Loma IQ2, Service Manual

Page: 89 / 106

Maintenance
Module 8023 6-19
•
Check the values of resistors RD1, 2 & 3. The values are 4.7K
Ω
220
Ω
& 2.2K
Ω
respectively as standard, but the values on the old
board may have been changed to accommodate an excessive
product signal. If they have been changed then copy the changes to
the new board.
•
Check the values of capacitors C23 & C24. These are both 1.0
µ
F as
standard but may have been changed to 2.2
µ
F to optimise sensitivity
at slow belt speeds. If they have been changed then copy the
changes to the new board.
•
Check the values of resistors R35 & R44. These are both 470K
Ω
as
standard but may have been changed to 1 M
Ω
to optimise sensitivity
at very slow belt speeds. If they have been changed then copy the
changes to the new board.
•
Check the values of resistors R34 & R41. These are both 47K
Ω
as
standard but may have been changed to 100 K
Ω
to optimise
sensitivity at very slow belt speeds. If they have been changed then
copy the changes to the new board. This modification is usually done
in conjunction with R35 & R44.
•
Re-fit the new board to the plate and the plate to the detector,
ensuring the metal spacer is fitted to the correct corner. Reference
Figure 7
on page 17
, in this section.
•
Carefully solder the wires back onto the new board in their original
positions.
•
Turn on the power to the detector. Connect the DMM set on the 20v
DC range or equivalent between (+ Vo and A gnd) and adjust R51 for
a voltage of 9v +/- 0.05 V. Move the DMM lead from (+ Vo) to (- Vo)
and check the voltage is 9 V +/- 0.3 V. Switch off the power to the
detector.
•
Refit the end plate as described in “End Plate Removal & Refitting”
on
page 15
earlier in this section.
Restore the power to the detector and carry out a head balance check as
described in “Balance”
on page 2
in the “Functional Testing section” of this
manual, before re-calibrating for good product.