Kenwood R2000 Mode Switch Inputs Inop

Discussion in 'Radio Circuits, Repair & Performance' started by KH6CS, Jul 18, 2019.

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  1. KH6CS

    KH6CS Ham Member QRZ Page

    Greetings from Hawaii

    I am repairing an R2000 with multiple problems for a friend. Can any of you suggest an avenue of attack for the following symptoms?

    I repaired a stuck display by replacing NAND gates IC 9 - 11 and IC17

    Radio worked for 2 minutes, then the following problems developed:

    Mode switch inputs inoperative, but changing memory channels changed mode lights.

    Tuning speed stuck on fast.

    Tuning jumps in 5 KHz steps, no 100 Hz change.

    I replaced the backup battery and reset U12 CPU.

    I replaced all electrolytic caps on the PLL BOARD.

    When pressing mode or tuning speed buttons, can see a scope signal on appropriate U12 data inputs. However, it does not draw the TTL level down to 0 volts! Activating memory buttons produced expected TTL levels, however.

    U12, VCC pin 40 only reads 4.7 V. But rail at 5V. When unplugged 2.7 Volts with the new Lithium Manganese backup battery.

    I suspect the P53 data line, as it is common to missing functions. Replaced D11 with a 1N4148 for good measure. No change.

    My intuition suspects a mechanical problem. Reseated all connectors, put DeOxit on connectors 18-21. No change.

    The receiver is in physically poor condition with some rust damage and poor receiver sensitivity as measured on a calibrated RF signal generator. These will be investigated in due course. I hope I don’t have a defective U12.

    Has anyone seen these problems before, and can offer any suggestions?


    Charles. KH6CS
  2. KDUQW

    KDUQW Guest

    My R-2000 is inoperable also, so I am following your post.
    My display has a constant "P" and none of the input button LED's are lit or operate.
    I have had it apart several times reseating connectors, checking for cold/bad solders with no success.
    The battery was replaced, and reads 2.7 vdc also as yours.
    +9 and +5 checked good.
    I also have the VHF plug-in module.
    My only bench equipment at present is a DVM.
    I would like to get it running again, it has great reviews.
    I have the service manual plus schematics.
    VERY frustrating! What's next?

    Bill Malona
  3. KH6CS

    KH6CS Ham Member QRZ Page

    Hi Bill

    I returned the R2000 to the owner, without resolving the mode switch problem. So far, you are my only response!

    However, The display was originally stuck, and was fixed by replacing the indicated NAND gates. That problem was easy enough to find with an oscilloscope. There was no output on one of the NAND gates in iC9 when the dial was spun. The exact replacement CMOS chips were unobtanium from Moser, but available from a vender in Ft. Lauderdale on Amazon. I suspect that any generic TTL quad NAND gates with identical pin outs would work, if you have them in your junquebox. Use sockets, if you want to experiment.

    A scope is an essential tool in troubleshooting such problems. It does not have to be fancy or new. I would suggest looking for an old analogue triggered scope at a ham fest, or getting one of the inexpensive Chinese digital ones. (Siglent is good) If used, have it tested before buying by touching the probe to the 1 KHz calibration pin on the front panel.

    Try recalling memories and seeing if the modes change. If so, the problem is not in the output of U12, but the input.

    You might also try rebooting U12 by following instructions on Google by grounding pins 40 and 26. (Look it up.)

    Since the mode switch problem was intermittent for me, I suspect a micro crack in the PCB, which was undetectable by my poor eyesight. You might try shining a strong light through the PLL PCB around connector 21 and the P53 data line.

    Yes, it is frustrating. Good Luck and keep in touch.


    Charles KH6CS
  4. KH6CS

    KH6CS Ham Member QRZ Page

    Hi again Bill

    Upon rereading your post, I had a second thought. Perhaps your symptoms may be somewhat different than mine.

    My memories and MHz display worked, so U12 was at least partly operational. If none of your mode, numeric or memory buttons operate, U12 may be completely inop. With a scope, check for clock near the U12 crystal. I think U12 is a custom chip for the R2000 and finding a replacement may be difficult.

    Guess the next step would be checking all inputs and outputs from U12. Just follow the logic.

    Getting access to the PLL PCB is a little involved. I had to unplug all connectors except the coax cables, unscrew the rear panel, remove all brass colored screws from the PLL PCB, remove 2 screws from the display, then slide the board toward the rear.

    Again Good Luck.

    Aloha es 73

    Charles KH6CS
  5. KD0UQW

    KD0UQW Ham Member QRZ Page

    Yes I will discus it with the most senior ham I know, August KG7BZ tonight at our ham club meeting. He has offered to help and has oscilloscopes and necessary test equipment. Yes I sincerely thank you and hope that the processor isn't dead as I have read it is then terminal. It must be the firmware that is proprietary to Kenwood? Anyway I will let you know what we come up with!
  6. KD0UQW

    KD0UQW Ham Member QRZ Page

    Well I am glad to report that my radio is alive and fully operational again. Thanks to August Johnson, KG7BZ who got her running. So great to watch a senior ham tech and troubleshooter debug a problem on the bench.
    He found there was a dirty function switch, causing logic signal line P51 on the PLL board to be partially pulled down to a low level. This effectively took away all the led's for the front panel, and tricked the processor chip U12 into a confused state.Once the function switch was removed, disassembled and clean the signal returned to a normal state and the R2000 returned to original operation. We used a scope to follow signal status and finally found the stuck logic line. Service manuals are worth their weight in gold! Older radios are so different than modern electronics with much more IC's and miniature circuits.
  7. KH6CS

    KH6CS Ham Member QRZ Page

    Hi Bill and August

    Congrats on a great job of detective work. Perhaps my friend’s R2000 has a similar problem. If he wants to bring it back, I will take a second look.


    Charles KH6CS

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