Yaesu Ft-891 Service Manual -

Troubleshooting Guide: TX Problem

1. Adjust the TX Power Setting: Ensure the TX power setting is at a reasonable level.
2. Replace Faulty Components: Replace any faulty transistors or diodes found during the troubleshooting process.
3. Adjust the ALC Circuit: If the ALC circuit is faulty, adjust the ALC detector diode (D703) and amplifier (Q703) according to the adjustment procedure outlined in Section 7 of this manual.

• Ham radio repair technicians – For accurate realignment after component failure.
• Advanced DIY operators – Adding modifications (e.g., cooling fan upgrades, filter changes).
• Second-hand buyers – To check if a used FT-891 has been tampered with or misaligned.
• Service centers – As an official reference for warranty and out-of-warranty repairs.

Circuit Type

Understanding the baseline performance is critical when verifying if a unit is within factory spec: Factory Specification Triple-conversion (SSB/CW/AM) / Double-conversion (FM) 1st IF Frequency 69.450 MHz Output Power 100W (SSB/CW/FM), 25W (AM) Supply Voltage 13.8 VDC ±15% (Negative Ground) Current Drain 2.0A (RX), 23A (TX max) Common Troubleshooting & Maintenance Tips

• No public alignment data exists in the owner’s manual. Attempting alignment without a service manual and proper test equipment (spectrum analyzer, RF generator, wattmeter, oscilloscope) will likely destroy the final transistors.
• The FT-891 uses SMD components and tight tolerances — not a beginner repair project.

Look at the PA unit block. The signal flows from the driver transistor → final MOSFETs → low-pass filter → directional coupler → antenna jack. yaesu ft-891 service manual

Part 1: What Exactly is the Yaesu FT-891 Service Manual?

The service manual goes beyond the basic operating instructions to provide deep technical data: Troubleshooting Guide: TX Problem