Simpson 260 - Sub-panel Parts Replacement; Rectifier Replacement and Recalibration

MAINTENANCE
JAUTION: If the following maintenance operations
ге to be carried out successfully on a Model. 270,
it is most important that you have access to pre-
sision standard meters, if the original high ac-
suracy of your instrument is to be restored. It
is strongly recommended that your Model 270 be re-
,urned to the factory or authorized service depot
or this type of repair.
SUB-PANEL PARTS REPLACEMENT
Beneath each resistor on the printed circuit
сага is its circuit designation (e.g. RIC) as it
is shown on the schematic diagram and in the parts
list. This mark will eliminate any doubt which may
rise as to the location of any of the resistors.
tECTIFIER REPLACEMENT AND RECALIBRATION
There are two small rectifiers which are loc-
ited at the top of the printed circuit, near the
large 1.5 volt cell. These are used to rectify
she А.С. voltages for measurement. They are shown
2s D-l and D-2 in the overall circuit diagram.
In the Model 270, these are beneath the small
superimposed circuit board which carries the A.C.
,emperature compensation network and the protective
liode.
Both rectifiers act in the meter circuit to
sffectively create а full wave rectifying action.
[f either or both should fail, the meter will show
incorrect indications.
In case of rectifier failure in the 260, replace
she defective rectifier with another 1N478, and be
sure to observe polarity when you connect it into the
circuit. If a type 1N478 is not available, use any
ооа quality small crystal rectifier as a replacement.
3l ~