Fitting Frequency Standard 9421 Or 9442 - Racal Instruments 9916 Workshop Manual

(5)
(6 )
(7)
(8)
(9)
(10) .
(11)
Unsolder the connections to the
LF
multiplier, jf fjtted, and the
connections to the three transistors on the left hand side panel.
Unsofder the connections to the two smoothing capaci tors and withdraw
them until the lugs ore clear of the holes in the p.c.b. Note the
polarity of the connections.
Unsolder the two wires between the main p.c.b. and the POWER switch.
Unsolder the
coaxial
eonnedion between input
'A'
and the p.c.b.
Unsolder R200 From the pin on the display p.c.b.
Unsolder the three earth braids on the underside.
Remove the four screws securing the main p.e.b. and slide it out to the
rear.
5.59
Reassembly
is
carried out in the reverse manner.
If it has been necessary to cut
the
tie
for the smoothing capacitors repl ace it with Racal-Danapart number
24-0155.
FITTING FREQUENCY STANDARD 9421 or 9442
5.60 It should be noted that the frequency standard model 9421 cannot be fitted iF the
battery pock is fitted.
5.61 Remove the top cover of the instrument (see paragraph 5.1). Unsolder the three
leads from the fitted frequency standard. Remove the retaining screws (and spacers
in the case of the discrete component osci Ilator) and the black plate (iF fitted). Remove
the frequency standard.
5.62 Attach the replacement frequency standard to the inner face of the rear panel
using t·he retaining screws removed in the previous paragraph.
5.63 Solder the leads from the main p. c. b. pins 30, 29 and 28 to the frequency standard
base pins 1, 4 and 7 respectively. If model 9421 has been fitt,ed ensure pins 5 and
6 on its base are linked.
~
5.64 Carry out the instrument check procedure to verify satisfactory functioning, and
calibrate the frequency standard as detailed in paragraphs 5.47 ta 5.49.
5.65 Replace the instrument cover ..
5-15
9916 Vol.2