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The Icom IC-38A is a 220 MHz amateur mobile transceiver. Two of these ended up on my bench with audio problems. I had the luxury of two radios AND a printed service manual for this repair. The service manual saves time tracking down bad copies on the internet and the second radio...well... I noticed when I powered up the first radio idle receive current was around 250mA. Advance the volume -- not only would it sound like crap but current consumption peaked up near 1A. The second radio had no audio and hovered around 1A current at idle receive. It was nice to be able to compare two radios with similar problems. I admit to not doing much diagnosis here, I just assumed it was output audio caps, ordered some replacements for all six from DigiKey and decided to test, measure and replace when they arrived. On both units, C80 and C83 -- 220uF 16V electrolytic capacitors -- showed bad ESR in circuit, as high as 294 ohms at 1kHz. Out of circuit the four capacitors measured bizzare values between 40uF and 6pF -- completely out of spec for a 220uF capacitor. The other capacitors were close to their 20% tolerance boundaries. For the minimal effort and cost of replacing -- I replaced them. Icom used Rubycon brand capacitors in the unit. A decent brand, I suspect these either just got old, overheated or suffered some sort of manufacturing defect. After closing up the units, both exhibited good audio quality, good sensitivity and good power out. I gave the cases a quick wipedown with a cleaning cloth and declared victory. This page last modified Fri Jun 26 22:59:39 CDT 2020 by timc! |