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  • daver2's Avatar
    May 21st, 2017, 11:55 PM
    daver2 replied to a thread RK11-C / RK05 restore in DEC
    Fritz, you are 'the man' :-). Nice work! Dave
    51 replies | 3521 view(s)
  • daver2's Avatar
    May 21st, 2017, 11:59 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    I think what you have said is basically correct (if I understand correctly what you wrote)... Basically, IC51/52/53/68 and IC13b form a frequency...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 21st, 2017, 10:07 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    Give me a short while and I will reply with a detailed (but simple I hope) description of how the Nascom 2 video circuitry works. I will be...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 20th, 2017, 12:04 PM
    daver2 replied to a thread Multibus open hardware? in Other
    Our stuff is not 'open' but I will talk to my bosses and see if I can make the files for the Multibus 1 backplane available in the first instance. ...
    22 replies | 531 view(s)
  • daver2's Avatar
    May 19th, 2017, 11:51 PM
    daver2 replied to a thread Multibus open hardware? in Other
    Andrew, All of our Multibus nodes are diskless. They boot over a network from a host machine (non MULTIBUS). A small EPROM (located on the CPU...
    22 replies | 531 view(s)
  • daver2's Avatar
    May 19th, 2017, 11:31 PM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    I wouldn't worry too much about what you are seeing on the scope. As long as you have something around the correct frequency and voltage levels you...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 19th, 2017, 06:42 AM
    daver2 replied to a thread Multibus open hardware? in Other
    We still run MULTIBUS 1 equipment at work. In fact, I am re-manufacturing some of it as we speak (a 4-port intelligent synchronous/asynchronous...
    22 replies | 531 view(s)
  • daver2's Avatar
    May 18th, 2017, 12:14 PM
    Welcome to VCFED! Dave
    1 replies | 53 view(s)
  • daver2's Avatar
    May 18th, 2017, 08:07 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    So, I've been re-acquainting myself with the NASCOM 2 video circuitry and there is a possibility that there may not be a 'fault' with your NASCOM!...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 18th, 2017, 06:57 AM
    daver2 replied to a thread PDP-8/I at the RICM in DEC
    Ditto - sounds interesting... Dave
    6 replies | 418 view(s)
  • daver2's Avatar
    May 18th, 2017, 06:48 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    It 'should' be 16 MHz (as marked on the crystal). Can you modify the timebase a bit to get only one cycle on the screen horizontally and reduce...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 17th, 2017, 11:30 PM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    Excellent - it is not the line synch. pulse then! The fact that the text on the screen moved wholescale to the right effectively rules that out. ...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 17th, 2017, 07:01 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    I concur. Assuming the timebase indication of 10 microseconds per division - the 15 kHz clock looks OK but the pulse seems longer than the datasheets...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 17th, 2017, 01:41 AM
    daver2 replied to a thread PDP SBC - J11 Hack in DEC
    Thanks for the correction Don. You are perfectly correct. The text in red is incorrect. (a) That will teach me for writing things late at night......
    126 replies | 9203 view(s)
  • daver2's Avatar
    May 16th, 2017, 01:13 PM
    daver2 replied to a thread PDP SBC - J11 Hack in DEC
    I think the confusion may be what we are referring to as 0 and 1 possibly. 'True' RS232 (I will avoid TTL RS232) defines the 'idle' or 'default'...
    126 replies | 9203 view(s)
  • daver2's Avatar
    May 16th, 2017, 11:30 AM
    daver2 replied to a thread PDP SBC - J11 Hack in DEC
    No problem - just wanted to make sure others reading the thread many years in the future get the right information. That's why I love debugging...
    126 replies | 9203 view(s)
  • daver2's Avatar
    May 16th, 2017, 10:32 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    I was just looking at the schematic again and I had another 'lightbulb' moment. Can you do what's in the previous post first though... Can you...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 16th, 2017, 10:07 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    Right, back from work, had tea, ready to debug... IC52 pin 13 should have a frequency of 15.625 kHz on it (= 64 microseconds between the high to...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 16th, 2017, 04:01 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    Excellent. So it sounds like we have isolated the problem to the video circuitry. I still think it has something to do with the line...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 15th, 2017, 07:07 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    Sorry, been in meetings all day... To convert from time to frequency take the reciprocal of it: 1 second = 1 Hz 0.5 seconds = 1/0.5 = 2 Hz...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 15th, 2017, 06:38 AM
    daver2 replied to a thread PDP SBC - J11 Hack in DEC
    Just to clear up a little issue. A BREAK character and a NULL character are not the same thing. A NULL character is a valid serial frame...
    126 replies | 9203 view(s)
  • daver2's Avatar
    May 14th, 2017, 02:46 PM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    Ok. We know one thing that it isn't then! The CPU just writes into a shared piece of memory. It is hardware that takes what is stored in this...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 14th, 2017, 07:59 AM
    daver2 replied to a thread PDP 11/45, Part 5 in DEC
    That's in the back of my mind Marty! The 'big three' are screw type so they can be replaced easily later with just a screwdriver. My plan is to...
    300 replies | 19439 view(s)
  • daver2's Avatar
    May 14th, 2017, 05:23 AM
    daver2 replied to a thread PDP 11/45, Part 5 in DEC
    Well done Fritz and thanks for the encouragement! I have just pulled out one of my 5V regulators and looking to make a start on refurbishing that,...
    300 replies | 19439 view(s)
  • daver2's Avatar
    May 11th, 2017, 09:35 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    Well done that man :-)! Gut feeling tells me to swap out IC57 (SN74LS123) and/or C21/C22 to sort out your 'shift left by 1 character' issue. ...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 9th, 2017, 04:55 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    You should get activity on both pins 1 and 2 of the I/O decode PROM (IC 26) - so yes, this looks suspect. But note that pins 13 and 14 of this...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 8th, 2017, 09:29 AM
    Those values look fine. A few mV sounds remarkably good even! If you don't have L1 or C61 - then which of the 5V supplies feed the devices that it...
    19 replies | 646 view(s)
  • daver2's Avatar
    May 7th, 2017, 11:56 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    Had the same problem myself a few years ago with an Apple IIe disk controller. Some of the IC pins had been 'eaten through' but looked OK to the...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 7th, 2017, 07:41 AM
    daver2 replied to a thread Nascom 2.Troubleshooting in Other
    No sitting on the sidelines! This looks 99.9% to be keyboard related, so either the keyboard is 'simulating' a key press or (as SiriusHardware has...
    57 replies | 1888 view(s)
  • daver2's Avatar
    May 5th, 2017, 06:16 AM
    daver2 replied to a thread PDP SBC - J11 Hack in DEC
    Well done. That was what I was going to get up to tonight - but you have beaten me to it... At least getting XXDP to run once indicates it will...
    126 replies | 9203 view(s)
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SW/HW design engineer

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