Quozl's Uniden UH-040XR

The Uniden UH-040XR sold for $AUD99 per unit from Dick Smith in Australia in 2001. It is a 0.5W 40 channel UHF CB transceiver.

MIC and EAR connections

Solution: connect TNC to MIC input via 4.7uF polyester capacitor, connect PTT to MIC input such that a 1k-10k resistance to ground is in effect when the TNC wants to transmit. From a workshop supervisor, care of Peter Illmayer, 4th March 2002.

History:

In July 2001, Uniden declined to provide a schematic of the optional headset with PTT switch.

Relevant aspects of the design:

• the MIC connection is a standard 2.5mm mono socket,
  • the outer conductor connects to a diode visible on the PCB with cathode to the socket, and anode to ground. The diode is a reverse polarity protection diode. Further connections are hidden under the LCD.
  • the inner conductor connects to transceiver ground.

• the EAR connection is a standard 3.5mm mono socket,
  • the outer conductor connects to an SMT capacitor to transceiver ground.
  • the inner conductor connection is hidden under the LCD.

• the charger terminates to a 2.5mm mono plug,
  • the rating is 70mA at 7V.
  • floating voltage without load is 12V.
  • plug is wired centre negative.

• the PTT switch is grounded on one side, and on the other has an SMT capacitor to ground before the trace continues under the LCD.

• the transceiver can operate in receive mode while connected to the charger, but pressing the PTT button yields no transmission. Without batteries in the case, 6.25V is found on the battery terminals. The circuitry includes a charging function.

• the transceiver PTT switch functions fine if the charger is connected but not powered.

• the transceiver transmits for a short time when the charger plug is inserted. A slow insertion yields a long transmission, apparently as the pins are shorted.

• inserting a multimeter probe into the MIC socket to short the pins causes transmission of silence.

• connecting stereo headphones to the EAR socket gives the receive signal in the left headphone, and the PTT switch continues to work. Therefore the MIC connection is non-essential.

The following picture shows the connections, the capacitors, and the reverse polarity protection diode.

Figure 4, Close-Up of MIC and EAR connections

Disassembly

• remove battery cover,
• remove batteries,
• disconnect any cables,
• unscrew and remove the belt clip,
• unscrew the four screws in the battery compartment,
• lever the case apart.

Figure 1, Location of Case Clips

Figure 2, Right Case Clip Close-Up

Figure 3, Left Case Clip Close-Up

Inside

Figure 5, Main Board, Rear Face

Figure 6, RF Board, Rear Face

Interfacing