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INTEK M-760 Plus - Service Manual | Radioaficion Ham Radio

INTEK M-760 Plus - Service Manual

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INTEK M-760 Plus - Service Manual Download


Table of Contents Page
Specifications …………………………………………………………….……3    
Test and Alignment Procedure ……………………………………….….…….4    
Block Diagram ………………………………………………………….……13    
Schematic Diagram  ……………………………………………….………. 14     
Printed Circuit Board  ……………………………………………………… 21    
Channel Frequency Charts  ……………………………………….…………23    
Parts List  ……………………………………………………………………32    
Semiconductor Voltage Chart ………………………………………………...38


THEORY OF OPERATIONS   
TRANSMITTER

A. RF Amplification
The output of double AMP Q14 is fed through tuning IFT L8 to the base of pre driver AMP Q15. The output is then supplied through tuning circuit L9 to RF driver AMP Q16. The output of Q16 is supplied with tuning circuit L10 and C116,C67,C95 and goes to the base of final RF AMP Q17. The output of Q17 is supplied to the antenna through L-C tuning circuit.


B. Circuit for Suppression of Spurious Radiation
The tuning circuit between the output of final AMP Q17 and antenna, 4-stage “PHI” network L13,
C142,C71,C72,L14,C74,C75,L15,C77,C78,L16,C79,C80,L24 serves as a spurious radiation suppressor . This network also serves to match the impedance between TX power AMP Q17 and the antenna.

 

C. Circuit for Limiting Power

After finished all alignment, the constant voltage supply circuit limits the available power 4 W or slightly less. RV4 and corresponding three transistors control supply voltage of RF amplifier and other circuits.

Tune all the trimmer parts for maximum indication of RF power meter and adjust RV4 to make 4 w indication of RF power meter.

The tuning is adjusted so that the actual power is from 3.5 to 4.0 W. There are no other additional controls for adjusting the TX output power.


D. Modulation Control
a. FM
The mic input is fed to mic audio amplifier IC KIA324 which drives modulation varicap diode D403 in the VCO circuit. RV1 limits the incoming modulation audio levels to inhibit over modulation. While reading the modulation factor on the modulation analyzing equipment, adjust RV1 shall not exceed +-1.7KHz/Dev. After 20 dB up from 1.25 KHz/1.2 KHz/Dev. Audio level


b. AM
Modulation signals are filtered with RC network and goes to the audio power AMP IC IC103 to make nominal signal level to achieve wanted modulation. To control incoming audio signal, diode D7 and corresponding ALC circuit limits the modulation shall not exceed +/-90% adjust RV3 +/-90% modulation under 1.0 KHz AF 60%  mod plus 20 dB of audio signal.


E. Receiver
CB receiver is dual conversion supper-heterodyne type with the first IF 10.695 MHz and second IF 455 KHz. Receiver is separated two blocks, 1stIF section and 2ndIF section. The PLL synthesizer supplies first local frequency 16.270 ~ 16.710 MHz.(for EU) and 16.90625 MHz ~ 17.29625 MHz (for UK) With the provided first local frequencies to Q2,Q3 mixes the incoming RF signal to generate first IF signal. Mixed signals were filtered with the XF1 (10.695 MHz) crystal filter and other tuning circuits. Output signal of mixer is filtered with CF1(455KHz ceramic filter). The 455 KHz signal from the 2nd IF filter was amplified and limits internaly. After amplification the signals fed the quadrature detector loop L20. Then we can see the recovered audio signals on Pin 9 for FM of IC7. With the amplitude of recovered signals, Q10 serves as an audio amplifier.  For AM signal Will be pass filter CF1 and induced to Q6, Q7 respective and detected to voice signal by D5.

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