Midland Radio SP-300 service manual Rx Vco

MAXON

SP-300 HAND HELD

15. Disconnect the test equipment.

Should repairs be required, the following procedures should be applied:

RX VCO

1.Set the unit to the highest receive frequency, 470 MHz(UHF), 174MHz(VHF) and adjust the VCO L303 to 10 volts.

2.Set the unit to the lowest receive frequency 440 MHz(UHF), 148(VHF) and check that the VCO voltage is above 2.0 volts. Adjust L303 for 2.0 volts.

zNote: Use TP1 to measure the voltage.

RECEIVER

1.Apply a standard test signal to the receiver antenna terminals.

2.Adjust T1 for maximum sensitivity and audio out- put with minimum audio distortion.

TRANSMITTER

Connect the unit to a Service Monitor with the power meter setting to the 10 W scale (or autorange).

TCXO

Set the channel selector to the mid-range frequency 460 MHz, adjust TC701(VHF) on the TCXO board, RV5 (UHF) on the Main board, for a reading of 460 MHz +/-200 Hz (155 MHz VHF models).

TX VCO

1.Set the unit to the highest transmit frequency, 470 MHz(UHF), 174MHz(VHF) and adjust the VCO L203 to 10 volts.

2.Set the unit to the lowest transmit frequency 440 MHz(UHF), 148(VHF) and check that the VCO voltage is above 2.0 volts. If voltage is below 2.0 volts, adjust L203 for 2.0 volts or more.

CTCSS, DCS & DEVIATION ALIGNMENT

1a. Set the unit to a mid-frequency range and a CTCSS of 67Hz. Push PTT and adjust RV403 for desired CTCSS tone deviation.

1b. Switch to a channel with the same frequency and CTCSS of 250.3Hz. Push PTT and adjust RV401 to desired CTCSS tone deviation, same as above step.

1c. Switch between the 67Hz channel and the 250.3Hz channel and adjust RV401 until the deviation is the same on both channels. It may be necessary to read- just RV403 to get the desired deviation.

2.Inject a 6mV signal of 1000Hz to the microphone input. This should produce a 3kHz deviation for 25kHz(S) channel spacing and 1.5kHz for 12.5kHz(N) channel spacing, measure transmit dis- tortion, that should be less than 5%. Increase the audio input level to 20mV.

3.Set the deviation by adjusting RV402 to 4.5kHz for 25kHz channel spacing(S) and to 3kHz for 12.5kHz channel spacing(N) on a non-CTCSS or DCS chan- nel for the initial setting. Select a CTCSS or DCS frequency and verify that the deviation is less than or equal to 5kHz(S) and 3kHz(N).

4.Vary the audio frequency from 300 to 3000Hz and verify that the deviation does not exceed 5kHz(S) and 3kHz(N).

APC

1.Select a channel which is programmed with high power. While transmitting, adjust RV1 in the APC circuit for 5 watts +/- 0.1 watt.

2.Select a channel which is programmed with low power. While transmitting, adjust RV3 in the APC circuit for 1watt +/-0.1 watt.

Page -22- May 2001