My NAD amp is fine, thank you very much. (Patreon)

I took out the old HP 428B current probe to check that the current going in my power supply components is normal, and that I just didn't cover up another fault, as the conspiracy mill says on YouTube. It is a very old instrument (using tubes!), but still in perfect calibration. I checked it of course, it is within 1% of my Tek DMM. Conveniently there are jumpers on the board for the 55V rails, I just made them longer so I could use the current probe.

It measured 237 mA on the top rail, which is right around what I expected (bottom rail is lower at 170 mA, as it does not have the extra 12V supply to support). Using that figure, one can calculate that the original components were indeed running within spec: the 3.3 Ohms 0.5W resistor was running at 0.19W, and the 3.3V 1W zeners were running at 0.78W. The replaced ones have of course more margin, but what I was really after was reducing the local temp to protect the thing that actually failed: the poor quality PCB.

So the amp is fine, thank you very much, there is no short or over-driven components or any other kind of imminent doom. Some cooked caps will sure need replacement, but since they are just decoupling and not filtering caps, even that should not have a measurable effect on power consumption [edit: and it didn’t, did not even change by 1 mA].

As expected, NAD cut it a little close with the Zeners, which they apparently corrected in the later models by putting a single bigger one, tells me the one commenter that actually looked instead of speculating. It is of course hopeless to get that point across on the YouTube comment section. But Patrons know better.