PDP 11 gear finally moved

Tothwolf tothwolf at concentric.net
Wed Jul 22 10:11:33 CDT 2015

On Wed, 22 Jul 2015, tony duell wrote:

>> Given that a typical aluminum electrolytic capacitor costs anywhere 
>> from $0.12-$0.15 (4mm or 5mm diameter radials) to about $1.00 (12mm or 
>> 16mm diameter radial), it also doesn't make much sense to desolder a 20 
>> year old part, spend at a minimum 5 or more minutes testing it, and 
>> then solder it back in. It it much more economical to pull the old part 
>> and install a new one and be done with it. (You also don't have to 
>> worry if the desoldering and resoldering process might have damaged the 
>> original parts end-seals.) That said, I personally pre-test new parts, 
>> in bulk, before I
> I don't remove parts unless they have something to do with the problem I 
> am solving. If the power rails are the right voltage with sufficiently 
> low ripple then I look elsewhere for probkems.
>> put them into my stock, so I know ahead of time that I'm installing 
>> known-good parts.
> You claim that electrolytics deteriorate with time whether used or not. 
> How do you know the ones you install haven't deteriorated since you 
> tested them?

When I pull capacitors from a board, I put them into numbered trays for 
testing. Each new part also gets another quick test before installation 
and the results of both get entered into a spreadsheet (along with date 
codes, part numbers, and any other data I have on hand). I did this 
initially for mission critical boards so I could provide the data to 
customers who needed that level of detail, but I later started doing this 
for all repairs because I found it wasn't all that difficult to do once I 
already had a system in place. When I'm testing old parts, I also note 
things like leaky seals, corrosion around the terminals, etc. Because of 
the historical data I've collected, I can also tell from my notes that 
there are definitely certain brand/series (both vintage and modern) which 
have common issues.

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