> On Jul 2, 2025, at 8:48 PM, Jon Elson via cctalk <[email protected]>
> wrote:
>
> On 7/2/25 11:25, Paul Koning via cctalk wrote:
>>
>>> On Jul 2, 2025, at 11:13 AM, Jon Elson via cctalk <[email protected]>
>>> wrote:
>>>
>>> On 7/2/25 06:08, P Gebhardt via cctalk wrote:
>>>> Dear list members,
>>>>
>>>> I was wondering if anybody is aware of VAX 86x0 schematics having survived
>>>> the product life cycle within DEC? I searched the web extensively but
>>>> could not find any hints on this.
>>>> It seems that DEC never published such details as schematics for the
>>>> successor of the VAX 11/78x systems, not even on microfiche, maybe due to
>>>> the macrocell array implementation (just a guess). All I could find is
>>>> that there were illustrated parts list on microfiche.
>>>> However, maybe Hewlett Packard handed DEC-internal documents over to a
>>>> museum such as the CHM? Or a former designer still have schematics in
>>>> their archives?
>>>> Any pointers would be greatly appreciated!
>>> I did have a KA630-AA print set at one time. That was about the latest
>>> prints I have seen.
>>>
>>> Jon
>> That makes some sense. Print sets were needed in older machines because FE
>> would actually replace failed components on a board. With "swap the failed
>> board" repair procedures, it isn't all that useful for support engineers to
>> know how a board works, much less what the detailed circuitry looks like.
>
> Yes, we had an FE replace components on an 11/45. But, they certainly NEVER
> did component-level repairs on an 11/780 or uVAX-II.
>
> Jon
The last one I remembered was an 11/45 also, an MMU data path failure. We
(Josh Rosen and I) diagnosed it while waiting for the DEC FE to show up. Josh
pointed to a particular chip (we had found a stuck bit somewhere in the MMU)
and Jim asked why that particular chip. The answer "because that's the most
expensive one in the signal path". Jim said "we'll see" but shortly afterwards
pulled out his parts box, soldering iron, and solder sucker to remove -- yes
indeed -- that particular chip. :-)
Once DIP chips started being replaced by PGA or other hard to replace parts,
replacing them on site became impractical. I suspect someone also did the
economics analysis to show that carrying a set of boards, diagnosing to the
failed board only, and swapping the board in question was faster and easier.
Of course it led to jokes like this one:
FE is driving down the highway. Suddenly, the ride gets very rough. He
mutters "must be a flat tire", pulls over, puts on the spare. He drives away,
car still goes "bump bump bump". He grumbles "I guess it wasn't that tire" and
pulls over again to swap one of the other tires.
paul
