mode (straight boot into Microsoft InterLink Server) and accessed the drives from a laptop over a null-modem cable.

Kermit Setup and CP/M

  • by

Don’t expect fancy setup utilities in CP/M. This is the process to create a machine compatible version of Kermit (terminal emulator software). MLOAD.COM takes the main program file in HEX and modifies it using the machine specific HEX file. The result is an executable file (COM) of the desired program.

Although there were text-based DOS programs around even in the 90s, their interface was usually far more user friendly with all the setup utilities, pull-down menus and other cool features. CP/M and early DOS programs were a perfect example of how simple and crude the software from the early- and mid- 80s was.

Kermit also reminds me a big advantage of the “PC compatibility”. In theory, the CP/M software was universal. However, different floppy formats, different pinouts on serial/parallel ports and different screen handling commands made life much tougher for both software developers and users.

Porting Sieve Benchmark to Mac

  • by

I play a lot with my PowerBook 100 these days. It’s a part of a large article about early Macs for my main blog (in Czech). PB100 is a cool office machine and it’s always a pleasure to work with it. I mostly run a text editor and a terminal emulator (the 9600 baud connection to a Linux box that can be used for the Internet access). When I need to relax, I have Test Drive II: The Duel (among other games). The Mac version of this game is somehow more fun than on PC even though it displays just black and write pixels.

Anyway, my obsession is to port our Sieve Benchmark to every single old computer I play with. PB100 was not an exception. I already had a version for Mac so I only needed to modify the code to run on the plain Motorola 68000 and System 7.x.

PB100 with a 16-MHz 68HC000 CPU runs twice as fast as Amiga 600 (with no fast memory). That’s not bad. However, my another small laptop from the same era – Toshiba 2200SX – is still three times as fast as PB100 thanks to its 20-MHz Intel 386SX. I’m not surprised that higher-end models (with 68030) from the first generation of PowerBooks were more popular. Still, this PowerBook is my favorite machine among early portable Macs.

Dead DEC Multia… any ideas?

I was given a Multia a few months ago from a former Digital employee. He told me that the machine could not start (no sign of life, even fan didn’t spin on). I cleaned it, checked all cables and the machine started without any issue. However, after an hour of work, screen went black and the machine was not able to boot anymore (no smoke effects).

I thought this was maybe the well-known issue with the two chips on the bottom side of the system board dying due to overheating. Ordering these chips looked easier than doing any diagnostic so we ordered the replacement and “fixed” the board. However, it didn’t help. My Multia still blinks the error code E – “Failed while configuring memory”.

These chips are octal bus transceivers – they are between the CPU and RAM slots. There are nine of them (8x8bit for data, 1x8bit for ECC). Two of them on the bottom side. We did some checks using oscilloscope to see what was happening there. At least OEAB signal was changing rapidly. !OEBA seemed H all the time (cannot tell for sure, maybe there were just too few changes). There was some data on two out of the nine chips. The rest of transceivers had no visible data receiving from the CPU (L).

We don’t have a usable logic analyzer at the moment so it is hard to move further. I tried to find some documentation and block diagrams of the machine with no success (I have a reference board design for the CPU though). Also, all Multia pages just mention that there are issues with the two transceivers that we already replaced… but there is no further explanation how the machine behaves if these are faulty (to check that we are on the right way).

Any ideas what to do next? Burn it with fire?

DEC Multia Restoration #2

  • by

In the first part, I cleaned this little machine and convinced it to boot. Sadly, it died an hour after the first start. Anyway, you can see photos containing:

  • Video card self-check (color stripes)
  • ARC firmware for loading Windows NT (blue background)
  • SRM console integrated in the firmware for booting UNIX and VMS (black background) … yes, it has dual firmware
  • Digital Tru64 UNIX boot
  • CDE graphics environment

Today, I will try to replace two suspicious chips. Let’s hope that it will bring the machine back to life.

Mac OS 7.1 CZ, Serial Cable and File Share

  • by

I’ve installed a new “hard disk” in my PowerBook 100 a few months ago. However, until now, there was no time to install an operating system other than the primitive System 6.0.8E that I used in the floppy-only mode. My goal was to have a Czech version that would allow me to read and write documents with our unique letters like Ř/ř. With a help of my friend, I got the floppy images of Mac OS 7.1 CZ and was able to copy them on real floppies (using my modern iBook G4 and a generic USB drive).

Working with old Macs can be painful due to use of file metadata (called resource forks) that can be lost very easily. Old Mac apps insist on this metadata and refuse to open a file if metadata is lost. Having a modern Mac is always handy to prevent these situations.

I don’t have a Mac serial cable. However, I recently bought two adapters for the conversion from Mac/SGI 8-pin mini-DIN to PC DB9. Connecting these adapters to a standard null-modem on both sides worked well and I was able to copy programs and documents from another old Mac. I’ve also managed copying files from/to a modern Windows PC. I pack the files into a ZIP file (to preserve resource forks) inside a Mac emulator and copy it using ZMODEM.

DEC Multia Restoration #1

  • by

Multia (1994) was the smallest Alpha-based computer made by DEC. It was intended as a low-cost workstation but never was really successful. One of my colleagues, a former DEC employee, gave me this machine in a non-working state and – being my first and only Alpha-based system – it deserved to be fixed.

I’ve completely disassembled the whole computer and cleaned every single component inside to get rid of dust and ugly mold smell. Minor issues were found and easily fixed. There were some partially disconnected cables which probably caused that the system didn’t want to boot when was found again in storage by the original owner.

Multia was incredibly small even by the office PC standards back then. DEC managed to squeeze a 64-bit Alpha CPU, enough RAM slots, 2-MB 2D graphics accelerator, Ethernet controller, IDE interface, PCI slot and two PCMCIA slots (bottom side) on a small mainboard. The hi-end configurations (like this one) were offered with a small PCI riser containing a SCSI controller chip combined with a 3.5-inch SCSI hard drive filling the last empty space inside the case. As a result, these configurations overheated significantly.

Certain Impact on SGI

  • by

This is my favorite photo from the Bytefest vintage computer show last year. A little girl playing Certain Impact on my SGI Octane2. Certain Impact is a flight simulator created by Paradigm for SGI in 1995. It was used as a graphics demo for the Indigo2 IMPACT line of workstations.

DECpc 325SLC & SimCity 2000

  • by

SimCity 2000 running on DECpc 325SLC (both from 1993) – This 25-MHz 386SL laptop was available with a color passive-matrix screen and thanks to its Western Digital graphics chip (512kB video RAM) it could handle 256 colors in a resolution of 640×480 (required by the game).

Not bad for a laptop that cost only about $2,100 when released.