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Should yaesu ft901dm drift constantly?

Discussion in '"Boat Anchor" & Classic Equipment' started by KG7HVR, Oct 2, 2018.

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  1. W9GB

    W9GB Ham Member QRZ Page

    Yaesu FT-901DM / FT-902DM HF Transceiver
    Survival Guide
    http://foxtango.org/Files/FT901-902 SG5.pdf
    Dave, WB5TKA (page 38) discussed Temperature Compensated Capacitors
    used in the VFOs of these models.

    FIRST, assure that your DC Voltage converters are CLEAN and STABLE (regulators working).
    The Yaesu FT-901DM/FT-902DM series often suffer Electrolytic capacitor leakage/failures after 20 years (exploding electrolytics). DC Regulation (like +6 VDC) are on Plug-In cards.
    Hundreds of these Yaesu models were abused and trashed by operators with no STEM/bench skills ... the Yaesu FT-101 series suffered similar fate, as they were often found in community electronics dumpsters 25-30 years ago.

    Opening up and properly adjusting (proper TC capacitors) the VFO may be beyond your skills.
    Most TC units, in 21st century, are Surface Mount Technology (SMT) components.
    http://www.capaxtechnologies.com/pdffiles/TemperatureCompCaps.pdf

    Thru-hole / Wire Lead TC capacitors are often found via Surplus outlets.
    https://www.surplussales.com/Capacitors/RF-TempDogbone.html

    Understanding Ceramic’s Capacitance Over Temperature Performance
    by James Lewis
    KEMET Online Education
    Tuesday, March 22nd, 2016
    https://ec.kemet.com/understand-ceramics-capacitance-over-temperature
     
    Last edited: Jan 22, 2019
  2. KG7HVR

    KG7HVR Ham Member QRZ Page

    There are no adjustable temp comp caps in here like the 101 and my 6v line appears perfectly stable. Ive replaced almost all the caps in both my ft901 radios.
     
    WB4IUY likes this.
  3. WB4IUY

    WB4IUY XML Subscriber QRZ Page

    Scratch. Just a LM7806 or some such, input/output caps, and install it. Much faster than poking around forever for a small issue. Just the way I do it, never had it fail.
     
  4. WB4IUY

    WB4IUY XML Subscriber QRZ Page

    Cool But from experience, it only takes a few .01v to drive you crazy. You can build the circuit and install it before you loose too many brain cells trying to overthink it.
     
  5. G3YRO

    G3YRO Ham Member QRZ Page

    I've never had any problems with the original 6V Regulator circuit in my FT101E drifting at all . . .

    However, it IS worth changing the 6V adj skeleton pre-set pot to a multi-turn cermet type (which are much more mechanically stable) . . . and the same goes for the Transceive alignment pot alongside it.

    I fitted ones like these:

    [​IMG]

    Roger G3YRO
     
    WB4IUY likes this.
  6. KG7HVR

    KG7HVR Ham Member QRZ Page

    Thats nice stuff there. I haven't had time to mess with the radios or really any radios for that matter since going back to work.
    I was watching the voltage with a fluke multimeter which is pretty accurate and I didn't see any deviation at all but that was last year I haven't dug into that radio since then a recap to both the power supply rectifier boards when I first got the radio and that helped a little bit.
    Every once in a while I've had a problem with my ft-101 B not transmitting and receiving on the same frequency and I have to go in and nudge the variable resistor.
    I might just end up getting rid of a lot of radios as I don't have the time to screw around with them and when I do get on the radio I want to operate without having a headache
     
  7. N8YX

    N8YX Ham Member QRZ Page

    Get yourself an IC-7300. Pair it with an R-8600. Much enjoyment will be had.
     
  8. KG7HVR

    KG7HVR Ham Member QRZ Page

    I havent heard a bad one yet but ive heard alot of bad 756 radios lol.
    After seeing the failure rates of kenwood dds chips im going to sell my ts450sat .
    I currently have the following
    Icom 706 icom 706m2g, ts450, ts711a(2m all mode), ft901dm, ft901dm, ft101b, ft101e, ft757gfxii, kenwood ts830s, ft2900r, alinco dr185 and thts it. I dont need all that stuff really.
    My friend n7rue got both a 7300 and a ft991 and previously had a 7000 and 706 he likes the 991 the best. Honestly i think his 706 and 991 sound the best
     

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