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Starting my first Pet, a 4032 in desperate need of some love

One more quick question. My keyboard has a 5x4 key numeric keypad and the matrix in the manual is 3x4 with a double wide 0 key. Is the matrix the same electrically on the different layout?

Mike
 
Mike Brixius said:
One more quick question. My keyboard has a 5x4 key numeric keypad and the matrix in the manual is 3x4 with a double wide 0 key. Is the matrix the same electrically on the different layout?

Mike
Click to expand...
Disregard this. I finally found the matrix for the graphics keyboard. It looks to me like the 74ls145 binary to bcd decoder is bad. The variances on the matrix make no sense. The keys all produce consistent results but they don't follow any logic for a bit or two being stuck or a key code having a bit off. I decided to scope the 74145 and pin 7 looks like it's off. It rises to 4ish volts then drops to 3 over a succinct second or two...

I'll find out in a few days when a replacement arrives

Mike
 
The simplest way is to swap the two banks of RAM around by swapping the two /CAS signals over by desoldering one end of each of the resistors in series with the two /CAS lines and swapping them over with a couple of short jumper wires.

Use PETTESTER then to test the lower bank of 16K as normal (which is now the 'upper' bank of chips)...

Dave
 
Mike Brixius said:
Disregard this. I finally found the matrix for the graphics keyboard. It looks to me like the 74ls145 binary to bcd decoder is bad. The variances on the matrix make no sense. The keys all produce consistent results but they don't follow any logic for a bit or two being stuck or a key code having a bit off. I decided to scope the 74145 and pin 7 looks like it's off. It rises to 4ish volts then drops to 3 over a succinct second or two...

I'll find out in a few days when a replacement arrives

Mike
Click to expand...
This device is tricky to test because it is an open collector output. In order to rest it, you require a 10k (or so) pull-up resistor to +5V on the pin you are measuring.

This has caught a few people out before!

Dave
 
daver2 said:
This device is tricky to test because it is an open collector output. In order to rest it, you require a 10k (or so) pull-up resistor to +5V on the pin you are measuring.

This has caught a few people out before!

Dave
Click to expand...
I had to do a refresher on open collector. You are right, it is fine. In fact it seems my issue is that I burned the wrong Edit ROM. I have found multiple things online on the keyboards and some call mine a graphics keyboard and others a business keyboard.

I used the edit ROM that was for the business keyboard but I apparently need the normal or graphics keyboard.

It works fine (Except a few keys) with the Romulator set to "BASIC 4, CRTC, 40C"

I will burn the correct edit ROM later today so... Back to the RAM

Mike
 

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It's OK Mike - this device catches a lot of people out!

You aren't the first, and you won't be the last...

Yes, the EDIT ROM revisions are a 'set' that need to be matched to the keyboard. It took me a while to work out which type of keyboard is which as well. My issue was trying to find a 'common' set of keys across the different ranges of PET keyboards. Guess what - they are all different and there is no common key (not a single one)...

Dave
 
I am off on a little bit of a tangent looking at the keyboard because its going to a meeting Friday of the group that gave me this machine (It was in such bad condition several members had already rejected it). They are going to "Bestow" a reproduction label upon it and all that is preventing it running with the romulator in it is the keyboard. With the correct ROM selected it works but a few keys did not work at all and some others were flaky (I thought it would be plungers but it looks to me like it is all the circuit board)

I found 2 cut traces. One I had noticed but it was so intentional looking that I thought that it was factory. I missed the one below in the numeric keypad and so I bodged over them using very fine wire wrap wire.
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The one key that is driving me crazy is the Z key. With the circuit board off I can place a plunger on the pad and get good continuity (About 20-30 ohms) ONLY if I offset the plunger a bit toward the shift key (Left of center). My gut says that the right side (As in the picture with the board flipped) is higher than the left preventing good contact but even after sanding with progressively greater material (Eraser, 5000 grit, 2000 grit) and close up photos I cannot for the life of me find an issue. Meter probes always get great contact throughout and I have tried different plungers that work fine in other keys but nothing is working.

20230502_122849Zm.jpg
Z Key Pad

I keep expecting the black beast of Arrrggghhh to appear!


Mike
 
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