Toshiba DP120F, Service Manual

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March 2000 © TOSHIBA TEC 7-41 DP120F/DP125F Circuit Description
3.8 Drum Unit Detect Circuit
The drum unit detect circuit consists of the PTC GA (IC45), A/D converter (IC54), I/OP-2 GA
(IC48), and other peripheral devices. It detects the presence or absence or new or old status of
a drum unit and controls lighting of the discharge lamp contained in the drum unit.
To detect the presence or absence or new or old status of a drum unit, the I/OP-2 GA causes
the PUCHKON signal to be HIGH to turn on Q272. At this time, the voltage of the PRO signal
applied to the emitter of Q272 is converted to a digital value by the A/D converter and input to
the PTC GA. It judges the presence of a new drum unit, presence of a used drum unit, and
absence of a drum unit.
When a new drum unit is installed, the I/OP-2 GA causes the PROCHG signal to be HIGH to
turn on Q11. This allows overcurrent to flow through the fuse in the drum unit to melt the fuse.
Then the drum abrasion loss stored in memory is cleared.
To turn on the discharge lamp, the I/OP-2 GA causes the PROCHG signal to be HIGH to turn
on Q11. This allows the DLL signal to be LOW so that voltage is applied to the discharge lamp
to turn it on.
Fig. 7-3-8
07-03-08
Signal Name Type Active Description Destination
PUCHKON O H Drum Unit Detection Enable Signal Q272
PRO I - Drum Unit Detect Signal A/D converter
PROCHG O H Discharge Lamp Lighting/ Q11
Fuse Blow Signal
DLL O - Discharge Lamp Signal Drum unit