The Icom IC-751A is a high-performance HF transceiver widely appreciated by amateur radio enthusiasts for its excellent receiver sensitivity and versatile features. Released in the 1980s, it offers a frequency range of 160 to 10 meters with modes such as SSB, CW, AM, FM, and RTTY. Known for its robust build, easy operation and good reception, the IC-751A remains a popular choice for vintage radio operations. And, with the additional filters, it sounds simply fantastic, both in RX and TX!
Inside views
Known problems
Symptom: No RX audio in any mode except FM. No TX. Unit is not unlocked.
Problem: PBT oscillator is not running.
Solution: Verify absence of 9.4665 signal at W86 on main unit in 751A, or W134 in the IC-751. Replace faulty X7 on main unit in IC-751A, or X5 in the IC-751.
Symptom: Distorted, or no RX/TX on one or more bands. Problem may be temperature related.
Problem: 1) Bad trimmer capacitors on PLL unit. 2) Noisy variable resistor on PLL unit.
Solution: Replace plastic trimmer capacitors C78, C88, C97, and C107 with ceramic types. Remove excessive wax from around replacement trimmers to prevent wax contamination. We suggest using a 12pf trimmer for C97 instead of a 7pf as listed in the service manual. This will allow you to properly adjust the HPL lock voltage for that band. Modification: If variable resistor R43 on the PLL unit is the 470 ohm type, replace it with a fixed-value 220 ohm version. If it’s the 2.2k type, replace it with a fixed-value 1.2k resistor.
Remarks: While the PLL unit is lifted, we recommend soldering all joints in the regulator section as this area runs hot. Also, inspect electrolytic capacitors C128, C129, C132, and C137 in the regulator circuit for discoloration caused by overheating. Replace all overheated capacitors to prevent future failures.
Links and infos
QSL.net informations: Icom IC-751 & IC-751A
eHam.net Reviews: Reviews For: ICOM IC-751A