Zip GSX - Troubleshooting

[Hugh Hood <hughhood@earthlink.net>]

Fellas,

I could use a little help troubleshooting a backup Zip GSX card that I
bought used installed in a ROM 3 IIgs.

The card appears to work fine with _one_ exception -- When it is installed I
cannot enter the Desk Manager (Desk Accessories/CDA Menu) using the
command-control-escape keyboard sequence.

As you know, when that key sequence is entered, (provided interrupts are not
disabled) the ADB controller sends an interrupt that is identified and then
the Desk Manager routine is initiated.

For some reason, the CPU on the Zip GSX is either not receiving the
interrupt, is ignoring it, or is not able to access the Desk Manager vector.

Here's what I've tried:

1. Remove Zip GSX and re-install original 65C816 - Desk Manager IS
accessible. (So, the computer and keyboard are functioning fine).

2. Re-install Zip GSX and re-seat Zip GSX cable and ensure all pins are
inserted correctly - Desk Manager is NOT accessible.

3. Enter the monitor and run short program to clear the interrupt disable
flag (CLI - 58) - Desk Manager is still NOT accessible.

4. Ensured that the S1 (Control Panel Disable) Jumper is not jumpered on the
ROM 3 motherboard - Desk Manager is NOT accessible. <BTW, this jumper may
just disable control panel access, not the CDA menu>.


So, what's left - bad CPU, bad cable, broken trace? Other than this issue,
everything else seems fine with the Zip GSX. I'm stumped.

Has anybody here experienced this before or perhaps can shed some light on
what is happening?

Thanks.

Hugh Hood