TS-940S No transmit on SSB or AM

Discussion in 'Radio Circuits, Repair & Performance' started by AD8BU, Apr 17, 2020.

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  1. AD8BU

    AD8BU Ham Member QRZ Page

    Hello all. My TS-940S started acting up earlier this week while I was operating FT-8. The output was dropping out. I could overcome this by cranking the mic gain, and smacking the top of the radio near the speaker would also recover it temporarily. The issue happens when inputting a signal from both the front mic jack, and the rear 13-pin ACC2 port.

    I cracked it open to re-seat the connections in this area of the radio and apply some contact cleaner on them. Now it has no output on SSB and AM. There is no meter movement on power or ALC. I have tested multiple (but not all) bands. It does still transmit on FM and CW. I have hooked up an external power/SWR meter and it confirmed no output on AM or SSB.

    Does anyone have any suggestions on where to look? (I do have a printout of the service manual, user manual, and schematics).

    Other notes that may (or may not) be relevant about this rig:
    From what I understand, this is an early production unit.
    I have replaced the original fans with computer fans and power them from an external 12v supply
    The Zener diodes on the AVR board have been replaced at some point in the past, but it does not appear to have been completely recapped.

    I will keep looking as well while I wait for replies.

    Thanks!
     
  2. AD8BU

    AD8BU Ham Member QRZ Page

    UPDATE: Found cold solder joints on a connector on the IF board. Its the connector near L35. The wire going to it is heavily shielded. I will update this after I get it re-soldered.

    Edit: Fixing that cold solder joint for that connector appears to have solved the entire problem. I will finish putting it back together and try to make some contacts.
     

    Attached Files:

    Last edited: Apr 17, 2020
  3. AD8BU

    AD8BU Ham Member QRZ Page

    Final update:

    The cold solder has indeed solved the problem. I am back on FT-8 as I type this, and will be on the air during the Michigan QSO party tomorrow, and the SSB Rookie Roundup on Sunday.
     

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