[HECnet] No connectivity to arsgea 4

[Dave McGuire]

   Sigh, yes, we all know of exceptions.  But even then, I doubt it can 
be proven that those PDP-11 systems in production since the early 80s 
have never had components replaced.

   Not everything is built to DEC standards.  That said, all my life 
I've been replacing chips, diodes, transistors, capacitors, and 
sometimes even resistors in DEC gear.  It does happen, and it's not 
uncommon.

   The regulator bricks in the H742/H7420 power supplies tend to blow 
Zener diodes.  That's fresh in my mind because we just lost another one 
at the museum recently.  Those are failing with such frequency now that 
I've purchased stocks of the components that tend to fail. (we have a 
lot of those at the museum)  And those ARE built to DEC standards.

   Speaking of not being built to DEC standards, I've got a Heathkit H8 
on the bench right now, I'm repairing it for a new exhibit at the 
museum.  Four failed (non-moving!) ICs replaced so far, it's very nearly 
done.

             -Dave

On 1/22/21 12:03 PM, Johnny Billquist wrote:
> Well, I know of PDP-11 systems out in production who have been running 
> since the early 80s. The only thing that fails is the damn RD53...
> Replaced those about 20 years ago now. The rest of the machine was 
> running just fine. At that at a steel mill, so not exactly a friendly 
> environment. Last I heard, things were still running, but it might have 
> been replaced by now. But anyway, it's the moving parts that cause 
> problems. The rest usually just keep running...
> 
>    Johnny
> 
> On 2021-01-22 17:53, Dave McGuire wrote:
>> On 1/22/21 11:41 AM, Thomas DeBellis wrote:
>>> 10 years used to be nearly unheard of for retail machines with moving 
>>> parts.  When nothing is moving, then supposedly there is nothing to 
>>> burn out.
>>
>>    I don't know who told you that, but he/she knows jack point squat 
>> about electronics.
>>
>>    Materials migration and diffusion across junctions causes 
>> semiconductor components to fail, tin whiskers cause shorts, some 
>> types of capacitors dry out and/or have their electrolyte deteriorate 
>> or crystallize, resistors drift, heat/cool cycles cause PCB flexure 
>> resulting in cracked solder joints, corrosion in air creeps into 
>> connector pin interfaces and forces pins apart, the list goes on and 
>> on and on.
>>
>>    To be fair, some of the above-listed failure modes do in fact 
>> involve things moving, though imperceptibly so, my point stands.
>>
>>                -Dave
>>
> 


-- 
Dave McGuire, AK4HZ
New Kensington, PA