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Author Topic: TS-820 VFO Adjustment question....  (Read 2388 times)
KB8BAB
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Posts: 101




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« on: December 02, 2012, 03:10:40 PM »

One of my current project is a TS-820 "semi" restoration.
Since this is not the "S" model, it had no digital readout. The original Kenwood version (DG-1) are far and few between.

Anyways I've installed the DFD2 kit/freq counter and it works very well.
Testing the TS-820 into a dummy with freq set to 7.200 results in transmitting at 7.200....so far so good I thought.

Listening on-air I compared the receive freq to two other rigs I have, this is where I noted the discrepancy. Signals coming in on the TS-820 were 1.5Khz off to the "reference" rigs.
The service manual procedure calls for an adjustment to the VFO board...
Where the heck is this board? Inside the VFO?

73
Bart


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KK5J
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Posts: 81




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« Reply #1 on: December 02, 2012, 03:30:35 PM »

I have the service manual here too. Where are you seeing reference to the VFO board? Page? I see VCO board adjustments or - VFO only if the external VFO needs adjustment. Are you using an external VFO? What is the status of your RIT?
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KK5J
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Posts: 81




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« Reply #2 on: December 02, 2012, 03:43:23 PM »

Yes there is a board inside the VFO unit but adjustments are made from outside the unit..
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KB8BAB
Member

Posts: 101




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« Reply #3 on: December 02, 2012, 06:02:03 PM »

The reference was on Page 48 I believe...that's where the procedure is.
"correct it with TC1 in the VFO unit"

If the adjustments are made from outside...then where outside...

73
Bart
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AA4N
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Posts: 110




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« Reply #4 on: December 02, 2012, 07:14:34 PM »

Are you sure that you don't just need to slip the dial a bit to one side?  It's normal to touch up the frequency scale by one or two kc every now and then on a 820.  You don't even need the frequency counter.  Just flip the function selector from vfo to 25kHz, then tune to the nearest multiple of 25kHz.  You should hear a beat tone.  Zero beat the tone (by tuning to a lower and lower pitch until it disappears), then slip the ring on the back of the main vfo knob until the scale reads right on 25, or 50, or 75, as is appropriate.  That will get you within 100 Hz or so of perfect, which is close enough for any real world HF work.  Really, the digital readout on th S version is just eye candy.  Doesn't serve much of a useful purpose IMHO.

73, mike. AA4N
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KB8BAB
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Posts: 101




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« Reply #5 on: December 02, 2012, 07:22:52 PM »

Mike,

That would be an easy fix certainly.

Problem is, when recieve 1.5khz low my transmit is low also. A station coming in at 7.200 (on my other rigs) is tuned in as 7.198.5 on the TS-820. If I key up, I'm transmitting at 7.198.5  which is 1.5khz off.

73
Bart
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AA4N
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Posts: 110




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« Reply #6 on: December 02, 2012, 07:36:55 PM »

So, it sounds like xmit and receive are happening one the same frequency.  If you tune another staition in by ear, never mind what the dial says, you sound on-freq to the other station?  If that's the case it still sounds like the rig is working fine.  Just adjust the dial by 1.5k.

If your xmit and receive are on different freqs, then it's time to pop the top on the rig and get out the little plastic screwdrivers.

Maybe I'm not understanding the problem.

Mike
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AA4N
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Posts: 110




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« Reply #7 on: December 02, 2012, 07:58:17 PM »

Here's another thought.  I've got the 820S model.  The digital frequency readout on mine actually changes by 700Hz when I key down in CW mode.  It only shows the actual carrier freq during xmit.  During receive, it drops by 700Hz so the bfo has something to beat against.  if I'm working a guy on 7.038, the dig readout shows 7.037.3 during receive.

 I wonder if it does something similar on sideband?  Does the 1.5kHz difference swap sides when you switch from LSB to USB?  I havent noticed whether mine does that.  I'm pretty much never on sideband...

Just thinking out loud.

Mike
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AA4N
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Posts: 110




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« Reply #8 on: December 02, 2012, 08:05:46 PM »

Okay nevermind that last bit.  Readout doesn't change when you key down in SSB mode.  I couldn't stand it.  Had to go check  Smiley

Mike
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KK5J
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Posts: 81




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« Reply #9 on: December 02, 2012, 08:20:14 PM »

As I remember TC1 and L1 can be found under the foil on top side of the VFO. TC2 is open and on opposite side. L1, if I recall is forward of TC1. Thats how I remember it-might look down the holes and see, as they are recognizable (cap vs inductor) from the top.
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VE7DQ
Member

Posts: 176




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« Reply #10 on: December 03, 2012, 12:34:59 AM »

TC1 and L1 are used to set the tracking on the top and bottom of the VFO's range. i.e. 3.5 and 4.0 Mhz, and won't have any effect on this problem.

I suspect that, being an external 'universal' counter, the DFD2 can't resolve the difference caused by the frequency offset of the Carrier Unit oscillator... which happens to be exactly +1.5Khz and -1.5Khz... unless a 1.5 Khz offset can be programmed into the DFD2.

The DG-1 takes input from the carrier oscillator, the VCO and the VFO to calculate its displayed frequency.

Look at Alignment of Receiver Section 2.1. Carrier Unit Adjustment.
« Last Edit: December 03, 2012, 12:42:20 AM by VE7DQ » Logged
KB8BAB
Member

Posts: 101




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« Reply #11 on: December 04, 2012, 01:41:41 PM »

Just to be sure, I checked the carrier unit.....its spot on frequency...

Need to dig deeper...
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