2.Check power on the lower channel. Adjust C124 in the direction that increases power output to a level half way between the initial lower and upper channel levels.
3.Recheck the upper channel power. If the upper channel power is reduced, reset to the previous level by adjust- ing C126.
4.Repeat this procedure until the power out on both channels is equal (±.1W).
∙For frequency spreads £ 10 MHz - power out ³ power minimum
∙For frequency spreads > 10 MHz - power out ³ power minimum - 1dB
Supply current levels should not exceed 1100 mZ (10V) or 800 mA (7.5V) with wide band tuning.
TX Modulation Set
With the transmitter keyed, apply a 1 kHz tone at 100 mV RMS to the MIC input. Adjust R230, located on the Synthe- sizer Board, until the following peak deviation is measured on the output modulation analyzer:
With Channel Guard - 4.5 kHz (±100 Hz)
Without Channel Guard - 3.75 kHz (±100 Hz)
RECEIVE ALIGNMENT
Change to a receiver test setup, with a frequency modu- lated RF signal generator connected to the antenna jack J3. Set the input RF signal to the highest programmed receive fre- quency and modulate it with a 1 kHz tone at 5 kHz peak deviation. Use a signal level high enough to measure the level of the 455 kHz 2nd IF signal at test point J501 with an RF AC voltmeter. Proceed with the following alignment procedure.
IF Alignment
Adjust the RF signal level for linear operation at J501. Tune L502 and L504 for a maximum IF signal level at J501.
An alternate method for making the IF alignment is as follows. Tune L502 and L504 for minimum audio distortion while monitoring the speaker output. Use either 5 kHz or 3 kHz of deviation.
Second LO Frequency Set
Remove all modulation from the input signal and increase the level to 0 dBm. Monitor the frequency at J501 and adjust L505 in the crystal oscillator circuit for 455 kHz ±100 Hz.
Quadrature Detector Set
Modulate the RF input signal with a 1 kHz tone at 3 kHz peak deviation. Load the speaker output at the accessory con- nector with 8 ohms to ground. Monitor the speaker output from the accessory connector while tuning L506 in the quardrature detector for a maximum audio level.
L.O. Notch Tuning
When it necessary to limit the L.O. leakage out the antenna port to a level less than -60 dBm, (Canadian D.O.C. RSS 119, 121 require -53 dBm for portables with batteries, otherwise -57 dBm) the L.O. notch filter may be tuned to the receiver L.O. frequency to meet this requirement. Observe the L.O. signal level at the antenna port on a spectrum analyzer capable of reading -70 dBm. Select the channel with the lower operating receive frequency and tune the notch filter adjustable capacitor (C136) for a minimum level. Check the level on the higher receive frequency. If greater than -60 dBm, turn the capacitor (C136) in the direction that lowers the level to the point that -60 dBm is reached and stop. Recheck the lower receive frequency.
TROUBLESHOOTING
This section provides a guide to troubleshooting the MPI-
IIVHF radio. The following procedures will assist in de- terming if the problem is in the RF circuits (Transmitter, Receiver or Synthesizer) or the Control circuits. The test set-up should be the same as that used in the Alignment section of this manual.
NOTE
Throughout the service procedures, the following information should be observed:
∙The bench power should be set for 7.5 Vdc (±0.1 Vdc) for a 2 watt radio, or 10.0 Vdc (±0.1 Vdc) for a 4 watt radio. If a battery pack is
used, it should be fully charged. Typical battery pack voltage should be within ±20% of set voltage over its full discharge cycle.
∙Logic Levels should be:
Logic 1 | = | high | £ 4.5 Vdc |
Logic 0 | = | low | ³ 0.5 Vdc |
∙Modules are not field repairable. Schematics and Outline drawings for the modules are pre- sented for troubleshooting reference only.
∙The personality information stored in the radio should be backed up on the PC computer before any service procedure.
Documentation To Help In Troubleshooting
∙RX and TX block diagrams with RF gains and levels
∙Synthesizer block diagram
∙Control Circuits block diagram
∙Audio Processing block diagram
∙Interconnection diagram
∙Outline diagrams
∙Schematic diagrams
∙Parts lists
∙IC data
TRANSMITTER
Transmit Power Output Problem, Inoperative or Low
1.Power sources and regulated power supplies should be checked before troubleshooting any transmitter problem. The radio’s power source, whether a battery or bench power supply, is especially important in
Tabel 2 - General Troubleshooting Guide
| | | | | |
| SYMPTOM | | | POSSIBLE CAUSES | |
| | | | |
| | | | | |
| Completely inopera- | | ∙ Dead Battery Pack | |
| tive (no audio) | | ∙ | Fuse blown | |
| | | ∙ | Control circuit problem | |
| | | | |
| At power-up radio | | ∙ Weak battery pack | |
| beeps continuously | | ∙ | Unit is not programmed | |
| | | ∙ | Synthesizer is not locked | |
| | | | |
| Receiver inoperative | | ∙ Squelch level set too high | |
| or weak | | ∙ | Channel Guard enabled | |
| | | ∙ | Defective antenna | |
| | | ∙ | T/R Board problem | |
| | | | |
| Transmitter inopea- | | ∙ Power levels set too low | |
| tive or low range | | ∙ | Weak battery | |
| | | ∙ | Defective antenna | |
| | | ∙ | T/R Board problem | |
| | | | |
| Tx and Rx inopera- | | ∙ Programming incorrect | |
| tive on one or both | | ∙ | Synthesizer problem: | |
| channels | | | VCO, prescaler, or | |
| | | | |
| | | | lock detect | |
| | | | | |
| | | | | |
troubleshooting a personal radio. Current consump- tion offers an excellent clue in the case of a dead or weak transmitter. See Table 3 in the Battery Informa- tion section on typical current consumption for dif- ferent operating conditions. Check supplies as follows:
a.Check for battery B+ voltage at J12-01, or inside fuse F1/switch S1. It should be present at the driver Q104 and final amplifier Q105, and meas- ure 7.5 Vdc for 2-watt radio, 10 Vdc for 4-watt radio.
b.Check for presence of B+ SW on buffer ampli- fier Q106 and predriver Q103. It should switch ON under control of the PTT switch through B+ switch Q805.
c.Check 5.4 V from 5.4 V regulator, which is required for and available on the Synthesizer board.
2.An early step in troubleshooting for the cause of low RF output power is to check that the programming is correct.
S E R V I C E
S
E C T I O N
