Disassembly and Repair of the HP 82059B 41C Power Supply

[akpoff]

I recently took an 82059B power supply apart, broke it, and then repaired it.

Why take it apart? Perhaps idle curiosity. I had previously disassembled the supply for an HP 45 that was in really bad shape. I appreciated the easy disassembly. Knowing the 41C-series supplies are stupidly expensive, I took one apart to see what I'd be in for if one quit working.

Disassembly is way harder than it should be. The trick is heat and persistent, gentle prying starting from the corners. I started at the top-right corner as your looking at the supply from the HP-logo side. The adhesive does not give up easily. You can see from the picture below I chewed the edges up a bit.

Since the 41C series supplies are AC output I assumed they'd be simple, probably just a transformer, and replacing a bad one should be pretty easy. And that's what they are, just a transformer. However, in the process I broke one of the magnet wires from the secondary. To add insult to injury, I broke it a few millimeters from the winding.

Still, a good opportunity to practice my repair skills. Preparing magnet wire for soldering isn't as simple as stripping typical electrical wire. 1) The magnet wire is sub-30 gauge (or is that super-30?). 2) The wire isn't PVC coated, rather it's enamel. There are at least two schools of thought to stripping enamel. One school says sand it with really fine sand paper, the other schools goes for burning it off as part of the soldering process. I tried soldering. That's a no go. Sanding is much easier.

I cut a small piece of 1000-grit paper, folded it and put the wire in between the folds and worked it until most of the enamel was gone. The longer piece of wire was fairly easy to work, the smaller piece near the secondary winding was a bit harder. Once I had removed enough of the enamel I tinned both pieces and then rejoined them.

       

I'm happy to say the power supply works. I'm debating what to use to seal the two halves. At the moment they're held together with a rubber band.

In short, the 82059B can be opened and repaired. You might even be able to reuse the case if you can find a small enough step-down transformer. You might have to modify the internal retention bracket and fasten the new transformed with an adhesive. You could certainly re-use the cord. The 82059A looks so much like the 82059B I'd guess the process and results would be the same.

I also have the 82040A. That's the one you can see into due to the cooling construction. It has a much larger transformer. Other than that, I think it also would be the same.

Edit: Add picture of top half of case. See measurements post below for transformer dimensions.

Cheers,

--Aaron