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PET 2001-8 220V black screen

There are some Commodore diagnostics (somewhere) that drive the LED.

You can set the LED to ON by setting the keyboard scanner driver (G9/74LS145) to an input pattern of 1011 by a POKE to PIA #1. Of course, the normal activity of the PET will then change the setting and turn it OFF again! If you disable the interrupts, and take over the machine, the LED can be driven correctly (i.e. within a diagnostic).

I was going to use the LED in my PETTESTER - but then they took it off all of the later PETs...

Dave
 
Jannie said:
- Could it be logical / practical to move the PETTESTER code to the Kernal ROM slot, so only the PETTESTER is needed, basically in the Fxxx block?
Click to expand...
FYI Patched PETTESTER attached.... this is the version that can live in a Kernel ROM socket.
 

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One point if you are adding a switch across a capacitor, always add a series resistor. This is because the peak currents shorting out the capacitor directly are very high. For this sort of application 47R to 100R is satisfactory this limits the peak current. If you don't, after a while, the switch will fail or become erratic as the contacts get microscopically burned and oxidized.

It was once found in automotive Kettering style ignition systems, that to keep the contact breakers clean required about 70mA. So most electronic amplifiers and CDI units to assist the ignition systems, generally ran about this much current via the contact breaker in the distributor.
 
Hi all, so update on the PET! I have cleaned the board, keyboard and reset the chips. Put it all back together with 2 x 2114 in the video Ram and 4 x 2114 in the l and j positions. I have life!! See attached. This is the base to test the other ram. Is 151 remaining correct??
 

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Actually, that is quite believable.

Try a simple program...

Code: 
10 FOR I=1 TO 20
20 PRINT "HELLO VCFED"
30 NEXT I

Dave
 
Hi AutomaticBirds,

That's awesome to see that it lives!

From what I recall, when using the stock BASIC:
7167 BYTES FREE when all 8 pairs of RAM are installed
2047 BYTES FREE with 3 pairs installed
1023 BYTES FREE with just those 2 pairs. That's what you should be seeing, because BASIC is about 1 KB. 151 BYTES FREE is not correct, and I haven't thought of a good reason for it yet.

What happens when you run a simple command? can you get the SYNTAX ERROR message, or get it to successfully print or loop?

You could also try and install some of the 6550s in I and J 3, see if it works and if you get more BYTES FREE.
 
He has a machine with 2114 devices, not 6550s. I think it is the same amount of RAM (but have not done the math).

Dave
 
DrAM19 said:
1023 BYTES FREE with just those 2 pairs. That's what you should be seeing, because BASIC is about 1 KB. 151 BYTES FREE is not correct, and I haven't thought of a good reason for it yet.
Click to expand...
I think the memory test at power-up just stops at the first location it gets an error. So, perhaps the first 152 bytes in the second 1K check out okay and then byte 153 fails. I wonder if it consistently powers up with "151 bytes free."
 
I built an adapter for my PET (running BASIC2) which limits the RAM to 1k or 2k for diagnostic purposes. When set for only 1k BASIC reports:
? OUT OF MEMORY ERROR IN 255.
And reports 1023 bytes free in 2k mode.
 
tsky said:
I think the memory test at power-up just stops at the first location it gets an error. So, perhaps the first 152 bytes in the second 1K check out okay and then byte 153 fails. I wonder if it consistently powers up with "151 bytes free."
Click to expand...
Good point. Swapping chips otherwise replacing I2 and J2 would confirm. And you're right, whether the BYTES FREE message has a consistent number is a good diagnostic datapoint.
 
Yes it consistently says 151 bytes free, I have ordered some more 2114 ram to swap out and extend to check the ram. I still have the 6550s but fear they may fry if constantly booted. I'll update shortly with pictures!
 
DrAM19 said:
Oh, my fault. I thought the machine was originally 6550s and he was using 2114s in an adapter since the 6550s are unobtainum.
Click to expand...

My bad. I see from the photographs that it was (originally) a 6550 machine.

Just a thought - are the lowest two RAMs OK?

Dave
 
They should be they are new 2114s I am going to replace all 4 tomorrow and see if it reports the same. If it does then there may be another issue maybe with the ram seats?
 
So success so far! I have swapped various rams around and now have 6 in the first 3 rows and the report looks good as does the basic!!!! I think it is just very temperamental on the ram and the sitting of the chips. I will hopefully now add the remaining 10 👍🏻
 

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