Yaesu FT-902DM

Discussion in '"Boat Anchor" & Classic Equipment' started by KE5GIP, Dec 28, 2017.

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  1. N8YX

    N8YX Ham Member QRZ Page

    Marker tone should be at 25KHz or 100KHz multiples; e.g., .100 or .025, .050 and .075. It shouldn't be way off (more than a few hundred Hz). If it is, you either have a counter problem or a heterodyne/mixer problem to sort.
  2. G3YRO

    G3YRO Ham Member QRZ Page

    So given that the Receiver is working, does the Preselector peak signals (or noise) OK ?

    (you said before that it didn't)

    Roger G3YRO
  3. KE5GIP

    KE5GIP Ham Member QRZ Page

    The accessory plug is in place, and the tubes do light up...
    when the rig switches to Transmit shows IC of 50MA
    as for visually inspecting, what am I looking for beyond that the tubes light up?

    thanks again for the help
  4. AI3V

    AI3V Ham Member QRZ Page

    Should be exactly every 100 khz.

    It is the legal frequency standard for the rig so you know where you are transmitting.

    Test it's accuracy by tuning in wwv and see if you get a "zero beat".



    Also, try to tune using the cw mode. Plug in a key and see if the final current goes up (and of course RF output)

    Since you see the correct bias current (50ma) this tells you the FINAL tubes have the correct voltages, and the tubes are ok, you should be able to adjust the 50 ma with the bias control, it's a set and forget kind of adjustment, but a great sanity check to see the bias change !
    Last edited: Jan 4, 2018
  5. G3YRO

    G3YRO Ham Member QRZ Page

    Clearly you have no drive on Transmit . . .

    But you haven't answered my question about whether the Preselector peaks signals on Receive?

    This is a clue as to what the problem is.

    Roger G3YRO
  6. KE5GIP

    KE5GIP Ham Member QRZ Page

    The preselector does peak noise on lower bands.
  7. N8YX

    N8YX Ham Member QRZ Page

    There's the first servicing clue.

    All the various band trimmers - starting with the upper bands - need to be in correct adjustment for the rig to develop rated power across the HF spectrum, and for the Preselector/Driver Tuning control to track properly. Some of these are additive (relying on proper adjustment of preceding bands).

    Additionally, the radio may have been converted to 11M and its 10M trimmers retuned to take this into account.

    Get ahold of the FT-901 Service Manual w/ FT-902 Addendum and study the alignment process thoroughly. Verify that 10M is actually 10M (ignore the display for now; you'll need to check the crystals in the XTAL assembly) then let's get 10M working before tackling the lower bands.

    The fact that you have no carrier on ANY band leads me to believe there's a problem with the BFO Board or the switching arrangement that controls it but this is a separate problem than the Preselector tracking.
  8. KE5GIP

    KE5GIP Ham Member QRZ Page

    Ok I can confirm 10meter is in fact 10 meter, I have listened to a regular 10meter net.
    BFO board - Looking at the signal tracing diagram I don't see this labeled I have
    Xtal unit
    PLL unit
    VCO unit
    Carrier unit
    Filter unit
    RF unit
    Rect. units
    Driver unit
    Final unit

    Can you tell me which board I should be looking at?
  9. N8YX

    N8YX Ham Member QRZ Page

    Carrier Unit is the BFO Board. Make sure you have the correct signals there.

    Might want to borrow a set of service extenders. Failing that, look at the connector underneath the chassis that the Carrier Unit plugs into. You should be able to put a scope on the pins which feed carrier to the next stage in the TX chain.

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