Re: Troubleshooting the disk drives in a 8296D

From: Marko Mäkelä (
Date: 2004-12-06 19:08:35

Hallo Nicolas,

> My drive uses the same EPROM, but a different 6530. Anyway, any 6530 from a 
> dual drive can be used, because the ROM is replaced by the EPROM.

Good that they didn't reprogram the mask-programmable pins.  Or maybe they
did; why else would the 74LS04 be needed on the daughter board?

> It seems the WP sensors aren't connected to an IO chip at all, but to UD9 
> which then inactivates the WE signal directly. (If I hadn't said so 
> already, my copy of the 8250LP schematics isn't very readable).

Could you please give me some pin numbers and IC positions to measure?  I'm
totally lost with this.

> drive 1 (left, viewed from front) is connected to P1 (right as viewed by 
> you) drive 0 (right) is connected to P2 (left)

Thanks, these happened to be right by coincidence.

> The 24 pin connectors are P4 for drive 0 and P5 for drive 1. On pin 1, 
> there is a red cable, and pins 2,23 and 24 are empty.

On mine, there are two more empty pins: pin 9 (key, i.e., plugged hole) and
pin 10.

On a closer look, I found the labels.  P4 is attached to drive 1!

> The other connector, P3, which goes to the logic board, is connected 
> somewhat weird, because it wasn't meant to be used with a ribbon cable, but 
> with a direct plug. It's this way in the 8250LP, where the analog board 
> sits between the two drives, under the logic board. So the ribbon cable is 
> split into two and there are two single row connectors at the analog board. 
> Just make sure the red cable goes to pin 1 on both ends.

It's a split ribbon cable also on the 8296D.  If I remember correctly, the
halves on the original board were swapped compared to the cable that was
attached to the spare board I obtained from Ruud.  Hmm, I hope this is the
cause of the malfunction, and I hope no damage was caused by the mixup.

A small anecdote: my first PET, a CBM 200 (a.k.a. 8032-SK) came with a
IEEE-488 cable connected between the user port and the IEEE-488 port, and
it had been powered up with the cable connected.  (On the CBM 220, the
user port connector and the IEEE-488 connector are "real" IEEE-488 connectors;
the card edge connectors on the motherboard are hidden behind the
left-hand-side of the case.)  The system worked when I got a 8050 for it.

I'll try swapping the cables and report back right after.  Cross your
fingers for me, please! :-)


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