Amiga A500 Restoration Trash to Treasure

We had in our possession a broken Commodore Amiga A500 with workbench/kickstart 1.3 roms installed. The amiga was one of my favourite computers from my childhood so I was looking forward to restoring and possibly completing some minor upgrades and making a dream amiga. The first thing we needed to do was repair the Amiga itself and then look at the memory upgrade. As a personal requirement we wanted to make an external floppy interface/drive to have 2 floppy drives (so the amiga can can play jesus on e's by lsd.. long story).

Step 1: Checking Things Over

The first thing to be done was to investigate the condition of the memory expansion installed. We opened the trapdoor on the bottom of the case, we removed the memory expansion, it was actually quite a good one that upgraded the amiga's 512k or ram to 2mb which for this computer was a dream amount in its day. However on further inspection it was evident that the memory expansion had suffered from the dreaded varta battery leakage and required immediate removal. We de-soldered the offending battery and scrubbed the area affected with a toothbrush, first with distilled white vinegar to remove and neutralise the leaking battery fluid. Following with a good spray and scrub with Isopropyl alcohol to remove any vinegar residue.

We now connected up and powered on the amiga with nothing connected other than power supply and modulator to be presented with a brown screen!

After a bit of investigation into Amiga colour error codes there was no reference to a brown screen. We next checked to make sure all the important chips had power such as the 68000, denise, agnus and paula. all power connections where present and seemed to be working, but upon feeling the top of paula and denise chips we noticed they were getting hot and if we tapped the top of the denise chip as powering on the amiga sometimes the screen would vary between a red and green and black as I was a little stuck at this point we reached out to the retro community. A youtuber called gadgetUK164 responded and suggested that it may be one of the I.C. sockets. so we ordered a replacement 68000f12 (a 16mhz version of the amiga processor), a replacement paula, denise all of which where reclaimed parts and we purchased some new 32 Way 2.54mm Turned Pin Single In Line SIL Sockets with 17.8mm legs. We de-soldered the old CPU socket and replaced it with the SIL Sockets then we inserted the newish CPU and first replaced the paula and the amiga powered up !!

Next we tried inserting the newly cleaned up memory expansion to get a green screen on power up.

Step 2: Repairing the Memory Expansion

We needed to find some way to test the memory chips on the expansion luckily the amiga was a rev 6a it had a fatter agnus chip which supported 1 meg chip ram and it had the empty slots on the board ready for the memory, so we modified the amiga to switch between 1meg and 512k chip ram by cutting through jp2 on the motherboard and adding a switch to select between the options. We then soldered some I.C sockets into the amiga's motherboard. Next we de-soldered all the ram chips from the upgrade board and tried the ram chips 4 at a time and they all passed the diagnostic tests, at the same time we de-soldered and replaced all the capacitors on the the board (electrolytic and ceramic). Next we used a multimeter on continuity mode to start checking all the connections from the expansion port on the memory board and discovered a missing earth, we connected the earth with a blue wire from the memory board isolation switch, then we populated the memory board with sockets and reinserted the chips and tried again. The amiga powered up and registered the 2mb of memory but up on running further diagnostic tests the amiga was reporting memory faults. upon removing the board to continuing checking the connections to the bus we discovered 2 of the chips were missing data connections to the bus, so we fixed these connections with some wire and success the memory board passed the tests full 2mb Ram yay!!! The ram expansion had a built in real time clock so now it was time to put in a battery, had a double cr2032 battery holder so it outputted 6v, We put 1n4148 Diode on the positive line of the battery holder to stop the amiga charging the battery as it would probably overheat is allowed to do so and connected it to the relevant points(red dot + and blue dot -) on the expansion board and we had a working clock.

Step 3: Other Issues

When the basic amiga and expansion was working we noticed the led on the keyboard caps lock was flashing twice and after so long the keyboard would stop working with the light still flashing twice then a delay of about 2 seconds then the light flashing twice again, upon investigating we found that this was a keyboard ram error message and it usually means a new keyboard controller as the keyboard ram is embedded into the controller, however it seemed to work fine for 5 mins or so then the error would start indicating that the fault was not in the chip itself. we simply replaced the capacitor in the keyboard near the controller chip and this solved the problem.

Step 4: Second Floppy Drive Using a 1.44mb PC Floppy Drive

We started looking at how the amiga external floppy port worked and discovered that the amiga used a slightly different system to a pc on how to read and use floppy disks the first major difference was the motor power was only a pulse and not a constant 5v to power the floppy spinning motor so we would need a flip flop on the motor to power the spinning motor, we found and excellent resource in the amiga system programmers guide which contained a suggested floppy interface but it required an amiga specific drive where we only have a standard 1.44mb PC drive. After more investigation there where 2 main differences between a pc and amiga drive as mentioned before the motor 5v power and the amiga has a disk CHNG and RDY line where as a PC floppy just has the RDY line. After tracking down a 23 pin D male Plug we set about making a floppy controller interface, which after much trial and error with various flip flops we managed to put together a working external pc floppy interface controller, we then designed a PCB for the interface and the gerbers are available free on a pcb website to download. Next we made a temporary case out of an old plastic sign and stuck it together with a hot glue gun. So now we had an amiga A500 with 2mb of ram and an eternal floppy drive.

Step 5: IDE HDD Emulator

When uploading the floppy controller gerbers on the pcb website we happened upon an IDE emulator which we figured would be perfect to use with one of those ide to mmc converters so we ordered the pc and the other parts and waited for them to arrive.

The IDE emulator was relatively straight forward to build but we had to order some reclaimed 74F00 as we couldn't find any new, (the "f" is the 100mhz iteration of the chip, the "hc" is 25mhz) so we ordered some from a seller in bulgaria. We recycled an IDE connector from an old broken SCSI interface controller, removing the SCSI connector using our hot air gun to heat up the solder side then pulling of the connector with tweezers when hot enough, we then cleaned up the connector and cut it down to size to be soldered into our PCB as out IDE header. We had a generic IDE to compact flash controller that could be connected up a flash card but it required a 5V supply, we use amigapcb.org to track down a 5v point we could solder a pin to the motherboard to get a feed from the amiga, we used pin 1 of RP109 as it was 5VCC point on the amiga (see photo 5) and pin 10 of RP109 which is ground we soldered connectors to these points and connected the red and black wires of a recycled floppy berg connector to power the IDE to FLASH adaptor and split off wires to power the IDE emulator. Now we had to power on the amiga and format and install the relevant software onto the compact flash card. First it is necessary to download the gerbers as the files contain the driver ADF with workbench pre installed. This is where we were stuck as we had no way of writing amiga ADF files to a physical floppy disk hmmm!!

Step 6: Writing Amiga ADF Files and Installing Workbench

After a bit of research we discovered instructions for an amiga adf floppy writer using an arduino mini by rob smith; so we set about building one of these bits of kit. The instructions where straight forward enough and we had fun building it. We do recommend that before you design something do some research and investigate what other people have made and learn from them, sometimes the offerings out there are perfect and it makes more sense to use the existing solution.

Now that we have a way to write ADF files we write the disk that is required from the previous step, We will also need an original workbench 1.3 disk (or you could make one using the adf writer)

We now boot the amiga with the provided IDE emulator floppy disk in drive DF0: and put workbench 1.3 in DF1:, on first boot you will get an error message

Can't Find DH0:

cd failed returncode 20

type in and press return after each line

format drive dh0: name mmchdd quick

this should format your compact flash card to a format the amiga understands, the display should say "initializing disk", next type

copy df0: dh0: all

then,

copy df1: dh0: all

this should copy the necessary files to your new HDD. Reboot the amiga this will take you to amiga workbench desktop.

Now we have a running Amiga with a virtual HDD.

Step 7: Upgrading the Processor

We happened to have a 68010p8 in our I.C drawer where we store all of our I.c's so we figured we would install this processor in the amiga and reap the the rewards of about a 10% increase in performance, not a massive upgrade, however we did try to make a 14mhz upgrade with the 68000f12 and failed miserably, as this cpu was available we went with this route as an alternative. After installing the processor into the socket, we turned the amiga on and it booted no problem.

To maximise compatibility with the 68010 its best to download decigel which is like a device driver that helps correct errors by correcting calls to 68000 and redirects them to the correct register in the 68010 and such. When it has downloaded extract decigel and place it some where on your hard drive you will find it later on, if you are using windows press windows key + r together and type md c:\amigadisk and click ok, then you can extract here, if you are having trouble extracting the file download winrar (32 bit version is free) and install, a right click option will appear when complete or you can just double click and extract via winrar.

To install decigel on the amiga it is required to copy it to an adf file and write that adf to a disk. To create an adf we will require a program called ADFOpus which allows us to create and add files to an ADF (amiga disk image).

First we create a new adf by clicking file then new then at the prompt as in the photos click browse, select or create a folder that you will be able to locate later and tick the "open after creation" option at the bottom of the prompt then click create.

next locate the extracted decigel files and drag and drop into the ADF window, (at this point we also put some games on the adf from aminet to fill rest of the disk to "test" the amiga ). Using the disk creator that we made earlier, write the adf file to a disk, boot the amiga and put into DF1: (the external drive) of the amiga.

When te Amiga has booted if you open you MMCHDD you will find some programs you copied over earlier first of all run "FileMaster"

in the right window browse to DH0: then the C folder, in the left window open DF1: and browse to the decigel folder highlight the file called DeciGEL and click copy as, this will copy the file to the right location, ten click the quit button in the bottom right corner.

now open CED on the amiga, when CED opens Right click at the tope left of the screen, when the menu appears float over project then click on open in te drop down menu, browse to df0: then go to the folder s and open the file startup-sequence. Insert a line and type the word DeciGel before the command loadwb to the startup-sequence file then right click the drop down menu again then click save, when saving is complete, reboot the amiga.

68010 installed and working :) .

Finally we should clean the case with Isopropyl alcohol, a cloth and a toothbrush. Spray the IPA onto the amiga case and wipe straight off, use the brush to get into the cracks of the case.

Step 8: What Now !!

Now we have a running amiga and a way to write ADF disk images to disk, you have the option of going on aminet and downloading some games for some retro gaming fun, if you google " amiga ADF files download", you will be presented with a plethora of amiga abandonedware, demos and utilites.

Future modifications:

Getting the 14mhz CPU upgrade working.

A RGB scart cable to connect to the T.V. for a better picture.