Image Map Image Map
Page 2 of 2 FirstFirst 12
Results 11 to 16 of 16

Thread: really strange issue on C64

  1. #11
    Join Date
    Dec 2012
    Location
    São Paulo country, Brazil
    Posts
    728

    Default

    I did some steps ahead.

    I found a couple of bad solders, redone, and now -at least- it's booting. But now I have a couple of issues:

    1) the drive doesn't work. I tried with the SD2IEC emulator, that works fine in the VIC-20, but no results here. BTW the 6526 should be ok, I swapped U1 and U2 and the keyboard still works.
    Remember that the first problem I had was the computer didn't boot if U2 was in place!

    c64-4.jpg

    2) Color issue: lines of different color.
    c64-5.jpg

    the following picture shows the problem better. I changed the 2114 chip and also the two 4066 ICs (I remember that I got a similar problem and I solved changing one of the two 4066. Well, not this time).
    c64-6.jpg

    Any idea? Quite tired tonight, I won't do further tests for now!

    --Giovi

  2. #12

    Default

    Well... I've never been so lucky as you are whenever I started pulling chips as an attempt to repair something. You know, the chance is that you introduce hidden problems. C64 pcbs are of rather low quality and are easily damaged.
    However, IEC bus, if U2 is working can be affected by U8, R28 to R30 and CR100 to CR105 and of course any bad connection between these parts, the chips and the connector. All the IEC bus can be easily tested with only a multimeter, a logic probe and/or an oscilloscope. Or you can replace random parts and introduce new problems, and so on
    About the color problem, it's quite strange. I would suspect the VIC-II addressing lines and their paths, U15, U27 and their interconnections. Can you peek() all the color ram memory range and verify that it reads all the same value?
    There's a whole lot of knowledge that can be derived from studying the schematic and poke-ing/peek-ing around to verify assumptions. You seem to like too much the soldering iron as a troubleshooting tool (which is not).

    Frank

  3. #13
    Join Date
    Dec 2012
    Location
    São Paulo country, Brazil
    Posts
    728

    Default

    Quote Originally Posted by iz8dwf View Post
    Well... I've never been so lucky as you are whenever I started pulling chips as an attempt to repair something. You know, the chance is that you introduce hidden problems. C64 pcbs are of rather low quality and are easily damaged.
    However, IEC bus, if U2 is working can be affected by U8, R28 to R30 and CR100 to CR105 and of course any bad connection between these parts, the chips and the connector. All the IEC bus can be easily tested with only a multimeter, a logic probe and/or an oscilloscope. Or you can replace random parts and introduce new problems, and so on
    About the color problem, it's quite strange. I would suspect the VIC-II addressing lines and their paths, U15, U27 and their interconnections. Can you peek() all the color ram memory range and verify that it reads all the same value?
    There's a whole lot of knowledge that can be derived from studying the schematic and poke-ing/peek-ing around to verify assumptions. You seem to like too much the soldering iron as a troubleshooting tool (which is not).

    Frank
    Frank, you're absolutely right when you say I uses the iron solder too much... I should to learn something more about hardware.

    So I tried to resist to fire it up, LOL, and just testing the connections on pcb I found the serial bus issue: the previous owner cut a trace, probably with a screwdriver. Honestly I didn't connected a 1541 to this C64 before, so I discovered the problem just now.

    about colour ram: I found what seemed to be a bad joint on a 2114 pin (or 4066? I don't remember...). Then I redone it and the problem was almost solved. I say almost, because sometimes, after a long time, a similar problem appears (I already closed it into its case because it seemed it was ok... )


    So I tried to poke and peek the colour ram address, but the result wasn't what I expected... I tried the same program in a VIC 20 (of course changing the memory address) with the same result.

    C64-3.jpg
    I expected the peek instruction always returned the same value written with the poke command. But it returned different values in both computers (C64 and VIC20).

    Where I'm going wrong?

    --Giovi

    EDIT: I tried with VICE, it returns the same error.
    Last edited by giobbi; June 16th, 2019 at 01:54 PM.

  4. #14
    Join Date
    Mar 2012
    Location
    Augusta, Georgia, USA
    Posts
    663

    Default

    Peeking color RAM will give you back random results, because only 4 (half) bits are connected. The other bits will always have random bus noise.

    Are you sure you tested the PLA as working in another C64? Some boards also don't work 100% with some PLAs.

  5. #15

    Default

    Correct: to get the expected results you must PEEK()AND15.

  6. #16
    Join Date
    Dec 2012
    Location
    São Paulo country, Brazil
    Posts
    728

    Default

    Quote Originally Posted by KC9UDX View Post
    Correct: to get the expected results you must PEEK()AND15.
    Thank you, it's working fine now.

    The annoying color problem apparently has gone; yesterday I play a lot with it, no issue. I believe it's some kind of oxide related issue, or some bad solder joint. I will keep testing, to see if it appears again, I don't trust in problems who solved alone...

    --Giovi

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
  •