Re: need a bit of early boot help

On 11/11/25 05:52, Johnny Billquist wrote:
>>> And VMS also hangs after printing a banner... Which would suggest 
>>> that there is something funny either with the printing on the 
>>> console, but which is interrupt related, or something else is getting 
>>> the machine stuck at an elevated privilege mode, preventing 
>>> interrupts from being processed.
>>>
>>> I would actually probably suspect something else isn't completing, 
>>> and the processor is stuck at some elevated prio. The console is 
>>> probably working just fine, including when interrupt driven. But 
>>> something else is not.
>>>
>>> I assume we're talking about a real machine here. So it has actual 
>>> Unibus. Simple suggestions would be to remove everything not 
>>> absolutely required to get the machine running, and really make sure 
>>> you have bus grants in all Unibus slots not having a card in it. 
>>> Also, make sure the NPR jumper is in place. This one can be a bit 
>>> tricky, since it's actually a wire on the back side of the backplane, 
>>> which might have been cut. There a double height bus grant cards that 
>>> also covers the NPR signal, but the small square ones do not.
>>>
>>> And if the Unibus isn't properly configured, you can probably get 
>>> things hung/stuck for some time.
>> It's a 780, Unibus is not involved here at all :-)
>> The PDP11 is connected directly to the backplane (SBI).
> 
> Well. Yes an no.
> The PDP11, which is the FE, don't have any Unibus at all. And the 
> machine boots, and there is terminal I/O to the console, and the system 
> starts running.
> 
> But something happens somewhere along the way. And the *VAX* have a 
> Unibus, and it will be probed somewhere along the way, and that is where 
> I wonder what might be going on.
> 
> I don't think there are any problems at all with the PDP11 FE.

    [I had sent this last night, but it didn't make it to the list, 
presumably due to the attached photo...sending without the photo this time]

    Summary: IT RUNS!

     The problem was in the CIB board, a failed 74S74 flip flop in 
interrupt handling.

    We'll post pics and such soon.

    Thanks everyone for the guidance.  We'll try booting VMS on it later 
tonight, temporarily from the VAX-11/750's system disk.  If all goes 
well there, we'll set up permanent system disks for it for VMS, NetBSD, 
and possibly Ultrix-32.

    Incidentally, this is the same '780 that Gunther Schadow had quite a 
saga with on this very mailing list, back in 2002.  To my knowledge he 
never did get it running.  We fixed a number of hardware problems in 
this machine, so it's no wonder he'd had such a tough time with it.  It 
was many months of work, off and on, over several years for us here at LSSM.

                -Dave

-- 
Dave McGuire, AK4HZ
New Kensington, PA