IC-7100 (almost) no RF output

Discussion in 'Radio Circuits, Repair & Performance' started by ND9H, Sep 10, 2015.

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  1. ND9H

    ND9H Premium Subscriber QRZ Page

    (Sorry if this is posted in the wrong forum)

    My IC-7100 stopped transmitting, or so I thought until I actually tried talking through the local repeater. It does open the repeater, but the display shows no power coming out. With the SX-1100 SWR bridge connected, it barely moves the needle at the 5W power level. The radio is consuming around 2-4 (aprox.) amps when transmitting on any band, be it HF/VHF/UHF (any mode). RX is normal. The fan starts for a second and then goes very low again or sleeps when keying. I opened the box and found nothing strange (well nothing strange for me, like melted things or desoldered parts, or loose screws, etc). The radio wasn't used as a mobile. Was though, connected to a LDG autotuner and used remotely, but, in theory, never at full AM-power while tuning, only around 20%.

    I've been doing some research and asking around, and I have a "concluded" that only the 2SK2854 (RF AMP) is working, with either the PRE-DRIVE (RD01MUS2) AND/OR Drive (RD15HVF1) not working, and because of that, the big amps (RD70HVF1) don't even bother.

    I have following questions for anyone wishing to answer them:

    1.- Does any of this make sense?
    1.5.- How can I know which part is defective without actually changing it?
    2.- What is a "Short plug"? (i was suggested to do some trials on the configuration menu, but can't get in there)
    3.- I am an agricultural engineer, should I even be doing this? ;-)
    4.- The screws holding the boards to the chassis are numbered, is that the unscrewing order or the screwing order, or both?

    Any other suggestions/help is greatly appreciated.
    Thanks a lot for taking the time.
    I will eventually take the radio to a pro (if necessary, hopefully not!)

    73's out of a currently very windy Cuernavaca, MX

  2. KO6WB

    KO6WB Premium Subscriber QRZ Page

    What does your ALC read?

    Have you tried it on a dummy load with a known good quality jumper cable?

    If the ALC never reads anything then you may have an internal problem. It could be from the sources you've mentioned.

    If the ALC reads high then the 7100 is cutting back power due to a problem usually related to the antenna system.
    A dummy load, in this case, will clearly show that.

    One more thing, check the voltage being supplied at the back connector of the 7100. A poorly conducting negative lead can show these symptoms. A resistive positive lead same thing.
    I had something like this happen when my negative lead from my power supply came loose. The negative lead made a path from the power cord, through the ground connection, back through the power cord for the amplifier and then through the coax from the amplifier to the HF unit.
    The path had enough conductivity to make reception possible but higher powered transmission was subdued by a lot. Funny thing was the front panel lights on the HF unit remained at full brightness, just like nothing was happening:rolleyes:.

    Hope this helps
    Last edited: Sep 10, 2015
  3. ND9H

    ND9H Premium Subscriber QRZ Page

    Hi Gary:
    Thanks for your reply. Sounds like you know your way around this radio. How would I measure the ALC? Or rather where? At the ACC conector Pin 6 and 2? Or are there other measuring points I couldn't see in the service manual?

    All screws are tight. But I'll measure the voltage as suggested.

    Yes, jumper cable is good and sorry no Dummy load available. I've used an incandescent lamp in the past. But as of now I'm only doing my tests on 2M, and there's plenty of free Spectrum here. Where I won't bother anyone. There's only like 2k hams in all of Mexico, as far as I know. Well and like 2 secs of carrier on HF when necessary. The antenna is good. 1.1:1 on the frequency I'm using (tried with another 2M radio).

    BTW, waiting since Sept. 2nd for a reply from Icom.

    Thanks for your time, I appreciate it.
    XE1/N4DMH dennis.hitzigrath
  4. KO6WB

    KO6WB Premium Subscriber QRZ Page

    On page 1-8 of the manual it shows the MULTI-FUNCTION METER INDICATION as item 18.
    Here's where you would use the touch screen to toggle between the various functions. The ALC reading is one of those functions.

    From your description, it is possible an internal fault has occurred. Being a microprocessor controlled device, it is always a good idea to perform a reset.
    Sometimes that returns the unit to operation. It's also one of the first things the guys at the repair shop would try. Try the partial reset and check the operations. If that fails the perform a all reset and recheck the operation.

    These are the simple things you can try outside of opening up the unit and checking for bad parts.

    Hope this helps
  5. ND9H

    ND9H Premium Subscriber QRZ Page

    Hi Gary.
    I'll have a look at the display ALC.
    I've done the reset (via the Menus several times).

    Thanks again.

    XE1/N4DMH dennis.hitzigrath
  6. ND9H

    ND9H Premium Subscriber QRZ Page

    Hi Gary:
    Just made a test on 20M (SSB), the ALC does not move (only on small vertical line on top of the dark horizontal one) on the display, neither Po or SWR, only ID goes up to around 2 and does not change with audio applied.
    If I activate the compressor, the display stays the same, except for the COMP bar, that will move with audio.

    Does that help you somehow? Sorry, but I'm not sure what I'm doing right now.
  7. KO6WB

    KO6WB Premium Subscriber QRZ Page

    You're now at the point where you either send it in or attempt repairs yourself.

    You'll want the service manual for self repair actions and access to some good test equipment.

    Sometimes you can do well with just a simple DMM. That depends on what happened internally.

    The service manual is here; http://www.pd0hni.nl/pdfdocs/7100/IC-7100_service_manual.pdf

    First thing to check is proper voltages on each portion that does not appear to be working.
    Keep in mind the parts within are tiny. This requires very good vision with magnification assistance.
    Steady hands help as well. This is not a task to embark upon for a novice but it couldn't hurt to do some checking at certain points.
    Just be careful not to slip and cause more damage by shorting components together. This is a likely event even for those with experience.

    First place to check is in the middle of the transmit section. This would be around Q101 on the PA UNIT board (page 10-13). An oscilloscope would be extremely handy for this, but checking around for proper voltages will require a simple DMM.

    Hope this helps
    Last edited: Sep 11, 2015
  8. ND9H

    ND9H Premium Subscriber QRZ Page

    How do I know what the voltages are supposed to be?
    I'm looking on youtube
    How to test MOSFETs with a DMM.

    But I'm open for suggestions!
  9. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Okay Dennis, first check the voltages on IC392. The input pin should be about your power supply voltage. The output pin should be +8VDC.
    That will tell you if Q101 and Q102 have their supply voltage. Without it you'd get some unusual results, like low power.
    The transistors Q101, Q102 and Q251 are common to both HF and VHF signal paths. That's why I suggest checking there first.
    If you had a problem with just the VHF finals then HF would still work. So, it should be something common to both transmit paths.

    Try that area and see what happens. It would be helpful if you had an oscilloscope rated at the frequencies under test. Lacking that you're left with just the DMM readings.

    Hope this helps
  10. ND9H

    ND9H Premium Subscriber QRZ Page

    Hi Gary:

    I have 13.2V of Voltage coming in from the PS.
    I have not measured the IC392 because it would mean to desolder the connectors, and I'd like to avoid soldering anything on the radio unless strictly necessary. (I will if you say so). All measurements done on 2M FM.
    I did measure the Voltages on Q101, Q102 and Q251 and it read the following:
    Negative on chassis and plus on the following:

    G: 0V
    S: 0
    D: 7.95

    G: 2.2

    S: 0




    Now, here comes the weird part. I learned on alldatasheets.com that you can Measure Drain-Source and Gate-source voltages:
    Q101, unkeyed: D-S 7.95V, Keyed 5V. G-S unkeyed: 0V, Keyed 2.0V
    Q102, S-D unkeyed: 7.92V, Keyed 7.7V. SG: 0V unkeyed and 2.5V keyed. However, while doing this measurement, the Po indicator will go up to 100%, the Id to around 15. The SWR meter confirms 50W on 2M (SX-1100). And the dimming of my ligths too!)
    But, it transmits on some other frequency, not the one I will transmit, with low power, if I remove the probes.

    Same thing now happens when measuring S-G voltage on Q101. I think it didn't do it in the past (it went up to 50% there and made some weird noises, so I stopped doing that).... Did I screw something more up now? I did have a short while measuring between Drain and source on the Q251, everything went off for a second and the radio rebooted. Can still get 50W out of the radio...

    I am very confused now, and I'll go to bed... I guess the good part is, I got it to transmit 50W on 2M. The bad part is, I don't know on what frequency... Don't have a counter at hand... And I don't really understand why... Maybe you have an explanation for this? Is this normal behavior?

    Anyway, I'd like to thank you again, I am really enjoying understanding (yeah, right, I have no idea) some of the black magic that happens inside that expensive and complicated black box.
    Sorry it took so long to take the next step. I will do more tomorrow, if you're willing and you believe it makes sense. The radio said SWR was low, don't remember the exact number but one or two lines only.

    Thanks, I've left the radio open on the table.

    XE1/N4DMH, dennis.hitzigrath

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