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MattisLind's latest activity

  • MattisLind
    MattisLind replied to the thread VT100 keeps blowing main fuse.
    I have had the “instantly blowing fuse” in a few VT100 terminals. As far as I remember this has always been the main switch transistor...
  • MattisLind
    MattisLind replied to the thread DEC H7441 5V regulator repair.
    What kind of temperature on Q5 are we talking about? Sometimes it is hard to target one single component by spraying it. It might be...
  • MattisLind
    MattisLind reacted to wh3016's post in the thread Restoring a DEC PDP-11/05 with Like Like.
    Good news everyone- The power supply works again. Q7 seems to have failed and triggered the crowbar circuit. Last night I swapped it...
  • MattisLind
    The method I have been using succesfully with around 100 TU58/DC100 and a few DC300 is to use a heatgun at lowest temperature. Perhaps...
  • MattisLind
    MattisLind replied to the thread Restoring a DEC PDP-11/05.
    The 8/M (and 8/F) uses the same type of supply. +5 and -15 is switched PSUs. +15 is linear. The switching is hysteresis switching so...
  • MattisLind
    MattisLind replied to the thread Restoring a DEC PDP-11/05.
    Is it connected to the machine? Verified that there is no short-circuit in the machine? Use a bench PSU and try to feed it from. It...
  • MattisLind
    MattisLind replied to the thread Restoring a DEC PDP-11/05.
    You should use a dummy load and check the supplies. It has been discovered that the power supplies behaves very badly if the output...
  • MattisLind
    MattisLind replied to the thread Restoring a DEC PDP-11/05.
    Here is the relevant part of the schematics. You need extenders to properly access the signals. I think it is a pretty good...
    • 00DBEC70-BB2E-47F6-BFC9-2822B5799934.png
  • MattisLind
    MattisLind replied to the thread Restoring a DEC PDP-11/05.
    You have clock signals that looks ok about right. Now you need to look at the microaddresses. /Mattis
  • MattisLind
    MattisLind replied to the thread Restoring a DEC PDP-11/05.
    Right. Then there are clocks! check the signals on E10, E64 and E84. What is the state of CK OFF signal? In my experience 7440 buffers...
  • MattisLind
    MattisLind replied to the thread Restoring a DEC PDP-11/05.
    You have to change the timebase to something like 500 ns / division. I have no clue what I am seeing.
  • MattisLind
    MattisLind replied to the thread Restoring a DEC PDP-11/05.
    BTW. Sometimes it can be useful just to probe with the oscilloscope and find signals that are sitting on levels that are not really...
  • MattisLind
    MattisLind replied to the thread Restoring a DEC PDP-11/05.
    Looks like there i no clock. Now you need to figure out why.. First I think that you should check on the oscillator itself. At E39:8...
    • Screenshot 2022-07-27 at 07.04.44.png
  • MattisLind
    MattisLind replied to the thread Restoring a DEC PDP-11/05.
    You are right. The front panel is connected to the datapath. There is a 74150 that selects a bit to serialize over the connection to the...
  • MattisLind
    MattisLind replied to the thread Restoring a DEC PDP-11/05.
    Ok. Then the problem is not the display. You need to get a board extender to raise the control board so that you can probe it. Douglas...
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