Part 2: Disassembling the Icom IC-735: A Beginner’s Guide
Opening up the IC-735 can seem intimidating, but with a few careful steps you’ll be inside in no time. Before you begin, unplug the radio’s power supply and remove any antenna or mic cables. Place the radio on a clean, flat surface and ground yourself to avoid static discharge. You will find three main circuit boards inside: the Main Unit board, the PLL Unit board (frequency synthesizer), and the PA Unit board (power amplifier with final transistors). The photo below shows an IC-735 board (with its silver metal shields in place) – the shield with the 4 holes covers the PLL section, while the large chips and backup battery on that board belong to the main logic. (The PA board is a separate assembly under the top cover.)
Above: An IC-735 circuit board. The big DIP chip and battery on this board are part of the radio’s main CPU/logic. The PA unit board (not shown here) is a separate module housing the RF power amplifiers.
1. Remove the Top and Bottom Covers
Most IC-735 models use eight screws to hold the top cover and four more for the bottom cover,. A typical order is:
Bottom cover: Turn the radio upside-down. Remove all screws from the bottom panel (often 4 screws around the edges and a 4 on each side). Keep a hand on the panel as you remove the last screw so it doesn’t fall. Carefully slide or lift off the bottom cover.
Top cover: Flip the radio right-side-up. There are usually 8 screws around the top perimeter and speaker (contained within the PA).
Back: There are 2 screws holding the PA to the back of the radio frame.
Lift straight up on the top cover. It should clear the rear panel studs; if it feels stuck, check for any hidden screws on the front or sides.
Take note of each screw’s location as you remove it. A good practice is to use small cups or a muffin tin to keep screws from different steps separate. Once the covers are off, you’ll have clear access to the boards and their shields.
2. Remove the Metal Shields
Inside the IC-735, some boards have sheet-metal shields soldered or screwed on. The PA board (power amp) is often covered by a metal “PA deck” cover and filter shields; the main logic/PLL board also has can shields. To remove these:
Locate the shields: The PA board’s cover is usually fastened to the chassis or PA heatsink. The PLL/main board shields are on the circuit board (like the silver cans shown above).
Unscrew or desolder: If a shield is screwed down, carefully remove the screws. If it’s soldered (as on many PLL cans), you may need a soldering iron. Gently heat one solder point at a time, pulling the shield away as the solder melts. Be very careful not to damage the board or lift the copper pads. Tip: Tape down the board or surround the shield with Kapton tape as a heat shield if the solder takes long to melt.
Work on PA shields: The PA cover may be heavy or have tabs that fit under the chassis. Support the board while unscrewing. Remove any screws holding the PA filter or heatsink cover, then lift the shield off.
With the shields gone, the PA board and PLL circuits are exposed. Watch out for sharp edges on the metal covers as you handle them.
3. Disconnect and Remove Each Board
Now remove boards one at a time, disconnecting cables and connectors as you go. Work methodically and label anything you unhook – this will make reassembly much easier. Here’s a board-by-board approach:
Remove the PA Unit (Power Amplifier) Board:
Note the heavy coaxial cable(s) and wires going to the PA board (e.g. the input from the driver stage and output to the antenna). Unscrew or unplug them carefully.
Unscrew any mounting screws or standoffs holding the PA board to the chassis. These are often near the heatsink area.
Slide the board out slowly. The finals (power transistors) may still be attached to the heatsink; support them if needed to avoid bending the board.
Once free, lift the PA board out of the radio. Set it on an anti-static surface or in a parts bin.
Remove the Main/PLL Unit Board(s):
Identify the board under the front panel (the one with the display ribbon cable and many ICs). This usually contains the CPU and possibly the PLL synth. Unplug any front-panel cables: the display, buttons, meter, etc. These are often multi-pin connectors.
Release ribbon cables or plug connectors carefully. Pull the cable straight out. Never pull on wires — always grasp the cable’s end or connector body. For friction-fit (no-flap) cables, gently wiggle while pulling out along the cable’s axis.
Remove screws or posts securing the board to the radio frame. Keep these screws with the board (again, use a labeled container).
Lift the board straight up and out.
As each connector comes free, label it (you can use masking tape) so you’ll know where it goes on reassembly. For example: “LCD cable,” “Speakers,” “PA input,” etc. Handle each board by its edges to avoid touching circuitry or bending components. You’ll notice on the underside of the board (see photo below) a dense pattern of solder joints – be very gentle so that none of these pads lift off.
Above: The underside of the IC-735’s logic/PLL board is packed with solder points. Notice the fine traces and solder pads – always support boards from the edges and avoid bending them, which can break these connections.
4. Tips and Precautions
Follow these simple tips to avoid common mistakes:
Take pictures and Label Everything. As one tech advises, “During disassembly, label each cable as you remove it, noting its position and routing”. This makes plugging cables back much faster and prevents mix-ups.
Handle Cables Carefully. Many wires in the IC-735 are small and fragile. When disconnecting ribbon or multi-pin cables, use tools if needed. Flip up locking tabs or pull from the reinforced end of a cable rather than tugging on the thin wires. For “no-fuss” flat flex cables, simply pull straight out with a gentle, even force.
Organize Screws and Parts. Keep screws from each step with the parts they belong to. For example, place screws from the PA board in one container and those from the PLL board in another. Using small labeled cups or a partitioned box works well. This prevents accidentally using a too-long screw where it doesn’t fit, which could short-circuit something.
Avoid Lifting Pads or Traces. If you must remove soldered shields or connectors, heat the solder just long enough to release the part. Lift straight up only when the solder is molten. Take care not to pull on wires that are still soldered or to bend the board. (The image above shows how dense the solder side is – it’s easy to rip pads off if you’re not gentle.)
Organize Your Workspace. Keep track of small parts and screws by using a clear workspace. A magnetic tray or small bowls can hold metal pieces. Lay out the covers and parts in the order you removed them so you remember where everything goes.
Stay Grounded. If possible, use an anti-static wrist strap or at least touch the metal chassis periodically to discharge any static. This is less critical on older boards like the IC-735’s, but it’s good practice when touching circuit boards.
With the covers off and boards safely out, you’re ready for the next steps in your recap or repair project. Take your time at each step: double-check that all connectors are labeled before unplugging and that no screws remain hidden. Careful organization now will make reassembly far smoother. Good luck – you’ve successfully tackled the toughest part of IC-735 maintenance!