Image Map Image Map
Page 7 of 7 FirstFirst ... 34567
Results 61 to 65 of 65

Thread: PET 2001-32N - Diag works in UD9, but with Kernal it fails to start

  1. #61

    Default

    Quote Originally Posted by dave_m View Post
    I would be suspicious of oscillations in RESET circuit. Check the 555 timer (A2) and capacitors C66, C67 and C68. This PET has some fascinating issues.
    Nope, I've looked at that super carefully. The 555 side of the inverter looks perfect. I'll break out the USB microscope soon to look over the traces.

  2. #62

    Default

    Quote Originally Posted by dave_m View Post
    This PET has some fascinating issues.
    That's what comes of 30 years marinating in mouse urine. It's clearly not good for electronics.

    That said, it appears that the waveform matches pin 3 on UC3, but has a difference in magnitude. This could be just coincidence, but I don't think so. I see a resistance of about 56,000 ohms between pin 3 on UC3 and pin 12 on A10. It climbs very slowly, so it seems almost certain that a capacitor somewhere is involved.

  3. #63

    Default

    Quote Originally Posted by dhoelzer View Post
    That looked ok. +5 on one side, 200khz signal on the other.
    And the value of R30 is still what is supposed to be, just checking?

  4. #64

    Default

    Quote Originally Posted by iz8dwf View Post
    And the value of R30 is still what is supposed to be, just checking?
    It appears to read as 470 ohms, which is correct.

  5. #65
    Join Date
    Feb 2009
    Location
    Southern California, USA
    Posts
    2,646

    Default

    Quote Originally Posted by dhoelzer View Post

    it appears that the waveform matches pin 3 on UC3
    That C3 (LS244) output is Buffered Address 1 (BA1) which should be similar to the input on C3-pin 17. The source there is A1 from the CPU (C4-pin 10). One of these signals is being coupled to the Reset signal.

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
  •