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Commodore PET 2001-8 stuck on garbled screen

Ok so just ran Dave's pet tester again with
H1 H2 H3 and H6. Here are the results.
One thing to note in the memory tests with Nivags 8k ram solution it is only showing as 4k.
Pic showing what is installed.
 

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Now seems the time to test your 6550s

I also note the D checksum is still wrong now correct! D=5045

PS
If you use the character ROM you had before... that would free up the OMNI ROM... which could be configured as a 4K ROM... replacing 2 bad ROMs... finally if you reconfigure the PETTESTER OMNI... you would have a complete set already. You might prefer to keep them as is if you don't want to confuse yourself and want to keep a PETTESTER around!
 
Last edited:
I noted the (now correct) checksum too!

A dumb question... Your PET does have the 8K link correct doesn't it?!

Dave
 
As for the 6550's I am quite certain they are sadly all dead. I have tried them all today and they just put junk on the screen.

Need to know why I am only getting 4k ram with Nivags 8k ram module.
 
Have you tried them in the main RAM location or the video RAM?

Check my post above for the 4/8K RAM issue.

Dave
 
daver2 said:
Have you tried them in the main RAM location or the video RAM?

Check my post above for the 4/8K RAM issue.

Dave
Click to expand...
Today I tried them in the main ram location. In the past I tried them all in the C4 location..all checker board apart from two. One displayed a screen of arrows and the other a screen of zeros.
 
How did you try them in the main RAM location? All in one go, or one at a time as I suggested?

I will let Nivag answer the 4/8K issue.

Dave
 
Nivag Swerdna said:
Now seems the time to test your 6550s

I also note the D checksum is still wrong now correct! D=5045

PS
If you use the character ROM you had before... that would free up the OMNI ROM... which could be configured as a 4K ROM... replacing 2 bad ROMs... finally if you reconfigure the PETTESTER OMNI... you would have a complete set already. You might prefer to keep them as is if you don't want to confuse yourself and want to keep a PETTESTER around!
Click to expand...
Certainly something to think about and for me to learn how to do.
 
Nivag Swerdna said:
Given you can get a Basic working but use onboard RAM you could write a program to POKE/PEEK a location at say 6K in a loop and then observe the Chip Selects.
Click to expand...
Nivag Swerdna said:
Given you can get a Basic working but use onboard RAM you could write a program to POKE/PEEK a location at say 6K in a loop and then observe the Chip Selects.
Click to expand...
Would you happen to have the txt of that programme that I can type in. I have repaired the chicklet keyboard now.
 
How about this for a starter:

10 N=6
20 K=1024
30 V=42
40 POKE N*K,V
50 Z=PEEK(N*K)
60 GOTO 40

This will write to (and read from) address 6K (6*1024 = 6144).

The value written is held in V. The memory address is in N.

Change the values N and/or V as required.

If you want a variable address you could modify the code as follows:

10 N=6
20 K=1024
30 V=42
40 L=16
50 FOR I=0 TO L
60 POKE (N*K)+I,V
70 Z=PEEK((N*K)+I)
80 NEXT I
90 GOTO 50

In this case, N = the Kilobyte boundary; V = the value to write into the memory and L = the number of bytes to modify from the specified Kilobyte boundary.

Of course, there are many variants of this code, for example:

10 S=6
20 F=7
30 V=42
40 K=1024
50 FOR I=S TO F
60 POKE (I*K),V
70 Z=PEEK(I*K)
80 NEXT I
90 GOTO 50

This code will test memory addresses from S to F (at every 1024 byte boundary). The block start is defined by S and finishes at F. In this case address 6K (6*1024 = 6144) and address 7K (7*1024 = 7168) will be tested.

Dave
 
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