PDP-11 with ATX power supply

js at cimmeri.com js at cimmeri.com
Sun Mar 8 11:03:36 CDT 2015

On 3/7/2015 10:38 PM, Earl Evans wrote:
> Hello fellow DEC enthusiasts,
> I have a BA11-N mounting box with Q18 9-slot quad-height backplane. The
> power supply is toast. My goal is to hack it into something useful.
> I'd like to replace the power supply with a sufficiently-powered ATX PSU.
> I've read the instructions at:
> http://www.diane-neisius.de/pdp11/index_E.html#atx
> However, unlike the DEC PSU, the ATX power supply won't supply a 60 Hz line
> time clock (LTC) signal to the backplane via BEVENT. So, my question - has
> anyone used a standard ATX PSU for a PDP-11 QBUS system, and if so, how'd
> you work around the LTC issue?
> Once I solve the power issue, I have 11/23 CPU cards, RAM, and SLUs galore.
> I'm not planning to make this very power hungry though.
> Thanks!
> - Earl

Earl, I did an ATX conversion on my 
BA123 to dual 500W ATX PSUs.    I used 
Brad Parker's QBus POR device for 
generating the LTC, but am not sure on 
current availability as past emails to 
him have gone unanswered.


A trick is that his LTC output is open 
collector, thus needs a pullup unless 
your backplane provides.

- J.

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