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SCHEMATIC OF THE XD-11
It may at first appear that the complete schematic. Fig. 41,
shows only tw o of the three IC's. However, the circled numbers
indicate the connections to the third IC — that’s H-IC, the
hybrid IC on the side of the mirror cage. All the parts enclosed
by the dotted line are inside H-IC.
The schematic shows all the components inside H-IC. It also
gives you a good indication as to the components inside the
other tw o IC's. Such detailed information can be especially
helpful in troubleshooting. No, you can't take apart an IC to
repair the innards. But you can tell w hat kinds of signals should
appear at the IC pins.
For example, the large triangle inside IC1 indicates the
amplifier for the silicon photocell (SPC in the schematic). The
connection at pin 19 charges the memory capacitor C2. You
then know at a glance that the voltage at pin 19 should go more
positive as you increase the light striking the SPC.
The center triangle inside IC1 is the comparator for the
diaphragm-control circuit. When the output of the comparator
switches low, it turns on transistor T13. T13 then switches on
T5. Now C5 discharges through the diaphragm-control magnet
M2 to arrest the diaphragm closure.
A t pin 16 of IC1, another comparator provides the switch for
the closing-curtain electromagnet M3. When the comparator
output at pin 16 drops low, current flows through M3 to hold
open the shutter. The voltage at pin 16 goes high to shut off the
electromagnet current.
Inside IC2, you can see the large triangle which represents
the individual comparator stages for the LEDs. The cathode of
each LED connects to a comparator output. Notice that the
anodes of the LEDs connect to ■+ 3V when transistor T1 turns
on. Each LED then has the anode bias it needs to conduct. As
soon as the cathode of a particular LED switches low, current
can flow through that LED.
The small comparator inside IC2 — the one connected to pin
3 — provides the release lock. When the release switch S3
closes, the comparator compares the battery voltage w ith a
reference voltage. Then, providing there's sufficient power for
proper operation, the comparator switches low. The low
voltage at pin 3 forward biases transistor T6 to release the mir
ror. Another triangle inside IC2 represents the analog-to-digital
converter w hich lights the "6 0 " LED when the flash unit
charges.
As yet, you can only reach one IC for voltage tests — IC1 at
the top of the camera. However, you'll be able to check H-IC
after you remove the front-plate/m irror-cage assembly. So,
before going through the rest of the electronic operation, we'll
describe the procedure for separating the front-plate/m irror-
cage assembly from the body casting.
