Icom IC-751A - "Bad Cap" Fix

Quoted directly from Icom America's web site, Knowledge Base article number 5B9F593A21

My 751/751A has distorted, or no RX/TX on one or more bands. Problem may be temperature related.

Probable Cause:
1) Bad trimmer capacitors on PLL unit.
2) Noisy variable resistor on PLL unit.

To fix:
Replace plastic trimmer capacitors C78, C88, C97, and C107 with equivalent ceramic types. Remove excessive wax from around replacement trimmers to prevent wax contamination. We suggest using a 12 pF trimmer capacitor for C97 instead of a 7 pF as listed in the service manual. This will allow you to properly adjust the HPL lock voltage for that band.
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 2.2 K type, replace it with a fixed-value 1.2 K resistor.

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 any future failures.

Page Updated :- 29th June 2009