Sinclair ZX Spectrum +2A RAM repair (eventually!)

I’ve had this Spectrum +2A for some time but it never booted correctly. It took me a while to even get power to it as I didn’t have an original PSU, in the end I made a makeshift adapter for my Amiga PSU that converted from the square Amiga plug to the DIN plug the +2A requires. I’m beginning to hate systems that require negative voltage or an AC supply, makes my life more difficult.

The system would either boot with a blank screen as shown above or with random vertical bars of various colors. This usually points to a RAM fault but with no spare 64k 4bit ram chips available nor any socketed in my other systems I couldn’t immediately test this theory. After ordering a new supply I got to work blindly replacing and testing what I could:

  • The Z80 cpu is always socketed so easy to test this and I have a few of those, but alas no luck here.
  • Next up I replaced the 74HCU04 and the TEA2000 chips socketing both for good measure, no luck here either.
  • I didn’t think capacitors would be causing a problem here but replaced them all anyway as its good practice on these older systems.

In all honesty I knew it was going to be the RAM as the chips looked slightly charred suggesting they had overheated at some point:

IMG_20180129_193858.jpg

Sure enough when the new chips arrived today and I replaced them, I was greeted with the familiar +2A boot screen. Loading up a game from tape worked successfully if a bit noisily (need to oil the cassette mechanics next). Another machine to add to the collection yay!

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