Introduction; Am Tuner; Fm Tuner - Marantz 105B Service Manual

INTRODUCTI ON
This service m anual w as prepared f or use by A ut horized Warranty Stations and contains service
information for Marantz Model l 05B Stereophonic T uner.
Servicing inform at ion an d volta ge dat a inc luded in this manual are intended for use by the
know ledgeabl e and experienced t echnician only . All instruction should be read carefully. No
att empt shou ld be made t o proceed without a good understanding of the operation in the
t uner.
The part lists f urnish informat ion by w hich replacement part may be ordered from the
Marantz Com pa ny . A sim pl e descr iptio n is incl uded f o r parts which can be usually be obtained
th rough local suppliers.
Th e Model 1058 is a tu ner version of t he Marantz's Model 20 15 T uner/Amplifier and almostthe
sam e circu itry as used in t he Mode l 201 5 is em pl oyed except the audio Amplifier, and power
su pp ly circu it.
1. AM Tuner
A ll com po nents except ferri t e bar antenna are mounted on a printed circuit board Pl00.
T he AM signals induced in
a
ferrite bar antenna are appli ed to the base of converter transistor
H113 t hrough a capacitor of C171, while t he loca l osci llator voltage is injected to the emitter of
H113 t hrough a capacitor C172. Both AM sign als and oscillating voltage are mixed at the
base- em itter ju nction and converted into 45 5 KHz intermediate frequency. The resulting I F signal
is app lied to the f irst I F transform er L 1 16 co nsisting of one ceramic filter and two tuned circuits.
T he output of L11 6 is led to the tra nsisto r H 1 04 which in turn apply its output to the
t ra nsistor of next stage Hl05. T he fu lly ampli f ied IF output is then applied to the diode H123 to
detect aud ibl e si gna l th rou gh t he detector t ransf ormer L 117. The detected audio signal is filtered
and th e final au dio output is obtained from pin terminal J118 and applied: to the output jacks
th rough the f unct ion switch.
T he DC com ponent of the det ected I F signal is used as a AGC voltage to control emitter
current of H 104 th rough th e resistor R 185. A part of I F signal output is also applied to the diode
H 124 th rough a capacitor C1BO and rect if ied t o obtain DC current for energizing the AM signal
strengt h meter M001.
1.1 Suggestions for AM Tuner trouble shooting
Check f or broke n A M bar anten na, nex t try to tune station by rotating fly-wheel tuning knob
sl owly and observe the AM signal strength met er whether it deflects or not. If the signal strength
meter gi ves a deflection at several frequencies received, no failure may exist in the stages at least
preced ing f inal I F transf ormer L 117. Next connect a oscilloscope to the pin terminal J118 and
ch ec k for aud io signa ls w it h t he tuning meter deflected. If the signal strength meter does not
defl ect , check the local osc ill ator circu it. Norm al oscillating voltage at the hot end of the
osci llator tuning ca pacitor is about 2 or 3 volts, varying with tuning capacitor position. When
measu rin g osc illati ng voltage use a RF V TV M, no circuit tester gives correct indication. If the
local osci ll ator voltage is normal , check all vo ltage distribution in the AM circuits by using a DC
VTVM and com pare t he measured values with t hose given in the schematic diagram.
2. FM Tuner
A ll com ponents are mou nted on a pri nt ed circ uit board P100.
FM signa ls induced by a FM an tenna are led to FM antenna coil L 101.
These signals are then applie d t o t he FET R F amplifier which in turn applies its output to the
next transi sto r m ixer Hl02 th rough a h igh
Q
tuned circuit.
The mixer convert its in put signal into 10.71V1 Hz intermediate frequency and amplifies it at the
same ti me. The H1 03 is a local oscillator and its output is injected into the base of mixer
t ran sistor , t he inj ect ion vol tage is abo ut 40m V.
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