22 Jul
2012
22 Jul
'12
2:23 a.m.
From: "Andrew Quinn" <jaquinn2001 at gmail.com>
Sent: Saturday, July 21, 2012 9:44 AM
To: "General Discussion: On-Topic Posts Only" <cctech at classiccmp.org>
Subject: Re: Ready to Power up the 11/04
It is possible that some of the HALT / Bus Error
problem might be with
the KY11-LB.... some of the keys on the keypad don't return the
correct values on the display when pressed. Specifically 3 and 6
which cause the display to show 1 and 4. These happen to be on the
same READ cycle as the CTRL and DEP buttons. My initial thought was a
problem with the 7404 that controls the READ signal but that looks OK
on the scope. I will pull the keypad off tomorrow and make sure it
isn't something in the switch matrix.
Not sure if anyone else has seen similar issues with the KY11?
The KY11-LB is "just another" peripheral on the UNIBUS. So if the KY11-LB
creates a problem on the UNIBUS the rest of the system will have problems
too. I once had a KY11-LB that misbehaved. What the symptoms were, I
can not remember, maybe that's described on my website.
Anyway, it turned out to be a faulty RAM chip. After I had found the cause,
I have replaced (sorry Tony, swapped) the module, because at the time I
could not find a replacement 4 bit, 16 nibble RAM chip. I am no longer
searching, but one day I hope to replace the RAM chip, if only to prove that
I did find the fault ...
- Henk, PA8PDP