Hewlett-Packard HP-E3644A power supply onboarding

Inside the Hewlett-Packard HP-E3644A

The Hewlett-Packard HP-E3644A is part of a range of power supplies (see also my short HP-E3641A page). They can be very cheap to buy: for some reason they don't get much love, or at least waaaaay less than the double or triple output models like the super-popular HP-E3631A. There's a big advantage in getting one power supply per rail though: you get one display per output and can monitor all your rails at the same time. Recent models have larger LCDs with all parameters of all outputs available but these older VFD models from HP can have a bit unintuitive UIs and displays. Anyway, I got this one for a "very good price" (less than $50) and it's quite clean inside. Nice score! The evil RIFA caps are present but are in good condition and since I can't find replacements with the right pitch on Digikey they'll remain in for the time being.

RIFA danger spotted!

This unit has the ultra-common problem of having its rear bezel cracked. This happens when removing the rubber bumpers and I must say it's a real design issue with Hewlett-Packard equipment of that era. A little corner of the front bezel was also broken but I had the missing piece (miracle!) so fixing it was just a little bit of epoxy away:

Chipped front bezel, also probably from removing a rubber bumper

Repaired front bezel

The rear bezel is cracked on both sides and will require the addition of more material to make it sturdy again. The epoxy keeps flowing! These parts are relatively easy to fix since they are mostly hollow (hence their fragility in the first place) and thus can easily accept extra reinforcement material. Come to think about it I could do this epoxy pours preventively in all my instruments that use the same part...

Epoxy pours inside the bezel for more strength

For those interested here are the differences between the HP-E3641A and this HP-E3644A. The larger/heavier double-transformer of the E3644A is required give the larger power output of that model (80W, versus 30W only for the E3641A). Interestingly though they share the same heat sink and fan. This HP-E3644A also has one area of the PCB fully populated while the E3641A was mostly empty there.

Comparison of the innards of the HP-E3644A (left) and HP-E3641A (right)

Zoom on the unpopulated (E3641A, top) and populated (E3644A, bottom) regions of the main PCB.