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ITT-METRIX
FIELD  MULTIMETER   » MX-202 «


This "small/BIG-SCALE" MultiMeter is a  "Classic":  No large central switch to
change ranges -  instead it has a thumb-wheel on the right side and a vertical
"Radio Scale" ( with rope & winch ) on the right side.  The A-Ω-V Scales cover
the whole front of the  140 x 105 x 50 mm3  ( 5_1/2" x 4" x 2" )  instrument.

M U L T I M E T E R     » MX-202 «    by  ITT-METRIX, Paris / France    (1975)
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Class 1.5 (DC)  &  2.5 (AC) ;           40 kΩ / Volt (DC)  &  1 kΩ / Volt (AC)
                                                              < Ri(I) = 2 kΩ >
   50 mV .. 500 V ;  25 μA .. 0.5 A   &  1000 V / 5 A  DC Ranges
   15  V .. 500 V ;  50 μA .. 0.5 A   &  1000 V / 5 A  AC Ranges

    (x1) .. 20kΩ ,   (x10) .. 200kΩ ,   (x100) .. 2MΩ ; 
            w.  1.35 V  SPECIAL BATTERY  »RM-1R«  MALLORY Cell
            Because of its stability, NO ZERO-Ω-CALIBRATION is necessary!

    0 dB .. +25 dB   ( as Difference Measurement )

(1.) The FUSE-"Repair" is quick & easy  ( see DETAIL Picture on the left ) ...

    (1.)      (2.) 

The ORANGE SQUARE covers a little SPOOL with a very thin 0.05 mm Ø SILVER-WIRE.
Pull it out of the SLOT and mount it between the 2 SCREWS over the "WINDOW".

(2.)  A T T E N T I O N :
-------------------------
DC & AC uses the same plugs for "Normal Ranges"  -  only the  "Extended Ranges"
uses the + 1000 V (DC)/(AC) or + 5 A (DC)/(AC) Plugs  -  The SELECTOR has to be
set either on DC or AC-Range. As a reminder, I put COLOR-MARKS beside the plugs
BLUE / RED, red, red ;  YELLOW / YELLOW, yellow, yellow.  ( See right picture )

In these cases there is  N O   F U S E  PROTECTION  as shown in the DIAGRAM ...


                              ... The components are mounted on a PRINT-BOARD.

(3.)  MODIFICATION  for  1.5 Volt  B A T T E R Y   R E P L A C E M E N T   ...
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  1.35 V  MALLORY Batteries
  are no longer available.

  1.5 V  REPLACEMENTS
  ( e.g. »PX1« or »LR50« )
  have the same size,

  BUT ...
The higher 1.5 V  Battery needs MODIFICATIONS OF THE WIRING, because ZERO-OHM
has to be in the CALIBRATION RANGE. The easiest way are ADDITIONAL RESISTORS,
between the TRIM-POTS: (x1)R30 = 50 Ω ; (x10)R31 = 500 Ω  & (x100)R32 = 5 kΩ.
The left picture shows (X) were the printed connections have to be cut ...

    

... HOW TO FIND THE RIGHT RESISTORS ?
=====================================
(a) CUT the printed connections on (X) with a sharp knife
(b) Solder "TEST-WIRES" at the open points
(c) Set the (x1), (x10) & (x100) TRIM-POTS to CENTER POSITION
(d) Place the  1.5 V  BATTERY in the holder ( see picture above )
(e) SHORT-CUT the input plugs
(f) Set SELECTOR to (x1), (x10) & (x100) and ...
(g) ... connect (e.g.)  HELIPOTS  to the "Test-Wires"
(h) The right  V A L U E S  are found, when the INDICATOR shows ZERO OHM ...

    (x1) R'30 = + 33 Ω ;  (x10) R'31 = + 330 Ω ,  (x100) R'32 = + 3.3 kΩ

(i) Remove HELIPOTS & "Test-Wires" and solder RESISTORS in place ...
    ( COLOR-CODES:  [orange/orange/black],  [or./or./brown]  & [or./or./red] )

                     ... The right picture above shows the final modification. 
Suggestion:
-----------
Dependent on its usage,  it may be convenient to drill  3 small holes into the
case to allow  ZERO-Ω-CALIBRATION  without opening the  MX-202.

impressum:
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© C.HAMANN          http://public.beuth-hochschule.de/~hamann         02/15/13