Grundig Micro Boy Schematic

Page 1

I32 RADIO SERVICING

GRUNDIG MICROBOY, MINIBOY

General Description: Six-transistor (plus two crystal diodes), medium-
wave (570-1620 kc/s.), personal receivers which can be fitted into a table
cabinet with large speaker for home use.

Power Supply: 9-volt battery (Type PP3 or equivalents).

Transistors: (TR1)OC44; (TRz) OC45; (TR3) OC45; (TR4) OC71;
(TR5) OC72; (TR6) OC72. Crystal diodes (Microboy) two OA70;
(Miniboy) two K5 /2. Adjustments with battery voltage about 75.

Servicing Notes: Current TR5, 6: Set volume control to minimum,
remove link, insert milliameter in series, adjust R24 when fitted for 1-4. mA.
(if not pre-set adjust by substituting different values of R24). Working
Point TR2: Connect voltmeter between R9 and chassis (+ to chassis).
On Microboy adjust 'R7 for reading of 4-3 volts (control or substitute re-
sistors). On Miniboy adjust or replace R6 for reading of 4. volts. During
operation there should be no signal input. I.F..' Inductively inject a
460-kc/s. signal and adjust I..F transformers with gang at maximum.
Oscillator: Inject 5101kc/s. and adjust core 4. (gang maximum). Inject
I620 kc/s. and adjust trimmer 5 with gang at minimum. Aerial: Inject
56o kc/s. and adjust core 6 Inject a 14.50- -kc/s. signal and adjust trimmer 5.
Afterwards recheck oscillator. Neutralisation: Check when I.F. transistors are
changed. Connect signal generator (460 kc/s. ) via o-I ,uF. to collector TR3.

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CIRCUIT DIAGRAM-