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  • daver2's Avatar
    Yesterday, 10:55 PM
    daver2 replied to a thread Repair of a PET 4032 in Commodore
    As this is your first post, welcome to VCFED. I am way too far away from you (being in the UK) but you have come to the right place! Let's hope...
    4 replies | 59 view(s)
  • daver2's Avatar
    Yesterday, 10:49 PM
    daver2 replied to a thread Help testing PDP-11/73 in DEC
    You shouldn't require any cards at all (other than the CPU and an external serial card if the CPU doesn't have one) to get ODT up and running. We did...
    6 replies | 96 view(s)
  • daver2's Avatar
    Yesterday, 03:05 PM
    I thought he ha the same sense of humour as me :-). ave.
    6 replies | 66 view(s)
  • daver2's Avatar
    Yesterday, 08:54 AM
    >>> And just to be clear, every other key on the boar works fine and comes up on the screen. It's just the one, so it has to be an issue with just...
    6 replies | 66 view(s)
  • daver2's Avatar
    March 19th, 2019, 11:44 PM
    +1 for Chuck's isolating transformer. Be safe! Dave
    16 replies | 187 view(s)
  • daver2's Avatar
    March 19th, 2019, 11:37 PM
    Hi, and welcome to VCFED (as this is your first post). There is a very long series of threads on fixing an O1 with a duff key. If you look at my...
    6 replies | 66 view(s)
  • daver2's Avatar
    March 18th, 2019, 04:05 PM
    >>> The Z80 was used in millions of CP/M computers. So it looks like an oddity for me that there is still no any CP/M version optimized for the...
    28 replies | 387 view(s)
  • daver2's Avatar
    March 18th, 2019, 12:15 AM
    daver2 replied to a thread Vintage years. in General Off Topic
    I sat on our company's Y2k committee and the numbers of equipment that failed the tests that we required for operation of our plant was quite large....
    7 replies | 145 view(s)
  • daver2's Avatar
    March 17th, 2019, 03:52 AM
    Hi Rob, Yes, I have learnt the hard way a few times that for a long or complex post you are better off editing your post outside of VCFED then...
    154 replies | 34174 view(s)
  • daver2's Avatar
    March 16th, 2019, 03:26 PM
    daver2 replied to a thread Nascom in Other
    I'll catch up with your posts tomorrow. Yes, the NASCOM 1 suffered from contention when accessing the video RAM at high speed (as you are doing)....
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 16th, 2019, 09:09 AM
    daver2 replied to a thread Nascom in Other
    Very interesting Mr. Spock... Having the 74S04 installed in IC9 is another modification to alleviate memory plague. I therefore suspect that...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 16th, 2019, 05:34 AM
    daver2 replied to a thread Nascom in Other
    Thanks for the vote of confidence Ziloo... Yes, that part of the movie was an absolute classic moment! Debugging computer systems used to be my...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 16th, 2019, 04:56 AM
    Well done, I was just thinking this morning on my walk that I hadn't heard back from you in a while. So, it was most likely the original and...
    77 replies | 4196 view(s)
  • daver2's Avatar
    March 16th, 2019, 04:16 AM
    daver2 replied to a thread Nascom in Other
    So, I can't see anything physically wrong with your RAM 'A' card scans. The 8K ROM BASIC upgrade seems to follow that as described - with the...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 15th, 2019, 03:26 PM
    daver2 replied to a thread Nascom in Other
    I thought you were a bit quiet today... No problem, you need to prioritise your work! It is a good idea to scan the cards though. I have had a...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 15th, 2019, 07:43 AM
    daver2 replied to a thread Nascom in Other
    The next thing to look at is the 4K and 16K decode logic on the RAM board. To do this, enter a very small program into memory via NAS-SYS and...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 15th, 2019, 07:20 AM
    daver2 replied to a thread Nascom in Other
    Ok, so I have reacquainted myself with the schematics. The problem is unlikely to be the 81LS97s on the RAM board. The ROM and RAM have separate...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 14th, 2019, 01:07 PM
    daver2 replied to a thread Nascom in Other
    81LS95 vs 81LS97 device. The 81LS97 is a dual 4-bit tristate buffer. It has two active low enable pins. Pin 1 enables the first half of the...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 14th, 2019, 10:51 AM
    On a project I am currently working on - we have some wire-wrap configuration posts on one of the cards we are remanufacturing. The PCB assembly firm...
    154 replies | 34174 view(s)
  • daver2's Avatar
    March 14th, 2019, 08:23 AM
    daver2 replied to a thread Nascom in Other
    The 7402 is associated with the address decoding for the BASIC ROM. Thanks for the photographs - the wire links make complete sense to me - although...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 12th, 2019, 08:42 AM
    Ditto for me. Dave
    16 replies | 429 view(s)
  • daver2's Avatar
    March 12th, 2019, 08:39 AM
    daver2 replied to a thread Nascom in Other
    Page 12 of https://80bus.co.uk.mirror.jloh.de/publications/magazines/INMC_news_5.pdf#page=13 describes the RAM A modification to add the 8K ROM BASIC...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 12th, 2019, 08:27 AM
    daver2 replied to a thread Nascom in Other
    Documentation at https://80bus.co.uk.mirror.jloh.de/pages/nascom/rama.htm. Yes, there was a 'bodge' to convert one of the 1K EPROM sockets to...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 12th, 2019, 07:12 AM
    daver2 replied to a thread Nascom in Other
    Thanks. So the first thing I would look for is the 4K block address decode logic implemented by the RAM A card. I haven't got access to the...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 12th, 2019, 01:45 AM
    daver2 replied to a thread Nascom in Other
    So when you say the NASCOM is 'losing' much of its available RAM, what do you mean? If you have RAM up to $0FFF - then this is the on-board SRAM. I...
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 9th, 2019, 12:02 PM
    daver2 replied to a thread Nascom in Other
    If C17 is broken - I would replace it. It is in the cassette demodulator circuit. I don't think it has a major function to play - but just in case......
    223 replies | 15511 view(s)
  • daver2's Avatar
    March 9th, 2019, 11:52 AM
    daver2 replied to a thread DECtapes on Ebay. in DEC
    And that's exactly what the German to English translation says as well... Dave
    2 replies | 183 view(s)
  • daver2's Avatar
    March 8th, 2019, 01:40 PM
    daver2 replied to a thread Nascom bad again in Other
    IC2 should NOT be enabled if nothing is plugged into the external NASBUS. Either you have a faulty 81LS95 or something driving it is faulty. What...
    10 replies | 413 view(s)
  • daver2's Avatar
    March 8th, 2019, 07:14 AM
    daver2 replied to a thread PDP-11/10 with TU60 on Ebay. in DEC
    Just thinking the same myself - although shipping to the UK will be somewhat prohibitivly expensive! Dave
    7 replies | 317 view(s)
  • daver2's Avatar
    March 7th, 2019, 01:32 PM
    daver2 replied to a thread Nascom bad again in Other
    This is the info I have found on the Nascom 1 buffer board: https://nascom.wordpress.com/nascom/hardware/nascom-1-2/buffer-board/ >>> Really wish...
    10 replies | 413 view(s)
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About daver2

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About daver2
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UK - Worcester
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SW/HW design engineer

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