LinuxJedi's /dev/null

Restoring an Amiga 500, part 2

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At the end of part 1 I had a lot of cleaning to do and a failed PSU. So I’ve been working on those things over the past few days, here is my progress.

So, first the PSU. Regardless of what failed here I suspect more things would fail. So I decided to look for a compatible PSU board that would fit inside the Amiga PSU case. I soon found the Mean Well RT-50B, it provides the +5v, +12v and -12v that the Amiga requires at the correct currents and it is small enough to fit inside the PSU case. More importantly it uses good quality components as should last a few more decades.

I basically cut the cables off the old PSU board, joined the power switch to the live wire, stripped the ends of the cables and screwed them to the terminals of the new board. The Amiga connector wire colours and pinouts can be found here.

So, with this wired up I figured I would use it to power up the Amiga board to see what I had here. I knew there was corrosion on a pull down resistor for RGB output but the black and white composite should be fine, so this was used first.

Bingo! We have a power up, the floppy drive is also making the right noises. I don’t have any floppies to use in it right now, but I do have a Gotek drive which emulates a floppy drive using a USB.

I hooked this up, booted the “flashfloppy” boot loader which brings up a menu to select which disk to use. This is where I hit problems. The keyboard doesn’t function so I cannot select anything.

I have also cleaned up and replaced R402 and the RGB output now appears to work fine (at least for the insert workbench screen). Not perfect but I’m getting a better PCB cleaner soon which should completely remove the remaining corrosion.

As far as functionality goes we have hit a roadblock, in part 3 I’ll cover the keyboard repair steps.

Next the cleanup. Using some soapy water I cleaned all the plastic parts, including the keys. This made a massive difference, it looks years younger.

Underneath the keys, lets just say it wasn’t pretty…

Some compressed air, a light scrubbing with a toothbrush and a cleanup with isopropyl alcohol later and it looked a whole lot better.

So… I’m left with cleaning a few more things, including removing the rest of the corrosion and fixing the keyboard. I may also get another Gotek drive just for this machine. Watch this space!

5 responses to “Restoring an Amiga 500, part 2”

  1. Marko Mäkelä Avatar
    Marko Mäkelä

    Unsurprisingly, the keyboard looks similar to the newer Commodore 8-bit computers (with no metal springs). To me, the interesting part of cleaning the keyboard involves not the ‘cosmetic’ cleaning of visible dust, but cleaning the parts that close the gold-plated contacts on the circuit board. This would involve desoldering the shift lock key, and removing lots of tiny screws that attach the black plastic cover to the underlying circuit board.
    Underneath the black plastic cover you should find upside-down rubber ‘cups’ that have black conductive rubber pads in the middle. Also those can be washed with soapy water. It would make a huge improvement (reducing the force needed to type, or the probability of missed keystrokes). In extreme cases, those rubber pads could run out of conductive material. There exist options for repairing that, but luckily I never had to do that.

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    1. LinuxJedi Avatar
      LinuxJedi

      On the A500 you just undo the ribbon cable and undo a bunch of screws. As far as I can tell it is either the PCB or the CIA which is faulty. I have a new PCB on its way.

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      1. Marko Mäkelä Avatar
        Marko Mäkelä

        Good luck! Please do not throw away the 6526. It can be used to save other Commodores.

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      2. LinuxJedi Avatar
        LinuxJedi

        Thanks! In the Amiga the CIA is a 8520, which is very similar to the 6526 (you can use an 8520 in a C64 and most things will still work I believe). I wouldn’t throw one away unless it was fried. Since the Amiga has two of them it is easy to swap them over to test.

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  2. Restoring an Amiga 500, part 3 – LinuxJedi's /dev/null Avatar
    Restoring an Amiga 500, part 3 – LinuxJedi's /dev/null

    […] time I left my Amiga 500 with a keyboard fault, is this issue that fault has been diagnosed and a new boot time fault […]

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