My QMX+ ceased to function last night after working well for a few days after build. It just didn't start up. After probing around I could see the output of IC101 linear reg was only at about 1v when the button was pressed. To establish if it was the regulator or load on VDD I removed D103.
The output of the reg went up to 3.3v , I checked it with a 15ohm load and it was still ok. I couldn't see a low resistance on VDD so planned to remove the obvious, like tant caps and check them when I noticed D109; I guess its for transient protection when the switcher changes frequency or on start up. So I took it out and measured it it was .5V one way as expected, but 0.1 V in the other direction at 1ma. So I Jury rigged a through hole device in its place, replaced D103 and everything burst into life. Just have to find the right component now.
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Hope this helps anyone with a non-starter, I wonder if anyone else has seen this diode fail?
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G0TXL (Paul)
