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CBM PET 710 WITH BASIC PROBLEMS

Desperado

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Joined
Nov 25, 2017
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Good evening everyone, how are you?
I've been missing from the forum for a while because I've been away from retrocomputers for a while. I bought an old Cbm Pet 710, I replaced the two Rifa capacitors in the power supply, because they had burned out. Now it turns on regularly but if I type a command in basic, the cursor disappears and remains blocked.
What do you think could cause this problem?
Thanks to everyone!
 

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Hello. I thought you were having a rest after the last marathon!

Faulty RAM or ROM?

If it has a 6502 CPU, has pin 7 (SYNC) given up?

Dave
 
When you were replacing the Rifa capacitors, did you visually inspect the board for any corrosion? Yes it could be RAM or ROM but it could be a disconnected trace that masks memory access and causing a hang. Happy fixing, Jim
 
Hello. I thought you were having a rest after the last marathon!

Faulty RAM or ROM?

If it has a 6502 CPU, has pin 7 (SYNC) given up?

Dave
Hi Dave, this evening I'll try to check the cpu when the computer freezes!
 
When you were replacing the Rifa capacitors, did you visually inspect the board for any corrosion? Yes it could be RAM or ROM but it could be a disconnected trace that masks memory access and causing a hang. Happy fixing, Jim
Hi, Yes, I removed the Rifas and cleaned the transformer board well... I noticed that I hear a hissing noise in the background when the computer is turned on... but I don't understand where it comes from, perhaps from the power supply.
 
Dave i have 6509 Cpu in this Pet and on pin 3 i have a Sync signal of 635 KHz !
 
if for example, write "print" and i press Return, the signal goes from 635 to 520 KHz...
 
But I haven't typed any commands yet...
You didn't tell me that did you?

Ok, so if the frequency changes then the CPU is executing a different software 'loop' somewhere.

Reset the computer.

Check the CPU pins 2 and 4 (/IRQ and /NMI) for activity.

Then enter a command and press <RETURN>.

Recheck CPU pins 2 and 4 and look for differences - especially if a signal disappears...

Dave
 
Check the CPU pins 2 and 4 (/IRQ and /NMI) for activity.
I have a 0,5 KHz signal on pin 2 (also when i enter a command and i press return) but i have only HIGH signal on pin 4 and not waveform.
 
I have a 0,5 KHz signal on pin 2 (also when i enter a command and i press return) but i have only HIGH signal on pin 4 and not waveform.
Pin 4 being HIGH is fine.

Pin 2 looks good also.

Do we know where the technical manual / schematic is for this machine?

Can you identify the magic Commodore assembly number on the PCB?

Dave
 
I can't find the specific schematic for this model..but I'm not desperate yet ;)
 
It is good you are not desperate yet...

I assume (by the look of it) that your ROMs are EPROMs in sockets?

If so, can you check the EPROM contents against the corresponding binary images on Bo Zimmerman's website (or wherever on the internet).

Dave
 
Whatever is written on them.

I assume 128k means 128k bits - so divide by 8 bits/byte to get the number of KB.

Or check the size of the corresponding binary file you are going to use to compare them against.

Dave
 
I have these eprom
 

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What are you showing me?

I se a picture of a 2764 (8KB) EPROM.

Is this what is installed or what?

Dave
 
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