From: Nicolas Welte (no_spam_at_x1541.de)
Date: 2007-01-09 18:07:27
MagerValp wrote: > The schematics: > > http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/sx-64/251103_l.gif > > 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: http://freenet-homepage.de/x1541/temp/im000048.jpg http://freenet-homepage.de/x1541/temp/im000050.jpg Nicolas Message was sent through the cbm-hackers mailing list
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