tkc8800

Technology and retro computer blog

Commodore 64C repair

A couple of months back I picked up this C64C for $10.  I suspected it wouldn't work but the case and keyboard were in very good condition, so if nothing else I though it would make a good parts machine.  On powering it up I got a very snowy picture, no colour and no basic prompt, but the typical C64 border could be seen, so there was an indication that something was working.


    


I took it apart and tried re-seating all the removable chips, there wasn't many as most were soldered.  Re-seating chips made no difference.  I eventually tried inserting a cartridge and that worked, although the snowy video was still there.  So at first I figured the problem must be the ram.  I bought some replacement ram chips and tried the piggy back trick but it made no difference.  I've got a C64 breadbin that I use for parts and most of the major chips in that machine are socketed so they can be easily removed.  I piggy-backed U3 (Basic ROM - 901226), from the spare machine and I got the Basic screen and prompt.  I entered some Basic commands and loaded a game using the SD2IEC and everything worked fine.  I de-soldered the bad 901226 and replaced it with a 24 pin socket and put in the replacement Basic ROM.


             

There was still the problem of the snowy video.  After doing some reading online I simply adjusted the pot near the VIC chip and this fixed the snowy video and colour.  See green pot in the top right of the square in the pic below.


           


There's still one problem with this machine, the audio output is very low.  I only get very faint sound through the TV.  I've checked the SID chip it's not that, so I suspect it may need some capacitors replaced.  Another C64 resurrected from the dead.


Amiga 500 rescue

I recently rescued this Amgia 500 from being recycled.  It looked like it'd been dragged through a river.  It was reasonably complete and surprisingly not broken.  I also managed to get the power supply, but both cords had been cut off.  I figured it most likely wouldn't work but it'd be fun to tear it apart and see what was inside.

 

The first thing I did was brush the dirt off the top to see what was under it.  There were a couple of missing keys but it started to look reasonably good.  With most of the thick dirt off I started to take it apart.  I noticed that the warranty stickers were still in tact so it doesn't look like the machine had ever been opened before.  This was a good sign as I expected that it was complete on the inside.

 

Amiga Amiga Amiga

 

On getting the top cover off it started to look pretty bad, it was really dirty inside and the RF shield was very rusty.  I took the shield off to expose the motherboard which looked a little better.  I could see that the bottom part of the RF shield was also pretty rusty, so I figured the motherboard would be damaged.  It looked like water had leaked into this machine at some stage and sat there for quite a while.  When I removed the motherboard I was surprised to see it had survived due to the plastic insulation sheet between the motherboard and the bottom RF shield.  After a quick brush off the motherboard looked really good.  There was some surface rust on the rear connectors but that was all.

 

All the chips were in tact and it also had a memory expansion module installed.  The clock battery on the expansion module had leaked and there was some leakage on the clock circuitry.  The internal floppy drive looked reasonably good.  I removed the memory expansion card and the floppy drive.

 

Amiga AmigaAmiga

 

I removed the bottom part of the RF shield, the rust from the bottom shield had covered the bottom part of the plastic case.  With the functional bits removed I figured I'd do a quick test to see if the machine would power up.  With the cords cut off the original power supply I used an ATX power supply instead.  I looked up the pinouts for the power connector, I recall from past reading that the Amiga 500 power supply can be replaced with an ATX supply so I knew it had all the necessary voltages.  I plugged in an old Amiga RGB to scart cable that I had in a box of parts.  I haven't had an Amiga 500 for over 20 years but I managed to get an RGB/scart cable with a box of parts I picked up a while back.  Luckily I kept the cable.  I connected the cable to a small LCD TV that has a scart input and on initial power-up all that I got was a white screen.  I did a web search about Amiga's with white screens and there were several reports relating to water damage and chips not seated properly.  I re-seated all the chips but no change.  I eventually had the idea to connect the Amiga's mono video connector to the composite input on the TV and I was greeted with a workbench disk screen.  The issue with scart cable was that my LCD TV didn't support RGB through scart.

 

Amiga

 

I found this very motivating as it showed that the machine was doing what it should.  I cleaned up the floppy drive and plugged it back into the machine and on subsequent power tests I got it to the point where the drive would spin ready for a disk.  This all looked very promising.  Not having been involved with Amigas for over two decades I had no software to test it with so I started doing some web searches on getting software.  There are utilities around that will transfer software from a pc to the Amiga but these only work if you boot the Amiga with a Workbench disk first.  I borrowed a copy of Workbench 1.3 and managed to firstly boot the machine and then use it to copy the existing disk, everything worked fine.  With evidence that the machine seemed to work ok, I got stuck into cleaning the case and other parts.

 

AmigaAmigaAmiga

 

AmigaAmigaAmiga

 

AmigaAmigaAmiga

 

Once cleaned up the case came out looking really good.  I got the rust off of the RF shield and the bottom case and re-assembled everything. I also created a better power plug for the ATX supply.  I extracted four pins out of a round DIN connector and soldered them to an ATX molex lead.  Since re-assembly I've connected the Amiga to my pc and used Amiga Explorer to transfer disk images across to it.  The process worked fine.  The memory expansion card also works fine, I removed the leaky battery and cleaned up the board, it now reports an extra 512k of memory.  The Amiga boots reliably and I've since tested it with a couple of games which worked fine.

 

1st November 2015

After the success with the main machine, I tested the power supply.  I hooked up a mains cable and checked the output voltages and all voltage were fine!  I've re-attached the mains cable to the power supply and I'll need to get hold of an Amiga square 5 pin power connector to fix the cable to the machine.  These plugs are not easy to come by so I'll have to attach the makeshift version until I can get one.  The A500 was perfectly fine, aside from rigging up a power supply and cleaning nothing special was done to get this machine to work.

 

Amiga Amiga


15th November 2015

I've now replaced the missing keys and created a good makeshift Amiga power cable.  I've also added a Gotek floppy emulator which allows loading of ADF images from USB stick.  I mounted the Gotek on top of the Amiga using some double sided tape.  I passed the data and power cables for the drive through the back of the case.  I still have the original floppy installed but just un-plugged.  I think this is a much better solution than hacking up the case to fit the Gotek internally.  This way you can revert the Amiga back to it's original configuration.


Amiga Amiga Amiga

Commodore VIC20 & 128 haul

I saw an ad on a local site for a Vic20 and Commodore 128 bundle. What really caught my attention was that both the original boxes for the computers were included. Both boxes are in very good shape. I've been wanting to get a Vic20 again since it was my first computer so it was a good opportunity. There was also a brown 1541, a cassette unit and a bunch of other stuff. I didn't realise until I got everything home how much extra stuff there was, mainly all the original brochures and manuals that came with the computers and the original Vic20 poster in mint condition.


Commodore 64 Epyx Programmer's Basic

 Epyx Programmer's Basic, originally Hesware Graphics Basic for the Commodore 64.  Read about it here: https://en.wikipedia.org/wiki/Graphics_BASIC

 

Epyx Programmer's Basic Toolkit

Manuals

Epyx_Programmers_BASIC_Toolkit.pdf (6.77 mb)

Epyx_Programmers_BASIC_Toolkit_Addendum.pdf (134.20 kb)

Epyx_Programmers_BASIC_Toolkit_Reference_Card.pdf (930.23 kb)

 D64 disk image: epyx_prog_basic.zip (86.90 kb)

 

Hesware Graphics Basic

 D64 disk image: graphics_basic.zip (89.05 kb)