Image Map Image Map
Page 1 of 4 1234 LastLast
Results 1 to 10 of 39

Thread: PET 2001 out of memory when loading

  1. #1

    Question PET 2001 out of memory when loading

    PET.jpg

    Thank you for looking at my question. I've owned my PET since 1978. It's been stored in a clean, dry closet for several years, and now I'm trying to get it working again.

    A lot still looks good! For example, I keyed in the following program:

    10 FOR I=1 TO 4
    20 PRINT I
    30 NEXT

    RUN
    1
    2
    3
    4

    SAVE "COUNT"
    WRITING COUNT
    READY.

    NEW

    (Rewind tape.)

    LOAD "COUNT"
    SEARCHING FOR COUNT
    FOUND COUNT
    LOADING
    READY.

    RUN
    1
    2
    3
    4

    So a lot of functionality still exists with this 40-year-old friend. However, when I try to load and run any actual saved program, I get an error:

    OUT OF MEMORY ERROR IN (LINE #)

    I assume that one or more memory chips have gone bad, correct? Do you think it's RAM, or ROM? What would be my next step?

    I really appreciate your help.
    Thanks!

  2. #2

    Default

    Welcome aboard!

    Indeed, you probably must have bad RAM. Your ROM is good, is the original 2.0 one; but if your PET is a 4K model the message must be "3071 bytes free" (or 7167 if you have a 8K model) , not 1023; so try to focus on RAM. Just in case you need to replace chips, the old 6550 RAM chips are hard to find; but 2114 ICs could be used by means an adapter.
    Check this page to find some useful tips: Commodore PET repair info

  3. #3
    Join Date
    Dec 2005
    Location
    Toronto ON Canada
    Posts
    7,213

    Default

    +1

    Is that your actual machine? 1024 bytes free ? That will give a clue as to which chip is bad.

    What type are the RAM chips?

  4. #4

    Default

    That's an excellent point that I hadn't considered. Mine is an 8K model which definitely used to say "7167 bytes free." I'll look into the 6550 adapter -- possibly a good option -- and I'll get back to you soon. Thanks!

  5. #5

    Default

    Yes, this is my actual machine that I've owned since 1978. How can I determine what type of RAM chips I have? I am very comfortable opening up the case and looking inside, if necessary.

  6. #6

    Default

    Check this page: Troubleshooting Common Problems with the Commodore PET 2001. Not only you'll find more tips to help you in repair the machine, there's also a nice mainboard layout.

    The System RAM is located in the left side of the pic, if your model is the 8K one, it must be like the one pictured, with two full rows of RAM ICs each one with 8 chips. Every 2 ICs add 1KB so each row are 4KB total, two rows equals 8KB.

    Obviously if the RAM is installed in sockets, it's more or less easy to replace. If it's soldered, you'll face the first real problem, how to desolder the RAM. If you have experience with the solder iron there's no problem, if not, it's a daunting task.

    To narrow the problem you can try an easy trick, put your finger over every chip and if you find hot ones (very very hot!) you have probably a bad IC and a candidate to replace. If all of them are cold, there's also a small chance that the piggyback trick works to locate or even repair the machine. If you can find a known good working RAM IC, you can try to install it over every RAM chip in the mainboard carefully aligned (double check this) and boot the machine. If the bytes free shows the right amount you've found the only faulty RAM chip, if it changes but still shows the wrong amount, you could have find a faulty IC but there're probably more of them, keep it trying over every chip.

    I've at least repaired an old TRS-80 M1 with a piggyback and without desoldering the bad one, yep, a dirty hack; but the PCB was very fragile and I didn't want to risk it applying too much heat.

  7. #7
    Join Date
    Dec 2005
    Location
    Toronto ON Canada
    Posts
    7,213

    Default

    The troubleshooting guide referenced above is pretty good; especially read the section on RAM about half way down.

    The RAM chips are either type 2114 or 6550; 2114s are still fairly easy to find, working 6550s are in the hen's teeth category (although apparently those do exist: https://www.sciencedaily.com/release...0223083601.htm

    The PET RAM is arranged in pairs of 4-bit 1K chips, at the front of the board starting at the right; the PET itself uses the first 1KB, so only 1KB free would suggest that one of the two chips in the third column is bad.

    Before you do anything, try moving the chips a bit back and forth in their sockets; early PET sockets were notoriously bad.

    If you still only show 1K free, try (carefully!) one at a time removing each of the two chips in column 3 and replacing them with the ones from column 8.

    What happens?

  8. #8

    Default

    Hello,
    I agree it must be some of the RAM, but I also suggest you to try the RAM chips in the video ram position, that will quite easily identify the bad chips. You can look at myself dealing with RAM/ROM problems on a 2001:
    https://youtu.be/x9dgbeFQwew?t=157
    Also I agree on what MikeS said: the IC sockets on those motherboard are really bad, so try to carefully remove and re-insert the RAM chips.
    HTH
    Frank IZ8DWF

  9. #9
    Join Date
    Oct 2009
    Location
    Huntsville, AL
    Posts
    1,253

    Default

    Yep, I think you've got bad RAM.

  10. #10

    Default

    Since you have a basically working machine, you can use PEEK and POKE to locate bad RAMs you can then use the table in the referenced trouble shooting to find it on the board. Although, it is possible that a single byte location may be failing I suspect that the memory test use just looks at the first byte of the different RAMs. Most failures are a single bit or all the bits.
    Entering a decimal value, it may help to have a lookup table of a calculator that will translate between decimal and binary. A couple used pattern to use would be all 0, all 1's ( 255 ), alternating 10's ( 170 ) or 01's ( 85 ). It should be easy to POKE a value and PRINT the PEEK. If you have socket, you should be able to move them around to test suspicious ones. Do turn off the power when moving parts, being careful to note the pin one end orientation. Also check the alignment of the part to make sure all of the pins are in the socket correctly. Often original parts will have been inserted with an insertion tool. Since it is likely that you don't have such a tool, you may need to slightly bend the leads to make them slide directly into the sockets, if when removed, you find the leads slightly angled out. I usually do this on a hard surface but be careful not to over bend them.
    Dwight

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •