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HP 16700 PSU in 230V region woes

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alan.bain:
I think I may have a slightly different version.  The secondary feed here is definitely to U1 - at least removing U1 removed the low Z to ground seen at the 390uF capacitor C18 (in honestly my first guess was a leaky capacitor) and continuity checks C18 +ve is connected to pin 15 of U1.

Seems logical really - usually the reason for an aux supply is to run the controller for the next stage.

nctnico:

--- Quote from: FrodeM on June 02, 2024, 01:45:28 pm ---
--- Quote from: alan.bain on May 31, 2024, 11:04:26 pm ---I've got a dead one here also in 230V-land.  R30 (the 10 ohm series resistor in aux power has exploded). Looks like the TOP223Y has also had a bad day and possibly also U1 (UC3854) as resistance to earth between pins 15 and 1 is about 35 ohms.  Do you have a service manual?
--- End quote ---

No, but I did draw up some schematics of the aux supply a few years ago. Those are available on Bitsavers:

https://bitsavers.org/test_equipment/hp/167xx/Celestica_7000_Aux_Power_Regulator_Schematics.png

--- End quote ---
Thanks for sharing. However, are you sure D6 is the right way around? It has been a long time ago I used a Topswitch device but I remember the datasheet being adament to clamp the voltage on the switching node. With D6 the way it is (assuming it isn't a zener diode), that won't happen which could cause the margins to be slim if this is a universal voltage design.

FrodeM:

--- Quote from: nctnico on June 04, 2024, 10:18:51 pm ---Thanks for sharing. However, are you sure D6 is the right way around? It has been a long time ago I used a Topswitch device but I remember the datasheet being adament to clamp the voltage on the switching node. With D6 the way it is (assuming it isn't a zener diode), that won't happen which could cause the margins to be slim if this is a universal voltage design.


--- End quote ---
I'll double-check later today. Maybe that's one of the reasons this failure-mode seems to be reasonably frequent with these?

alan.bain:
On the one I have the anode of D6 is connected to the TOPswitch D, cathode to C23 & D8 in parallel which is the opposite to the way drawn, but agrees with the TOP223Y datasheet.

Alan

FrodeM:

--- Quote from: alan.bain on June 05, 2024, 12:00:28 pm ---On the one I have the anode of D6 is connected to the TOPswitch D, cathode to C23 & D8 in parallel which is the opposite to the way drawn, but agrees with the TOP223Y datasheet.

Alan

--- End quote ---

Ok, on close inspection of where the trace goes, I see I have drawn it wrong. It must have measured as low enough resistance through the inductor for the multimeter to call continuity when I did the initial work on this.

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