Re: 251101-01 Kernal ROM chip for SX-64 (UD3)

From: Nicolas Welte (
Date: 2007-01-09 18:07:27

MagerValp wrote:
> The schematics:
> says 2364 (2564) for the kernal ROM. I guess C= used both. 

At least a 2364 (from the C64) will work in this socket!

This is not the case with one revision of the 8250LP/8296-D drive board. 
One was made for 24pin ROMs of 2364 type, another one for the 28pin ROMs of 
2564 type. Guess what, a 2364 ROM will not work in the latter case! It 
seems they made use of the extra CS input that the 2564 offers. For 
whatever reason ...

I had another similar problem with a 4040 drive. One ROM (2332 type) was 
broken (blink 3 times), so I replaced it with a pin compatible (so I 
thought) 2532 EPROM. The drive then responded with 5 blinks! I checked all 
other socketed ICs, all were good. I had the 2114 RAMs in suspicion, but 
didn't have time to unsolder them, so I put the drive away for some months. 
Now when I had another look, I remembered a strange story someone told me. 
He replaced a 2332 with a 2532 in a SuperPET, and the 6809 CPU wouldn't 
work, because the 2332 has two CS inputs, but the 2532 only one! So guess 
what, same thing in the 4040! Both inputs used! So I added a circuit to the 
drive and now it can also use 2532 EPROMs. Two RAMs were also damaged, 
after I changed them the drive is alive again :)

I made some pictures of the modification:


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