Fluke 336 current clamp meter

In the red rectangle are 2 resistors missing

Two of these meters came in for repair.  Someone already did his best to make the problem bigger. The first one had a problem with the function switch. It would not select a function. The cause was a man made problem. 2 resistors from the function voltage divider escaped. They were ripped from the pads. Probably when someone tried to remove the switch deck C ring. Number 2 was way off and  had unstable readings.

After placing new resistors the measurements were also on number 1 very unstable. The cause was hidden under the switch deck. I found it thanks to the microscope.

metal-dust between traces

The space between the tracks was filled with metal dust from the switch. It stayed there thanks to  the grease they used to lubricate the switch. This caused leakage current. After cleaning they were way off so probably someone first tried to adjust things. 

The meter without the top cover

They contain no special parts, except maybe the processor (that is placed out of sight under the display.) According to Fluke they are not repairable because there are no parts available. 

Adjusting them is not to difficult. Only the AC current is a bit a hassle. The trimpot is placed on the back and accessible via the battery cover. But not with the batteries installed. To make a big enough current you need something like a Fluke 5500 coil. You feed it with 10A. Because it has 50 windings all going through the clamp, the meter sees 500A. 

I have made my own version on a perplex plate so I can place the meter on it’s display and the clamp is still at the optimal centered place. That way the trimpot is accessible (without the batteries so I feed it with a lab supply. ) and I can see the display. 

The current multiplier

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