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Thread: PETunia's Repair Log

  1. #21

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    Quote Originally Posted by dave_m View Post
    This is indicating .75V of noise. This seems way to much for TTL if it is real. Where was your scope return for these measurements?
    I was using Pin 22 of one the empty 6550 sockets. I did wonder 750mV is quite some ripple.

    I will try that other ROM test... looks good.

  2. #22
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    Quote Originally Posted by Nivag Swerdna View Post
    Isn't that like asking a lady her age; I would never divulge. I did buy it on eBay earlier in the year... so you could search the sold listings.
    Well thats an absurd answer. I paid $275 for mine which was broken. And why would i search the sold listings when i can easily ask you directly? Whats the big deal with saying how much you paid????

  3. #23
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    Good spot about the pk-pk noise Dave - I missed that...

    So, there is nothing fundamental wrong if you can get someone else's PETTESTER to work. We just have to smoke out the metal mouse...

    Dave

  4. #24

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    OK... I burnt the PETTESTER into something I could put in H3.... and put the original MOS / MPS 6540 / 018 4478A aka rom-1-f800.901439-07.bin back into H7.
    I have just I1/I2 and J1/J2 populated with 6550s
    and turned on...
    FirstScreen.png
    ROM B is changing... not unsurprising since I think that part of the memory map is unpopulated?
    I am a bit uncertain about the ROM F checksum.... I am pretty sure the F000 ROM contains... rom-1-f000.901439-04.bin and F800 ROM contains... rom-1-f800.901439-07.bin; if I take those two .bin files and combine them and then put the 4K result into HxD I get
    Checksum-16: 0CA4 which is what appears on the screen?
    after a while it goes to...
    Capture2.PNG
    which although not very clear says MEM FAIL 0 0 0800 04 CC
    which I think means $0800 = 2k; and given I have 4x 1k x 4bit is about right.
    The PDF suggested their was a previous screen.... I didn't see it! On the first screen I saw in the KBD section which actually displayed as K@D the numbers were 17s.... I tried pressing keys.. but they stayed at 17s.

    On the subject of voltage rail ripple... does that suggest a bad main filter cap? Should I replace it? with?
    Last edited by Nivag Swerdna; July 28th, 2020 at 01:18 PM.

  5. #25
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    Quote Originally Posted by Nivag Swerdna View Post
    OK... I burnt the PETTESTER into something I could put in H3.... and put the original MOS / MPS 6540 / 018 4478A aka rom-1-f800.901439-07.bin back into H7.
    I have just I1/I2 and J1/J2 populated with 6550s


    ROM B is changing... not unsurprising since I think that part of the memory map is unpopulated?
    Good info, yes ROM at $B000 is empty. Key board is controlled by PIA #1 at G8. Is it in place or removed during this test?

    which although not very clear says MEM FAIL 0 0 0800 04 CC
    which I think means $0800 = 2k; and given I have 4x 1k x 4bit is about right.

    On the subject of voltage rail ripple... does that suggest a bad main filter cap? Should I replace it? with?
    Yes it passed up to $0800 of RAM which is all you have installed at this time. All OK with RAM.

    As far as filter cap, you may have to make an AC voltage measurement to find out. The +5 V regulator should have handled a modest amount of ripple as its input is +9 VDC unregulated.

    With good ROM and $800 of good low RAM, it should have gone further in boot sequence, strange.

  6. #26
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    Quote Originally Posted by Nivag Swerdna View Post
    I was using Pin 22 of one the empty 6550 sockets. I did wonder 750mV is quite some ripple.
    That should be a good place. Make sure the contact is good. All the old PET sockets are are notorious for being intermittent.

  7. #27

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    Quote Originally Posted by dave_m View Post
    Key board is controlled by PIA #1 at G8. Is it in place or removed during this test?
    I checked and G8 was not present! Sorry been playing the Hokey Cokey with chips recently... anyway B8 was fitted but G8 was out.
    I populated G8 and the Keyboard reports 00 00 00... 00 etc... and pressing a key shows a number e.g 02 or 04 somewhere... looks hopeful.
    I then swapped G8 and B8 (I think G8 faces left marked 40 on the board... B8 I think faces right)... but this produces Kbd D7 D7..... D7 and if wobble the chip I can get FFs and D6s and other combinations. So either that PIA is bad or maybe crusty pins.

    Oh... and with the monitor warmed up the initial screens show up as described in the manual... that looks OK.
    Last edited by Nivag Swerdna; July 28th, 2020 at 02:58 PM.

  8. #28

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    Quote Originally Posted by VERAULT View Post
    Well thats an absurd answer.
    Sorry. I did not mean to offend.

  9. #29
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    You are under no obligation in this forum to quote the price you paid although I would have told him $50 at a flea market and it would have made him cry!
    -Dave

  10. #30
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    Yes, the initial page appears to have some extraneous ".." and "K@B" which is clearly wrong. However, the initial tests (which passed) checked out the video RAM - so the errors are probably 'video output' related.

    The assumption is a minimum PET with 4K - so if you only have 2K of RAM installed then the first memory test it tries would fail (as identified). I would suggest adding the other RAM devices at some point and running the exhaustive memory tests for a while...

    Some of the screens will only stop if they detect an error. In my view, if the software doesn't detect any errors, it just carries on. The problem I have is one of assuming the keyboard interface works (if I wait for a keypress) and then I have the problem of the different key mappings for the various flavours of PET, keyboard type and internationalisation. Only one key (the RUN/STOP key) is common to all keyboards! OK, I could use the RUN/STOP key...

    You are very close - so there must be either a power supply related issue, a bad contact or an intermittent ROM/RAM causing your problems.

    Dave

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