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General Lee help?

Discussion in 'General CB Services Discussion' started by Keith710, Jul 10, 2018.

  1. Keith710

    Keith710 Member

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    Ok here’s the whole rundown. I ordered a new general lee in February, from a shop(advertised as a shop anyway) and paid extra for the peak and tune. Received it a month later and it came with a 520 driver and 2 fqp13n10 finals. Palomar max mod am regulator. Radio worked good doing about 60 w on high and 40 low. Dk was 2 on low and 8 on high. I always ran it on low power with no amp, just bearfoot. Radio got good feedback as far as getting out but the receive was noisy as hell. I did a Schottky diode and NTE107 recieve upgrade which helped a little there and it worked fine for a week. Then I notice the meter fluctuating under transmit. Thought maybe the mic was needing some attention. Then all of a sudden everything sounded like they were 50 miles away on recieve, I checked my work and reworked a solder joint. Went back to working fine. Next day, it stopped transmitting, both finals shot, and regulator bad. I put a regulator out of an old magnum s3 and tried new 13n10s with new irf520 driver. Even tried 2030s. Changed driver to 13n10. I mean I tried all my options but it simply heats up the regulator instantly and smokes up one final. It did not have any ekl companion parts only one zener attached to gate and drain of the driver. Tried with and without that. Tried a resistor and en369dr on the driver which helped a little bit but still overheats. I can’t seem to get the bias right but as I said when you key the mic it dead keys, about 4 watts but overheats almost instantly so adjusting anything while keyed up is impossible. These parts came from trusted distributors and not eBay or amazon so I trust the mosfets are real. Any help would be greatly appreciated here, I’m not a tech by any means but I love trying to fix old radios. Just don’t work on mine lol unless it’s completely necessary, nearest tech is a long ride down the road. Thanks and hope I covered everything


     
    #1 Keith710, Jul 10, 2018

  2. nomadradio

    nomadradio Analog Retentive

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    What size fuse was in line with this thing when it went south?

    Even if the SWR was high, running it on low side should have given you some safety margin on that, seems like.

    Makes it sound as if the final bias voltage is what started the whole downhill spiral, causing the original failure. If so, that fault is still there causing the overheating problem. What's different now from the first time it blew is that now you're watching to to see that the stress level is too high, and backing off before it blows.

    Gotta find a print of the MOSFET GenLee. Not that familiar with it. If they broke more often, I would be.

    73
     
    #2 nomadradio, Jul 11, 2018
  3. nomadradio

    nomadradio Analog Retentive

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    The closest thing you'll find to a schematic that I know is the Galaxy DX33HP2.

    The schematic pdf has a link to it on this page http://www.cbtricks.com/radios/galaxy/dx33hp2/index.htm

    Easiest test point for the finals' gate-bias voltage is the cathode (banded end) of each 5.6V zener diode. With the radio turned off, put the meter in ohms mode, ground the black lead to the circuit board's DC ground, not to the chassis. The negative pin of the power socket works fine. And if you didn't pull the power cord, this would be a good way to remember that step.

    Now touch the red probe tip the banded end of one final-transistor zener. Set the bias trimpot next to that zener for a reading of about 20k ohms. If it won't adjust much above or below that, you have a problem in the bias circuit.

    The driver transistor's bias circuit is wired a little differently. Can't check it that way. You can touch the tip of the red probe to the metal body of the trimpot VR11's rotating wiper contact to get your resistance reading. Same target, 20k ohms.

    If the trimpot won't turn down that low, this is the root of the problem.

    And if all 3 bias trimpots will adjust for this target, see if your current drain isn't more reasonable now. If the power is reduced too much, this setting is too low. I'm guessing the bias current is too high now.

    You DO have some way to read the current it pulls from the power supply, don't you?

    73
     
    #3 nomadradio, Jul 11, 2018
    OldTech03 and Shadetree Mechanic like this.
  4. Keith710

    Keith710 Member

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    Yes sir. I've never tried it that way. I will definitely give that a try this evening, Thank you very much. If this doesn't work for me, it's going to a tech and put back to original stock with bipolar transistors. I don't care for the MOSFETs myself, yeah you can get a few more watts but too much work and just not as reliable as the old 1969s imo. Thanks again!
     
    #4 Keith710, Jul 11, 2018
  5. Keith710

    Keith710 Member

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    Oh the fuse in my truck power cord should be 5 amp. Power cord came with the new radio so I'll double check it.
     
    #5 Keith710, Jul 11, 2018
  6. Keith710

    Keith710 Member

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    Driver bias I can get to 20k no problem. The middle will only go to 13k and the third will only get to 2.73k. The middle one gets hot almost emediately. 100k trimpots, could one be bad or maybe a bad resistor? I haven’t changed anything other than the driver and finals.
     
    #6 Keith710, Jul 18, 2018
  7. nomadradio

    nomadradio Analog Retentive

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    Whups!

    I just ran outta time on this one. All my diagrams on on the computer at work, and I'm heading to the airport in the morning for a little trip.

    The trimpot with the bad reading is telling us that some other component in the circuit has disrupted the reading. The trimpot may or may not be bad. Seems very likely that the middle transistor is running too hot because the bias can't be set for a safe current level on that final transistor. Just don't know what's disrupting the circuit that sets bias voltage for that transistor.

    Hopefully someone else will chime in to help before I get back to town.

    73
     
    #7 nomadradio, Jul 19, 2018
  8. Keith710

    Keith710 Member

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    Thank you! I will search for the problem part tomorrow.
     
    #8 Keith710, Jul 19, 2018
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