Ericsson MPI-II VHF User Manual

Battery voltage (7.5/10 Volts, B+) is supplied to a 5.4 volt

regulator circuit consisting of transistors Q801, Q802 and
Q803. Diode regulator U801 provides a 2.5 volt reference for
this circuit. Battery voltage (B+) is also supplied to the Syn-
thesizer Board for isolation amplifier U206. the 5.4 volt regu-
lator supplies both the synthesizer and most of the Transmit
and Receive circuits.

The BAND SW control input, initiated from the Trans-

mit/Receive Board, is used to bandswitch the VCO. This input
is low when receiving and high (greater than 3 volts) when
transmitting.

Pin 2 of the Phase Lock Loop U201 should have a wave-

form similar to the one shown for the reference oscillator
(Figure 5). If this waveform is not present, oscillator module
U203 is probably defective.

Connect a DC power supply to pin 3 of U204. With 2.0

volts DC on pin 3, the output on pin 5 of U204 should be
approximately 140 MHz for the low split and approximately
190 MHz for the high split. With 4.3 volts DC on pin 3, the
output should be approximately 220 MHz for the high split.

Power output of the VCO can be measured by connecting

a coax cable directly to the module, between pin 5 and ground,
through a 100 pF coupling capacitor. The output should be
approximately 0 dBm.

Connect 4.3 Vdc to pin 3 to VCO U204. With the radio in

receive, monitor the frequencies of the VCO at pin 5 through
a 100 pF coupling capacitor. Short pin 6 to U202 to ground to
cause divide by 65 to occur. The frequency output at pin 4
should be the VCO frequency divided by 129. Tie pin 6 to pin
2 (5 volts) to cause divide by 64 to occur. Check pin 4 to verify
that this occurs. Improper division may indicate a defective
prescaler.

Bilateral switch U205 is used to short around parts of the

loop filter during channel changes. A shorted gate (to ground
or adjacent gate) may be isolated by comparing voltages
through the loop filter to those of a functioning radio. Defective
gates might be suspected when the radio does not change
frequency quickly enough.

After checking for the proper operation, measure the loss

of the VCO, pin 5 to pin 1 of the Prescaler U202. The loss
should be 10 dB.

Surface mount components should always be replaced

using a temperature controlled soldering system. The solder-
ing tools may be either a temperature controlled soldering
iron or a temperature controlled hot-air soldering station. A
hot-air system is recommended for the removal of compo-
nents on the multi-layered boards used in the MPI-II radio.
With either soldering system, a temperature of 700°F
(371°C) should be maintained.

The following procedures outline the removal and re-

placement of surface mount components. If a hot-air solder-
ing system is employed, see the manufacture’s operating
instructions for detailed information on the use of your
system.

1.

Grip the component with tweezers or small nee-
dlenose pliers.

2.

Alternately heat the metallized terminal ends of the
surface mount component with the soldering iron. If
a hot-air system is used, direct the heat to the termi-
nals of the component. Use extreme care with the
soldering equipment to prevent damage to the printed
wire board (PWB) and the surrounding components.

3.

When the solder on all terminals is liquefied, gently
remove the component. Excessive force may cause
the PWB pads to separate from the board if all solder
is not completely liquefied.

4.

It may be necessary to remove excess solder using a
vacuum de-soldering tool or Solderwick

®

 Again, use

great care when de-soldering or soldering on the
printed wire boards. It may also be necessary to
remove the epoxy adhesive that was under the sur-
face mount component and any flux on the printed
wire board.

Waveforms associated with the synthesizer were
measured with 10 megohms, 30 pF probe using Dc
coupling. See Figures 5-8.

Figure 6 - F

in

 (Input to U201, Pin 10)

Figure 5 - Reference Oscillator

(Input to PLL Module U201, Pin 2)

Figure 8 - SYN EN (Input to Pin 13 of U201)

The top of the ramp is approx.  0.8 Vdc geater than
the control voltage out on pin 17 of U201.

Figure 7 - Remp (Generated in 

U201 and appears on Pin 15)

Avoid applying heat to the body of any surface
mount component using standard soldering meth-
ods. Heat should be applied only to the metallized
terminals of the components. Hot-air systems do
not damage the components since the heat is
quickly and evenly distributed to the external sur-
face of the component

The CMOS Integrated Circuit de-
vices used in this equipment can be
destroyed by static discharges. Be-
fore handling one of these devices,
the serviceman should discharge

himself by touching the case of a bench test instru-
ment that has a 3-prong power cord connected to an
outlet with a known good earth ground. When sol-
dering or desoldering a CMOS device, the solder-
ing equipment should have a known good earth
ground.