[Coco] Drive controller problem

[Bill]

I have a problem with one of my drive controllers. Whenever I swap out the
24pin chip for an HDBDOS chip, the controller works perfectly. When I put
the original chip back in it gives me an "EXTENDED COLOR BASIC" message.
Something tells me it's the chip itself.

I'm looking for someone who has a spare chip they would sell for a
reasonable price. It's the 24 pin TMS4764-30NL

Thanks