repair

Amiga 2000 (1987) – Part 2

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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.

Dead DEC Multia… any ideas?

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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?

Repairing IBM PS/2 P70 before Bytefest

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I shared a photo of computers we brought to Bytefest (a vintage computer show in Czech Republic). IBM PS/2 P70 was one of those which needed fixing before the show. In this case, there were issues with an Alps floppy drive and power supply. I have to admit that this was one of the most painful disassemblies we did.

This is a dream machine for a user but total nightmare for maintenance. One example – it was necessary to disassemble a half of the unit just to connect a floppy cable back to the drive.

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.

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

SGI Visual Workstation 320 restoration #2

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We’ve managed to replace all the capacitors on the SGI 320 logic board and it works. This was the most difficult de-soldering we’ve ever done. The board is much thicker and with large ground planes distributing all heat out of the de-soldered parts. I’m really surprised that the board survived the surgery.

We have even been able to setup the firmware properly to load Windows 2000. It looks like the unit was used only for demo purposes in Czech SGI so nothing interesting is installed on the hard drive.

Quaderno Resurrection

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After several hours and twenty replaced capacitors this Olivetti XT-compatible sub-notebook is finally alive. Yay!

Fixing and Cleaning Amiga 500

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Another dead Amiga was repaired. There was necessary to replace a blown capacitor next to main CPU. We also cleaned the motherboard which was covered with some dirt.