PDP 11 gear finally moved

Mike Stein mhs.stein at gmail.com
Tue Jul 21 22:52:19 CDT 2015

----- Original Message ----- 
From: "Tothwolf" <tothwolf at concentric.net>
To: "General Discussion: On-Topic and Off-Topic 
Posts" <cctalk at classiccmp.org>
Sent: Tuesday, July 21, 2015 9:46 PM
Subject: Re: PDP 11 gear finally moved

> On Tue, 21 Jul 2015, Mike Stein wrote:
>> FWIW I'm certainly not about to spend 100s of 
>> dollars, not to mention time spent in sourcing 
>> and replacing, to replace the caps in systems
> 100s? Where are you sourcing your components 
> from? The typical board I rebuild has a 
> component cost of about $20 or less. Smaller 
> switchmode PSUs with a bunch of 10-18mm radials 
> might be closer to $35-50. Larger PSUs /might/ 
> cost closer to $100 if they have several large 
> screw terminal capacitors in them. All things 
> considered, that isn't very much money in 
> today's dollars, and considering the full 
> replacement cost of some of these boards (if 
> they are even available), those preventive 
> maintenance costs are an absolute bargain, 
> /especially/ if you are doing the work yourself 
> on your own time.

Maybe it isn't much money in your world, 
especially when someone else is paying. I just 
priced the main power supply caps in one of my 
Cromemco systems and it comes to ~ $120 (and all 
special order of course); if I replaced all the 
caps in all my (working) systems as you and a few 
others are suggesting across the board regardless 
of the system, condition etc., it would easily 
exceed $2000 if I could even find suitable 
replacements. And what about those prone to 
explode tantalums while we're at it...

If you're recapping 20-year old or newer circuit 
boards for customers as you apparently are then it 
does indeed often make sense to replace all the 
aluminum electrolytics, especially if the board 
has problems or there's visual evidence of 
failure, but let those of us with older, 
well-working systems use our _judgement_ whether 
to replace or not. OK?

To each his own...

>> that are running perfectly "just in case"...
> How do you -know- they are "running perfectly"?

They reliably do what they're supposed to do.


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