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Kenwood TS 820S

Discussion in '"Boat Anchor" & Classic Equipment' started by VK4KL, Jul 27, 2018.

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  1. VK4KL

    VK4KL Ham Member QRZ Page

    I recently received as a gift a Kenwood TS 820S with a few issues. The main issue is the VFO drops out. With a frequency counter on the VFO and the VFO dial set to 0 the counter reads approx 5.500MHz (give or take a few Hz) now as I rotate the VFO everything is ok until I reach 5.018 MHz where the frequency counter drops to 0 and the 820's digital readout also goes to 0. I have removed the VFO and cleaned the grounding wiper. I have removed all boards cleaned and inspected and resoldered the digital display boards, including the through board connections by placing component lead cut offs. Any idea where to go from here?
    Second issue the digital display on the 820 as lost the leading digit ie if I am on 14.175 it displays 04.175 if I am on 21.175 it displays 01.175.
    I would really like to get this radio working and any advice gratefully received

    Adrian VK4KL
  2. G3YRO

    G3YRO Ham Member QRZ Page

    Firstly, I would tune the VFO to just before where it cuts off, say 5.1 MHz . . .

    Then hang something like a 33pF fixed capacitor across the variable capacitor, and see what you get.

    If it goes lower in frequency OK, then it must be the variable capacitor.

    I would disconnect the leads to it, and using an ohm-meter check the vanes aren't shorting to ground when nearly fully meshed. Also check that the moving vanes remain properly grounded (despite you saying you cleaned the wiper, this is the most likely problem)

    Regarding your frequency display, so you always get a zero on the first digit, not completely blank?

    Roger G3YRO
  3. VK4KL

    VK4KL Ham Member QRZ Page

    Always a 0. Except 160/80/40 meters no leading 0

    Adrian VK4KL
  4. G3YRO

    G3YRO Ham Member QRZ Page

    I'm not familiar with how the frequency display works on that rig . . . but I would presume that they just switch the first digit . . . either OFF on 160/80/40 . . . and switched to display a 1 or 2 on the other bands.

    So it's probably quite a simple fix. (I'm presuming you have cleaned any push-on connectors, and the bandswitch wafer that controls it)

    Someone like Clif will probably tell you what causes this straight away, as he knows all these Kenwood rigs inside out!

    Let me know how you get on with the VFO . . .

    Roger G3YRO
    VK4KL likes this.
  5. VK4KL

    VK4KL Ham Member QRZ Page

    Thanks for the advice. I will try the cap trick and see what happens

    Adrian VK4 KL
  6. W9GB

    W9GB Ham Member QRZ Page

    Unfortunately, N6WK extensive Kenwood hybrid service page is gone (He died 2014).

    START with Kenwood Service Manual Service Manual_W0NTO.pdf
    and CLEAN (Readible) Schematic Diagrams
    TS-820 VFO is a Mechanical and Electronic Assembly.
    While your issue is Likely Mechanical (poor rotary contact for variable capacitor/electrical),
    Here is printed circuit board schematic.
    This board has FET devices, sensitive to ElectroStatic Discharge (ESD).
    ESD most common is home static electricity, that can silently damage sensitive FETs.
    Follow standard Electronics Bench ESD precaution.
    Kenwood Hybrids Service Page by WB4HFN

    ERRATIC VFO Behavior (Kenwood Hybrids)
    Common service issue with these 40 year old Kenwood hybrids. Erratic VFO Flow Diagram.pdf
    Kenwood TS-820 : VFO Removal and Lubrication (PHOTOS)
    by Gregory Graham, NR6C REPAIR.pdf

    Greg manufactures replacement sprockets for Kenwood hybrids.
    Last edited: Jul 27, 2018
    AF7XT, N8VIL and KD2ACO like this.
  7. KD2ACO

    KD2ACO Platinum Subscriber Life Member Platinum Subscriber QRZ Page

    Hi Adrian,
    The 820 series are very nice radios... well worth the time to get them going.
    The counter circuit boards are known for their bad solder joints and plate throughs. Fixing these requires a good magnifier, bright lights, and a tin of flux to reflow the connections. I use a binocular microscope for this type of work but a large desk magnifier can work well for this too.

    Wiping the connector pins with a good contact cleaner and a lint free cloth is a good job to do all over the radio.

    It's not a bad idea to have some spare pins and a crimp tool handy, and be careful about flexing the wires... they are solid core and a bit fragile.

    best wishes on your repair journey!
    Last edited: Jul 27, 2018
    VK4KL likes this.
  8. N8YX

    N8YX Ham Member QRZ Page

    Look at the Band Switch wiring on the main schematic.

    There's a wafer on said switch which supplies voltage to the "1" or "2" tens-Megahertz lines of the Counter Module. Identify the correct pins on the Counter Module header and make sure they're getting voltage.

    As far as the VFO dropout is concerned: Does the happen on all bands, just one or more than one?
  9. K0OKS

    K0OKS Premium Subscriber QRZ Page

    That sounds like the VFO is dirty and not making proper contact. If this is the case it will fail around the same spot (physically) on all bands.

    Sometimes just working it back and forth can help, but you really need to clean it. Some of the links above cover this or search for Kenwood 820 or 520 VFO cleaning. There are videos on YouTube. Pay very close attention when disassembling the VFO from knobs and rings. It can be a slight (or massive) pain to reassemble. Don’t rely on the written instructions... observe it, maybe video it on your phone, etc. as you go.

    I love my TS-820S. It is my favorite rig to listen to (receive sound is so nice), and I always get incredible unsolicited audio reports; people are amazed I sound so good on a 40 year old rig. I use it with an MC-50 mic, which I put a foam ball cover on and close talk with my lips right against it for maximum bass response.
    KD2ACO and N2IIE like this.
  10. VK4KL

    VK4KL Ham Member QRZ Page

    Happens on all bands. Always at 5.018 MHz. I am now thinking its a mechanical problem. When I can work around my health problems I will have a good look.

    Adrian VK4KL

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