Philips LFH 0388, Руководство по обслуживанию

Страница: 15 / 41

LFH 0388/LFH 0488/LFH 0588
13
These machines are completely built with chip technology and are equipped with two inte-
grated circuits, forming the marking tone and alarm tone generator (IC 1) and the final ampli-
fier (IC 2).
On the LFH 0588 the LCD control and the marking timing is done by the µP IC 201.
TS 1:1, it means, that TS 1 is conductive.
TS 1:0, it means, that TS 1 is not conductive.
IC 1-11:1, it means, that IC 1 has a »1« or high condition at pin number 11.
IC 1-11:0, it means, that IC 1 has a »0« or low condition at pin number 11.
IC 1 represents a fourfold Schmitt trigger: Basic function
A B OUT
0 0 1
1 0 1
0 1 1
1 1 0
Via SK 1a supply vA arrives at the final amplifier IC 2, the motor control circuitry and
the turntable detector.
Via SK 1b, the BIAS oscillator, the Schmitt trigger IC 1 and the LED control receive supply
vB.
The BIAS (generated by the BIAS oscillator TS 12) is coupled into the record circuitry by the
oscillator coil L 1. The Diodes D 4 and D 5 keep the oscillator voltage on 12 Vpp.
By using TS 7, C 19 and R 30 a filtered supply voltage is available for both the built-in micro-
phone and an external microphone connected to SO 2, e.g. LFH 0172 (phantom supply).
C 19 is charged rapidly by D 3.
The signal from the microphone arrives at the DC-coupled record pre-amplifier TS 6/TS 8 via
the high-frequency emphasis circuit C 17/R 23, SK 2d and C 16. The gain of the record pre-
amplifier is determined by feedback from R 4/R 17.
On models LFH 0588 and LFH 0488 the signal arrives at the record sensitivity switch
(DICT/CONF) SK 3. The record sensitivity level can be switched over between DICT and
CONF mode. On model LFH 0388 no adjustment is foreseen.
Via SK 2c and C43 the signal arrives at Pin 7 of the integrated final amplifier.
From the output of the final amplifier IC 2-1 the signal arrives at the record/playback head
K 1 via the loud speaker (due to the low current not audible), SK 2a, C 33, R 47 and oscilla-
tor coil L 1 (mixed with BIAS).
C 40 forms a high-frequency emphasis.
C 35 closes the HF-circuitry.
SK 2b switches on the oscillator in RECORD mode. In PLAYBACK the oscillator coil L 1 is
shorted out. With C 4 interfering voltages are suppressed.
When an earphone is connected to socket SO 3, the recording signal can be heard in
RECORD.
During RECORD the erase head (permanent-magnet) is turned mechanically against the tape
by pushing the record button.
Electrical description
E
Definitions
Record +
A
B
OUT