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Kill-A-Watt Resurrecting

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>


I figured it out :-)))

The Kill-A-Watt is calibrated at 110.0 VAC at 10.00 amps.  You need a 
variac and an 11.00 Ohm 1100watt! resistor...  Then it is just a matter of 
saving those readings/calibrations permanently using the front panel 
controls...  Beefing up the 5V supply inside it would probably prevent the 
whole darn problem in the first place.  Apparently, it can just as easily 
be calibrated at 220VAC too...  Here is the exciting test/calibration set 
up :o)))


Hopefully, minor modification to a new unit will render it "Tesla coil 
proof" so it will not flake out.  I am not sure the meter is real well 
protected against accidental re-calibration =:o  Probably best not to go 
pushing buttons....  Easy to see how wild voltage fluctuations and 
transients may hit on the calibration code stuff and mess it up...

Maybe time to fire off a letter to Prodigit asking for the "real" 
calibration procedures in trade for how to harden it against "us" ;-))


My meter is pretty torn up at this point, but it is spewing its secrets all 
over the place ;-)) I don't have a good current load so it is reading 
currents like "P4.99" and stuff :o))  I can calibrate the frequency to 
33Hz...  Stay tuned...




Hi All,

I have now replaced all the silicon and individually tested all of the 
front board components on my killed Kill-A-Watt (kKAW :o)).  Replacing the 
LM2902 "seemed" to help many things and all the other components were 
fine.  I am not certain the LM2902 was really bad.  It got ripped out 
before too much testing was done ;-))

I now think that the internal "big" IC (Prodigit 53920005) is a soft 
calibrate chip.  It has it's own internal "nonvolatile" memory.  I guess I 
violated it ;-))  I note the display PC board has a jumper that sure looks 
like it may have has something to do with calibration or testing.  It looks 
like it was soldered by hand after the fact.

While a few of the front end components were out, the "Hz" display read 
"dc" so this ain't no dumb meter ;-))

Here is where the fun begins...

If you push both the "volt" and "Hz"buttons at the same time you get "open"!

Then push "Watt" and get "C110".  Push "Watt" again and get 
"C220".  Push"Watt" again and you get a flashing (probably test) full 

Or, if after step 1, you push "amp" you get "save"!!

Since this meter is supposed to be a 0.2% deal, I can only assume that the 
critical volts and amps calibrations are soft programmed into memory.  All 
the other displays are just hard digital calculations off that.  I would 
guess they just plug in a magic load and a person that knows the right 
buttons programs the calibration right off the front panel.

C110/C220 could mean "110 volt" or "220 volt" or they could be voltage and 
current cal...

Note this interesting photo of the front panel PC board under the buttons:


"menu", "up", "down", "enter", "output"....

So it is like one of those evil little Chinese puzzles as to how to restore 
the calibration...

So I'll goof with it and see if I can affect the calibration...  If its 
calibration can be reset, we are home free ;-))  But this also indicated 
that the big chip may have gotten bad signals that should not be too hard 
to clamp or filter...

Oh yeah!!!!!!!  I can set the "volts" to read 220 or 110 now >:o)))))

I don't recommend anyone with these meters going and pushing these "magic" 
buttons...  You may mess it up...

Possibly the PC board jumper is a hard program vs temporary program thing 
since the "new" calibration is lost if the meter is unplugged right now 
with the jumper in...




Hi All,

Last Sunday I blew my Kill-A-Watt meter playing with my coil.  I am not 
sure when it went (too dark).  Grounding was poor and we were sticking it 
all around the systems AC wiring.  We were bypassing filters and such 
trying to track down what turned out to be a MOV problem.

It was pretty messed up.  Drifting, big currents with nothing connected, 
voltage and frequency readings randomly off.  Nothing inside was obviously 
burnt up.  It appeared that the basic logic worked, it was just that the 
input metering was bad.

I replaced the LM2902 with a LM324 (fast Radio Shack replacement).  That 
fixed a lot of the trouble.  The drift and offsets are gone now and the 
frequency reads right again.  The only problem now is that the voltage 
reads 60% high and the current is 23% low.  I think the LM324 is "close 
enough" to the LM2902 so that should not be the problem (but it is only 
running on 5V in this design)?  I had already ordered parts from Digikey 
before I knew I needed some more LM2902's...

I am going to try desoldering and carefully testing the input parts 
next.  Maybe a bad part in there I am not seeing.  Hopefully I can get it 
going again since the problems don't seem unfixable.   I did order up two 
new meters just in case ;-))

So I guess even the latest ones can be damaged by Tesla coils.  But this 
kind of damage my be eliminated if I can find out "why" and add a few extra 
protection components.  Stay tuned...