lc75

LC75_Calibration_Adjustments

Sencore LC75 Z Meter 2 Calibration Adjustments

All of the information below assumes that the instrument is functional before attempting adjustments.
Attempting to adjust a failed instrument may make things worse rather than better!

Adjustments not mentioned may be labeled on the schematic but the adjustment sequence is not known. So
before tweaking anything take note of where the adjustment is currently set mechanically so
that you can return setting to its as found setting. 

One would expect that there may be some interaction between adjustments based upon information found 
on previous models.

Note: Some of the adjustments are obvious from the schematic, others (Capacitance) were derived from 
referencing a schematic of the LC53 (which does not do ESR) so caveat emptor!  

Complete the DVM Zero and the C and ESR Zero after 15mins of power on and recheck before
calibration. 

Also note that this is an instrument that was designed for electronics servicemans use and was not meant 
to be a lab standard measurement system. If you need high accuracy find a good LCR meter or bridge 
GR, HP, ESI, Wayne Kerr and SRS make excellent ones that can be found at Hamfests or on Ebay at 
very reasonable prices, usually a mere fraction of their original cost. 

That being said, it does not diminish the utility of the instrument for its intended use as it does pack a
lot of usable performance in a easy to carry around package.

The most useful features are the ESR, capacitor leakage and capacitor forming capabilities as well as 
inductance ringing.

Adjustment Location

Pots on the Digital Board

R68	Function Unknown (Timing?)
R71	Function Unknown (Timing?)

Pots on the Analog Board

Inductance Cal
Use inductors 80uH,800uH, 8mH,80mH,800mH,8000mH

0-90uH			R14
90uH-900uH		R23
900uH-9mH		R29
9mH-90mH		R35
90mH-900mH		R42
900mH-9900mH		R48
Inductance Linearity	R106
Probably adjusts range tracking

ESR Cal 

Use Metal Film Resistors close to 8,80 and 800 ohms

0-9		R56
9-90		R62
90-999		R68
 
R77 Function Unknown

Capacitance

Use Silver Mica, Mylar and Tantalum if GR standard capacitors are not available.

8000pF		R123
0.800uF		R125
800uF		R128