Re: need a bit of early boot help

On 11/27/25 12:05, Anders Magnusson wrote:
>>    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.
> Cool! Real hardware fix!
> 
> How did you manage to find the failing chip?  I.e. the error isolation 
> process? :-)

   Well, the big break was information on this list, that the first 
character of the line where it stalled was the first thing printed with 
interrupts.  That quickly led us to the console TX interrupt flip flop 
on the CIB board.  Three of us looked at the schematics that night, 
separately at home, and all reached the same conclusion.

   Booting VMS on the machine told us nothing, but the NetBSD kernel is 
far more verbose.

   The microdiagnostics specifically flagged the M8230 (CEH) as being 
bad, but it was the CIB.  Now the M8230 tests pass too.

             -Dave

-- 
Dave McGuire, AK4HZ
New Kensington, PA