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Thread: PC6300 no longer POSTs

  1. #71

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    Or I could devote the funds to a better spam filter.

  2. #72
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    The solid lights, then blinking lights, means the CPU is running through POST, which generally means the board is still worth salvaging. If you got zilch or no flashing lights, that would be "bad".

    If you hook up a "laptop diagnostic code" diag board to the parallel port (extended conversation here), the 6300/M24 POST outputs various checkpoints to the port. I have a system that outputs 43h and then nothing else, and looking at the BIOS source code (contained in the "System Programmer's Guide AT&T Personal Computer 6300" PDF), I can see that's right before the 8237 DMA chip test, so I know I probably have to replace the DMA chip on that board someday.
    Offering a bounty for:
    - The software "Overhead Express" (doesn't have to be original, can be a copy)
    - A working Sanyo MBC-775, Olivetti M24, or Logabax 1600
    - Documentation and original disks for: Panasonic Sr. Partner, Zenith Z-160 series
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)

  3. #73

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    Many thanks Jimbo.

  4. #74
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    With thanks form Trixter I have received a board that is "better". It's still not a fully working board but it at least initiates POST.

    The tester by the way indicates it hangs up at 45h, so either it starts testing the base ram and runs into bad ram (?) or it's actually stuck on a Programmable Interrupt Controller fault. I will have to swap some IC's from the dead board to see if I can rule out the PIC but for ram......the tip on my Weller 5088AS is shot and I do not know where to find replacements anymore. Would piggybacking be of any use?
    = Excellent space heater

  5. #75

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    Dollar stores often sell soldering iron. you may have to find the old kind of dollar store. My weller lost its plating. Poc.

  6. #76
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    Yeah, it's not that kind of Weller. This station was around $560 at one point.
    = Excellent space heater

  7. #77
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    Quote Originally Posted by NeXT View Post
    With thanks form Trixter I have received a board that is "better". It's still not a fully working board but it at least initiates POST.
    Sorry about that -- it was untested, but glad it gets further than your other board.

    The tester by the way indicates it hangs up at 45h
    According to the BIOS source listing (page 8-90 of the System Programmer's Guide), it outputs 45h when it has completed everything it considers fatal, then puts the original vector table back in place at the first 1024 bytes of RAM, then determines system settings from DIP switches, then enables video, then displays all of the tests that passed onscreen.

    Have you verified the DIP switches are set correctly on the board?
    Offering a bounty for:
    - The software "Overhead Express" (doesn't have to be original, can be a copy)
    - A working Sanyo MBC-775, Olivetti M24, or Logabax 1600
    - Documentation and original disks for: Panasonic Sr. Partner, Zenith Z-160 series
    - Music Construction Set, IBM Music Feature edition (has red sticker on front stating IBM Music Feature)

  8. #78
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    Oh, by no means am I complaining it doesn't fully POST yet. I'm already further ahead than I've been in over half a decade.

    Have you verified the DIP switches are set correctly on the board?
    Likely no. I think I defaulted them to the base config for the Hackery's M24 board but I believe its ram arrangement was different. I will have to double check those tonight.
    = Excellent space heater

  9. #79
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    Verified and properly set the dip switches to reflect the hardware and ram config (640k onboard, with 512K on bank 0 and 128K in bank 1, no NPU, one 360K floppy, 8250 UART, 80x25 Monochrome display and no ISA cards installed)

    No change. 45h, blinking keyboard LED's and nothing on the screen.



    Went over the board and verified all other jumpers were good and swapped in the known good 1.43 BIOS EPROMs and PAL chips. Replaced the battery damaged power LED and replaced the reset button as only one contact side was working. Also verified continuity on the dip switches. Still nothing.
    Last edited by NeXT; November 8th, 2018 at 07:23 PM.
    = Excellent space heater

  10. #80
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    *Squishes bug with thumb*

    Got it.

    I thought about how Trixter said the machine progressed once 45h was passed and if it was not reaching display initialization and was not reaching the programming of the keyboard controller and it could not be hanging on the dip switches the only thing that it could hang on is the vector relocation in ram, indicating the first bank of ram could have a problem.

    Bank 0 is 18 of the usual 1-bit 256k DIP chips with 16 pins. Bank 1 is 18 64k chips. I've seen configurations where these were flipped and others were it was all in sockets but on this machine it's all soldered in so testing ram is a pain in the ass. I've never really tried piggybacking as the mileage seems to vary wildly but I had nothing to lose here so I fit in 18 chips and tried again. It worked.



    Through the very careful process of elimination I pulled chips one at a time until it failed to POST again. Eventually I found one chip would fail every time the piggyback was removed.



    Okay then. I guess I will have to see if I can get one last shot out of the tip on my weller and we should be good to go. Thanks Trixter!
    Last edited by NeXT; November 9th, 2018 at 08:05 PM.
    = Excellent space heater

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