Weird Behaviour of VAXstation 4000 Model 60 Power Switch

Peter Coghlan cctalk at
Sun Apr 12 14:20:22 CDT 2020

> This machine acts oddly. After powering it off, you usually can't power it
> back on again for about 30 seconds or so, it just seems to ignore the power
> switch. Similarly, if it has been switched off at the front power switch, it
> will switch itself on after maybe a minute of two of being switched off. In
> all other respects the machine seems fine. I have not opened up the PSU at
> all, just wondering if anyone has ever seen this and might know what the
> problem is?

Not quite the same thing but I have noticed that many DEC power supplies
will sulk for a while if their overload trip is triggered.  Switching them
off and on again straight away is not enough to reset them even though the
overload is cleared.  The H7821 seems to need to be switched off for around
16 seconds minimum before it will contemplate coming to life again.  I have
come across similar behaviour with the power supplies in various other small
VAX and Alpha machines but I have not measured the exact time period
involved in any other cases.

Peter Coghlan.

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