CYBERNET 134 CHASSIS
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         YORK , ROTEL , CYBERNET BETA, MIDLAND 76-900 BASE STATION,
         RADIOMOBILE 202
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PLL CIRCUIT DESCRIPTION / TESTING
  The 134 has a conventional VCO circuit, controlled by the LC7137 PLL chip.
The VCO has only a limited frequency range, however (a deliberate design
feature to improve stability) and since the VCO frequency on TX is roughly
13.5MHz (half the TX frequency) and RX is around 16MHz (RX - 10.240MHz), you
will realise why the design requires the VCO centre frequency to be shifted
down on TX. This function is performed by a transistor which connects a
trimmer capacitor across the VCO inductor during TX. If the VCO requires
adjustment, it is necessary to first adjust the inductor during RX, and
then adjust the trimmer capacitor during TX. If you monitor pin 14 of the
LC7137 PLL IC you will find that the voltage is around 7 volts when the VCO
is correctly adjusted (locked in) and 0 volts when the PLL is out of lock.
If you monitor the voltage on pin 15 you will see that it changes by approx
0.06 volts each time the channel switch is turned. There are very few things
that can stop the VCO / LC7137 from working properly.
  Firstly, if the radio lights up, makes a noise, but otherwise refuses to
operate, check Pin 18 of the LC7137 for around 6.5 volts. If less than 6.5V
check that the 6.2V Zener and current limit resistor are ok. If ok then
check Q16 and D8 (voltage reg).
  Assuming the LC7137 has 6.5V, check the 10.240MHz crystal is oscillating.
If no oscillation replace 10.240MHz crystal and then PLL chip.
  Next check LD on pin 14. If high then all is ok, but to be sure check the
voltage change on PIN 15.
  If the VCO is out of lock, try adjusting the VCO coil during RX. If pin 14
remains low, ensure that the VCO is, in fact oscillating. If it is not,
replace VCO transistor Q1 and re-check.
  If the VCO still refuses to lock, check D3 (varicap), then Q25 which feeds
the VCO frequency back to PIN 19 of the LC7137.





IMPROVEMENT OF SQUELCH ACTION:
Change C109 (10 uF next to Q14) to 1 uF to speed up the squelch action

Chassis squelch improvement:
Remove the front leg of R60 (10k) from the board (RHS front of PCB).
Solder a wire into this hole (connects to Q14 collector) and solder the
free end to the post near the front of the board which has a wire - usually
blue going to the top (loud) end of the volume control.

Power output lower than usual - Replace L4 (22uH), L5 (68uH) and 
L7 (24 turns of 28SWG enamelled coppper wire on a 27R resistor).

Almost no power output on TX. Monitor rig reveals weak, noisy TX.
Try turning CT1 slightly because maladjustment can cause this effect.

Volume control turned down but continues to give sound dependant on
squelch setting! Try replacing C109 which might be open circuit.

NO RX NO TX - Try replacing Q18 (2SC1318).

10nF cap across vol. control acts as treble cut if rig has no tone switch.

TO CHANGE CH9 TO CH19 priority. Disconnect track from LC7137 pin 9 and
reconnect to pin 8. Add 2 off 1N4148 diodes with cathodes (bar) connected
to common ends of D251 - 256 and anode ends to d' and b' segments on 
CH display. On rigs without a CH9 switch, use a changeover switch to 
disconnect power from CH switch and CH display and to connect power
(up to 8V) to pin 8 and to the diodes added to produce a '19' on CH display.

CRYSTAL FILTER:  Remove C67 (2pF) between T* and T9. Fit the crystal filter
in its place with the centre lead soldered to T8 or T9 can. Tune T8 and T9
for optimum signal strength, then readjust slightly for best sound on a loud
but distant signal. If T9 is not present, fit a 85FC4402EJ 7mm Toko coil.

PLL NOT LOCKING - Replace Diode D2 (6v2 Zener)

LOW AUDIO - Replace Q15 (2SA733)

LOW AUDIO/ POOR SENSITIVITY ON RX/ LOW POWER ON TX
Replace transistor Q18.