Thanks Dan - and all. All good pointers for investigation - so much appreciated.
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I'm using the V1 board schematics, but as far as I can see the SMPSU board component numbering has been maintained in the V2 PCB, so l'll follow it as far as I can to find where the short is. Hopefully it'll be something that's relatively easily replaceable. I'm 50/50 on the cause being a short to the case under the PCB or on a rapidly fluctuating external supply voltage.
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I'll posting my findings when I, um, find them!
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Thanks again,
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Steve MW0KST
