Yaesu FT-101E, R40 "cigarette lighter"

Discussion in '"Boat Anchor" & Classic Equipment' started by N4ZAW, Nov 7, 2018.

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  1. G3YRO

    G3YRO Ham Member QRZ Page

    Well I have never known them fail !

    And because they are compression trimmers, you really DO need to peak them while transmitting, or you won't get a proper peak.

    Roger G3YRO
  2. N4ZAW

    N4ZAW Subscriber QRZ Page

    I used to ruin those compression trimmers all the time. It was too easy, Roger... Just key up the amp, grab the ole venerable golden screwdriver (not real gold, but always seemed to be metal) and "adjust" the outputs of a Motorola brick, and viola -- Instant smoke ;)
    Until I started using that "tweek and un-key" method, I could 'make book on it'. And yes, granted, the method mentioned was tedious and less then ideal..
    "Fudd's first law of opposition (which states, "If you push something hard enough, it will fall over"), came into play often when I was a kid. But what can I say? I've found there is a learning curve to this stuff. It's a miracle I survived.
    Speaking of learning curves, I also have a long way to go to understand this 101 circuit. With R40, (found open) C109, (found leaky) both replaced, I still have enough of a short to set the new R40 to smoking instantly. If the short was beyond T103 and T105A and the L2 choke, I would think they all would smoke, or burn-open before the R40 could even begin to get hot.
    Anyhow, I just got back from vacation, and plan to pull the driver and see if the short goes away. If not, I guess I should start clipping cap paths to ground one-by-one until I find the short. Where would you recommend I look next, Roger? I'm sort of shooting blindfolded at the moment.
  3. G3YRO

    G3YRO Ham Member QRZ Page

    Well with the rig off, what does the DC resistance measure across C109 ?

    And the high current draw COULD simply be down to a faulty 12BY7A . . .

    Does R40 get warm with no 12BY7A plugged in?

    Roger G3YRO
  4. N4ZAW

    N4ZAW Subscriber QRZ Page

    141 ohms in circuit, open out-of-circuit (new and still good).
    Yes, R40 smoked and burned-open again within the 5 seconds or so with V1 removed.
    I re-tested the rf choke L2/R6, and it's still ok.... Why, I have no idea. It should be charcoal, shouldn't it? This is very strange to me. V1 was replaced by me when I got it from the previous owner ten years ago, so it is relatively new hours-wise, and rechecked on B&K 747 tube checker for value/emissions/shorts while I had it out.
    Receive was working, but quit this last time, when R40 smoked-open again, and meter lamps went out. It died with an audible "squeal" sound.
    I guess I'm going to try to clip all components to the socket of V1 one-by-one (once my urge to throw it in the canal subsides) and see if they, or the circuit they go to, are the problem. Outside of that, I got nuthin.
    I really appreciate the input and advice, Roger.
    Last edited: Nov 27, 2018
  5. G3YRO

    G3YRO Ham Member QRZ Page

    Do you mean that you're measuring 140 ohms from the bottom of R40 to chassis ALL THE TIME?

    If so, no wonder R40 is burning up! You have a short circuit somewhere . . .

    See if that DC resistance changes between 80m and 20m (as it could be the resistance of the two RF coils . . . only one is in circuit on 20m and above, both on 40m and below)

    Roger G3YRO
    WQ4G likes this.
  6. N4ZAW

    N4ZAW Subscriber QRZ Page

    Ok, Roger, will do. That makes sense, too.
  7. N4ZAW

    N4ZAW Subscriber QRZ Page

    I knew there is a short somewhere, but I'm running out of suspects, outside of the tube socket and components on it's pins to ground. Getting to the undercarriage of that tube socket looks like it might be a fun 'all-niter'. ;)
    Anyhow, yes, the short is the same resistance on all bands.
    Is there anything on that schematic that you would check before that tube socket 'major operation'? I'll perform a resistance 'pin check' to ground on the socket from the top before going in.
  8. G3YRO

    G3YRO Ham Member QRZ Page

    I was going to say that there is NO capacitor going to ground on the Driver Anode circuit that could have broken down . . .

    BUT there is - the 1000pF feedthrough capacitor that feeds the output of R40 into the screened compartment under the Driver valve. (C110)

    Maybe that has broken down? Easy to disconnect the wires to check.

    Roger G3YRO
  9. G3YRO

    G3YRO Ham Member QRZ Page

    Have you checked that Feed-through?

    Roger G3YRO
  10. N4ZAW

    N4ZAW Subscriber QRZ Page

    I previously did check both of them while waiting for the resistor to arrive in the mail, Roger, but when I get back home this weekend, I'll re-check those. I actually have about 10 nos feed-through caps and will just change them both out.

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