ScuzzBlog: Diaries April 2018
Entry 23rd April 2018: Post: 3
Commodore CBM 3032 - Lost my keys
OK following my session this morning I was using the CBM 3032
and had a black out on the screen for a split second. Next I
noted the loss of keys A D G J L 5 6.. every other key in a line.
I found a picture of the keyboard circuit and discovered all
these keys run on one circuit that terminates at Cable Connector 5.
Also that circuit runs off the 5V and has resistor R18 all
connecting to chip 6525A.
***UPDATE***
Finally tracked down a wiring circuit diagram for the 3032 and
even that was incorrect.The keyboard socket goes first to a
chip reference 74L5145 and has four outs A B C D on chip UC9.
I checked the continuity in and out and it was fine. The next
chip in the chain is the big one 6520-11 or UC7. Again I checked
as far as possible and the chip was showing continuity on all
in and outgoing tracks
I checked pretty well every circuit and capacitor and resistor
and didn't find any issue with anything. I am still troubled
that there are three screws missing from the motherboard and
it is loose. I sense this is deliberate and may suggest a
problem. Really don't know.
I am minded to think that the black screen and keys are not
related. I did have an issue getting those keys to work before
I had the problem and I think now that either there is a wire
loose off the connector, or more likely a damaged track on
this line. Either way I am not minded to do anything. I can
run the tape from the right shift and RUNSTOP and also run
programs. I may try to track down a diagnostic tape and see
how that works. The computer still fires up no issue.
***END UPDATE***
[ Previous post ]
I opened up the computer to find a very very dusty interior.
Surprisingly the motherboard was loose and also noted that if
you press on the port connectors you can move the motherboard.
When I used the tape today I would have certainly moved the
motherboard. The keys I was using would have included the A G
and L when I had the blackout.
And so I sense one of three things... First that there is a
broken track somewhere, or the wiring to the keyboard cable
connector is dodgy, or the 5V took a hit and either blew the
resistor or damaged the chip. I have no way of finding out.
The computer is otherwise working fine and all other keys
working. I always look for changes in activity when looking
into a problem and I can't help feeling this was related to
the tape machine and that wobbly motherboard. Anyway I make
a file note and put the computer to bed now and do some
further research. I have a PET and a 4032 so no great hardship.
FILE NOTE:
Lost use of A D G J L 5 6
Tracked this to one circuit
Terminates at Cable Connector 5
This connects to U28-6525A chip
Connecting to pin 29/PC4
There is 5 volt on a six connector
to this circuit
1. There is either a loose cable connector
off the keyboard wiring.
2. There is broken circuit.
3. Or the chip just went bad.
Problem: I was using the tape on the system
and not sure whether this may have blown the chip
PS: I have now cleaned the motherboard since taking these pics
Keys working earlier
One of the screws missing top centre
UC9 bottom right and UC7-6520 just above
The board is a lot cleaner now
|
