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[TowerTalk] RE: TS-870 I.F. changes

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Subject: [TowerTalk] RE: TS-870 I.F. changes
From: (
Date: Fri, 14 Mar 1997 17:08:37 -0800
Hi, John.

It took a little doing, but finally located the chip resistors and the 
information about the changes. The following is the Service Technical Report 
(wording as transcribed from the report):

MODEL TS-870S (~S/N 712xxxxx ONLY)

NOTE: the changes do not apply from S/N 801xxxxx because production has been 

If there is any large power input signal in the proximity in the CW mode in the 
low band (such as 3.5MHz and 7MHz band), it will cause mutual modulation to 
create a "ghost" signal.
It may occur in the contest operation or during the pile-up reception.

A larger power input signal causes the second mixer output, the NB amplifier 
input, and the third IF amplifier input, and the third IF amplifier output to 

Change the gain allocaiton of the IF stage to raise the limit of saturation. 
This countermeasure will cause almost no deterioration of receiving sensitivity.

Antenna, amplifier, mixer, 73.05MHz filter
Amplifier, mixer, 8.83 MHz filter ----->noted gain is -10dB (minus 10)
Amplifier, mixer, 455kHz filter
Two Amplifiers------------------------->noted gain is +10dB (plus 10)

XX4-3210 (A/9) RF UNIT
        R1157           :  1.8k --->    560     (RK73FB2A561J)
        R160,R161:      :  2.2k --->    1k      (RK73FB2A102J)
        R164            :  1.5k --->    560     (RK73FB2A561J)
        L76,L79         :  3.3uH--->    0(zero) (R92-0670-05)
        R169            :  1k   --->    330     (RK73FB2A331J)

X57-4620  TX-RX UNIT
        R332            :  2.2k --->    6.8k    (RK73FB2A682J)

Do not forget to perform the re-adjustment of the S-meter after taking the 
countermeasures. Refer to "8. S-meter adj." on P.95 of the Service Manual for 
how to do it specifically.
If you cannot adjust the display to "05", even after you follow the steps 
described in "8. S-meter adj.", change the resistor as instructed below and 
the re-adjustment.
X57-4620  TX-RX UNIT
        VR-1            :  470 --->     3.3k    (R12-6737-05)

There are then drawings showing the locations of the parts on the schematic and 
on the related PC boards.


Hope this helps! Maybe this plus the software changes will take care of the 
majority of the problem. Now to locate and acquire the software.....

                73, Tom, N6BT
                Force 12 Antennas and Systems

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