PDP-11/94-E

[Paul Koning]

> On Jun 3, 2016, at 10:33 AM, Rod Smallwood <rodsmallwood52 at btinternet.com> wrote:
> 
> 
> On 03/06/2016 14:58, Jerry Weiss wrote:
>> On Jun 1, 2016, at 8:39 AM, Jerry Weiss <jsw at ieee.org> wrote
>>> …..
>>> Have you checked the Unibus supply voltages?
>>> …
>>>    
>> As a rule-out make sure the Unibus cards are getting power correctly.   The Power Supply sounds like is fine and powering the QBus side of things, but if the connections to the Unibus backplane are wonky it might create symptom that the cards don’t exist.   Note: I’m not referring to the AC and DC LOW that Paul K mentioned earlier  (which also are good items to check), but just the raw power to the backplane.
>> 
> Measured at the MLM  -14.8v and +4.98

That's probably close enough.  But I remember from DEC that some Unibus cards don't obey the power tolerance specs.  The spec is +/- 5% which is common.  But some, the DMC11 is an example if I remember right, will not function reliably unless the voltage at the connector is at least equal to the nominal value.  In other words, they want -0% to +5%.  We had a machine that wouldn't work right, and the FS engineer went around with a voltmeter tweaking all the supplies until they were set a hair above nominal.  At that point the machine was fine.

	paul