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INTRODUCTI ON
This ser vice man u al w as prepared f or use by Auth or ized Warranty Stations and contains service
i
nformation for M arantz Mod el l 05B Stereophonic T un er.
S ervic ing in
for m at ion an d v oltage data i ncluded in this manual are intended for use by the
k
no w ledge abl e and exper ie nce d technician on ly . All instruction should be read carefully. No
atte mp t shou ld be m ade to p roc eed wit hout a good understanding of the operation in the
t u ner .
The
part l ists fu rnish infor m at ion by w hich replacement part may be ordered from the
Maran tz Co m
pa ny . A simple descr ip tio n is i n cl uded fo r parts which can be usually be obtained
th roug h local suppliers .
Th e Mod el 1058 is a tu ner version of the Marant z 's Model 20 15 Tu ner/Amplifier and almostthe
sam e c ircu itr y a s u sed in th e Mode l 201 5 is em pl oy ed except the audio Amplifier, and power
supp ly circu it.
1.
AM Tuner
A ll com po nents exce pt ferri te bar an tenna are m ounted on a printed circuit board Pl00.
The AM signals in d uced in a ferrite bar a ntenna are appli ed to the base of converter transistor
H113 th ro ug h a capacitor of C171, whil e t he loca l o sci llat or voltage is injected to the emitter of
H113 th rough a capacitor C172. Bo th AM sign a ls and oscillating voltage are mixed at the
base- em itter junctio n and converted int o 45 5KHz intermediate frequency. The resulting I F signal
is ap plied to th e f irst I F tra nsf orm er L 116 co nsisting of one ceramic filter and two tuned circuits.
T he o
utp ut of L11 6 is led to the tra ns isto r H 1 04 which in turn apply its output to the
t
ransi st or of nex t st age Hl05. The fu ll y ampli fie d IF output is then applied to the diode H123 to
detect aud ibl e signa l th rou gh th e det ector tra nsformer L 117. The detected audio signal is filtered
and th e final au dio out pu t is obtained from pin terminal J118 and applied: to the output jacks
th ro u gh the fu nc t ion sw itc h .
T he DC c
om ponent of the detected I F sig nal is used as a AGC voltage to control emitter
curr en t of H 104 throug h the resistor R 185. A part of I F signal output is also applied to the diode
H
124 through a capac itor C1BO and rectif ie d to obtain DC current for energizing the AM signal
str e
ng th met er M0 01.
1.1 Suggestions
for AM Tuner trouble shooting
C he
ck fo r broke n AM bar anten n a, nex t try to tune station by rotating fly-wheel tuning knob
slowly and observe the AM sig nal streng th meter whether it deflects or not. If the signal strength
m e
ter give s a deflection at sever al fre que nci es received, no failure may exist in the stages at least
pr ec ed in g fin al I F trans f
or mer L 117. N ext conne ct a oscilloscope to the pin terminal J118 and
ch ec k for audio signa ls w it h th e tuning meter deflected. If the signal strength meter does not
deflec t, check the local osc ill a tor circu it. Norm al oscillating voltage at the hot end of the
osci
llator tuning ca pacitor is a bo ut 2 or 3 volts, varying with tuning capacitor position. When
me asu ring osc illati ng voltage use a RF V TV M, no circuit tester gives correct indication. If the
l ocal oscillato r
volt age is normal , check all voltag e dist rib ution in the AM circuits by using a DC
VTVM and compar e th e m easur ed values with those given in the schematic diagram.
2. FM Tuner
A ll com ponen ts are mou nte d on a pri nte d circ uit board P100.
FM signa ls induce d by a FM
an tenna are l ed to FM antenna coil L 101.
These sig n als are then applie d to the FET RF
amplifier which in turn applies its output to the
next transis to r m ixer Hl02 th ro ugh a hi gh Q tuned circuit.
The
mixer convert its in put sig n al int o 10.71V1 Hz intermediate frequency and amplifies it at the
same time. The H1 03 is a local o scillator and its output is injected into the base of mixer
tran sistor, t he inj ectio n vol tage is abo ut 4 0 m V.
1
