Adjust/Repair of Wattmeter Lutron DW-6090 / Peaktech 2510 / PCE-PA 6000

[butech]

Hello to everyone,

I acquired one of these "cheap" wattmeters used, but my unit is not working properly. E.g., the meter shows a current and watt value even if nothing is connected to the terminals. The voltage measurement seems to work correctly (although slightly out of spec).

The unit has several trim pots (i think approx. 10) for adjustments (behind the front panel). Using the first of these 10, I was able to fix at least the DC current measurement by adjusting the offset of one opamp at the input. The dc measurement is now working.

Maybe it would be possible to use the other trim pots to adjust the other measurements as well, but for this, I would at best need a service manual/schematic, as I have actually not the time to figure it out.

Maybe anyone has a schematic? Or did the adjustments? 

I would appreciate any help.