Kenwood TS-850S RX I.F. Board Mods

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Kenwood TS-850S RX I.F. Board Modifications:

As with the DSP-100 TX mod, if you are a purist and want the fullest and flattest receiver response possible with the 850/DSP-100 combination for SSB, you will want to perform this modification which enables the receiver to respond flat from 20hz to 6kHz.

Kenwood TS-850S i.f. Board Flat Frequency Response Modifications Instructions:

Place the 850 upside-down and remove all the screws on the bottom and sides of the case. Remove the bottom cover. Locate the I.F. board (X48-3080-00) and remove all Molex connectors and Ribbon Cables from the board. Remove all screws and carefully remove the board.
Note: If you will be completely replacing the capacitors, use the following replacements available at Mouser: Part # C1206C105K4R - (1mF) These are the larger 1206 SMT's Part # 80C0805C105M4V - (1mF) These are the smaller 0805 series SMTs They ARE both rated at 16 Volts. If you are simply bridging over the capacitors in parallel, then tantalums will work okay. However, since the I.F. board must be removed anyway, you will probably just want to use the surface-mount type capacitors and preform complete replacements. Note: C155, C167 and C187 are Electrolytic type capacitors. The Three CRITICAL Caps are indicated in RED. The rest are optional but recomended since they will lower the final receiver frequency response down to about 20Hz, including the Headphone, Speaker and ACC2 outputs.
Capacitor Value Changes:	Click Corresponding Links Below For Photo Details NOTE: Please notice the installation notes below for convenience
C151 .047uF to 1uF	(Click to See Photo C151)
C155 1uF to 10uF Mouser Part # 140-XRL16V10 (Electrolytic)	(Click to See Photo C155)
C156 .1uF to 1 uF	(Click to See Photo C156)
C164 1uF to 10uF	(Click to See Photo C164) Remove this cap BEFORE installing C 161
C161 .1uF to 1uF	(Click to See Photo C161) Install this cap before re-installing C 164
C163 1uF to 10uF	(Click to See Photo C163)
C167 10uF to 100uF Mouser Part # 140-XRL16V100 (Electrolytic)	(Click to See Photo C167) This cap is an Electrolytic
C170 0.1uF to 1uF	(Click to See Photo C170)
C172 0.1 uF to 1uF	(Click to See Photo C172)
C187 470uF to 1000uF or greater Mouser Part # 140-XRL16V1000 (Electrolytic) In series with the speaker/headphones	(Click to See Photo C187) This cap is an Electrolytic

CAPACITOR ORIENTATION NOTE: The orientation is relevant ONLY if using any polarized capacitors to bridge over the existing surface mount caps, and when using the Electrolytic type capacitors as in C155, C167 and C187. (The polarity of C155, C167 and C187 are clearly marked on the I.F. board.)
C151 (+) lead toward the IC4 side.	(Click to See Photo C151)
C156 (-) lead to the base of Q27.	(Click to See Photo C156)
C161 (-) lead to the emitter of Q27	(Click to See Photo C161)
C170 (+) lead to R225	(Click to See Photo C170)
C172 (+) lead to IC7	(Click to See Photo C172)
See the X-ray trace (Photo 4) for hilighted location details.

If you will performing the direct Balanced Modulator feed for AM, leave the I.F. board out and see the "AM MODS" page.
Otherwise, you can now reinsert the I.F. board, replace the screws, connectors and bottom cover.

455 kHz I.F. RECEIVER FILTER MODS:
If you would like the widest receiver bandwidth possible, (RX and TX on AM) there are two methods of doing this:

- Place a jumper wire from pin 2 to pin 2 of the optional 455 kHz 500 Hz filter pins. (Photo 21)
Or:
- Install a Murada 20kHz filter on an Inrad/850 filter adapter board and install in the 455 kHz 500 Hz filter position. (Photo 22)

Make sure that you enable the 455 kHz I.F. 500 Hz position by setting the top panel dip switches appropriately.

These 455 kHz filter mods dramatically improve the receiver frequency response on SSB and AM but is most useful on AM.
Additionally, you can transmit through this filter position on AM when using the direct balanced modulator feed.
When using the DSP-100 with SSB, the 455kHz I.F. filter is not active, since the DSP-100 does all 455 kHz I.F. processing.

Kenwood TS-850 I.F. TX Bandwidth Power-On Menu Settings:

With the 850 turned off, press and hold the "SCAN" and the right "M.Ch" buttons simultaneously while turning on the radio.

Select menu 1 by rotating the "M.CH/VFO.CH" knob.

Turn the option to "ON" by pressing the "UP" button.

Press the "CLR" button to exit the power-on menu.

On transmit, you can now select the following filters in the 8.83 MHz i.f. resulting in the following on-air bandwidths (with the DSP-100):

None	= 6 kHz TX bandwidth (with DSP-100)
6k	= 4.5 kHz TX bandwidth
2.7k	= 2.4 kHz TX bandwidth