Kenwood TS-950sdx SDXCC 6Kc TX Unit

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There's Modness to ar Methods!!  TS-950sdx Transmitter Mods  There's Modness to ar Methods!!

Talk dat VOOODOOOO!!!

We're finally finished with em!!!

We know...we know...sure took our sweet time with em,
but we wanted em to be the best they could be.

Sooooo....without further adue...

oh...ya got to read the
Bla...Bla...Bla, Bla, Bla...Blaaaa....

Disclaimer Notice
These modifications should be accomplished by qualified personnel who
have had enough knowledge and practice in SMD soldering techniques, at the owners risk.


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well here's some enlightenment into the Dark recesses of the SDX...

TX Audio Mods

Circuit Description:

TX Audio Path:

       The Stock TS-950sdx actually has very clean Mic Audio Amplification circuitry.
The only problem is its limited Low Frequency capability.
It starts to roll off the Lows quite heavily below about 90cps.
This is due to the components and circuitry that Kenwood decided to use.
The High Frequencies are only limited by the SDX DSP Unit and the IF Filters.

       The TX Audio Circuitry receives the Audio Signal from several inputs.
These inputs come from the front 8-pin Mic Jack, the rear Phone In" jack,
Pin-11 of the Acc2 Din Jack, and an input from the DRU2 unit.

       We'll follow the circuitry of the front 8-pin Mic Jack first.
The mic audio from the 8-pin front Mic Jack is input to the SW Unit(A)(X41-3240-00)(H-10) via "MIC"(pins #4 & #5 of CN15).
This is the Main TX Audio Amplifier board.
The audio is sent to Q251, a 2sc3324(g) bi-polar transistor for amplification.
It's then sent to a buffer Transistor Q17, which is another 2sc3324(g).
These two transistors significantly contribute to the TX Low Frequency Roll off.
They'll be bypassed for the Rack Line Audio Input.

Mic Unit Schematic.

       The DRU2 TX Audio is input to the SW Unit(A)(X41-3240-00)(H-10) via "V1" (pins #1 & #2 of CN13).
It's then injected just before Q251.

       The "Phone IN" and the ACC2 inputs are on the IF Unit (X48-3100-00).
These inputs pass thru some very restricting .1uf Caps that drastically cut the Low Frequencies,
much more than the front Mic Jack.
We're not going to mess with them since we're goin to inject the Line Audio upstream from here.
These two signals are then combined and are amplified by Q42, a 2sc3324(g) bi-polar transistor.

IF Unit TX Audio Inputs.

       This audio is then input to the SW Unit(A)(X41-3240-00)(H-10) via "ANI" (pins #1 & #2 of CN12).
There, it is injected just before the Buffer Amplifier Q17.
After Q17 is C29, which is a 33uf coupling Capacitor.
The signal then splits and goes to the Mic Gain/Processor Controls, and the VOX/FM Tx audio inputs.
This is the place we'll be injecting the Line Audio from the Rack.
We'll have to add some other circuitry here to get some isolation from C29 and R39.
If the Line Audio is directly injected here, C29 and R39 act as a RC Filter and kill the mid and high frequencies.
What we'll have to do is add 2ea 3.6Kohm resistors and create a sort of mixer.

Mic Unit Schematic.

       The Mic Audio signal then goes thru the Mic Gain Control (VR2)
and is sent to Switch Unit(A)(X41-3240-00)(G/10) via "MICVR2" (pins #3 & #4 of CN26).
It's then sent to the Signal Unit (X57-4130-00) via "MPV" (pins #3 & #1 of CN3)
where it goes thru C152, a 1uf Coupling Capacitor.
This cap restricts some of the Low Frequencies and will be changed to a 4.7uf.
The TX Audio then leaves the Signal Unit as "DMC" and goes to the DSP B Junction connector (pins #11 & #7)
Then arrives at the DSP Unit (X53-3390-00)(A/3) as "DMIC" (pins #3 & #4 of CN1).

Signal Unit C125.

Gotta have PARTS!!!

TX Audio Mod Parts
Part Numbers
Jensen 4:1 Input Transformer
Jensen ---- JT-10KB-D
Switchcraft 1/4" Gold Plated TRS Jack
http://www.onlinecomponents.com ---- MN112BX
C152 - 1uF changed to 4.7uF
Electrolytic on Signal Unit
Digikey - P10315-ND ---- EEU-FC1H4R7
Mix #31 Ferrite Bead
Fair-Rite ---- 2631540002
RG-174 Coax
Belden ---- RG-174/U
47uF SU series Bi-Polar - 1ea Needed
Electrolytic Capacitor
Digikey - P1179-ND ---- ECE-A1EN470U
.01uF - 1ea Needed
Radial Lead Capacitor
Digikey - BC1146CT-ND ---- K103Z15Y5VE5TL2
51 ohm - 1ea Needed
1/4 watt Axial Resistor
Digikey - P51BACT-ND ---- ERD-S2TJ510V
3.6K ohm - 1ea Needed
805 Chip Resistor
Digikey - RR12P3.6KDCT-ND ---- RR1220P-362-D
3.6K ohm - 1ea Needed
1/6 watt Axial Resistor
Digikey - 3.6KEBK-ND ---- CFR-12JB-3K6
2.4K ohm
1/6 watt Axial Resistor
Digikey - 2.4KEBK-ND ---- CFR-12JB-2K4

What do you mean...Drill a 3/8" Hole??!!

       Yes, Yer gunna have to drill a 3/8" hole in the back of the rig to do this modification.
Or...another option could be the use of a Greenlee Chassis Punch if available.
This is to mount the Switchcraft MN112BX 1/4" Gold Plated TRS Connector for the Rack Line Audio Input.
You will need to gain access to the bottom of the rig.
To access it, Very carefully turn the TS-950SDX upside-down. The DSP Unit (normally on the bottom) will be on the top now.
Squeeze the DSP Cable connectors and carefully jiggle them while pulling to disconnect them from the back of the rig.
Remove the 14ea countersunk screws from the bottom cover, then remove it.
This will expose the inside of the rig. You will see 4ea circuit boards side by side.
Your target area will be between the two rear circuit boards. See Pic.

TRS Mounting Hole.
This is the 3/8" Hole in the back of the TS-950sdx.

TRS Connector Installed.

       We'll describe the "Drilling" procedure as it is rather tricky compared to the chassis punch method.
This is a fairly easy process if you follow some basic procedures, and use the proper tools.
First step is to "Center Punch" the starting hole location.
This is a must and will keep your starting drill bit from "walking" and scratching up the paint.
Another trick to protect the paint, is to place some masking tape over the area.
You'll just drill straight thru the tape.

Tapeing the location for the TRS Hole.
We usually put some masking tape over the area and drill straight thru it.
That's an old Aircraft Mechanics Trick, keeps from scratching the surface.

Centerpunch location for TRS Hole.

       Eyeball the back and front of the rear panel to be sure you give yourself plenty of clearance for the final 3/8" hole.
Needless to say, it's a MUST to catch the shavings generated from the drilling operation.
Definitely don't want those nasty conductive buggers down inside your rig.
We used strategically placed pieces of Duct Tape to capture the shavings, see pics.

Duct Tape installed to catch Shavings.

Drilling and catching Shavings.

Final Hole Size.

       The secret to making a great hole is to step drill. Start with a small bit and progressively go bigger.
Be careful not to go too big (or small) in step size, as the bits will have a tendency to "bite" and "grab"
just before going thru the hole. Especially if using a 2 fluted drill bit.
We used a set of "Core Drills" for the final hole sizing.
These bits are a cross between a Reamer and a drill bit. They are piloted 4 flute bits.
They cut beautiful holes, but are very expensive. We got them from our Aircraft Mechanic days.

Core Drills.
These are called "Core Drills". They are 4 fluted piloted drill bits.
After you drill a hole with one size, it leaves a hole
just big enough for the pilot of the next larger bit to go in.

       Use a fairly low speed and light pressure.
Then "deburr" the hole when you reach the final size.
We'd suggest you try this out on some thin sheet metal BEFORE you attempt it on your $2000.00 Radio.

       After the Hole is made in the rear of the SDX, now the 1/4" TRS Gold Plated Connector can be installed.
These are fairly hard Switchcraft Connectors to find.
Most distributors don't carry the Gold Plated ones.
I have been getting them from Online Components
There P/N is MN112BX.

TRS Connector Installed.

TRS Connector Installed.

       The next step is to attach the coax and grounding components.
Jensen suggests to place a 51 ohm axial lead resistor and a .01uf disk ceramic capacitor to
chassis ground from the SLEEVE solder tab of the TRS connector.

Jensen Transformer Connector Chassis Ground.

       The hardest thing to do here, is to get a good chassis ground.
We took a dremel tool and burnished the Chassis near the TRS Connector.
Flux was applied there and scrubbed into the burnishing.
Then a high powered Soldering iron was used to heat the area enough to get the solder to flow onto the burnished area.
Be Careful not to apply too much heat or the paint will burn on the other side!!

       Now install an appropriate length of RG-174U coax to the TRS connector pins.
It'll have to be long enough to be routed up to the front of the rig.
Attach the center conductor of the coax to the TIP solder tab,
and the shield of the coax to RING solder tab.
The coax will be run with the SDX wiring harness to the Jensen Transformer location.

TRS Connector Installed Complete.

Jensen Transformer Installation:

       The Line Input Transformer we used, was a Jensen JT-10KB-D 4:1 Step-down.
These can be purchased from Jensen.
We searched for a suitable location to mount the it on the Inside of the SDX.
There really isn't that much room in there!
But we did find a great place to mount it.
Everything is still accessible/removable as it was in stock configuration.

Jensen Xformer Installation Complete.

       Of course there is a down side (there always is), yer gunna have to drill another hole!
Not a big hole, but it is in a rather bad location.
The Control Unit (X53-3380-00) is going to have to be removed in order to do this.
We drilled a 7/32" hole to install a 10-32 Nylon Mounting Screw with nylon washers and nut.
Be sure to capture the shavings!

Jensen Xformer Mounting Hole Location.

Jensen Xformer Mounting Hole Location Close up.

       The Jensen Transformer must be installed totally insulated from chassis ground.
This is because the SDX Mic Amp circuitry ground is isolated from chassis ground.
This is to eliminate any chance of Hum.
We installed Heat Shrink to our Jensen Xformer to insulate it.
We then used the Nylon Screw, nylon washers, and nylon nut to mount it.
These nylon items were purchased at Home Depot.

Jensen Transformer Insulation Job.

       You can now mount the Transformer. Leave the wires uncut at this time.
After installation, check the continuity between the Transformer Case and Chassis ground
It should be infinity.
If so, the Control Unit (X53-3380-00) can be re-installed.

Jensen Transformer Wiring and Connection:

       With the Jensen Transformer installed in the rig, we can now wire it in.
Look below, at the hack job of a circuit schematic we made.
This shows how the Jensen JT-10KB-D Transformer's Input/Output are to be wired and connected to the sdx.

Jensen JT-10KB-D Transformer wiring.

Jensen Input Wiring:

       This is were we connect the RG174 coax coming from the TRS connector.
But before the wires are permanently connected, a Mix #31 Ferrite Bead needs to be installed.
This bead is installed close to the Transformer itself.
This is safe insurance to impede any stray RFI from getting into the transformer.
We installed it by looping the Orange and Yellow twisted pair of input wires thru the Ferrite Bead. (see Pic)
The wires are then connected to the RG174.
The Yellow "+" wire is soldered to the center conductor of the RG174, this connects to Pin #2 of the Mini XLR.
The Orange "-" wire is soldered to the Shield of the RG174, this connects to Pin #3 of the Mini XLR.

Mix #31 Ferrite installed on twisted input wires.

Jensen Output Wiring:

       Jensen suggests installing a 2.43 Kohm resistor across the output of the Transformer for "Perfect Transient" response.
A 2.4 Kohm value is close enough for this requirement.
This Resistor will be installed from the Red Wire to mic ground (Black, Brown , and White wires).
A 47uf SU/Bi-Polar Panasonic capacitor is installed next to isolate the transformer output impedance
from the Mic Gain/Processor potentiometers and other circuit resistance downstream.

       We installed the 2.4K Resistor and the 47uf Cap at the transformer,
Encapsulated them in heat shrink tubing,
Then ran RG174 coax to the Mic Amp Circuit Board.
Reference the schematic & pic below.

Jensen JT-10KB-D Transformer wiring.

JT-10KB-D wiring completed and routed.
Here's the Jensen Transformer, the Ferrite, and the Heat Shrinked components
all mounted and the wiring routed and tied.

SW Unit (A)(X41-3240-00)(H-10) Mod:

       Now it's time to modify the Mic Amp circuitry to accept the Line Audio Input.
After allot of research, We found that the best injection point
would be right before the Mic Gain Control.
The Center Lead of the RG174 coax was soldered to Pin #6 and the Shield was soldered to Pin #7 of CN14.
This would allow full functionality of all the original Processor, FM, & VOX circuits.
It would also allow for front control gain adjustments for the Line Audio Input.

SW Unit(A) Line Audio Injection Point.

       The problem we ran into was that if directly injected at this point,
All the Mid and High Frequency audio energy was being cut.
After investigating this, it was found that C29 and R39 were acting as a RC Filter.
We originally cut the trace leading to these components, and all was well.
The only problem with that, is the loss of the original Mic Audio Inputs.

SW Unit(A) Trace Cut.

SW Unit(A) Trace Cut.

       So, in order to keep the other Mic Amplifier inputs, plus the Line Audio input,
A form of a mixer had to be created to feed both these inputs into the desired injection point.
This took the form of 2ea 3.6 Kohm resistors installed at the injection point.
One 3.6K Chip Resistor was soldered in across the Trace that was previously cut,
The other was a 1/6 watt Axial lead resistor soldered in between the RG174 center lead and Pin#6 of CN14.

       We also drilled a small hole in the edge of the circuit board in order to
"tie" the coax to the board. This added strain relief for when the front face is tilted forward.

Trace Cut for 3.6K ohm Resistor.

SW Unit(A) Complete, Front View.

SW Unit(A) Complete, Side View.

SW Unit(A) Complete, Side View.

SW Unit(A) Resistor Schematic.

Signal Unit MODification

       Yer gunna have to get to the Signal Unit (X57-4130-00) board and
remove it from the radio in order to do this modification.
The Signal Unit is located in the bottom of the radio.
With the front of the rig facing you, the Signal Unit is the circuit board on the Right,
closest to you, with the 455Kc Filters on it. See Pic below.

       Now that the Signal Unit is out and on the bench,
ya got yer one electrolytic capacitor, ya ready to change it.
Thats right...all that for just one capacitor!!
Well, you could go ahead and do the AM Mods while the board is out of the rig...
only thing is that we don't have them posted yet...Damn it!!!

Electrolytic Cap:

       The board is marked with both the Capacitor Number and the Polarity.
It's really just a matter of unsoldering and removing the old capacitor, and installing the new one.
The size is close to the same so it should fit with no problems.
This cap is nestled in between two connectors.
No surprises here.
Be sure to install the Capacitor with the correct Polarity!!

Change this Electrolytic Cap:
C152 - 1uF - Change this to a 4.7uf

C27 Capacitor Location

Signal Unit Re-Installation

       Before you attempt to re-install the Signal Unit, take the time to look over the board extremely well.
Be sure all the Flux from your soldering is cleaned up.
Look for any accidental solder bridges that might have happened while you were soldering.
Be sure all the cut leads from the installed components are not "stuck" on the board anywhere.
Give it a good inspection.
The installation is just the reverse of removal.
Be gentle, don't force anything. Double check all the connectors and ribbon cables.

       Well, that aught to do it.
You should be able to transmit some very clean audio at a much lower frequency.
Don't forget to wire up the TRS Plugthe same as you did the TRS Jack.

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