Discussion in 'Radio Circuits, Repair & Performance' started by KJ4BJ, Sep 12, 2019.

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  1. KJ4BJ

    KJ4BJ XML Subscriber QRZ Page

    Need help. If anyone has any ideas, or better yet, knows exactly what the problem is, I am up for suggestions.


    Some time ago I was on 160 meters talking to some local hams. All was going well when I noticed my amp was only doing about 400 watts. I retuned my antenna. Flat SWR on antenna, amp, and radio. No fix. Then I checked the FT-1000D barefoot. The TX output power had dropped from 90-100 watts down to about 60 watts and could not do more. Turned up the DRIVE control to full meter deflection. No change. Later, after finishing on 160 meters, I started checking all the bands. On 80 meters, got 200 watts output but the DRIVE control would only deflect the meter to about 1/4 scale. Then from 40 meters through 10 meters, full 200 watts output and DRIVE control would deflect the meter to full. I thought it was just something in the 160 meter portion of the radio.


    Popped the covers and started looking around. Still had same readings as above into a 50 ohm dummy load. After weeks of looking, I decided to take the PA/PS units out and check the boards. As I was setting the assembly on the bench, a disc capacitor just fell out and landed on the table. I thought that was the problem. Replaced the cap with same value and reinstalled the assembly. Still no fix. But now the situation was worse. Now I had no TX output power at all on any band. Eventually per the service manual, I discovered I did not have the 31.5 VDC on the PA but did have the 13.5VDC. So I thought the PS board went out but could not determine which components were bad. Finally, decided to search for, and acquired another working PS board. After I installed it I now have the 31.5VDC and the 13.5VDC on the PA board after setting it per service manual. Still no TX output power on any band. I started thinking it was the driver and/or finals. Per service manual, I do not have any idling current on either the driver or the final, best I can tell. When in transmit, the rig's meter shows 31.5 VDC on the VCC scale and shows 2A on the IC scale. DRIVE control has no effect whatsoever and no TX output power on any band. I have even resoldered some possible cold solder joints to no avail. Everything else on the radio works fine. It receives like it was new. All the controls and buttons work as well as all the RX filters. Only thing the rig does not do is TX power. As of this writing I am going to connect a mic and see if I at least have audio output by listening to another rig.


    If anyone has any idea how to fix or troubleshoot, please let me know. Much appreciated. I am hoping the PA is ok and something else is the problem? If it IS the PA, well, I can pray I find a PA board. So far, it's like looking for a needle in a haystack. Thanks to all in advance for any assistance.
    N2ZD likes this.
  2. NK4K

    NK4K Ham Member QRZ Page

    Man, if I were you, I'd just throw it away!
  3. WD8BWW

    WD8BWW XML Subscriber QRZ Page

    That is a great radio. I would guess you lost the finals. If you want to throw it away I'll pay shipping. Even broken it is worth more than a lot of working radios. The D model has a treasure of filters in it.
  4. VE1IC

    VE1IC Ham Member QRZ Page

    I think you have 2 problems. One your finals or drivers are shot. Second if you fix that, you still should have the low output on the 160m band and that is probably something on the bandpass filter board.
  5. N2ZD

    N2ZD Ham Member QRZ Page

    My comment was deleted, because I posted a picture of how some people need to behave.


    I suggest you look at the swr foldback circuit first. A common issue is failed diodes on Ft-1000’s, also try bypassing the tuner and antenna relay, some Yaesu and Kenwoods use a light bulb as a protection circuit by the antenna jack. Check that.
    See if the radio has output on other bands, sometime stuff fails on the bandpass filter boards.
    Once you check those out, start checking the pre-driver, drivers and finals.
  6. G4COE

    G4COE Ham Member QRZ Page

    oops sorry -deleted-
  7. NK4K

    NK4K Ham Member QRZ Page

    My posting was merely a joke, because Bobby (KJ4BJ) and I are owner and helper, respectively. I did it to see if he (or qrz.com) were listening to postings, ONLY. He and I are good friends. I guess I should mention it to him, but so far (APRIL 16TH, 2020) I have not.
    I thank y'all equally for your replies.
    I currently have the PA on the work bench but my health (knees, back) has not allowed me much time on the project. The longer I sit or stand, the more damage it does to my piece parts.

    I have replaced the temp diodes on the drivers that somehow escaped testing methods.
    I have done more than a cursory examination of the board. There were MANY shorts between traces. In fact, I don't know how the thing ever worked, because the solder there was OLD and some actually swapped C and B on the transistors!
    We replaced the large resistor (R7014) on the driver (MRF486) collector circuitry and strapped it to the heat sink instead of gluing it to weak (physically) components as the service bulletin suggests. We used the 25 watt version of the 2.7 ohm resistor instead of smaller units.
    I set the bias for the driver and finals in a different manner than the manual suggests -- using the Motorola recommendations instead.
    I removed the board from the heat sink and found two mica insulators on the wrong transistors. The third required insulator was missing. Again, how did it work for Bobby -- ever? I dunno. None of the insulators was on the correct transistors.
    I squirted & spread some new/fresh temp compound on the transistors and verified locations of the mica insulators before bolting circuit board back on the heat sink. Then I checked to see if somehow if the mica insulators had been damaged causing shortage to heat sink using a Fluke meter. They were okay without heat and voltage at least.
    I replaced the 10uH/1.4a/0.22 ohm inductor, L7001, that had been fried by who knows what. It looked fried and measured fried (series resistance).
    I replaced the V+ connection to L7003, because it was broken off and may have been shorting to ground.
    I double-checked all the components in the 8v bias circuitry and associated switching. They seem to work.
    The last and only thing left is a slight variation of the resistors R15+R16 vs. R17+R18, the final bias resistors. They are around an ohm different, but that may not matter initially. I'd love to see some waveforms first.
    I replaced the two electrolytics, c37/c50(? can't read) at 35v with 50 volt versions on the 30V feed. The gluing of R7014 to them broke them.
    These changes are a subset of the changes Bobby made that are listed, above. Just because "I" did it here doesn't mean "he" didn't do it originally.
    The next step is to hook up all the voltages and keying bias and run a signal through it.
    Unknowns: RF voltage/wattage input and a source of 30v. I do not have the radio here, as I'm in Columbia, SC and Bobby's in Dayton, TN. The complete radio is over 65 lbs. The PA and other stuff shipped for about $12.
    I have not checked it, but I believe the capacitor voltage on an Astron RM-35 will be somewhere above 23-25vdc. If so, I'll just use that for the 30v. PA should work with diminished output.
    Today or tomorrow I'll see what's going on. If it's bad transistors, I may spring for encapsulated cement with leads from Communist Coronaville. If that won't work, I'll head to ECG substitution route or some BU from EU transistors that I think may work.
    If none of that works, I may try an eBay circuit board substitute. SOMETHING SIMILAR TO THIS ONE, even though only 100w. That will allow the D to drive most linears.
    I'm sure I've forgotten a few more things, so don't hesitate to axe. Functional transistor substitutions or other ideas will be appreciated, of course.

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