Instruction manual

012-03175E
6
④ The replacement MOS-FET will probably come in
an anti-static bag or may be wrapped in aluminum
foil. The leads will be protected by a thin ring or
spring that is wound around the leads near where
they protrude from the base of the transistor. Gently
remove the MOS-FET from the bag or foil, but do
not remove the thin wire ring that is around the
leads. Leave this wire ring in place until after the
MOS-FET is seated in the socket.
⑤ The MOS-FET has a small metal tab protruding
from one side (see Figure 6). The lead directly be-
low the tab (as seen from the top side of the transis-
tor) is lead number 8. Count back to lead number
5, as shown, and gently bend the lead up.
⑥ Insert the leads of the MOS-FET, except for lead 5,
into the socket so that the metal tab lines up with
the notch on the side of the socket as shown in the
figure.
⑦ Insert lead number 5 into the socket that is con-
nected to the adjacent binding post. This may be
done by
inserting the lead through the slot in the end of the
socket, and then bending the end of the lead back
and crimping it tightly. Now gently pull off the thin
ring of wire that is wound around the leads. This
may require thin nose pliers or "tweezers".
⑧ Replace the cover.
Repair
Should your Electrometer have problems that are not
covered in the preceding sections, we strongly suggest
you return it to PASCO scientific for repair.
Calibration
① Remove the four screws that fasten the front panel
to the case, then gently lift the front panel out of the
case.
② Turn the POWER switch to ON.
③ Set the FUNCTION switch to 3.
④ Flip the Zero Switch to ZERO LOCK. With the
¯zero adjust knob midway between its extreme cw
and ccw positions, adjust the Zero Calibration Po-
tentiometer to zero the meter.
⑤ Set the Function Switch to 30, zero the meter using
the zero adjust knob on the front panel, then con-
nect the INPUT of the Electrometer to a known, ac-
curate 30 VDC source.
⑥ Flip the Zero Switch to the PUSH TO ZERO set-
ting.
⑦ Adjust the Calibration Potentiometer (see Figure 5)
until the meter reads 30 volts.
⑧ Press the Zero Switch, then release it. The meter
should still read 30 volts. If it doesn’t, readjust the
Calibration Potentiometer until it does.
MOS-FET Replacement
If the meter can’t be zeroed using the ZERO ADJUST
knob with the Zero Switch set to ZERO LOCK, the
MOS-FET has probably failed. (MOS-FET is an
acronym for Metal Oxide Semiconductor-Field Effect
Transistor). You can order a replacement from
PASCO scientific (Part # 422-001) . When ordering a
replacement part, be sure to include the model number
of the Electrometer.
To replace the MOS-FET:
① Turn the Electrometer off.
② Remove the four corner screws that fasten the front
panel to the case, and gently lift out the front panel.
③ Gently pull the MOS-FET out of its socket (see Fig-
ure 5). Avoid yanking or twisting it, as this may
damage the transistor socket.
1
3
2
4
56
7
8
MOS-FET
Align pin 8, the pin
directly below the
tab, with the notch
in the socket, as
shown.
Insert pin 5 into
this socket
Figure 6 MOS-FET Installation