Re: Troubleshooting the disk drives in a 8296D

From: Marko Mäkelä (
Date: 2004-12-05 22:42:09

Hallo Nicolas,

> >Interestingly, the FDC ROM is no way close to "fdc-2.7b.bin" from
> >a 8296D.  The diffs of the upper 1024 bytes are 130 lines, while
> >the diffs above are only 18 lines.  The back plate of this CBM 220
> So this machine doesn't have an EPROM installed on an adaptor board, but it 
> has only the 6530 installed? In this case, I don't believe the drive can 
> work. What is the part number on the 6530?

The digital board (251120-01 rev. A) has two 6532s at UAB17 and UAB18,
a 6522 at UAB1, and next to the 6522 a daughter board that contains
a 901885-04, an EPROM labeled 251474-01B, and a 74LS04.  According to
information composed by Mr. Levak, the 901885-04 is 6530-47 for Micropolis
drives.  The drives are from Matsushita, Japan.

Hmm, the FDC ROM is identical with the one that was archived on FUNET
as "8250romfdc-fc00".  So, the possibility of faulty firmware has been
ruled out.

> In any case you have to have the adaptor board with the correct EPROM 
> installed. The FDC ROM contains all the drive specific stuff (stepper 
> control, all sensors and stuff), so with the wrong version it'll never 
> work. In both the SFD1001 and 8250LP/8296D I've never seen a 6530 without 
> adaptor board and EPROM. And these are the only drives with the low profile 
> mech.
> >Is the FDC ROM responsible for controlling the drive LEDs?  Does the
> >main processor control the green/red status LED?
> All these LEDs are connected to the 6532 at UAB17, PB3-5 and controlled by 
> the main CPU.

What about the write protect sensors?  I figured out that the wires are
red, white and a twisted pair of orange and black, connected to the 24-pin
connectors on the analog board as follows: pin 1=red, pin 2=empty,
pin 3=orange, pin 4=black, pin 5=white.  I also noticed that the drives have
index hole sensors, but I forgot the colors.

Do you have a 251121 rev. B analog board?  If you look at it so that the
power connector is at top left and the R/W head connectors are at the top
right, then which R/W head connector is for drive 0 and which is for drive 1?
I have tried swapping them without success.  I'd like to make sure that they
are connected properly before trying something else.  The two 24-pin connectors
are easier to get right, because the drive LEDs are connected to them.

The 8050 schematics on FUNET weren't very helpful, as already the digital
board is completely different.


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