Interface 1 Rom Upgrade

cj7hawk
Posts: 8
Joined: Sat Oct 09, 2021 7:43 am

Re: Interface 1 Rom Upgrade

Post by cj7hawk »

As an accomplished threadmancer, I once again raise this thread from the dead, though mainly to make my first post and thank those who contributed to this thread before me, since it helped me out.

I recently bought a faulty Interface 1 that was crashing the Spectrum when an Interface 1 command was tried. After a little guesswork, I decided to desolder the ROM rather than ordering a new ULA. It was the right move. Bit 3 of the ROM had failed and a hex dump showed all the second nibbles were 8 or higher, indicating it was reading high.

The 4764 threw me a little at first, but then I noticed most of it's pins were aligned with the 27128, which allowed me to install it in it's place. It's a tight fit, but it does fit OK. I burned the v1 and v2 roms into it, which was fortunate, because the Version4 PCB only works with the v2 ROM, and it wouldn't be good to replace the ROM twice in this interface. Burning the v2 into the upper space ( 2000-3FFF ) allowed me to switch between them once it was installed.

I burned the 27127 and just cut the pins that didn't match the 4764 and bent them upwards to allow soldering of wires. There's only a few wires, so it's not a difficult task. Then I installed the 27127 in the 4764's socket and soldering in the extended A11 and A12 lines, gave it power and permanently wired CS to Gnd.

It works OK. A quick fix.

I pic in case anyone else needs to try this;
Image
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