Teardown Tuesday: Uniden CB Radio

May 01, 2018 by Nick Davis

In this teardown, we disassemble a CB radio, from Uniden, to see what interesting things we can find.

In this teardown, we disassemble a CB radio, from Uniden, to see what interesting things we can find.

This professional CB radio—the Bearcat 680, by Uniden—allows for chitchatting on 40 different channels. It integrates both volume and squelch control on the same rotary-switching device, and provides a large channel-display, all in a fairly small form factor.


Uniden's Bearcat 680 CB radio looks easy-to-use given its large display and minimal controls.

Let the Disassembly Begin

Fortunately, gaining access to this unit's internal components is rather easy and straightforward since only a handful of Phillips and hex screws are used for holding everything together. In the figure below, we can begin to see, with the top sheet metal piece removed, that this CB radio uses multiple PCBs.


Our first glance inside the unit reveals the speaker and four PCBs.


Upon close inspection of the device's innards, we can see that the sparkies (i.e., the electrical engineers) and the wingnuts (the mechanical engineers) worked together and communicated closely and effectively by ensuring that the sheet metal mounting holes aligned properly with the associated PCB holes.

Also, as can be observed in the image below, two of the ICs make use of the sheet metal frame for their heat sink. Again, this design effort required collaboration... nice job, Uniden!


At this angle, we can see how the design nicely fits together.

Removing and Inspecting the Guts

In the figure below, we can clearly see four PCBs:

  • The main PCB, which is comprised of all the ICs and the CB radio's intelligence;
  • the display PCB, which connects to the main PCB via a simple ribbon cable;
  • and, two simple rotary switch PCBs—one for each of the control switches.

Using dedicated PCBs for each of the control switches is a solid design approach as it allows for, obviously, much more freedom and independence of where each of the switches can be located. An alternative approach—although perhaps a more cumbersome approach—would've been to solder these switches directly to the main PCB.


The four PCBs removed from the radio's enclosure.


The list below calls out some of the major components identified in the figure above:

  • Power MOSFET: Part marking IRF520
  • Audio Amplifier: Part marking UTC TDA2003L
  • Relay: Part marking HFD27/005-H
  • Voltage Regulator: Part marking L7808CV
  • Microcontroller: Part marking M38D58G8HP
  • Potentiometer: Part marking TOCOS A503 6502 57C
    • Note: This switch is a dual-switch, meaning that it is comprised of two independent rotary switches.
  • Rotary Switch: Park marking CTR SR476 1564C (similar to this part)
  • Frequency Synthesizer: Part marking MCD2926
  • CB Transceiver Driver: Part marking C2314

When viewing the PCBs' opposite sides (see image below), we can see that the PCB layout person/team did an excellent job by locating all (or most) of the main PCB's components on the PCB's top-side; it appears that the single axial resistor on the back side is most likely from a rework task.


The opposite sides of the PCBs and switches.


The display screen contains no part markings, which, in my experience, appears to be the norm for similar devices. And while the pushbuttons/tactile switches also have no markings, they appear to be similar to this part.


Although I did not actually use this Bearcat 680 CB radio prior to tearing it down, it does indeed look to be a solid design, both electrically and mechanically. And, given the use of multiple sheet metal mounting points, as well as hefty heat sinks for the hot ICs, this unit should provide years of service in a home or a big rig.

Do you have any experience with this particular CB radio? If so, please share in the comments section.


Next Teardown: Battery Charger

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    alleebell May 02, 2018

    WOW! Let me be the first to give you comment on this project. I am a retired electronics engineer. I built my own CB when I was a teenager from designing schematic to etching my own PCB. I still remember the block diagram of my CB. Thanks for the pictures. Technology has changed. Other than the MOSFET and the audio amp, I see no transistors at all. My CB used all transistors. Thanks for this article! It brings back a lot of good memory!

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    Iatros55 May 04, 2018

    All surface mounted components too, plus through-hole mounts for heavier components.  Should be quite free from microphonics!  Impressive.

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    • 377Ohms May 07, 2018
      @latros55 Said: "All surface mounted components too, plus through-hole mounts for heavier components. Should be quite free from microphonics! Impressive." Exactly the OPPOSITE is true. Microphonics are far more common in SMT versus PTH assemblies. This is primarily due to piezoelectric and electrostriction effects in the dielectric material used in MLCC SMT capacitors and the very close mechanical coupling between the SMT package and the PCB. Read more here:
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