[Kenwood] TS-940 Improved AGC function if R149 and R 150 be swapped around to match Kewnood circuit diagram

[Jeff King]

>From ZL4AI:

Dear TS-940 owners, you may find this improves the AGC function.

While searching for the fault described below I found that on the IF
board Kenwood mistakenly labelled R149 (68K or 150K ohms) where R150
(2.2M ohm) should be and vice versa. This is in the heart of the AGC
timing section. This means many TS-940s may have R149 and R150 in the
wrong place.


I changed R149 and R150 back to the way Kenwood intended in the circuit
diagram and the result was:
-The fault of the rising S meter when cold {see below} disappeared:

- S meter with AGC ON is quite lively in the region of S1 to S4 signals.
Before it did not move much in this region. I always wondered why it
behaved differently to other transceivers which reacted much faster over
S1 to S4.

- When R149 and r150 swapped S meter dropped back to S1 on both AGC OFF
and AGC SLOW, with no antenna signal.  I needed to reset VR3 to bring
the S Meter to S0.
=======================================================


ACKNOWLEDGEMENTS TO PERSONS WHO SOLVED THIS 

T.Soranaka Kenwood Japan was most helpful. You will see in the emails
below Kenwood have readily confirmed that these components are around
the wrong way.


Traian Belinas 
traian at deck.ro
who diagnosed the problem and really understands these circuits. Traian
appears to have amazing skill and after reading the symptoms pointed me
to look at R149. From there it became obvious the circuit was not
assembled according to the circuit diagram.


Garey Barrell
'k4oah at mindspring.com'
Who provide some very useful advice on functions of components and
explanations how to read the circuit diagrams. 
==============================================================

A CAUTION:

Not all boards are the same.
I tried another IF board installed as per factory spec with R149 and R
150 in their other components position in my TS-940. It did not have the
rising S meter problem. It could be that changing these resistors has
little effect on some IF boards.


================================================================


THE INITIAL PROBLEM SYMPTOMS 
AGC: 
Only happens in SSB: 
If TS-940 left not running for a couple of days, when you turn it on, 
with the AGC turned off or set in fast position, then the meter needle 
goes to up 25db + 9 (approx). The signal is diminished like RF gain 
turned up. Over the next 25 minutes the meter needle slowly moves it way

back to s0. 
SSB in normal position, and TS-940 turned on this does not happen. 
Needle is initially at s0. 

During the first 25 minutes if you switch between off - fast - normal 
then the needle goes back to zero in less time ... say 20 minutes. 

If TS-940 left for a couple of months, and then turned on same behaviour

but worse. 
Meter needle goes full scale right in all positions (off - fast - 
normal) 
It takes longer say 40 minutes for the needle to move to the s0. then 
ts-940 functions as described above. 

========================================================================
=





COMMUNICATIONS WITH KENWOOD JAPAN BELOW:

-----Original Message-----
From: Customer Service Section [mailto:css at kenwood.co.jp] 
Sent: Tuesday, 15 March 2005 7:11 p.m.
To: jaking at es.co.nz
Subject: Re: Question about TS-940 R149 and R 150: Appear to be in wrong
places!


Dear Customer,

Thank you for your reply. I suppose that currently R149 and R150
are mounted correctly as the screen printing lettering R149 and R150
are reversed. Please confirm actual resistors comparing the circuit
diagram. The circuit diagram is correct.

Yours sincerely,

T.Soranaka
++++++++++++++++++++++++++++
Customer Support Center
Kenwood Corporation
(Japan)
URL:  http://www.kenwood.com/
Email:  css at kenwood.co.jp
++++++++++++++++++++++++++++

----- Original Message -----
From: Jeff King
To: 'Customer Service Section'
Cc: k4oah at mindspring.com ; traian at deck.ro ; Bill Bailey ; Ken McVie
Sent: Tuesday, March 15, 2005 1:53 PM
Subject: RE: Question about TS-940 R149 and R 150: Appear to be in wrong
places!


Dear T.Soranaka


Thank you for your advice.
Could you please advise if it would be advisable to swap  R149 with R
150 and vice versa,
so
the TS-940 functions in accordance with the circuit diagram?

Yours sincerely
Jeff King



-----Original Message-----
From: Customer Service Section [mailto:css at kenwood.co.jp]
Sent: Monday, 14 March 2005 10:29 p.m.
To: jaking at es.co.nz
Cc: kcc-amateur at kenwoodusa.com; sabura.tech at kenwood.com.au
Subject: Re: Question about TS-940 R149 and R 150: Appear to be in wrong
places!


Dear Customer,

We are sorry for inconvnience. I have checked with our communication
department as to R149 and R150.  Unfortunately reference number of R149
and R150 on the borad are reversed.
R150 and R149 are 2.2M and 68K or 150K respectively as shown in the
Service Manual.

Yours sincerely,

T.Soranaka
++++++++++++++++++++++++++++
Customer Support Center
Kenwood Corporation
(Japan)
URL:  http://www.kenwood.com/
Email:  css at kenwood.co.jp
++++++++++++++++++++++++++++
----- Original Message -----
From: Jeff King
To: css at kenwood.co.jp ; kcc-amateur at kenwoodusa.com ;
sabura.tech at kenwood.com.au
Cc: k4oah at mindspring.com ; traian at deck.ro ; Bill Bailey ; Ken McVie
Sent: Saturday, March 12, 2005 6:41 AM
Subject: Question about TS-940 R149 and R 150: Appear to be in wrong
places!

Dear Kenwood Customers Services,

I have found that when emailing Kenwood USA about a Kenwood USA product
I got redirected to contact a Kenwood representative close to my home
location. I am not sure who is best to send this to.
So I am sending it onto to all Kenwood contacts.

Thank you for your recent replies.
While trying to find a fault in my TS-940 I have been going over the IF
board.
It appears to me when the board was made it was marked with the screen
printing lettering
of
R149 being where R150 should be and vice versa.
I have followed the board traces both in the Service Manual and on the
back of a board, and these resistors both seem to be in the wrong place.

This means:
Specified in First Service Manual: 
R149 68K 
R150 2.2M

Specified in Revised Service Manual:
R149 150K
R150K 2.2M

Resistors as actually installed on my board if you follow the logic of
the circuit diagram. 
R149 2.2M
R150 150K

I have two IF boards here and they both have the resistors installed as
required by the screen printing and
hence on both boards both resistors are reversed. Possibly this is the
case for every TS-940 ever made.

I cannot understand how the circuits would function as the designer
intended, as the installed resistors are very different to those shown
on the schematic diagrams.
Could you please advise if my observation is correct, and after later
when Kenwood has investigated if it would be advisable to swap  R149
with R 150 and vice versa?

At this time could you please just confirm that the question will be
investigated?

I look forward to your reply.

Yours sincerely
Jeff King ZL4AI