vintage computer

Vienna 286: cleaning

It took me five hours to clean whole computer. I had to remove all components to properly clean the case, but It looks much better now. Anyway, the complete disassembly allowed me to take higher quality photos of all cards inside. I’ve never seen a standard desktop PC with so large mainboard – everything is done using many single-function chips instead of large multi-function chipsets (btw the missing chips are for an FDD controller).

Installed cards:

  • AST RAMvantage RAM card (supports up to 3 megs of XMS)
  • Western Digital WD1003A-WA2 HDD/FDD controller (connected to a ST-4038 hard drive)
  • GeniScan interface (for GeniScan hand scanners)
  • ATI Graphics Solution rev3 (the first ATI chip – supports Hercules and CGA)

Atari Stacy And a New Display

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You can still buy a new white-on-blue LCD for Atari Stacy (a 30 years old system). The reason is simple – the same screen is used in multiple medical/industrial devices. The result is better than backlight replacement we did on a different unit although the new screen is glossier. Now we have two fully working machines.

I don’t have much experience with 16-bit Atari computers so I was quite surprised that the system has also some tricks to get more than 16 colors our of the machine. Albeit not as useful as the HAM mode on Amiga, this is still impressive.

Repairing PowerBook 100

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It took us three evenings to get two of the three PowerBooks back to life. The logic board of one of them was so damaged by leaked capacitors that it was impossible to fix it. The other two are now in a working state except for the SCSI hard drives. The most difficult part was to disassemble the display panel. The layer with liquid crystals contained several electrolytic capacitors that needed to be replaced as well. The original Conner drives did not properly spin up but that was expected behavior – I think that all first gen Conner 2.5-inch drives are already dead.

The only way to boot the laptop is to use an external floppy drive at the moment (or an external SCSI device). Running the System 6.0.8 from floppy is not very convenient. Fortunately, there is a nice solution. You can create a RAM disk, install the operating system into it and then set it as a boot device. PowerBook 100 is the only PowerBook with a persistent RAM disk function which content is backed up by three coin cell batteries. Data remains intact even after shutdown.

Apple PowerBook 100

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This is the smallest model from the first generation of PowerBooks. It was very thin and light for its time but didn’t have an internal floppy drive, which resulted in poor initial sales (before discounts). The logic board is based on a low-power version of 16-MHz Motorola 68000 coupled with up to 8 MB of RAM and 20 or 30-MB SCSI hard drives.

I have three non-working units and all of them need (at least) to replace bad capacitors. Their owner told me that I can keep one if I fix another for him.

CGA Color Palettes

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The infamous default 4-color palette with pink, cyan, black and white is probably the first thing that comes to mind when somebody starts to talk about CGA. I previously wrote a post about 16-color modes available for composite monitors but it’s good to add also something about the palettes for RGBI TTL monitors. These started to be used heavily when people stopped using TVs with their IBM PC compatibles.

The CGA palettes were designed for good viewing on NTSC TVs. That’s the reason behind the strange color combinations. The default one can, however, be modified using a video chip register – it replaces pink with red but also disables color burst on the composite output. Such trick was used in many games, but it did nothing on newer cards (EGA/VGA).

CGA also supports changing the color 0 (usually black) to any other color. Several games used this with the default palette to get blue, cyan, pink and white which allowed for better color transitions. Anyway, the easiest way to get more visually appealing games was to use the second palette – red, green, yellow and black.

CP/M running on Sinclair ZX Spectrum +3

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Unlike previous ZX Spectrum computers, +3 is equipped with an internal 3-inch floppy drive (compatible with Amstrad computers) and it is fully capable of running CP/M. The system runs snappier and more responsive than Commodore 128 in the CP/M mode but there are two caveats. Multiple keys are missing in the crippled keyboard layout and these are replaced with cumbersome keyboard shortcuts. This can be especially annoying when working with spreadsheets.

Another issue comes from the fact that the video circuit works in a resolution of 256×192 so it cannot handle the standard 80×24 text-mode typical for CP/M machines. The computer normally displays only 32 characters per row which would not be enough for any CP/M program. The +3 version of CP/M therefore uses a reduced font resolution with just 5×8 pixels for each character (including space between characters). Such font allows to display 51×24 characters and that’s the default text mode when +3 is booted in CP/M.

Of course not all programs work correctly with the reduced screen size so there is a program called SET24x80.COM. It provides a virtual 80×24 screen and you can quickly switch between displaying the first 51 columns or last 51 columns of the screen using a keystroke.

A few nice things from last weeks

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I’ve salvaged two SGI O2 workstations in a very good shape. They were used in Military Research Institute Brno (a state-owned enterprise in Czech Republic). Both have 300-MHz MIPS R5000, 128MB RAM and an extremely noisy 9GB hard drive made by IBM. One of them is full of dust and needs cleaning really bad but the other (which held classified information according to stickers) is clean like new. They were for free.

I was also given two packs full of CDs with SGI marketing materials, sets of hi-res photos of SGI computers for printed magazines and technical presentations for SGI customers. Most of it can be shared with public so I’m thinking about uploading it somewhere.

Amiga 2000 (1987) – Part 1

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This quite a nice upgraded machine waited two years for a repair. Now I am on sickness leave so I finally have enough time to look inside. The logic board is covered with a lot of dust and the EMI suppression capacitor exploded so it needs to be replaced. Before the explosion (which happened when the machine was off) there was also another issue – it could not boot without the (CPU) accelerator card and even then, under certain situations it displayed the green screen error (= chip RAM).

Except for the CF-IDE adaptor, there are no modern upgrades in this A2000. The logic board contains just 68000 with 1MB of chip RAM and it is expanded with following:

  • A2630 rev 9 – an accelerator board with 25-MHz MC68030 CPU, MC68882 FPU and 2MB of 32-bit (fast) RAM
  • IDE controller for a hard drive and CD-ROM
  • Multivision 2000 – a scan-doubler (VGA compatible) with a stereo audio amplifier
  • A25000 – 2MB RAM expansion
  • PC Emulator A2000 – a PC XT emulator card with 4.77-MHz 8088 and own RAM
  • Tseng ET4000AX – a video card that allows to display the DOS session on a separate VGA
    screen

CP/M and Input/Output Redirection

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It is nice about CP/M how easily the input from a keyboard and output to a CRT can be redirected to another computer over a serial port using a single command.