Broken H724 power supply from PDP-8/e

Marco Rauhut marco at
Wed Jan 7 22:58:23 CST 2015

I think it is the Crowbar to... The voltage when it is fireingis adjustable. One time if i want to adjust 5V i adjusted the crowbar to less 5V ... And bang! 20A was blown...

> Am 08.01.2015 um 04:10 schrieb Al Kossow <aek at>:
>> On 1/7/15 6:24 PM, Michael Thompson wrote:
>> The H724 power supply in my PDP-8/e works OK for about 5 seconds and then
>> the +5V output goes to about 3.0V. If I leave it on for a few more seconds
>> it will blow the 20A fuse for the +5V output.
> sounds like something is firing the crowbar (Q207)

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