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    How about the Lunar Lander? Did it work with...

    How about the Lunar Lander? Did it work with BASIC 4? I've been looking for it. Is it strictly command line or does it have some graphics like the PC version?
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    Congratulations on fixing this machine. What was...

    Congratulations on fixing this machine. What was the finally tally on bad 6550 RAM and 6540 ROM?

    I think BASIC 1 hanging without a 6522 is due to checking the Video On (SYNC) signal going to input...
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    OK, you have BASIC 1 with the Revised H1 ROM. I...

    OK, you have BASIC 1 with the Revised H1 ROM. I forgot what Revision 1 fixed, but I think the IEEE488 its still not fully functional.

    If you have a lot of bad 6540 ROMs and 6550 RAMs, then you may...
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    What is the part number on the H1 ROM? Is it...

    What is the part number on the H1 ROM? Is it 901439-01 or 6540-011, then you have BASIC 1. If 901439-09 or 6540-19, then you have the the revised version of BASIC 1. If 901439-13 or 6540-020, then...
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    So it looks like the 6522 VIA was keeping the PIA...

    So it looks like the 6522 VIA was keeping the PIA from issuing the 60 Hz IRQ? I suppose that is possible. You will need to replace the 6522 with a new one and try it again as there may be timers in...
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    You must fix the display raster logic before the...

    You must fix the display raster logic before the RAM/ROM replacement will do you any good. Can you get a scope photo of the Vertical Drive (J7-pin3)? What signal on the D8 NAND seems stuck?
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    daver, excellent point as I'm not sure the OP...

    daver, excellent point as I'm not sure the OP checked the data lines when the NOP Generator was installed?
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    Yes, check the 40 pin sockets on the CPU and...

    Yes, check the 40 pin sockets on the CPU and PIA#1 (G8 ) very carefully. They do go bad. Then make sure there is a 60 Hz pulse at G8-pin18 input. The PIA is setup to issue an interrupt when there is...
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    Robert, Great articles. Thanks for posting. Do...

    Robert,
    Great articles. Thanks for posting. Do you know how one purchases the video called 'Growing the 8 Bit Generation'?
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    Dwight, You are right. The Tynemouth board will...

    Dwight,
    You are right. The Tynemouth board will get him on the air soonest. But as he has mentioned, he has purchased the older replacement board with more test options which will allow him to map...
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    Remember that in the $E000-$EFFF memory space not...

    Remember that in the $E000-$EFFF memory space not many addresses will output data. The bus will be mostly tri-state and the voltage may be around the input level of a 6502 gate, maybe 1.6 V.
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    Happy Holidays to Mike and all at the Commodore...

    Happy Holidays to Mike and all at the Commodore forum.
    -dave_m
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    Dwight, I missed that suggestion. What message...

    Dwight,
    I missed that suggestion. What message number was it?
    -Dave
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    Also check that the signals through the address...

    Also check that the signals through the address buffers are the same as the input. The address signals through the Screen address mux (D2, D3, and D4) will be a bit harder to check.
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    Yes, this is important. It means the CPU does...

    Yes, this is important. It means the CPU does start running for a short period. The CPU can hang up if it executes an illegal KIL instruction. This may possibly be due to a lot of low RAM not working...
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    Sad day for all Commodore PET enthusiasts.

    Sad day for all Commodore PET enthusiasts.
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    Yes, that will do it as long as cap is removed as...

    Yes, that will do it as long as cap is removed as it may be shorted.

    You never know when a component will come in handy.:p
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    With the symptoms, I'd have bet the house that...

    With the symptoms, I'd have bet the house that the 555 timer was bad.
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    Andy, What is the Supersoft board? Should the OP...

    Andy,
    What is the Supersoft board? Should the OP disconnect it until the PET is functional?
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    Dwight, Op is a new member, and his posts are...

    Dwight,
    Op is a new member, and his posts are reviewed which causes a delay.
    -Dave
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    OK, then Sync (pin 7) low means the CPU is not...

    OK, then Sync (pin 7) low means the CPU is not fetching instructions and is hung up. This usually means one of the ROMs is bad or something has caused CPU to execute in RAM area and it hit an illegal...
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    Ditto Daver and Dwight. A diagnostic EDIT EPROM...

    Ditto Daver and Dwight.
    A diagnostic EDIT EPROM will perform sum checks on every 4K blocks of ROM (two of your ROMs). That will tell us quite a bit about the functionality of the ROMs. Also it will...
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    If it turns out that you have a lot of faulty RAM...

    If it turns out that you have a lot of faulty RAM (6550) and ROM (6540) and have no viable spares, you may have to consider the Tynemouth RAM-ROM replacement module that fits in the CPU socket....
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    Please post a large photo of the screen only....

    Please post a large photo of the screen only. From what i can see so far, we on the forum should help you fix this problem.
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    The random data is correct on power up. A blank...

    The random data is correct on power up. A blank screen may just mean your CPU is not running in program yet. A checkerboard pattern is not good. It means the video RAM is outputting all ones ($FF)....
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