I’m fixing a hole where the rain gets in
–The Beatles, “Fixing a Hole”
And stops my mind from wandering
For a while I’ve had an old HP 3435A desktop digital multimeter. Picked it up at a surplus place for $60 so I could have a meter that sits on a shelf and is always ready, doesn’t need batteries, has a decent readout, autoranging, basically a bunch of features that my existing meters did not have. Recently when I went to use it, I found that the voltage it was showing was impossibly wrong – I seem to recall it was an AA battery I’d just removed from something marginally working but it read 0.2V – and then shortly after the only thing it would display is “OL”, its code for out of range. Around the same time as that, I saw a video from Great Scott! that talked about a portable DMM that also has a two-channel 50MHz oscilloscope. Now I already have an old analog scope here, but .. well, it’s old, and it doesn’t have a lot of the nice features that newer scopes do. So after getting that new meter in my hands, I decided recently to take the old one apart and see if I could find out what was wrong with it.
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