AVO Multiminor Mark 4 Service manual

Multiminor Mark 4

6 Π η

ΙΛΛ

© Avo Lim ited 1968

CONTENT S

English

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OPE RAT ING INS TR U CT IO N S
FOR MULTIMINOR Mk. 4

General: The instrument is s upplie d in an attra c

tive p lastic ca se w ith leads, pro ds and clip s.

Preliminary Check. T o ensu re accura te read

ings, the ins tru m ent m u st be used fac e upwa rd.
If the p o inter does not read zero, the slo tted
mech anical zero adjuster whic h is located below
th e scale should be re adjusted.

The Scale Plate. Tw o basic sc ales are provided,

ea ch appro xim ately 2.75 inches (6.98 cm .) In
length. T h e inne r scale is for re sista nce m easure

ments on ly and is scaled 0-20k β(1 2 5 Ω mid -scale ).

The outer scale is fo r a.c. and d.c. voltage and d.c.
current; it has 50 div isions w hich are calibrated
0-25 and 0-100.

USING THE INSTRUMENT

A.C. and D.C. Voltage Measurements. T o

measure a.c. or d.c. voltage th e leads sho u ld be
connected a cro ss the so u rce to be measured, the
bas ic scale sh ould be used (i.e. 0-25 o r 0-100), The
re adings o b tained s hould be m u ltip lied by the
appropria te facto r, e.g., a ssuming that a 250V
mains supply is being m easured, the range switch
sho uld be set to 250V a.c. The reading s should
then be made on the scale marked 0-25 and m u lti
plied by ten.

D.C. Current Measurements. T o m easure d.c.

current the m ete r m ust be connected in series
with the c ircuit u nder test. M easurem ents are
made in a similar manner to that previous ly
des cribed , except th a t the scale marked 0-100 is

used th roughout. The re adings obtained, however,
shou ld be m ultiplie d o r divide d by the appropriate
facto r.

N o te . If the voltage or c urrent to be measured is

unknown, always sw itch to the highest range, then

switch progre ssively to a lower range until a suit-

6 able p oin ter deflection is o btained.

Warning. It is dangerous to make con nectio n s

to e quipm ent w ith the pow er on. Make a habit o f
Connecting the instru m ent before s w itchin g on.

Resistance and Continuity Measurements.

Select the resistanc e range req uired , jo in th e leads
together, and adjust th e ohms zero control un til
fu ll scale defle ction is ob taine d (the o hms zero
control is s ituated above the range s w itch). On

switch ing to the other ohms range, again che ck

the zero and adjust if necessary.

If it is not p ossible to set the poin ter to read zero,
it is m ost likely due to the in ternal cell (Ever
Ready type D M -ft in. dia . x 2 In. long; 1.43 cm. x

5.08 cm .) bein g d is charged. This sho u ld be
checked and, if necessary, replaced. If the in stru

ment is to be sto red for any length of tim e, it is

advisable to remove the cell.

To m easure resistance, con nect th e leads

across th e component und er test; if th e “ ohms x 1 "
range is used, a d ire ct reading is given on the
scale marked 0-20k Ω. W hen using “ ohms x 100”
range, use the sam e scale and m ultiply re adings
by 100.

Note. When switched to resistance ranges, a

positive potential appears at the negative socket;

this is of particular importance when testing metal

rectifiers, electrolytic capacitors and other polarity-
conscious components.

External Accessories. Four external acce ssories

are available fo r this Instrument. T hese are; (a)
a m ultiplier fo r the measurement o f volta ges up to

2500V d.c., and (b) sh u nts fo r the m easurem ent of

5,10 and 25A d.c.

To use the volta ge m u ltip lier, the range switch
shou ld be set to the 1000V d.c. position and the
m u ltiplie r p lug ged in to the high po ten tial soc ket
on the instrument (norm ally this w ill be th e +
socket). The test lead is the n inserted in to the
soc ket on the multiplier.

To measure d.c. current th e In strum ent sho uld
be s e t to the 0.1 m A range. The sh u n t is the n
plugge d Into th e te s t sockets, and the te s t leads
transferred to the sh u n t sockets.

Attractive Carrying Cases. Can be supp lied

7 in two ve rsions: one to house the instrument,

leads, clip s and p rods; the oth e r to h ouse
th ese and also the high voltage m ultiplier, a d.c.
shunt and a pair of prod clip s.

200mV

0-1OV
0-25V
0-100V
0-250V
0-1000V

,·

Tab le of Ranges

D.C. C u rre nt D.C. Voltage

First indication

2 μ Α

0-0.1 m A (1 00

0-1 m A 0- 2.5V

0-10mA
0-100m A 0- 25V
0- 1 A

•Set th e range switch to its .1mA (1 0 0 μ Α)
position to obtain the 100mV range.

Resistance. First in dic a tion 5 Ω.

0-20.000 42125 Ω m id-scale \U s in g Internal
0-2M Ω 12,500 Ω m id-scale / 1.5V cell

Accu racy. Con forms to B .S.S. 89/1954.

D.C. 2.25% o f fu ll sca le
A.C . 2.75% o f full scale

Sensitivity

(10,000 β /V ) <1t00 0 fl/V )

First indication

/a

A )

2mV

0-100m V*
0- 10V
0-100V

0-250V
0-1000V

A.C . Volta g e

Sensitivity

First indication

CO M PO N EN TS L IST

Cct.
Ref.

R1
R2
R3 22.5 Ω )
R4 225 Ω
R5
R6 10.4 Ω
R7 286 Ω
R8 113 Ω
R9
R10 24k Ω
R11
R12
R13 73k Ω
R14 1.3k Ω
R15 150k Ω

♦P re-s e t fo r m ovement re sis tanc e of 1667 Ω ± 0.2%

Description Remarks

0.25 β Ί

2.25 Ω i-

1450 Ω

11.36k Ω

9.35k Ω
15k Ω

Part of

Shunt Board

Assembly R18

± 1 %
± 1 %

± 1 %
± 1 %
± 1 %
± 1 %
± 1 %
±20 %

± 1 %

Cct.
Ref.

R16
R17

R19 680 Ω
R20

RV1
RV2* 100 Ω Swam p
RV3*
M R 1\
MR2 J
M1
BY1

Description

750k Ω

1.5M Ω

7.5M Ω
33k Ω

800 Ω
500k Ω

OA95
60μ.A , 1667 Ω

1.5V cell

Remarks

%

± 1 %

± 1 %

Ever Ready

D14

R* „ ^ SiHcb ·

10-«

CIR C UIT D IAG R AM T HE MULTIM INOR M k. 4

Avo Limited Avocet House Teleg ram s & Cab le s:

Dover, Kent, E ngland Avoc e t Dove r

Tel: Dover 2626 Telex: 96283

THO RN

Pari No 10072-319

Printed In En gla nd