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Instructions for balancing
HTH, June 29th 2000
Issue 3
Ability 1 and similar meters
All potentiometer designations used for the Emeter setup stem from the
sheet for the Mark VII and the one for the Ability 1. If you find
designations in round brackets that means they differ in the two sheets.
They still have the same function.
1. Balancing working voltage: Between OV[1] and +UB. The Voltage must be
7.5 Volt +/- 0.05. It is ajusted with Potentiometer R1 (if necessary R9).
2. Allowance for the needle from Set between minimum and maximum
amplification +/- one tooth[2] (Tick = T). If this is not the case,
regulate by adjusting the potentiometer "balance" (R50, Bal.). The set
position for this test is adjusted with sensitivity setting = 40.
3. Replacing TA potentiometer (20K linear) (necessary because of Rock
Slamming potentiometer). The three potentiometer
- (R46, MALE [VR]) for balancing TA=3 dead man,
- (R45, VR4 [Inf.], J) for balancing needle position with open PC terminals
� TA = 6.5,
- Trim fine[3] (R44, Mark VII only)
to middle position. Replace Resistor R5 (R5 is a resistor of ca. 1,000 Ohm
which is connected in front of the TA-potentiomenter) by a 5K x 10
potentiometer (potentiometer that can be turned 10 times around the axis to
cover the span of 5,000 Ohm) and bring to middle position (from now on
designated as R5'). Needle on Set position and 5,000 Ohm at pc terminals,
this equals the position 2.0 on the TA scale, so this is where the TA knob
of the new TA potentiometer should point to. TA position 3.0 means 12,500
Ohm on the pc terminals and needle in set position, TA knob points to 3.0.
Work on maximum sensitivity.
a) Dead female. Connect 5K to pc terminals, let the TA knob point to 2
and pull needle with R5' towards set.
b) Now open pc terminals, turn TA knob on 6.5 and turn R5'until the
needle appears on the scale. Then with the help of R45 (VR4 [Inf], J)
pull needle to set or as close as possible to set, in no case into
Rise area. (With "pull" I mean turning the potentiometer.)
Repeat steps a) and b) until no more improvement possible and needle
on open pc terminals as close as possible to set.
c) Now the same for the dead male.Connect to PC terminals 12.5K, let TA
knob point on 3 and turn R5' until needle on set.
d) Now open pc terminals. Turn TA knob to 6.5 and turn R46 until needle
on set or as close as possible towards set. If needle doesn't come on
the scale and sticks to the right end of the scale you can use R 5' to
help. In no case pull into Rise area.
Repeat c) and d) until no more improvement possible and needle on open
pc terminals as close as possible to set.
Repeat a) to d) until you have a stable point and on connecting 5,000
Ohm to the terminals the needle is on set and the TA potentiometer
points on 2.0. This must be precise. If on connecting 12,500 Ohm needle
is on set and the TA close to 3 (+/- 1 or 2 Ticks are tolerable), the
meter is adjusted correctly.
At the end measure R5' and insert a series resistor (trim fine) of this
exact resistance in front of the new TA potentiometer. In this way the
manufacturing tolerances are compensated.
.
4. Minimum Amplification: TA = 2, PC 5K, needle on Set position, now
connect a 62,5K 1% in parallel to the 5K. The needle must move 2 teeth to
the right on a sensitivity of "1". This is adjusted with g (VR1).
5. Maximum Amplification: TA = 2, PC 5K, needle on Set position, now
connect a 935K 1% in parallel to the 5K. The needle must move 5 teeth to
the right on a sensitivity of "40". This is adjusted with G (VR6).
6. It is helpful to construct a testing box. The testing box contains all
resistors and switches to test and adjust an e-meter. A diagram is
attached.
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[1] Virtual zero to which the measuring circuit relates; is different from
"minus" of the battery.
[2] Tooth is 1/8 inch on the emeter dial.
[3] Fine adjustment PC input, often not built in.