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Making progress with the RX02 drive

Posted <2017-12-09 Sat 23:09> by Aaron S. Jackson.

I've been trying to get my RX02 dual 8in floppy drive to work this week. Thanks to Dave A for the RXV21 controller! It's been a bit of a hassle, basically failing all diagnostics on xxdp, but an interesting learning experience.

Here is a full dump of the XXDP diagnostics: https://aaronsplace.co.uk/private/o/48859c14f6a619a5316d6af37d60579c.txt

Here is a snippet:

CZRXFB0 DVC FTL ERR  00034 ON UNIT 00 TST 031 SUB 000 PC: 003476
 SECTOR ADR - LGC TST
  SECTOR ADDRESS ERROR
       EXPECTED SECTOR= 9.
         TARGET SECTOR= 8.
  POSSIBLE FAILING "FRU'S": 
            R-W ELECT - M7745
            PHYSICAL DRIVE
            CONTROLLER - M7744

  UNIT#0 RXCSR=004040 RXESR=000000 CMD=000017 ->READ ERROR CODE
  ERR CODE=150 ->GOOD HEADER TRACK ADR NOT=SELECTED TRK
  WORD CNT=000
  CUR TRK DV0=76. CUR TRK DV1= 0.
  TARGET TRK =76. TARGET SEC = 8. SOFT STAT=000 BAD TRK=75.

There were many other types of errors, but this type was quite interesting in particular. For some reason, it was unable to locate the correct sector, it was always one sector behind. A single sector on an RX02 floppy disk contains the following information:

As you can see, one byte is reserved for storing the track number, and another is for storing the sector address.

Marc came over and we spent some time trying to figure out what was wrong. Feeling apathetic we both stare at the R/W board inside the RX02 for a while. Within a few seconds of each other we both discovered a small piece of wire sitting across some of the tracks, next to a 7400 series quad AND gate. I'm not sure what it was actually doing, but perhaps it was pulling one of the gate outputs low or high. Either way, we removed it and ran the diagnostics once more.

To our amazement it passed all diagnostics!

Next we tried again to dump the floppy disk with VTserver, but no such luck. It seems there is still something wrong, but I think we are quite close now :)

Hopefully good news to follow shortly...

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Copyright 2007-2017 Aaron S. Jackson (modified: Sat 9 Dec 23:28:02 GMT 2017)