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Thread: CBM 8032 Resurrection Project

  1. #11

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    Quote Originally Posted by dave_m View Post
    You say you did not detect any pulses on the CRTC chip select (UB13-pin25)? You can keep the logic probe or counter (set to TTL) on this line while you quickly ground the RESET line at UB13-pin2, or at the expansion connector J4-pin22 to the pin opposite (all grounds). A wire wrap jumper is good for this.

    There will be about 34 pulses on the line to select 17 register addresses and write 17 bytes of data. If you catch a pulse, then replace the 6545.
    Hi Dave

    Did the above and can report that the CS on UB13 is permanently high and stays that way even when doing a manual reset. I looked at UD2 and UE13 and can see BA7 pulsing, but no activity on x8xx or I/O
    Nor does the unit chime when powering up, so I am guessing it is not running any meaningful code at start.

    The plot thickens!

    Pip

  2. #12

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    MODP5165_S- Copy.jpg

    IMG_1645_TS - Copy.jpg

    IMG_1646_S - Copy.jpg

    For a bit of context, here are some photos of the sick puppy.

  3. #13
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    Initializing the I/O is one of the first things done, so your CPU is not getting far. If data and address lines toggling as you say then you may have a bad low RAM chip (A5, A7, A9, A11, A13, A15, A17 and A19) or a bad Kernal ROM (UD6) or a bad EDIT ROM (UD7). Things to try: PETTEST2KV4 2716 EPROM in the EDIT socket (UD7) as it does not rely on good RAM to start, a NOP Generator to confirm good addressing and data lines. Replace kernal ROM with 2532 EPROM.

  4. #14
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    What's that extra chip in UD12? Might as well remove it for now.

  5. #15

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    Quote Originally Posted by MikeS View Post
    What's that extra chip in UD12? Might as well remove it for now.
    UD12 ROM is for a dot matrix printer.

    The ROMs present are:
    UD6 = 901465-22 KERNAL for BASIC 4
    UD7 = 901474-04 Screen editor for BASIC 4, business keyboard, CRTC, 80 columns, 50 Hz
    UD8 = 901465-21 d000 BASIC 4 ROM
    UD9 = 901465-20 c000 BASIC 4 ROM
    UD10 = 901465-23 b000 BASIC 4 ROM
    UD11 = Emptey socket
    UD12 = 901472-04 4022 (Tractor Feed) Printer

    UD7 is a 2716-5 which I will be looking at more closely as it is ~40 years old going by the date codes on the other chips, so maybe it has lost some of it's contents. Again due to lock-down I don't have access to an EPROM programmer. If push comes to shove I will purchase a cheap one from eBay or Amazon. But I am thinking the computer would still do something even with a dodgy UD7 ROM?

    Thanks for taking time to comment MikeS

    Cheers
    Pip

  6. #16
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    Quote Originally Posted by Pipcicle View Post
    UD12 ROM is for a dot matrix printer.
    I think you'll find that this is actually used as copy protection for the Visicalc program; in any case always a good idea to remove any non-critical chips while troubleshooting.

    See:
    http://www.zimmers.net/anonftp/pub/c...her/index.html

    The ROMs present are:
    ...
    Looks good

    ... I am thinking the computer would still do something even with a dodgy UD7 ROM?
    Not necessarily.

    What do you see if you disconnect the video signal to the monitor?

  7. #17

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    Quote Originally Posted by MikeS View Post
    I think you'll find that this is actually used as copy protection for the Visicalc program; in any case always a good idea to remove any non-critical chips while troubleshooting.

    See:
    http://www.zimmers.net/anonftp/pub/c...her/index.html



    Looks good



    Not necessarily.

    What do you see if you disconnect the video signal to the monitor?
    Looking around it would appear that the 901472-04 is a printer ROM that was somehow used as copy protection for VisiCalc

    See:

    http://cbm-hackers.2304266.n4.nabble.com/Looking-for-the-elusive-quot-Expanded-VisiCalc-v1-76a-for-the-Commodore-8096-quot-td4665323.html


    It could be either or both as my PET came with a floppy disk drive and a dot matrix printer, and the previous owner most likely used a spread sheet, but yes I will remove the ROM as you suggest.

    The disk drive and printer will be the next restoration project.

    Without the monitor attached I am still not seeing any VSYNC so it is not being held down by the monitor itself, if that is what you were thinking.


    Pip

  8. #18

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    Quote Originally Posted by daver2 View Post
    >>> First of all, I have to say that this forum is awesome. I only posted the thread a few minutes ago.

    We try!

    A frequency counter will be very useful if you need to build a NOP generator...

    I just connect my analogue multimeter between 0V and the /RESET pin of the CPU and power up the PET. The value should stay low for a short period after power-up and then go high.

    You could have a duff CRTC - but the data writes to the CRTC could also be faulty - or the data bytes initialising the CRTC (stored in the EDIT ROM) could also have become corrupted. Just thinking of various scenarios to check.

    Two useful things in your arsenal to fault find are:

    A NOP generator. This is a couple of 40 pin sockets sitting between the CPU and the processor socket 'forcing' NOP instructions ($EA) onto the data bus of the CPU.
    My PETTEST code burnt into a 2716 EPROM to replace the EDIT ROM. I will have to provide a link to this later.

    Dave
    Hi Dave
    Could you direct me towards the binary for the PETTEST ROM that you mention. I would like to burn an EPROM and pop this in the computer and see what happens.

    Cheers
    Pip

  9. #19
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    Quote Originally Posted by Pipcicle View Post
    Looking around it would appear that the 901472-04 is a printer ROM that was somehow used as copy protection for VisiCalc
    Didn't I just say that? Sheesh!

    It has nothing to do with any disk drives or printers (except that it is a printer ROM that Commodore probably had a lot of and was happy to find another use for).
    Last edited by MikeS; April 8th, 2020 at 10:03 AM.

  10. #20
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    >>> Could you direct me towards the binary for the PETTEST ROM that you mention. I would like to burn an EPROM and pop this in the computer and see what happens.

    Sure can...

    https://drive.google.com/drive/folde...cx?usp=sharing

    Dave

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