Re: strange electrical issue - anyone have any knowledge of what to do.


Christopher Erickson
 

Sounds like there is a short in the power supply electronics to the frame ground.
 
Could be a wiring problem, a circuit board problem, a transistor insulator problem or a screw fastener problem (oversized screw head, too long, etc,)
 
My speculation is that the most likely cause is a mica power transistor insulator wafer is either missing or otherwise not working as designed for some reason and the case of the power transistor is directly connected to the power supply's frame ground.
 
Use a large USPS Flat Rate Priority Mail box to send it to me and I can find out for sure.  And pay another $15 to have me ship the repaired power supply back to you.
 
 
-Christopher Erickson
Observatory engineer
Summit Kinetics
Waikoloa, HI 96738
www.summitkinetics.com
 



From: ap-gto@... [mailto:ap-gto@...]
Sent: Friday, October 20, 2017 9:38 AM
To: ap-gto@...
Subject: RE: [ap-gto] strange electrical issue - anyone have any knowledge of what to do.

Jimmy,
 
Thank you for this.  I'm no electrical engineer, but I think I ran the test you suggested.
 
1) I set my meter to read DC volts.
 
2) I turned the PS ON.
 
3) I put the red meter lead on the red +13.8v DC screw terminal on the front of the PS, and the black meter lead on the chassis ground screw.  The meter read -11.72v,  not 0.
 
4) I put the red meter lead on the black -13.8v DC screw terminal on the front of the PS, and the black meter lead on the chassis ground screw.  The meter read -25.58v,  not 0.
 
So it looks as if I have a definite problem.  I don't see any obvious stray wires or strands.
 
Could this be caused by a bad cap or two?  Or am I just wasting my time with this thing?
 
Woody
 
 
 


I remember one member had warm cables back last year(?)

His DC power supply +13.8 V DC lug was touching the power supply chassis.

I think the current loop would be from
 +13.8 V DC to chassis to protective ground (green wire) to Desktop computer protective ground.
 The Desktop pc protective ground is connected to DC ground inside PC
 DC ground wire connects CP3/4 and then to the negative lug on 13.8V DC power supply completing the ground loop.
 
 With a DC voltmeter,
 I would check voltage from power supply chassis to it's negative 13.8 Volt lug at front and
 then chassis to positive lug on front of power supply.  Both should be 0 volts.
 
 The member from last year saw -13.8 volts from power supply chassis to negative lug on front of power supply.
 That means his +13.8 volt lug on front was shorted to chassis.
 
 As always, I may be! wrong again.
 
 Jimmy
 


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