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Ham Radio Circuits and Repair / Kenwood TS-140s strange receive audio issue has me confuzzled.
« on: October 11, 2017, 11:59:47 PM »
I have an issue in my Kenwood TS-140s that has me a bit puzzled. Whenever I tune to anything between 4.000Mhz and 7.499Mhz, the radio has very low audio. The weird thing is that if I tap the PTT or turn the send/recieve switch on/off, the audio comes up and usually stays up until I go to another band and come back.
Tonight I started digging and believe I've narrowed it down to something funky with the signal path through K5 and K6 on the filter board. The notation on the schematic indicates that these relays switch on the frequency range of my problem.
Voltages at the source (IC1 on the signal board), connectors, and relays are all good and match voltages measured on the other relays. But i know that does not necessarily mean the relays are latching.
Something else that I noticed is that when I touch any of the even numbered relays (output side) including K16, the audio sometimes changes either up or down but this does not happen on the odd numbered (antenna side) relays. Also lightly touching the board with my finger in random places will change the audio. All of this only happens when tuned between 4.000 and 7.499.
I'm thinking about pulling the board and swapping K5 and K6 with K7 and K8 (one at a time) and see if the problem follows the relay(s). If it does, I'll order the relay(s), but if not, what else should I check? Or is there something els I should check before trying a relay swap?
Filter unit schematic is attached for reference.
Tonight I started digging and believe I've narrowed it down to something funky with the signal path through K5 and K6 on the filter board. The notation on the schematic indicates that these relays switch on the frequency range of my problem.
Voltages at the source (IC1 on the signal board), connectors, and relays are all good and match voltages measured on the other relays. But i know that does not necessarily mean the relays are latching.
Something else that I noticed is that when I touch any of the even numbered relays (output side) including K16, the audio sometimes changes either up or down but this does not happen on the odd numbered (antenna side) relays. Also lightly touching the board with my finger in random places will change the audio. All of this only happens when tuned between 4.000 and 7.499.
I'm thinking about pulling the board and swapping K5 and K6 with K7 and K8 (one at a time) and see if the problem follows the relay(s). If it does, I'll order the relay(s), but if not, what else should I check? Or is there something els I should check before trying a relay swap?
Filter unit schematic is attached for reference.