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Electronics => Repair => Topic started by: sweatybetty on August 05, 2021, 04:52:05 pm

Title: HP 8640B power supply problem
Post by: sweatybetty on August 05, 2021, 04:52:05 pm

Hello all!
Picked up a 8640b last week. Not getting any output nor am I getting +44V. I think I have that part figured out.
While looking through the FSM, I found a term I have never seen before and am hoping someone can enlighten me to the meaning or point me in the right direction. The term is "crowbar"
It is shown on the schematic and in the troubleshooting section as well.
Appreciate the help!

Title: Re: HP 8640B power supply problem
Post by: TimFox on August 05, 2021, 05:09:40 pm

A crowbar is a fast-acting circuit that shorts the output should the voltage exceed a threshold, to protect the load or regulator.  It’s analogous to throwing a crowbar across the third rail on the subway.

Title: Re: HP 8640B power supply problem
Post by: sweatybetty on August 09, 2021, 02:45:37 pm

Thank you Tim.
I found more info after changing search words around :-+