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cratered ULN2003
Tuesday, July 11 2023
I'd taken a recreational 150 mg dose of pseudoephedrine this morning, which made me unusually productive in the remote workplace (something I can't necessarily predict). At noon, I drove out to 9W (drinking a Stewart's-brand energy drink) to buy booze for the laboratory and more electrical supplies for the cabin (mostly PVC boxes and conduit for installing electrical outlets on the inside of the foundation walls in the basement).
Back at the house, I noticed that the solar hot water system was boiling over, a process that makes audible hisses and the sound of clacking pressure-relief valves. I thought it just needed more fluid, but when I went to add some, it was obvious that the fluid wasn't circulating. I was about to start Tuesday afternoon group QA in the remote workplace, so I basically hot-wired the system to get it to pump until I could come back and figure out what the problem was.
Later, when I had some time to check on it, I went to measure the voltages on the ULN2003, the chip that switches the high voltage necessary to drive the relays that control the valves (that in turn control the 120v circulator pump). The voltages were good, but as I checked them, I rested a finger on the ULN2003 (which was a little hard to see in the gloomy boiler room) and could immediately feel what the problem was: the ULN2003 had a large crater in it, indicating it had exploded in a puff of foul-smelling smoke at some point. The system wouldn't've been able to work after that. Fortunately, I have a good number of spare ULN2003s, and when I swapped one in, the system began working as expected once more.
This evening, Gretchen was going to have a long call with her old college friends Katie and Mary, so I went down to the greenhouse to avoid having to hear all of that. It was where I would end up spending the night. There are few places where I sleep better.
The damaged ULN2003 that had been switching on the valve-control relays in the solar hydronic system.
Click to enlarge.
You can see the seven separate drivers on the ULN2003's exposed silicon chip.
Click to enlarge.
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