PDP 11 gear finally moved

John Robertson jrr at flippers.com
Fri Jul 17 16:06:00 CDT 2015

On 07/17/2015 11:53 AM, Mouse wrote:
>> I do find this witch-hunt against capacitors to be curious, given how
>> few I've found to have failed.  I suspect a lot of it comes from
>> audiophools who think this is the way to fix anything...
> Perhaps.  But not all of it, certainly.  I'm currently four for four
> fixing dead flatscreens by re-capping their power supplies; I imagine
> others have similar experiences.  It's not a huge stretch to imagine
> that other power supplies may have similar issues; even if it turns out
> to not be the case, there is probably at least a little "can't hurt
> anything, right?" running around.
> /~\ The ASCII				  Mouse
> \ / Ribbon Campaign
>   X  Against HTML		mouse at rodents-montreal.org
> / \ Email!	     7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B

This is not surprising given the vintages of the machines. Modern 
machines using switching power supplies (15kHz+) must have capacitors 
with low ESR and high capacity to run properly.

Older linear power supplies ran at 50/60hz and as such the capacitors 
had much less ripple current (and low frequency to boot) to deal with 
and the engineers typically over designed the values of capacitors to 
allow for some degradation. The machines you are playing with cost 
fortunes back in the day - they HAD to be reliable as possible.

Modern caps run at or near their rated temperature (105C) last around 
1,000 to 5,000 hours. The old linear supplies rarely heated the caps 
much over 40C and thus the caps would last decades...I put fans on our 
LCD monitors in our games and they last just fine.

No fan? Expect a year or two at most before failure.

John :-#)#

John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
"Old pinballers never die, they just flip out"

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