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TS-940 VFO off freq  

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kd2hdz
(@kd2hdz)
Active Member

I am the original owner of a 940 that after it was serviced, now has it's VFO display is slightly off frequency. 

For example 28.385 is 28.384.75   -- It's low...  

It over almost all bands like that. 40/80 are better, closer, to freq.  

I know there is a trimmer cap for the master oscillator. Can someone point me there? On the bottom of the rig? 

Switching from USB to LSB on WWV yields two different tones.  Neat trick when you dont have a scope. 

Is the recv tracking the xmit?  YES... So the display is off just a little.  Or, the display is right on, and the master o is off.. ? 

If it's not the master, is there a calibration pot for the display?  (Don't think so.. )  

Any help appreciated. 

KD2HDZ 

 

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Posted : 01/11/2018 7:15 pm
ak6ok
(@ak6ok)
Member Admin

Good morning,

The trimmer cap for the frequency is on the left side of the rig toward the front. There is a small hole there that is for adjusting the frequency. I would suggest using a metallic type screwdriver to access it. It will put you right on frequency. Thank you! Jeff 

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Posted : 05/11/2018 2:14 pm summitradio liked
kd2hdz
(@kd2hdz)
Active Member

You sire are a giant!  What a simple fix.... It was just a simple 1/364 turn of the that trimmer, and bang, right on freq! 

I did let the rig warm up for an hour or more before doing this...  

Thanks for a great fast fix.

73 from KD2HDZ --- (now W2ADX ) 

 

THANKS AGAIN!  

This post was modified 3 months ago by kd2hdz
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Posted : 06/11/2018 2:54 pm summitradio liked
dave
 dave
(@dave)
New Member

It sounds to me like the carrier offsets have shifted, which is common in older radios due to component value shift with age.

On the TS-940, there are four separate Voltage Controlled oscillators that generate the master frequency references.  Known as CAR1, CAR2, CAR3, and CAR4, they are relatively easy to adjust if you have an accurate frequency counter.

 However, I suspect the problem you are experiencing is more likely to be a suggestive "appearance", or "sounds like" the radio is off frequency, caused by the carrier balance settings, also known as "SSB Response".  This is the most common malady I see in both TS-930 and TS-940 radios, although the actual alignment steps are different for each radio.

In the TS-940, this adjustment sets the offset from zero-beat for each of the sidebands to ensure that the received audio is shifted appropriately 1.5 kHz below or above the actual dial frequency.  The adjustments for this are TC1  (USB) and TC2 (LSB) on the DG-B Unit, which is easily accessed once you remove the top cover.  The DG-B unit is located on the right front of the radio, and TC1 and TC2 are the two trimmer capacitors located on the top left of the DG-B Unit.  The simplest way to adjust them is to set your main dial at the frequency you know to be accurate for a transmitting station, then adjust the appropriate trimmer cap to bring the audio up or down to the point where it sounds natural.  Turn the caps very slowly, they are quite sensitive.  Of course, the better method to use to align these adjustments requires some serious test equipment, but you can usually achieve quite acceptable results by adjusting them to meet your expectations.

Feel free to contact me if you have any problems, questions, or just want to  chat.

73's

Dave

KB7JS

This post was modified 1 month ago by dave
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Posted : 18/12/2018 11:15 pm
summitradio
(@summitradio)
Active Member

Hi Dave 

What is the procedure for the 930? I want to check mine as I remember it was off a little the last time I used it.

I should be getting the PS kit today. I'll check the frequency and then do the PS mod and check again to see if there was any appreciable effect.

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Posted : 19/12/2018 1:43 pm
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