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HP 16700 PSU in 230V region woes
FrodeM:
Have anyone here experienced problems with the power-supply of the HP 16700 logic analyzer blowing up when running in 230V regions? I am in particular thinking of the Celestica 7000 variety, which does claim to handle 230V just fine but I have had two blow on me so far.
The first time it was the switcher for the standby power source. An all-in-one TOP227Y switch mode regulator in a single TO-220 package. This blew quite violently, taking out a whole trace on the PCB, some resistors in its path, as well as D7.
For the second one , it was a small 8-pin chip, probably part of the main regulator. Fortunately, not as violently and this far I only found D7 as the only other part that has blown.
Is it just me, or does this PSU have really slim margins?
Some notes on the design. I plan to fix the second one with parts from the first one, and I'm in the process of drawing up a schematics as a consequence. I now see that the main board of the PSU uses a charge-pump type of design, instead of switching a transformer. That explains why D7 is very prone to damage: it's the main boost converter diode. All current driving the unit passes through it, and with 230V mains it is natural that the flyback suges it needs to pass will peak harder.
Does anyone else have similar experience with these supplies?
alan.bain:
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?
FrodeM:
--- 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
The 10 ohm resistor is a natural thing to go when the TOP227 goes, since it's the only thing between the high voltage reservoir and ground when that happens.
alan.bain:
Thanks for sharing that very useful schematic. I'm a bit surprised by the 12V marking though as the UC3584 needs more than that - thought somewhere > 15V.
I'll replace the obvious failures and see what goes bang next!
FrodeM:
--- Quote from: alan.bain on June 02, 2024, 03:23:47 pm ---Thanks for sharing that very useful schematic. I'm a bit surprised by the 12V marking though as the UC3584 needs more than that - thought somewhere > 15V.
I'll replace the obvious failures and see what goes bang next!
--- End quote ---
That 12V doesn't go to the UC3584, that has it's own supply on the lower half of the regulator board. The Aux-supply is completely standalone and is in the PSU only used to drive fans, as well as the U6 "Aux Power Good" and the U5 "On/Standby" optocoupler enabling/disabling the bank of secondary regulators providing the main supply for the analyzer.
The problem here, using an inductive charge-pump design for filling the high-voltage side, is that any sort of short to ground after the absolutely huge inductor is not immediately going to trip the fuses before it. What's worse, if something trips short and then open (for example, by blowing a PCB trace), you can get additional voltage-spikes over the inductor, potentially causing more carnage for anything connected to the high-voltage bus. There should really have been a clamp in there on the HV bus to prevent spikes accidentally exceeding maximum ratings of components, but from this far into the reverse-engineering/schematics project I can tell you there are none.
In my own case, I ultimately ended up getting one of the older PSUs made early in the life-cycle of the 16700 series. This was made by a different company, Autec Power Systems (Model MFC75-WEDDGG), so it hopefully has a better design internally.
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