Restoring Amiga 500 #2, part 1

I recently acquired another Amiga 500, I knew it was dirty and it was the machine only, no PSU or accessories. Beyond that I did not know much about it. So, I have started documenting the repair of this machine.

First of all I disassembled the machine and removed the motherboard, the warranty seals were untouched so this was the first time it had been opened. There was quite a bit of rust on the shielding, I think I will strip this down and spray paint it to preserve it. The good news is there was an A501 expansion board inside this machine, that would need opening up to remove the battery.

Once the motherboard was out I plugged it in and turned it on…

Yellow screen. Not good. This suggests that there is a very early hardware problem, before the memory test is executed. No problem, I’ll use DiagRom with an RS232 cable and it should give me a better indication of what the problem is. Then I looked at the RS232 port…

Yea, that isn’t going to work. I took it to a friend’s lab (Embedded µ Systems) nearby, he has much better desoldering tools than I have and using them I was able to remove the connector and once home I soldered a new one on.

Excellent! So, hook it all up with DiagRom and try again, nothing on the RS232 port. I buzzed the port to the PCB with a multimeter to make sure the solder joints were good. No problem there. I then got a logic analyzer and tested the TX out from the Paula chip and the the 1488 line driver chip which is where the RS232 port is wired.

I also used it to test the data path ICs and a few other things which is why it is grounded in a weird place. The analyser showed the data coming out of Paula and into the line driver, but nothing out of the other end of the line driver. Yep! The line driver is faulty. A new one has been ordered and it looks like another trip to the lab is in order.

That is where I’m leaving things in this post. Next up the A501 and keyboard.