The CPC lives!

I was meant to post this a week ago but was busy building up the new display unit, so it got forgotten.

Anyway, the good news is the CPC464 lives again! I stripped it all down and checked the temp of all the chips on the board and found one of the memory chips was getting very hot so that was the first job, removing all the current chips, replacing them with sockets and then fitting the new memory chips.

After this, I powered it back up but unfortunately, there was still no picture. No other chips seemed to be getting very hot but maybe the Z80 was getting a bit warmer than I expected. I swapped this over with the Z80 from my Speccy +2 though and found that wasn’t the issues either.

So at this point, I dragged out the oscilloscope and after watching some youtube videos I started to check things like the clock signal for the Z80. That checked out fine, but the data lines on the Z80 were dead and I was seeing weird 1Mhz signals dotted over various different pins. After some discussions on forums, it seemed like the Z80 was getting stuck in a loop and not running correctly. But the Z80 only runs what it is told, and that is the job of the ROM chip.

So next step was removing the ROM from the board, at this point, I placed it into my EPROM programmer and read the contents of the chip to see if it matched the original ROM file. The result of this was a chip apparently filled with “FF”. So no ROM code on there whatsoever. This chip is fried!

A new blank EPROM chip was purchased next and then programmed with the original ROM file A socket was then fitted to the board and the new ROM chip inserted. And the result of this? a working CPC464!!!

I still need to give the computer a proper clean so will be stripping apart again soon. I also hae a new drive belt for the tape player to go on (although the current one is actually still working). The tape counter button is also jammed so will look at this and may need to 3D print a new part on the resin printer to get this bit fixed.

All in all, I was pretty happy with my first computer repair. I have now placed the CPC on my new display unit and am actually going to use it with the green screen monitor as it really seems to add to the experience. The only issue with this setup was the cables are not very long from the monitor to the computer so I ordered an extension for the video and the power which I am still awaiting the arrival of the video extension. But everything else is in place and ready to go 🙂

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