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[W1JPP]

I have a kenwood ts-820S. Most everything seems to work fine..alc meter deflection, full power out, receive good audio reports...

But recently, when I unkey the mic, my s meter jumps up, and then backs down. Sometimes I miss the other party's initial words until the meter backs down. I attached a video to show what happens when I "unkey"...(in this case when I flip the "send" switch down to stop transmitting.

https://www.dropbox.com/s/dl2qhhtd321519y/IMG_6978.MOV?dl=0

Its intermittent - probably happens 70 percent of the time...and sometimes the meter doesnt peg, but still jumps a bit...

it always backs down within a couple seconds...

any ideas what would cause this?

[AI5BC]

Sometimes I miss the other party's initial words until the meter backs down.

Sorry, do not have a definitive answer for you, but that strongly suggest something to do with the RX AGC circuit stuck in SLOOOOOOOOOOOOOOOW!

Try disabling the AGC and see where that takes you.

[W9IQ]

Try changing the position of your AGC switch on the front panel - set it to fast or off and see if it makes a difference. It is on right end of the switch bank that has the 'Send' switch.

- Glenn W9IQ

[W1JPP]

well that agc is definitely having an impact - when I have it on slow, and stop transmitting, the S meter jumps all the way, or close to all the way, towards +40 over, and the slowly backs down...in the video below it shows it jumping but often it jumps all the way to 40 over...

on fast, it still jumps, but backs down much faster...almost instant...

and on off, it doesn't jump at all, but I still hear that slight scratch (or chirp)  sound, like I hear on slow or fast immediately when I release the transmit key...like a feedback sound, not mechanical...just for a fraction of a second...

unfortunately when AGC is on off, I don't have any meter deflection - is that normal?  and a lot more static - the voices on receive are a bit louder though, as is the static ...

so my best option short term would be leave it on fast...

so now my question is what would cause that - an antenna relay (the omron 300ohm towards the back of the radio, on the bottom) that is going bad or is bad?

here is a video comparing slow and off positions

https://www.dropbox.com/s/y4v7wpkkyhkopf5/IMG_6981.MOV?dl=0

Thank you,
Joe / W1JPP

[WB6BYU]

...unfortunately when AGC is on off, I don't have any meter deflection - is that normal?  and a lot more static - the voices on receive are a bit louder though, as is the static ...

Exactly as expected.

The Automatic Gain Control is designed to keep the audio
level of received signals at a constant level.  Whenever
the meter is reading, the AGC is reducing the gain.  So
turning the AGC off will increase the gain of the receiver.

The S-meter is driven by the AGC voltage, so it doesn't
move when AGC is turned off.

...so now my question is what would cause that - an antenna relay (the omron 300ohm towards the back of the radio, on the bottom) that is going bad or is bad?

It sounds like the source of the symptom is that the
AGC voltage is getting charged up while in transmit,
or while switching between transmit and receive.

One quick test would be to see if it makes any difference
whether you transmit a signal, or just switch to transmit
mode without actually transmitting (CW key open, or no
audio on SSB for example).

Otherwise, details will depend on how the radio handles
the AGC functions while in transmit mode.  If it uses the
same circuitry for transmit ALC, then the line might not
be getting discharged properly when switching.  In that
case, reducing transmit drive to reduce ALC indication
might reduce the problem when switching to receive.

On the other hand, if the radio is designed to disable
the AGC circuitry in transmit mode, then the problem
seems more likely to be the AGC line getting charged
through a leaky switch or otherwise not getting shut
off properly.  It is possible that some electronic
switching is not happening at the proper speed, so some
of the transmit energy gets coupled into the receiver
during the switchover.  For example, there usually is
some intentional delay in the switching, and if that
isn't happening, the receiver might be turning on
before the transmitter is fully off, which could cause
such a spike.

I wouldn't expect a mechanical T/R relay to be the problem,
as that isn't as likely to be leaky in this way.  But if one
set of contacts were used to mute the receiver, and
those contacts were dirty, that might cause it, depending
on the rest of the circuitry in the radio.

[W1JPP]

OK - understood on the AGC - thank you!

so, if I'm in SSB, and I key the radio, no audio, so no meter deflection while keyed, as soon as I "unkey" I still do get the spike on the S meter and then it backs off - slowly (takes about 1.5 seconds or 2) when on slow AGC...and on fast AGC, it spikes but drops off almost instantly...with agc off, I hear the chirp sound as in the video, but no spike -

this happens whether in usb, lsb, cw...and in ssb whether I speak or not

[W9IQ]

Joe,

Thanks for running that test.

First try reseating all connectors on the IF board with special attention to IF-3 which is the largest with 17 pins.

If that doesn't clear the problem, I would suspect D20 on the IF board.

- Glenn W9IQ

[K1KIM]

When you have those boards out of their sockets, clean them with a little De-Oxit and wipe clean.
Most times just the old "in and out" does it without a cleaning though.

[W1JPP]

Dumb question from a neophyte.

That IF board that’s on the left as you face the ts-820s from the front, the IF board is in a vertical orientation.

It appears there is a bracket holding the board in with two screws, one on each side. I’m assuming once these screws are out, the only thing holding the board in are all the pin connections along the bottom.

At that point it would seem if I push the board in towards the center of the transceiver the pins will come out and I can lift the board out.

And then I can clean the pins.

Am I missing anything.

[W1JPP]

OK - I figured out how to get the board out and disconnect the connectors..clean each pin carefully

bad news is I did not take a pic...and when I first plugged the connector back in I had extra pins/connections...at first did it wrong, and had no receive at all...

then took some time, and made my best educated guess, and it rec'd as it did before...here are pics of where I ended up...I took 3 pics, all the same thing, the first is a wider view for reference, the next two zoom in...but you can see there are two open pin connections, just to the right of connector labeled 3

https://www.dropbox.com/home/hf%20radio/if%20board%20pins

but still have the S meter spike when I unkey..

Glen, W9IQ - I did find D20 on the board - the small diode...you said you would expect that next...any way to test that diode? Or are you suggesting just replace it? Looks like it would be fairly easy to desolder and replace...

[W1JPP]

OK - I figured out how to get the board out and disconnect the connectors..clean each pin carefully

bad news is I did not take a pic...and when I first plugged the connector back in I had extra pins/connections...at first did it wrong, and had no receive at all...

then took some time, and made my best educated guess, and it rec'd as it did before...here are pics of where I ended up...I took 3 pics, all the same thing, the first is a wider view for reference, the next two zoom in...but you can see there are two open pin connections, just to the right of connector labeled 3

https://www.dropbox.com/home/hf%20radio/if%20board%20pins

but still have the S meter spike when I unkey..

Glen, W9IQ - I did find D20 on the board - the small diode...you said you would expect that next...I tested D20 and D21 diodes and they seem fine - they show .614v drop in one direction and OL in the other...so they seem to be functioning as a one way gate/valve...

[W1JPP]

well, it seems I have a new problem...when tuning, when I go thru the process with my switch in the tune position no problem...just the expected lower output...

when I switch from tune to cw and flip up the send switch I have no cw tone/output on my ts-820s meter (and my external power / swr meter shows no forward power)...

but If I go to usb/lsb and whistle. I can get to close to peak 100wats on my external meter, and my rig ALC meter is deflecting as usual, so I have full power out...so it seems its the rig not sending a cw tone....could I have changed a switch somewhere along my troubleshooting that prevents a cw tone from being sent when I am on cw and flip the send switch...

[WB6BYU]

Is that the way it normally works?

I’d expect that you need to close the key
to get output in CW mode, but I’m
certainly not an expert on such rigs.

[N8YX]

You have to have a key connected to the "Key" jack and have it make contact (close circuit) in order to get output when in CW mode - regardless whether or not the "Send" switch places the rig in transmit or you use VOX ("semi break in"). The owner's manual clearly explains how all this works.

As far as the jumping S meter: I'd suspect the T/R relay, an Omron MH4P. It's possible the relay contacts have become oxidized and intermittent. The same symptoms will occur in an R-820 w/ a questionable relay. I've had to clean several of them over the years in my collection of '820 gear.

Remove the relay from its socket, remove the plastic cover and use an index card soaked in DeOxit D5-100L to clean the contacts by sliding it back and forth between each contact pair. Don't bend the contact arms (wiper) and do not (repeat: DO NOT) use abrasives like sandpaper or an emery board on these.

Run a clean file card edge through the treated contacts, replace the relay cover and replace the relay. This should cure the problem.

[W9IQ]

If you have a key plugged into the key jack, the key must be closed (shorted) for there to be a CW carrier. If you don't have a key in the jack, it will not develop a carrier if the internal shorting switch in the jack is dirty.

- Glenn W9IQ