LisaList2

Oh thanks James for your thorough post. I have a few comments and answers

QuoteHaving established that the FDC RAM seems to work ok by your previous tests, we can be semi-confident that the values you wrote went into the FDC RAM

mmm, I must be too much of a HDD guy thinking that you could have faulty memory location in a RAM chip, and perfectly good ones at the same time on the same chip. So, writing OK at $FCC017 implies that you will write OK at $FCC001 ? As I told you, I write and read back OK at $FCC017, but can only write up to $7F at $FCC001. Past $80, I always read back 00

QuoteThe FDC code will zero the command byte (that you wrote to FCC001) when it executes the command.

Even after I write in service mode, and read straight back ?

QuoteIn any case, good work finding the FDC code listing and working through it!

Thanks !

QuoteAFAIK, the only listings available are for the 400K versions of the 3.5" drive version of the I/O Board ROM

Yes, that's the one I saw on bitsavers

QuoteWhen error 57 occurs, are both FCC017 and FCC011 returning 01?

No, FCC011 returns 00

OK, so after a long hiatus, I'm reviving this thread. I was able to change the two RAM chips on the IO board, and it did not solve the Error 57 issue. I am afraid to admit that I had made a mistake initially, thinking that the error code at FCC017 was 1. In fact, it is 16 (10 in hexadecimal), which indicates failure to leave track zero location. Upon observing the FDD during boot, I see that the head always seeks in and out, whereas in does not with a good IO board. I suspect that the SNS signal coming to pin 11 of U3B-LS3s3 is what's often called TRK0, and it likely goes low when the head hits track zero, and high otherwise. This is what happens with the good board (5V on pin 11 after boot up), but 0.2V on the bad board. My tentative conclusion is that the LS323 shift register is defective. Does this make sense to any of you ?

Thanks in advance