Commodore 64 Issue

[+Just Jeff]

Good Morning,

 

I bought a Commodore 64 on Ebay and it seems to work fine, but the startup screen says 11122 Basic Bytes Free. Isn't it supposed to show 38000 more or less? Does anyone have any idea what is causing that? Bad RAM?

[carlsson]

Yes, it should say 38911. Probably you have faulty RAM and the startup routine stops counting.

 

11122 bytes counting from address 2048 would equal 13170 ($3372). If it boots to BASIC, I suppose you could POKE and PEEK around there to see if you get back the values you store. Exactly what it means of actual RAM chips would need to be looked up.

[thetick1]

Are you sure it is C64 ? Can you show a screenshot of bytes free and if possible a picture of the case and motherboard ?

 

If it is a C64 then see https://retrocomputerverzamelaar.nl/commodore-64-problems/

RAM Problems U9 – U12, U21 – U24

Description
Startup screen problems with:

• out of memory error,
• wrong number of memory available,
• colored random characters.

General
Blank screen, no border. Shorted chips may get warmer (sometimes very hot) than the other RAM chips.

Partial failure: will sometimes produce “garbage” screen, abnormal number of bytes free (lower than 38911)

or “OUT OF MEMORY IN 0” error on startup screen.

Cause

Bad RAM chips or bad socket contacts of the RAM
(M41464) 2 RAM CHIPS (64K X 4 DRAM)

Please see description of the images for the cause

Edited May 29, 2019 by thetick1

[carlsson]

What else would it be? A VIC-20 with 8K expansion should report 11775 bytes free, and the expansion normally is external anyway.

[+Just Jeff]

Thanks yes its a c64. Says so on the top, and the screen. In fact the screen says its 64K at the top.

Carlsson- do you have a website? I was looking around for more info today and found one repair site run by someone with that name.

[carlsson]

Yes, I've got a website but the site you found most likely is Ray Carlsen's site, which obviously is not me.

http://personalpages.tds.net/~rcarlsen/cbm/

[+Just Jeff]

Ah.. OK

 

I tried pokes and peeks. I don't seem to be able to use the $ though. I can peek (3371), (3372), and (3373) and get 0,255,0 respectively. When I poke 9 to those 3 locations, I peek a 9 back.

 

I'm not that familiar with BASIC anymore... In my world, leaving the $ off means I am using a decimal number instead of a hexadecimal. Is that the difference here?

[carlsson]

Ah, my mistake. You should POKE 13170 and subsequent addresses. The hexadecimal notation I gave was just for reference as I believe I've seen you in the Atari 2600 programming forum where you'd know hexadecimal by heart.

[+Just Jeff]

Ahh then you've probably seen my quixotic attempts to make an Atari 2600 become a Commodore 64

 

So yeah its acting funny:

 

poke 255 in peek

13170 055

13171 239

13172 didn't write it down but I think it was 255

13173 132

 

poke 0

13170 055

13171 039

 

What do you think?

[carlsson]

I believe you have a partly damaged RAM chip, unless there is something else that can cause part of the memory to work but part doesn't. The PLA chip is a kind of memory manager I think but it probably would be greater errors if it was the cause.

[+Just Jeff]

So from what I've read. I should buy a few chips, then piggyback one at a time to see if results change?

[ToddL]

Yes, I've got a website but the site you found most likely is Ray Carlsen's site, which obviously is not me.

http://personalpages.tds.net/~rcarlsen/cbm/

 

He has a new website although the repair information seems to still link to the old website at least for now:

 

http://carlsenelectronics.net/