From: ka3pgn
Newsgroups: rec.radio.amateur.misc

Subject: Re:TS850S features and mod file (long)

Keywords:features, mods

Date: 27 Oct 91 11:02:47 GMT

Organization: Internal Revenue Service, Washington, DC

Lines:150



I really appreciated your remarks about the 850. I've owned mine for

about four months now and one of the first things I did was to disable

the broadcast band attenuation.

Being an avid BCB DX'er, I found this little device quite an annoyance!

So, the first day out of the box, I did away with it and very easily at

that.



HERE ARE THE STEP BY STEP INSTRUCTIONS TO DISABLE THE BROADCAST BAND

ATTENUATION FOR THE KENWOOD TS-850S. This mod greatly improves the

sensitivity and likewise the reception on the AM broadcast band.  

No noticable unwanted side effects have occured following this procedure.

I live within three miles of a 5,000 watt broadcast station on 1150 kc's

and am able to listen to stations on either side of that station. There

is some splatter but using the notch filter and the attenuation on the

front of the radio takes care of that for the most part. This is *NOT*

complicated and can be done in fifteen minutes. Only one caution here:

you WILL BE SOLDERING TWO POINTS ON A CIRCUIT BOARD THAT IS LOADED WITH

SURFACE MOUNTED COMPONENTS!!! There is little room to work on the board,

so be very careful with your iron! If you don't feel comfortable soldering,

get someone else to do it as you can cause a solder bridge and ruin your

radio without even trying. With that in mind, here goes:



1) remove the eleven screws that secure the bottom cover to the rig.

   the six ones on the sides and the five on the bottom cover itself.

2) remove the bottom cover. there are no wires attached to the cover.

   lift it right off. leave the top cover of the radio ON.

3) locate the RF BOARD. it's number is:X44-3120-00. this is the board

   where you plug the optional filters into. with the open radio in front

   of you, and the front of the radio facing you, the RF BOARD is the

   one on the left. (there are only two boards under the bottom cover)

4) locate the chrome like shield on the rear of the RF BOARD. it's made

   out of shiney steel. remove the four screws that hold this shield to

   the board.

5) remove the shield by lifting the front of it up while sliding it

   forwards, towards you. watch out for all the little wires and ribbon

   cables going to and from the RF BOARD.

6) look at the rear of the board and towards the left corner.(the radio

   is stil facing you upside down) notice two I/C's numbered IC1 and IC2.

   directly behind the I/C's are a bank of adjustable coils in metal cans.

   there are nine of these coils in a group. directly to the left of these

   coils are many green and red inductors which are standing up. they look

   like resistors but they're really small coils.

7) these inductors are part of the bandpass filtering for each of the bands

   on the radio. the capacitors and resistors that complete the bandpass

   filtering are on the other side of the board and are of the surface

   mount type. you are only concerned with the bandpass filter for the

   .5 to 1.6 band. notice the numbers for the inductors. find L8 and L9.

   they are right at the edge of the board in the left rear corner

   you will notice that .5 - 1.6 is stamped right next to L9.

   BINGO! you have found the part of the circuit that you will modify.

8) look at where the .5 - 1.6 is stamped on the board next to L9. you

   will see two bronze or gold solder points there directly next to the

   numbers .5 - 1.6 . there is nothing soldered at those two points.

   this is where you will solder a jumper wire between the bronze points.

   do NOT confuse it with the other two solder points with the line

   running in between them next to the phillips head screw!!! you want the

   two points that are spaced very close together that is right next to

   L9.

9) you will have to do the soldering on the OTHER SIDE OF THE BOARD.

   remove the nine phillips head screws that hold the RF BOARD to the

   chasis.

10) on the back of the radio, look for the switch stamped SW 1. it's right

    below the grounding post and has the two postions:INT and EXT. remove

    the two screws that hold the switch to the back of the rig. the switch

    is soldered to the RF BOARD and you wont be able to lift the board up

    until the screws are removed.

11) unplug enough cables from the board so you'll have enough room to lift

    the RF BOARD up to solder the jumper. there is no need to remove the

    board from the rig. slide it towards the front of the rig until the

    switch SW 1 clears the back of the rig and lift the left side of the

    board up and prop it up with a small block of wood.

12) locate the bronze solder points on the underside of the board.

    there will be a small amount of solder at these two points on the

    underside of the board.

13) bend a small jumper out of wire that fits the two bronze points on top

    of the RF BOARD. you will place the jumper on the top and solder on the

    underside of the board. with a pair of needle nosed pliers, place the

    jumper into the holes and simply heat up the existing solder on the

    underside until the jumper slips down farther into the holes.

    you'll notice the large amount of components on the underside versus

    the lack of components on the top of the board. be carefull when

    heating the solder on the two points. you don'y want to disturb the

    surface mounted parts or cause any excess solder to run  onto them or

    the foil nearby.

14) you are now done. re-assemble in reverse order, plugging the wires

    back in carefully, making sure they don't get plugged into the wrong

    place. also, avoid pinching them when replacing covers.





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                 FRONT OF RADIO



Sorry, that's the best art work I can do. The purpose of the jumper is to

bypass the two 150 ohm resistors that are in series after the bandpass

filter. The resistors add between 20 and 25 db attenuation to the AM

broadcast band. For some reason, Kenwood thinks that the receiver would

become overloaded by strong nearby broadcasting stations, which would

cause distortion. I simply don't find that to be the case. It's funny,

Kenwood already had those two points there on the board, but without the

jumper......it seems to me that they had anticipated the need to bypass

the attenuation in Europe or Asia. Thus, all export models going to the

states were missing that jumper. Who knows? I can't find any other reason

for the jumper points to be there.



Anyway, you'll notice an immediate increase of signal strength. You'll

hear stations that you never knew were there! As I said, if you are

bothered by strong stations in your area, try using the 6 and/or 12db

attenuation buttons on the front of the rig.

I'll be glad to assist in any way possible. You can e-Mail me or feel

free to call at the radio station. Have fun DX'ing!



Dave







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