Confused Kill-a-Watt

[edpalmer42]

My old Kill-a-Watt (P4400) has become confused.  When I plug it in, it initializes normally and reads the line voltage correctly.  Current reads zero for 10 sec. and then jumps to 0.14A with nothing plugged in.  That's where it sits from then on.  An ammeter confirms that the Kill-a-Watt is NOT drawing 0.14A by itself.

I opened it up, inspected everything, checked solder joints, etc.  I tested the main dropping capacitor and it's fine.  I managed to perform the 110V/10A calibration procedure which completed successfully and worked fine over a power cycle.  But the fault still remains.

The 10 second delay has me baffled.  Does anyone have any idea what's going on?  Or should I just bin it and buy a new one?

Ed

[floobydust]

I found these schematics for Kill-A-Watt P4400 and P4460 but there are a few different versions.

The 10 second delay is weirdly long and might be a dud electrolytic capacitor or something warming up.
I would check the main +15V and +6.2V (op-amp) rail is OK, the 100uF cap. The current-sense op-amp or shunt might be damaged and drifting around or open circuit.

[edpalmer42]

Yes, the second drawing is my unit.  My next step was going to be powering the unit up just with DC on the bench and see what happened.  I thought I'd ask and see if anyone else had seen something like this.

I agree that the delay is weirdly long.  The other thing that's weird about it is that it's absolutely consistent.  In fact, according to my stopwatch (and my reflexes) it's 11 sec. (not 10 - sorry) from the moment the voltage reading appers or 13.4 sec. from the moment of power-up with a tolerance of +- 0.1 sec.  Every - single - time!

Ed