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  • Nivag Swerdna's Avatar
    September 5th, 2020, 07:27 AM
    Yeap the hinge appears good. I guess I will have to try and get physical with it at some stage.
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    September 5th, 2020, 05:03 AM
    Away from the electronics I have a physical issue with the case... at some point in its previous life the bracket at the back has been bent so the...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    September 5th, 2020, 04:19 AM
    It's been a while but I had to wait for a 74LS157 and some DIP16 sockets... Firstly, an admission :sigh: I looked very very hard at the reset...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 30th, 2020, 04:34 AM
    From memory, it is flatline low and independent of nRESET. I'm pretty confident that I have a problem with the 74LS157 at D2 and that could explain...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 30th, 2020, 02:15 AM
    I noticed that when started from cold the nIRQ line appears to be flat lined but on soft restart I see periodic (blanking period) interrupts. ...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 28th, 2020, 05:59 AM
    I am not making any material progress but... I removed H8 and H9 the buffers to the onboard RAM section... no change. And I replaced CR3 the...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 27th, 2020, 12:18 PM
    In the screen images above one of them shows a PC of 371F which clearly doesn't sound feasible.... and the screen images show corruptions... which...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 27th, 2020, 12:25 AM
    I did try freeze spray before, particularly on the 75154 and 6x 74LS244s but could not see any change in signals or behaviour. I don't have the...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 26th, 2020, 12:24 PM
    I checked out some signals at the VIA socket and CS1, nCS2, RA0, RA1, RA2 & RA3 look OK. Checked some other signals and again cannot spot...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 26th, 2020, 10:54 AM
    Yeap... it doesn't boot to a cursor but a soft reset will reset it to the cursor state and workable with the VIA removed. I also tried the original...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 26th, 2020, 08:38 AM
    I measured nRESET versus phi0... and zoomed in... So clock happily running before nRESET goes high
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 25th, 2020, 01:31 PM
    I haven't tested anything yet... it was an acknowledgement that I need to. :D
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 25th, 2020, 10:00 AM
    re:XTAL OK I received my replacement VIA, I ordered... https://www.mouser.co.uk/ProductDetail/955-W65C22S6TPG-14 and just put it in... and things...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 25th, 2020, 09:41 AM
    Well it was my day off so I have tried a few things... and although I have made no material progress I made a few changes... I changed the 74LS04...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 25th, 2020, 08:19 AM
    I have a RAM/ROM memory, NOPulation board of my own design which has a reset switch...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 25th, 2020, 07:56 AM
    For the sake of it I changed the timing capacitor C5 1uF tant and C6 .1uF and C14 .01uF ceramics... no change to behaviour... the only things left in...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 23rd, 2020, 05:53 AM
    Here's the state so far... VIA out, PIAs out... Added VIA... machine won't boot... black screen.... VIA (or associated circuitry problem) ...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 23rd, 2020, 05:15 AM
    One thing I did notice is that I got garbage at the lower screen on one restart... and I saw inconsistent restarts into the tester before... is there...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 23rd, 2020, 03:40 AM
    I measured video outputs whilst on the bench and there is something coming out of video... so putting board back into case... Current state is...
    160 replies | 6935 view(s)
  • Nivag Swerdna's Avatar
    August 22nd, 2020, 02:03 PM
    I think you might be right about the beat frequency.... I really don't know... I do know that for very infrequent samples (slow timebase) then fast...
    160 replies | 6935 view(s)
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About Nivag Swerdna

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About Nivag Swerdna
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London, UK
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Technical Consultant - Computing - Distributed and Embedded Systems

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