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Thread: 32k PET 2001-N - Video and running issues

  1. #21

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    @daver2 , I wanted to try this also. What kind of Eprom would you recommend burning this to? Probably need an adapter socket for a 27xx?

  2. #22
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    Quote Originally Posted by Hutch View Post
    @daver2 , I wanted to try this also. What kind of Eprom would you recommend burning this to? Probably need an adapter socket for a 27xx?
    For the EDIT ROM socket only, you can use the following without any adapter: 2716, 2516

    And due to a quirk in pinouts, you can also use a 2732 without adapter as long as you put the 2K image into the upper 2K of the 4K EPROM, address $0800 to $0FFF.

    For the other ROM positions, you must use a 2532 with no adapter, or a 2732 with an adapter to swap a few signals.

    -dave_m
    Last edited by dave_m; June 29th, 2019 at 12:46 PM. Reason: Added info on ROMs other than EDITOR.

  3. #23

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    Quote Originally Posted by daver2 View Post
    Wonderful!

    Well, from cold start, that gives me a beautiful incrementing character display followed by lots of Gs... However, subsequent restarts and the CPU seems not to start. Something's still up in there. I'm going to have a good look at the reset circuit soon. In the meanwhile, check out the next post..

  4. #24
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    Just beat me to it Dave!

    Bog standard single-rail 2716 - no adapter required at all. It goes into thecEDIT ROM socket of course.

    Post a picture of the results and I will walk you through the tests (until I get some time to finish the documentation!

    Dave

  5. #25
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    Ah, if it 'sticks' on the G/g screen you may notice the odd non-G/g character (i.e. Indicating a B/b - bad - memory location)...

    Dave

  6. #26

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    (TLDR: If you are interested in troubleshooting the CRT but don't care about the rest, jump down to the last paragraph.. )

    Moving to the CRT itself... Wow.

    I had done some serious cleaning in here previously because, as I indicated, an entire nation of mice seem to have spent generations living in the monitor housing. The fur, feces, and corpses (bones really) were removed a a few years back when I decided to kick the tires on this thing. However, the board itself has always been exceedingly difficult to remove because the standoffs were completely corroded by mouse urine and the wires to the yoke must be desoldered or the entire yoke removed... All in a pretty small housing (9" CRT). Add to this my general aversion to working with high voltage vacuum tubes (I used to repair 19" CRTs in the late 1980s)...

    Anyway, given the video weirdness, I decided it was time to wrestle this beast to the ground. Upon removing the board, it became apparent that there's a *lot* of damage to components and the board. I should have taken a separate photo of the heat sink, but you can see the amount of mouse chewing damage to it in this photo, to some extent:
    IMG_3091.jpg

    Still, that's just the start. Between the years of soaking in mouse urine and the exceptionally long through-hole parts (I think the person who assembled this board either didn't care or it was his first day. I just went through and trimmed the legs... These things were, seriously, 1/4" to 3/8" out of the bottom of the board. A fair number were bent over, contacting or nearly contacting others.. Not good...), the legs of some of the transistors actually look to be delaminating (!! I've never seen this before... It's as though there are "splinters" of metal pulling away from the legs). Additionally, the wires to the yoke are pretty well chewed on with more than 30% of the plastic insulation gnawed through. I couldn't really see that before since it was all packed into the chassis. Surprisingly, the wires other than the ones to the yoke look untouched... Maybe a different chemical in the sheathing?? (Not as tasty?)

    I've taken some before and after shots.. They really don't do it justice.
    Before:
    IMG_3089.jpgIMG_3090.jpgIMG_3092.jpgIMG_3093.jpgIMG_3094.jpgIMG_3095.jpg

    After some serious scrubbing, a vinegar bath to neutralize any remaining urine "stuff", followed by a good dowsing with 99% alcohol to finish it all off:
    IMG_3096.jpgIMG_3097.jpgIMG_3097.jpg

    You might have noticed that I've removed all (but one... oversight) of the electrolytics. This was for cleaning (lots of space under them) and as a preventative measure. I did notice the following...

    With the PETTESTER in the Kernal socket, I had a great picture... and the longer it was on, the more there started to be a bit of a "wave" in the sides of the image... Not a moving wave.. Instead, the warmer it got, the more the entire screen developed a subtle sine-wave appearance that was noticeable at the sides if you looked. I take from this that there's a heat related something happening, but I'm not super sure what to look at next. In the meantime, I'm recapping it and I'm going to see if I can locate all of the transistors that look very sketchy.

  7. #27

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    Quote Originally Posted by daver2 View Post
    Ah, if it 'sticks' on the G/g screen you may notice the odd non-G/g character (i.e. Indicating a B/b - bad - memory location)...

    Dave
    Oh! I didn't let it run that long since I was noticing a bit of a static vertical wave down the sides as it got warmer.. which lead me to flip it on and off, after which the CPU didn't seem to restart.

  8. #28

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    Quote Originally Posted by daver2 View Post
    Just beat me to it Dave!

    Bog standard single-rail 2716 - no adapter required at all. It goes into thecEDIT ROM socket of course.

    Post a picture of the results and I will walk you through the tests (until I get some time to finish the documentation!

    Dave
    If you have any 2532s, they work great too. Larger than you need, but they work fine and seem to be less hard to find.

  9. #29

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    Hey-

    Does anyone know where I can find the BoM/Parts List for the 9" CRT board? I don't see it on Zimmers; they have the schematic and a board layout, but not the parts list as far as I can see..

    Some of these parts are very tough to read with the years of mouse urine.

  10. #30
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    Quote Originally Posted by dhoelzer View Post
    If you have any 2532s, they work great too.
    It is not good practice to use the 4K 2532 EPROM in the 2K EDITOR socket with the Model 2001 PETs. They are chip enabled over the entire $E000 - $EFFF address space and may interfere with the I/O devices at $E8XX due to bus contention.

    This problem is inhibited in the PET Model 4000/8000 with the 'Universal' board so 2532s are OK for the EDITOR socket on those computers.

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