Marty Goodman KC6YKC June 1992 Home packet BBS: WD6CMU Richmond, Northern CA I recently acquired both a PK88 TNC and a Kenwood 731a dual band mobile transceiver. I wanted to hook the Kenwood to the PK88. What I found was that the audio output on pin 6 of the eight pin microphone connector on the front panel was not the same as the audio that comes out of the speaker or out of the rear speaker connector. What you get out the audio from the front panel mic connector on pin 6 is an UNSQUELCHED audio. Kenwood does this, apparantly, to support their RC10 remote controller for the unit, to allow the RC10 independent control over the squelch on the audio at the RC10's speaker. This causes a problem, for when you feed that into the audio input of the PK88, its DCD light stays on ALL THE TIME. The PK88 will receive data just fine when hooked to pin 6 of the TM731a mike connector, but it will refuse to key the transmitter because it perpetually thinks the air is "busy". The simple approach to hooking the PK232 to the Kenwood involves using a separate cable with a 1/8 in mini phono plug at each end, and run that between the audio phono connector on the PK88 and the speaker output jack for "main audio" on the TM731a. This will allow packet operation, and is no doubt the approach that virtually everyone uses. THere are some drawbacks to this arrangement, tho. Using two cables is a tad clumsey. Worse, when you plug in the cable in the rear speaker connector, there is no way to enable the speaker to audibly check your signal. It also makes it impossible to make a switch box to switch the TM731a from packet to audio operation at the flick of a switch, for as long as the phono plug is plugged into the back of the TM731a, you CAN NOT enable its internal speaker. Finally, this arrangement requires you to adjust the volume control to the right level and leave it there. What follows is a mod that give you a SQUELCHED, LINE LEVEL audio signal available on pin 6 of the microphone connector. With such an arrangement, you can turn your speaker volume up and down as you like, and it will not affect the audio going to the packet box. You can use a single cable to connect the packet box to the transceiver, and it is easy to rig up a switch box that switches between the packet box and the hand microphone. The only disadvantage of doing this mod is that your TM731a will NO LONGER be compatible with the RC10 remote control device. The Modification: This modification requires skill at fine soldering, a good ultra fine-tipped pencil type soldering iron, and a short piece of 28 gauge stranded wire. You really should have at hand a Kenwood service manual for this rig, with complete schematic and board layout diagrams, before you attempt it, tho I HAVE tried to write my description so that you can do the mod without a service manual at hand. (1) Turn off power and disconnect the rig from its source of power (2) Remove the BOTTOM cover of the rig. (3) Lay the rig on your work table with the front panel pointing away from you, and its rear heat sink pointing toward you. On the right will be the main volume and squelch control. Look at the little connectors that hook the front panel of the radio to the board you have exposed and are looking at. On the extreme left is one connector with eight pins in a row, with the third pin from the left unused. To the right of that is a five pin connector with the middle pin not used. To the right of that connector is an electrolytic capacitor, to the right of the cap is a two pin connector, and to the right of the two pin connector is a phillips screw that is one of the screws that hold the board you are looking at inside the rig. Locate that five pin connector mentioned above, the one that has its middle pin unused. The SECOND WIRE from the LEFT of that connector should be a RED wire. That spot on the connector will be labelled on the main board you are looking at as "RDM". (4) CUT this red wire about three quarters of an inch from where it leaves the connector. Tape up the portion that goes to the connector. (5) Strip off about a quarter inch of insulation from the portion of the red wire that dives into the rig and heads toward the front panel. (6) Locate "IC 8" on the radio. This is actually NOT a real integrated circuit, but rather is one of six little vertical circuit boards that jut up like fins from the main board. IC 8 is the left most of the six such boards, and is right next to IC 9, which is a zig zag in line pin integrated circuit. IC 8 is located just toward you from the five pin connector with the four wires... the one from which you cut the red wire. IC 8 is labelled as "IC 8" in silk screening on the circuit board. (7) Solder a short length (2 or three inches) of stranded, insulated, 28 gauge wire to pin 9 of IC 8. Pin 9 of IC 8 is the next to last pin of this single in line pin "IC". The "last" pin of IC 8, or pin 10, is located closest to the rear of the rig (closest to you, given the orientation of the rig that I suggested). (8) Now solder the other end of this wire to the stripped, cut portion of the red wire that you prepared in step 5 above. That's it! you now have modified your rig to provide line level, squelched audio on pin 6 of the microphone connector. For those technically inclined, you should note that this audio is leaving an audio amplifier, and going thru both a 1K ohm resistor and a .1 mfd capacitor before it arrives on pin 6 of the microphone connector. Thus the signal is DC-blocked and reasonably protected against minor nastiness that might appear on pin 6. I'd appreciate any feedback from those attempting this modification, tho of course I must note I cannot take responsibility for any harm that may come to your radio due to either proper or improper implimentation of this modification. I CAN say honestly that I HAVE done this to my radio, and it appears to work quite well. Marty KC6YKC @ WD6CMU.NOCAL.USA.NA on packet MARTYGOODMAN on Delphi MARTYGOODMAN@BIOTECHNET.COM on internet mail - EOF -