Toshiba DP120F, Service Manual

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March 2000 © TOSHIBA TEC 7-101 DP120F/DP125F Circuit Description
Signal Name Type Active Description Destination
CHVON O H Charge Voltage Supply Signal IC52
DEVON O H Development Roller Voltage Supply Signal IC52
TCVON, O H Transfer Charger Current Set 1/2 Signal IC52
PCU
DRBIS1-2 O H Drum Bias Voltage Set 1/2 Signal IC52
To supply constant-current to the transfer charger, the I/OP-2 GA causes either of the THVON
and PCU signals to be HIGH. Then Q5 on the HVPS turns on to supply 24VSW to IC3. IC3
causes Q9 to turn on and off and repeat supplying and cutting off of current to the primary
circuit of the transformer (T3). This allows power to be emitted from the secondary circuit of the
transformer and constant-current to be supplied to the transfer charger.
At this time, the value of the current to be supplied is set according to the signal levels of the
THVON and PCU signals.
When the THVON signal is at LOW level and the PCU signal is at HIGH level, Q7 and Q8 on
the HVPS turn on and off respectively to 210µA to the transfer charger.
When the THVON signal is at HIGH level and the PCU signal is at LOW level, Q7 and Q8 on
the HVPS turn off and on respectively to 180µA to the transfer charger.
When both the THVON and PCU signals are at LOW level, Q5 on the HVPS turns off to cut off
the supply of current.
To supply constant-voltage to the drum, the I/OP-2 GA causes the DRBIAS1 signal to be HIGH.
Then Q10 on the HVPS turns off and Q11 repeats turning on and off to repeat supplying and
cutting off of current to the primary circuit of the transformer (T4). This allows power to be
emitted from the secondary circuit of the transformer and constant-voltage to be supplied to the
drum.
At this time, the value of the voltage to be supplied is set according to the DRBIAS2 signal
output from the I/OP-2 GA.
When the DRBIAS signal is at LOW level, the photo-coupler (PC2) on the HVPS turns on to
supply -100V to the drum.
When the DRBIAS signal is at HIGH level, the photo-coupler (PC1) on the HVPS turns on to
supply -200V to the drum.
When the DRBIAS1 signal is at LOW level, 0V is supplied to the drum.
Constant voltage is supplied to the grid when the anode side of the series of Zener diodes
(ZD4-7) with the cathode side connected to the PG is connected.