Mike's PCjr Page

I have a few PCjrs I have collected over the years (including the original one my father bought back in the day) and I got my jrIDE working and booting DOS 5.0 on one machine (more on that later). So, I thought I would try to troubleshoot one of the machines I've been getting a double beep on.

I started off removing one thing at a time and trying to boot inbetween to see if that would reveal the problem. First floppy, then floppy controller then IR, and finally RAM board. Double beep all the way. Then I swapped out the power supply. Double beep. Read in a thread that the basic cartridge being in could sometimes have an effect but still gets a double beep.

So I added the power attachment and jrIDE from the working machine to get the POST code and got a double beep with a post code of 'F6'.
I read in a different thread that the post codes are in The Technical Reference manual but I can't find them in there. Closest I could find the contents listing "Power-On Self-Test" was on page A-7. But that is all assembly and I fear I don't know assembly.

Does anyone have a list of the error codes and/or let me know what F6 means.

I would also love any other troubleshooting steps people would recommend.

Thanks!

P.S. I suppose it could also be an 'Fb' instead of an 'F6'.

Two-beeps-no-video means that an early part of the POST failed and a basic function of the system needed for video isn’t working.

So is the POST code `Fb` or `F6`? That makes a difference. Is the top, horizontal segment of the digit lit? That would make it a `6`. Your uncertainty makes me think you’re seeing a `b`.

The technical reference does contain the POST codes and their meanings, but only in the BIOS source code. You have to look at the source code to see what the tests are and what the results mean. The comment blocks before each test help.

That said, there’s an internal IBM document that lists all the codes and their meanings.

If you’re getting `FB`, that indicates a bad RAM chip on the motherboard. A code of `F6` points to a problem with your 8253 timer chip.

Quoting from the document:

Code: Select all

MANUFACTURING ERROR CODE        SERVICE CODE            CUSTOMER LEVEL CODE
------------------------        ------------            -------------------

...

      FB04XX (FVT/PFT TESTER)   2 BEEPS                      2 BEEPS
      ??04XX (BURN-IN/RUN-IN)   -------                      -------
      ------
        MEMORY ERROR ON PLANAR BOARD MEMORY. XX=BITS IN ERROR (ANY BIT
     "ON" IN "XX" IS A FAILING BIT (I.E., CHIP)

...

      F608XX (FVT/PFT TESTER)   2 BEEPS                      2 BEEPS
      F508XX (BURN-IN/RUN-IN)   -------                      -------
      ------
        8253 TIMER ERROR.
        XX=00 STUCK BITS IN TIMER 0
        XX=01 TIMER 1 CANNOT BE CLOCKED BY TIMER 0
        XX=02 TIMER 0 INTERRUPT (LEVEL 0) FAILED
        XX=03 STUCK BITS IN TIMER 1
        XX=04 TIMER 2 OUTPUT HIGH WHEN IT SHOULD BE LOW
        XX=05 STUCK BITS IN TIMER 2
        XX=06 TIMER 2 OUTPUT DOES NOT GO HIGH WITH TERMINAL COUNT

It is indeed a 'b'.

Thank you DoctorOctal!