TS-790 with serial frequency control

by Kohjin Yamada, JR1EDE
3 Jun'90

This note is the summary of our discussion made among W9FMW, JA6FTL and myself. The first report has been brought by WB0KSL expressing TS-790 has audio drops at the frequency change command in it's serial control. JA6FTL confirmed the data loss at the product detecter on his scope too. These are as terrible as if we use KCT Tuner in it's serial control option.

Kenwood replied to my inquiry "It is made as so to prevent the noise of PLL, about 100m sec mute is created". Kenwood suggests the modification as below but it should be made on user's responsibility. This should be solved in their next products, I strongly told them.

JA6FTL and I confirmed that it now works perfectly on FO-20's actual test and uSATs too with the following modification.

Kenwood suggestion (Refer to IF DIAGRAM)

You could disable the mute function by following methods, both or item 2 only.

• Delete D20 or R191 (for SUB audio)
  As far as you would use the rear data port (ACC2), it's *NOT* necessary to do this, although you would still have the audio drop at the sound of loud speaker. Of cource, you should do this modification when you would hook up the audio data from Microphone Plug.
• Put a jumper between Q4 collector and emitter (for SUB RF Block)
  This modification is a *MUST*.
  You can do this by several ways but the above is most easy.

The following discussion might help you a bit; (partly eddited by me)

I wrote to W9FMW;

>Cut the line between Q4 Collector and R15 (470 orhm) and Ground the end of
>R15. JA6FTL made the mod removing Q4 entirelly and grounding the end of R15.
>Q4 located the left of Q5, they are located roughly oposite side of L2, L3.
>JA6FTL says the modification needs a magnifying glass, Hi.

There is 1 Reply.

 
#: 18154 S5/Amateur Satellites
    01-Jun-90  09:08:20
Sb: #18148-TS790 mod for KCT
Fm: Sueo Asato JA6FTL 71701,251
To: Kohjin Yamada, JR1EDE 76662,111
 
Here is additional info. to the modification.
 
Yes..... Need magnifying glass (I am not farsighted nor shortsighted Hi.)
This modification is to disable the blocking line for IF amp.
Audio muting function remains unchanged, but it is no problem to use rear
data port. (Audio muting circuit consists of D20 and Q12)
 
1.Put the frontside toward you and remove the bottom cover of 790.
2.remove the 13 screws that fix IF board. Lift over up the board toward you.
3.Q5 and Q4 are located just opposite side of L2 and L3.
  Chip Q5(printed "V11") has 4 solderd legs, and it's located next to R15
  (470 ohm surface mount resistor, printed as "471").
  Q4 is located just beside R15 and has 3 legs.

       Thanks Kohjin,JR1EDE             de    JA6FTL

* This file was uploaded to FO-20 MBox and CI$ by JR1EDE

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