BC-235 Mods (COS and Phone Jack)

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(KDJ advises you to read this entire page before beginning any mod.)

BC-235 COS Mod (carrier squelch)

This mod locates a signal on the circuit board where the voltage stays in excess of 3V when the radio is squelched. When the radio receives a signal in either trunked or conventional mode, this voltage goes to less than 0.2V.

The idea is to feed this signal to a transistor switch which picks a relay or whatever. I would not try to sink a relay directly on this pin. Put as little load on it as possible. A little transistor switch is really nothin'.. a couple of 2N2222s, a couple resistors... if you can't figure it out then you shouldn't even think about attempting this mod.

Now of course I make no claims of warranty or fitness for any particular purpose, and I am certainly not responsible if YOU fry YOUR radio. That said:

You Need: Phillips screwdriver, soldering iron & solder, hookup wire, small sharp X-Acto knife, SMT board repair skills, etc...

  1. Remove battery cover and battery.

  2. Remove 4 screws from rear... Remove rear cover by pulling apart from the bottom.

  3. Remove the RF/AF board by lifting at the lower left (connector below the power jack).

  4. Disconnect the speaker cable.

  5. Orient the RF/AF board component-side-up, with the grey plastic bracket on the right; RF connector at the lower right.

  6. Look at the 22-pin connector to the left of the power jack. On the OUTSIDE row of pins (facing you) numbering left-to-right from 1 to 11, solder one end of a wire to pin 4.

    NB: to avoid dislodging the connector pin, do not allow the soldering iron to linger on the connection; do this quickly. Tin and trim the end of the wire first; now apply just a touch of fresh solder to the pin/PCB junction & allow to cool; wipe the iron tip; touch the wire end to the connection and heat the connection; as soon as the solder melts, get the iron away; wire should be securely soldered to the junction and the pin must be straight and in-line with the other pins.

  7. (optional break-out to the phone-jack mod below)

  8. Re-connect the speaker cable and re-install the RF/AF board.

  9. Re-assemble the radio.

BC-235 Phone Jack Mod

Did you know that the earphone jack on the 235 is actually a stereo (tip-ring-sleeve) jack?

Don't know about you, but I don't normally use stereo headphones to listen to the thing, so I might want to use that extra wire out of the radio for something else (like the COS mod above) to avoid drilling a hole.

  1. Orient the RF/AF board solder-side (bottom) up, with the grey plastic bracket at the top (away from you); RF connector at the upper left.

  2. Under where the earphone jack is mounted, locate a row of four pins in two groups of two. The pin on the extreme right is "tip" and the one on the extreme left (next to the RF connector bracket) is "ring".

  3. Look for a small circuit trace coming off the top of the left-most pin's land. Using a sharp carefully-controlled knife blade, cut this trace.

  4. With an ohm-meter, verify that the outside pins (tip and ring) are no longer shorted together.

  5. Solder your wire to the left-most pin.

  6. Swear or otherwise affirm and resolve to yourself that, henceforth, you will NEVER plug a 2 circuit tip-sleeve phone plug into this jack again.

  7. (return to the procedure which sent you here.)

External Relay Circuit

I couldn't build this small enough to fit inside the case, and it's too much drain on the battery, so that's why it's "external". I am using this circuit to drive a wireless (carrier current) intercom; could also be used on a modified 49 MHz. baby monitor or to kick a tape recorder, etc. Have fun!

Ken Johnson KC4YOZ

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