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TS-940SAT is deaf above 13.999 MHz

Discussion in 'General Technical Questions and Answers' started by N2ZDH, Jan 15, 2020.

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  1. KA5IPF

    KA5IPF Ham Member QRZ Page

    Only one minor correction. On IC1 pin 10 will go low when pin 12 goes high ONLY if pins 13, 14, & 15 are low. All 4 pins have to be correct for the output to be correct.
     
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  2. N2ZDH

    N2ZDH Ham Member QRZ Page

    Steps taken with “[Edit] Correction” Blog section #9

    Dave, I walked through your reply and took a survey, here are these findings.

    Working with band group H, I performed voltage sampling at IC-1 pin 10:
    with group H selected, pin 10 = 0.18 vDC;
    with group H NOT selected pin 10 =13.97 vDC

    Working with band group I, I performed voltage sampling at IC-1 pin 9:
    with group I selected, pin 9 = 0.18 vDC;
    with group I NOT selected pin 9 = 15.65 vDC

    I took voltage samples at the 7 other output pins with a “received frequency” selected; the Rx BPF select data was verified at pins 15, 14, 13, 12 for RB0 RB1 RB2 RB3.

    Pin 7 = 0.45 vDC
    Pin 6 = 0.45 vDC
    Pin 5 = 0.41 vDC
    Pin 4 = 0.46 vDC
    Pin 3 = 0.47 vDC
    Pin 2 = 0.46 vDC
    Pin 1 = 0.44 vDC

    This tells me IC-1 functioning correctly.

    We know pin 8 is ground. Pin 16 Vcc.


    With reference to vDC presented at cathode side of each D17 and D18, my findings did not agree with voltages depicted in the schematic!!!

    For D17 I Expected 8.3 vDC, but measured 16.91 vDC
    For D18 I Expected 2.5 vDC but measured 16.9 vDC

    When I sampled anode side of D18 I would get a click from the speaker. Keeping mind the Klein Tools m300 meter being used has its COM black lead clipped to ground.

    .? So why are these D17 and D18 values so far out???
    There must be a failed component to be identified, but WHAT?

    I Explored further and found the following .....

    I changed bands then sampled the cathode side vDC values in the diagram. This is a digression.
    I am expecting the values I will measure to be similar to those suggested for D18 and D17 of Rx BPF "H" when it is selected. So...
    For Rx BPF "I" selected I found both D20 & D19 measured 16.91 vDC Just like Group "H"
    the following are functional bands.
    For Rx BPF "G" selected I found D16 at 2.47 vDC and D15 at 8.16 vDC
    For Rx BPF "F" selected I found D14 at 2.45 vDC and D13 at 8.19 vDC
    For Rx BPF "E" selected I found D12 at 8.38 vDC and D11 at 8.38 vDC
    For Rx BPF "D" selected I found D10 at 2.49 vDC and D9 at 8.16 vDC
    For Rx BPF "C" selected I found D8 at 2.48 vDC and D7 at 8.17 vDC
    --- Stopping There ---
    I now re-selected (normalized) to compare with diagram Rx BPF "H" and tested for actual diode cathode values of D6, D5, D4 and D3.
    D6 = 16.73 vDC
    D5 = 16.79 vDC
    D4 = 17.12 vDC and anode side 17.82 vDC !!!
    D3 = 17.10 vDC
    Your thoughts, and the thoughts of others interested.???
    Thank you in advance. de N2ZDH, Raoul
     
  3. KA5IPF

    KA5IPF Ham Member QRZ Page

    The IC is working correctly. The pull down from the IC is not getting to the diodes. Trace the schematic.
     
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  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    As Clif posted your IC is fine as is its input.

    So compare what you see on pin 10 with band group H selected to what you see on either side of R21. You either have a broken connection (e.g. cracked solder joint at board feed thru via, at a component lead or a cracked trace) or R21 has failed (unlikely but possible).

    IOW, if you know pin 10 is pulling low when band group H is selected but the diodes are not pulling low then all that's left is R21 and the circuit path between IC1, the resistor and the diodes.

    [Edit] Two things come to mind for further troubleshooting:

    - You can troubleshoot at this point with the rig turned off with an ohm meter. Measure the resistance from pin 10 on IC1 to either side of R21. One one side you should see near zero resistance (just the traces) and measuring on the far side of R21 you should see its resistance (47 ohms).

    - Since both band groups H and I seem to have this problem I'd suspect a pair of cracked traces side by side one for each band group. IOW it's fairly normal to run traces like that parallel to one another and something that scraped and cut or a flex in the board that cracked one trace or pad connection could easily have cracked the one next to it as well.
     
    Last edited: Jan 23, 2020
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  5. N2ZDH

    N2ZDH Ham Member QRZ Page

    Clif and Dave,
    With your good guidance I have demonstrated function.
    With the VFO tuned to 14.250 Mc (Rx BPF H) I used a piece of #22 AWG to jump the 'second pin' of RB1 to the "inbound" side of R21, and BINGO the receiver came alive.
    I have done this for pin 1 of RB1 jumped to the "inbound" side of R23, with the same success.
    Now I need to pull the board, or at least "fold" it out so I can identify and repair the broken trace or solder joint that has failed.

    I have learned much from your mentoring and say I greatly appreciate it.

    My thought is if the foil trace is broken, I may just solder a jumper from each effected RB1 pin to R21 and to R23.

    I will place post an update with my findings and solution.
    73 de N2ZDH (Ral) Raoul
     
  6. N2ZDH

    N2ZDH Ham Member QRZ Page

    Please sit down before you look at the images.
    I pulled the screws and flipped the board.
    OMG Dear Lord Who would have done this ???
    Please see the 3 photos I uploaded.
    I welcome remarks.
     

    Attached Files:

    Last edited: Jan 24, 2020
  7. KA5IPF

    KA5IPF Ham Member QRZ Page

    I can see it but can't figure out why unless something got on the board and ate the traces. Cat urine is a great trace remover BTW.
     
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  8. N2ZDH

    N2ZDH Ham Member QRZ Page

    Soldered in Jumpers, mounted board.
    Normalized ant. , energized, grounded.
    Receiver is working, though the bands are dead.
    checked voltages at diode cathode check points, A-ok.

    My thanks to all that helped and supported this ham through the puzzle.
    It has been a great education.

    Photo of completed jumpers uploaded.
    73, de N2ZDH Raoul
     
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  9. N2ZDH

    N2ZDH Ham Member QRZ Page

    Jumpers installed.
     

    Attached Files:

  10. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Wow!

    Yeah it looks like something caustic ate those traces away and someone tried fixing them but obviously there were still problems on 2 of them.

    Nice job.
     
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