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Electronics => Repair => Topic started by: dxl on September 04, 2021, 08:41:10 pm

Title: HP 16700/16702 Power supply repair
Post by: dxl on September 04, 2021, 08:41:10 pm

Hi,

i've got my hands on a HP16702A Logic Analyzer. Unfortunately, a few seconds after power on the Power supply died. It looks like there's a small standby power supply in these units. An unknown TO220 Mosfet(?) bursted, so i can't read any part number anymore. I've attached a Picture of the PCB with the missing part. Does anyone know, what this part is?

What is strange is that Pin 2 connects to GND, and Pin 3 connects to the small standby transformer. I would have expected it the other way round.

Title: Re: HP 16700/16702 Power supply repair
Post by: bob91343 on September 04, 2021, 11:02:28 pm

Perhaps an IRF840 or similar part.

Title: Re: HP 16700/16702 Power supply repair
Post by: FrodeM on April 25, 2024, 08:04:56 am

Not sure if you figured it out, but it's a TOP227Y integrated switch and regulator. You can see the schematics around this part here:
https://bitsavers.org/test_equipment/hp/167xx/Celestica_7000_Aux_Power_Regulator_Schematics.png

Note that 360V might not be correct. I have since figured out that the high-voltage side that source all of this is generated by a boost-converter regulator, not just rectified power-grid voltage. It is more likely something like 400V, but I have not measured it. Also make sure to check D7 down at the main board, this is by far the weakest link in the main current-path of the PSU.