Icom M700 Mods !!top!! -

(and its successor, the M700PRO) is a legendary marine HF transceiver prized by mariners and amateur radio operators alike for its rugged construction and 150W output. While originally designed for marine SSB channels, a few key modifications can transform this workhorse into a versatile HF rig for the ham bands or specialized data use. 1. Transmit Frequency Expansion (MARS/CAP Mod) The most common modification for the

is "opening up" the transmitter. In its stock configuration, the radio often limits transmission to marine bands.

The Jumper Fix: To enable transmit on all covered frequencies (approximately 1.6 MHz to 23.999 MHz), check the Logic Board for jumper W37 (W1037).

If the jumper is cut or missing, the radio may be locked to marine channels.

Action: Solder the jumper (or a wire bridge) back together to unlock general frequency transmission.

Limitations: While this mod covers most HF bands, reaching the 10-meter band (28 MHz) typically requires more complex hardware modifications beyond a simple jumper. 2. Memory and Programming Unlocks icom m700 mods

Some regional versions of the M700 have locked memory banks (A and B) to prevent users from accidentally overwriting critical marine frequencies.

W33 Jumper: To allow full front-panel programming of banks A and B, ensure that jumper W33 (W1033) on the Logic Board is NOT installed.

Keypad Issues: If your 10-key keypad isn't responding, look for switch S1228 on the Matrix board. Toggling this switch can often restore keypad functionality for field programming. 3. Digital Modes and Pactor Integration

Modern operators often want to use the M700 for FT8, Winlink, or Pactor. Because the M700 lacks a modern "Data" port, custom cabling is required.

Audio Interfacing: Modifications often involve tapping into the internal PTT (Push-to-Talk), Line In, and Line Out lines to create a DIN plug interface for a PC or Pactor modem. (and its successor, the M700PRO ) is a

Microphone Upgrades: Newer modifications include adapting the 8-pin connector to accept high-quality dynamic microphones or XLR inputs, which can significantly improve audio punch in difficult conditions. 4. Mode and Power Adjustments

AM Emulation: The M700’s AM mode (A3H) actually operates as upper sideband with a carrier. It provides a robust, "loud" signal that is well-suited for broadcasting on non-marine frequencies.

Power Output: While rated at 150W PEP, internal adjustments (usually found in the service manual) can fine-tune the ALC (Automatic Level Control) to ensure you aren't overdriving the final amplifiers during data operation. Comparison: IC-M700PRO ICOM--IC-M700-user-manual.pdf - QRZCQ

Page 3. SECTION 1 SPECIFICATIONS. GENERAL. Frequency Coverage: Receive. Transmit. 1.6MHz ~23.9999MHz. 2.0MHz - 2.9999MHz. 4.0MHz ~ IC-M700 - Single Sideband Radiotelephone - ICOM Canada

2. The "Glowing Meter" / Backlight LED Conversion

A common failure point in the IC-M700 is the incandescent bulbs behind the LCD display and meter. They run hot and burn out, making the radio unreadable at night. Disassembly: Remove the front panel assembly to access

Modification:

• Disassembly: Remove the front panel assembly to access the display unit.
• Replacement: Remove the old grain-of-wheat bulbs.
• LED Install: Replace them with 12V LEDs (often with a dropping resistor).
  • Tip: Use "Warm White" LEDs to maintain the vintage amber/green look of the original display filters. Blue LEDs often look anachronistic and wash out the black text.

The Schematic Hack: Bypassing the De-Emphasis Network

The receiver uses a de-emphasis circuit (a simple RC filter) that kills treble. By changing a few capacitor values, you can get a much flatter, more pleasant audio response.

Specific Steps:

1. Locate the Main Unit schematic. Focus on the audio amplifier IC (often an LA4422 or similar).
2. Find capacitor C123 and C124 (values vary by revision; look for 0.01uF to 0.1uF range).
3. Replace these with capacitors 1/10th the value. For example, change 0.1uF to 0.01uF. This raises the cutoff frequency.
4. Alternatively, add a 10k resistor in series with C123 to reduce the de-emphasis effect.

The "Audio Tap" Mod: For digital modes, tap the audio before the de-emphasis network (directly from the FM detector IC) and route it to a rear-panel RCA jack. This gives you a clean, flat 300–2700 Hz output for your sound card, vastly improving FT8 decoding performance.

---

Add a Rear-Panel ACC Jack

The M700 lacks a standard 6-pin accessory jack for amplifiers or TNCs.

• Mod: Install a DIN or SO-239 on the rear panel connected to:
  • SEND (PTT line)
  • Audio out (from detector)
  • Mod in (balanced modulator input)
• Use case: Connect to an SDR panadapter or a linear amplifier.

Step-by-Step Guide (Common Method for early M700 models)

1. Power Down & Unplug. Remove the top and bottom covers.
2. Locate the PLL Board. This is usually a vertical board near the rear panel, often labeled "PLL UNIT (IC-751 style)" – the M700 shares DNA with the Icom 751 amateur radio.
3. Identify Jumper Diodes. Look for a matrix of small diodes labeled D1, D2, D3, etc., or a set of solder pads (jumpers). Note: There are several M700 versions (M700, M700TY, M700Pro). The M700TY is the most common and easiest to mod.
4. The "All Band" Configuration:
   • For the M700TY: Remove diode D13. Add a jumper at JP1 (on some board revisions). Or, set the binary code on the PLL to all F's. The classic mod is to remove D11 and D13, add D12.
   • Pro tip: Search for "Icom M700TY PLL jumper chart" – it varies by serial number range.
5. Reassemble & Test. After the mod, hold the LOCK button while powering on to enable expanded coverage. You should now be able to VFO tune across all HF bands.

Expected Result: Transmission and reception from 1.600 MHz to 29.999 MHz continuously.

---