Fixing an RK8E ....

Josh Dersch derschjo at
Fri Jun 19 14:43:24 CDT 2020

On Fri, Jun 19, 2020 at 12:24 PM Robert Armstrong via cctech <
cctech at> wrote:

>   It appears that my RK8E has a problem - it fails the diskless control
> test
> with
>         .R DHRKAE.DG
>         SR= 0000
>         PC:1160 GD:0000 CM:0001
>         DHRKAE  FAILED   PC:6726  AC:0000  MQ:7777  FL:0000
>         WAITING
> Ok, maybe a bad bit in the command register so I'll check it out.  But then
> it dawns on me - how do you work on this thing?  It's three boards
> connected
> with "over the top" connectors - you can't use a module extender on it.
> Worse, the M7105 Major Registers board is the middle one of the stack!   Is
> there some secret to working on this thing?  Has anybody fixed one?  Any
> suggestions?

I did some debugging on mine with two quad-height extenders and one
half-height (used upside down).
In such a way you can raise up two of the boards in back (on the quad
extenders) with the one in front installed normally but with the
half-height extender upside-down and plugged into the top connectors, so
the edge fingers of the extender plug into the top blocks.

Yes, it's ugly, and it only gains you access to half of the board you're
trying to poke at.  Building some sort of ribbon cables to substitute in
for the top blocks/upside-down extender would be more, uh, flexible, but I
was fortunate that what I needed to look at was on the unobscured side.

- Josh

>   I hadn't thought about it before, but the KK8E CPU would have the same
> problem.  Fingers crossed that one never dies...
> Bob

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