FT-857D - RX Gain Alignment Troubles

Discussion in 'Radio Circuits, Repair & Performance' started by KC8QVO, Jan 16, 2020.

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  1. KC8QVO

    KC8QVO Ham Member QRZ Page

    All,

    I have, I believe (hope not..), a troublesome FT-857D. For some background it had the ubiquitous "corrosion in the filters" problem. It sat out of commission for about 7 years or more. I finally got around to replacing the filters before Christmas (there is another thread on that here on QRZ somewhere... it was a nightmare getting the old ones out).

    With that out of the way, the radio performs OK now. I have made several contacts on it. However, the S meter is goofy. It goes straight from off to S9+.

    I am in the service menu trying to set the S1 level in the initial RF Gain calibration (starting on 160m). I can not get the meter to read anything until it hits S9.

    On service menu item 1 (HF1-RXG) and a 9dBuV signal injected I get no meter response at a setting of 73 or less. At 74 the meter jumps to S9. No in between.

    Am I missing something? Is there any merit to going through all the prior calibrations even though the radio works fine otherwise? Frequency calibration seems right on the money... so I really don't want to go adjusting things that do not appear to be broken - unless there is something in that tuning that will affect the receiver gain control and meter reading?
     
  2. KA5IPF

    KA5IPF Ham Member QRZ Page

    Back up and look for an AGC voltage setting, just guessing.
     
  3. KC8QVO

    KC8QVO Ham Member QRZ Page

    That is a good thought. However, the only mention in the service manual of AGC is in the circuit description/theory section that talks about how it works and the radio configuration for the alignments stating that the AGC mode should be on/auto. There isn't anything in the manual that states voltage levels or a test procedure specific to AGC - just the receiver gain I am trying to set (with the described behavior in my first post). That is - unless I am missing something or not understanding something.

    I have it on the work bench now and will dig in to it a bit more - both the service manual and the rig - and see what I can find.

    I copied all the service menu item settings/values in to a spread sheet so I have those to recall.
     
  4. KC8QVO

    KC8QVO Ham Member QRZ Page

    Update -

    I adjusted the RXG settings to the level that achieved no meter response, as opposed to S1. Again, the meter response was either S9+ or nothing.

    Then I went back through the S9 and full scale SSB settings and tuned those. They were adjustable.

    The meter now appears to be "working" - both with varying the signal injection level and on the air. However, I don't trust the settings due to the lack of response on the RXG items.

    Still doesn't make sense. Getting what looks like a working meter now is better than 0 or S9+ before, though.
     

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