Replacing a Pollcat Power Supply

Replacing a power supply should not be a noteworthy task; but when an exact replacement for the failed power supply isn’t available, one wants to exercise some care and diligence installing a compatible-but-different power supply.

Shamefully long ago (cue Wham’s delightful “Last Christmas” and sing along to ignore the guilt), one of the two redundant Pollcat telephony call-detail-monitoring gateways at work didn’t recover after datacenter electrical maintenance. Last weekend I finally looked at it, confirmed that the power supply was dead, and confirmed that the rest of the unit operated fine when run from bench power.

Pollcat shown with new and broken power supplies

I couldn’t find a reasonable source for the original model of power supply (the right of the two, toward the center of the photo); so after a bit of searching came up with different a 5-VDC 2-A open-frame power supply (the left, on some bubble wrap) that can physically fit into the available space in the enclosure and that can also operate from 100-240 VAC (important for datacenter 208 VAC) for a very affordable $10. We ordered a couple of them and I got it replaced this afternoon. I expected from the beginning to have to make a mounting adapter, but I also had to mind the polarity of both the AC and DC power connectors.

two open-frame power supplies

The new power supply came without connectors installed for the AC input and DC output. Fortunately each connector has the same pin spacing on the old and new power supplies (even though parallax in my pictures suggests otherwise), making my job easier. But the DC pins are in the reverse order, so I checked the connector orientation twice before soldering and once after.

two open-frame power supplies

The AC side of the replacement power supply has only a two-pin connector — which is all that’s connected from the power line anyway, but required chopping the original plug to get it to fit. Here again, the two pins (load and neutral) are in reversed positions from the original. I was able to remove the hot pin from the plug and move it from the right end to the left, so it all fits together.

replacement power supply with 3D-printed mounting bracket

I drafted the mounting adapter with the corner flanges the same thickness as the original PCB so the standoffs are at the same height as before. I was prepared to recess the new power supply below the upper surface of the adapter; but the new power supply is shorter than the original, so I was able to leave it like this.

Of course, on the first draft of the mounting adapter, I angled in the stems from the outer corners and had the inner frame inset below the power supply instead of surrounding it … which interfered with the solder-side of the through-hole components.

Pollcat running with replacement power supply

After final assembly, I did a bench test to make sure it all works. Now it can go back to the office with me on Monday.

All of which is to say: Replacing failed power supplies with different models is commonplace when there’s a lot of room in the case; but even when space is tight, the resources we have available today make it pretty doable.

… And this post is documentation for whoever does the next one, when the power supply in the other Pollcat fails a few years from now.

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