Checking The Electromagnet; Checking The Metering Switch And The Release Switch - Minolta XD-11 Repair Manual

across the timing capacitor. When you
push the release button far enough to
close the metering switch, a slight voltage
appears across the timing
However, the timing capacitor can't
charge any further until the trigger switch
opens. Opening the trigger switch then
allows the timing capacitor to charge as
shown in Fig. 38. When the timing
capacitor reaches around 0.5V, it shuts
o ff the current through the electromagnet
to end the exposure.
You can't as yet reach most of the
components shown in Fig. 36 and Fig. 37.
But you can often pinpoint the problem
from the top of the camera. So, before
covering the complete electronic opera­
tion, let's run through the techniques you
can use to check the switches and the
electromagnet w ithout disassembly.

CHECKING THE ELECTROMAGNET

An open electromagnet coil causes the
shutter to deliver only its mechanical
speed (1/1000 second or faster). A l­
though you'll have to remove the Seiko
shutter to replace the electromagnet, you
can check the coil w ithout further dis­
assembly. Remove the small section of in­
sulating tape at the top of the flex circuit.
You can now see the brown wire and the
red wire coming from the electromagnet.
Check the continuity of the coil by
measuring the resistance between the red
wire and the brown wire. You should
measure around 300 ohms. Alternately,
you can perform a quick shorting test to
determine if the electromagnet is good.
Try shorting between the brown wire and
ground as you release the shutter. If the
coil is good, the shutter will hang open
for as long as you maintain the short.
W ith most electronic shutters, you can
check coil continuity by measuring the
voltage at each electromagnet lead. If you
Figure 39
measure a voltage at one lead but not at
the other, the
However, you've seen that the transistor
capacitor.
in series w ith the XD-11 electromagnet re­
mains o ff until you release the shutter.
So, at the red electromagnet lead, you'll
measure 0V — not the full battery voltage
as you would w ith most other circuits.
You'll also measure 0V at the brown lead.
W hen you release the shutter, the tran­
sistor turns on and connects the red elec­
tromagnet lead to positive battery, Fig.
38. So, w ith the shutter open, you should
measure 3V at the red wire, Fig. 39. But
you should still measure 0V at the brown
wire. The brown wire now connects to
0V, keeping a 3V potential difference
across the electromagnet.
The voltage at the brown wire switches
high to end the exposure. If you leave the
positive voltmeter lead on the brown
wire, you can see the voltage switch high.
You should see a voltage indication at the
end of the exposure. But the voltage only
appears briefly. When the mirror returns,
switch S7, Fig. 38, once again opens to
shut o ff the
tromagnet leads then return to 0V.
A poor ground connection in the circuit
may also cause the shutter to deliver only
its fastest speed. Suspect a poor ground
connection if you measure a voltage at
the red electromagnet lead when you par­
tially depress the release button. If you
measure around 2.5V, try retouching the
solder connections to the black ground
wire, Fig. 39. However, you may have to
rem ove the
assembly to correct the ground contact.
A screw on the section of flex circuit that
mounts to the mirror cage makes the
ground connection through the camera
body.
If you measure the full 3V to the red wire
and the brown wire, the switching tran­
coil must be open.
transistor. Both elec­
fro n t-p la te /m irro r-c a g e
sistor may be shorted. Fig. 38. A 3V
reading could also indicate a problem with
the electromagnet current source. Both
components are inside H-IC, the hybrid IC
on the side of the mirror cage. You'll have
to remove the front-plate/mirror-cage
assembly to replace the IC.
CHECKING THE METERING SWITCH
AND THE RELEASE SWITCH
Both the metering switch and the
release switch are at the back of the front-
plate assembly. As yet, you can't reach
the switches. But you can reach the
switch connections for troubleshooting.
The metering switch connects to the
green wire, and the release switch con­
nects to the orange wire, Fig. 39.
Fig. 40 shows the portion of the
schematic that includes the tw o switches.
As you start pushing the release button,
the metering switch S5 closes. The
metering switch turns on transistor T1,
applying the positive battery voltage to
pin 1 of IC1 and to pin 2 of IC2.
Pushing the release button the rest of
the way closes the release switch S3. The
release switch now tells the electro­
magnetic release circuit to release the
mirror. Also, the power-holding circuit —
transistor T11 in Fig. 40 — turns on. T11
now keeps transistor T1 conducting. So,
even if you allow the release button to
return, the circuit continues to operate.
Transistors T1 and T11 are both inside
H-IC on the side of the mirror cage. Diode
D2, a transistor connected as a diode.
Fig. 40, is also inside the hybrid IC. You
m ight suspect a problem in this portion of
the circuit if the camera draws power
constantly — even though you haven't
depressed the release button.
W hat if the metering switch S5 fails to
make contact? Obviously, the LEDs will
not turn on when you partially depress the
release button. Yet, thanks to the power-
holding circuit, the LEDs will turn on when
you fully depress the release button. With
a defective release switch S3, the shutter
w on 't release at the electronically con­
trolled settings.
To check the metering switch, measure
the voltage at the green wire, Fig. 39. You
should measure around 2.5V. When you
depress the release button part way, you
should measure 0V at the green wire. If
the voltage doesn't drop to 0V (ground),
the metering switch isn't making good
contact.
Alternately, you can check the metering
switch by connecting an ohmmeter be­
tween the green wire and ground; you
should measure direct continuity when
you push the release button part way. Or
you can simply short the green wire to
ground. Connecting the green wire directly