I haven't seen many driver board failures personally (I typically only repair 7K's for local hams over the past 15 years, so I don't see a lot of units).? I have looked into the driver's design and signal levels at various drive levels and on all bands, while using an auto-tuner into various mismatches.? I do feel that antenna tuners and perhaps operation at LOW power seem to be a somewhat common thread for units that have multiple driver failures, but haven't seen direct evidence of it on units I've worked on.?
Many operators use antenna tuners to try to match antennnas well beyond the tuner's design spec.? This often damages the tuner, which then damages the radio.? Poor connections in the feed line and antenna are often intrmittent problems that lead to voltage/current transients that can damage the radio.? I feel that poor installations damage more radios than design flaws in the radio itself.
The added resistor change issued by icom was only for certain countries that had a different frequency range or band -- I forget the details.? Several postings indicated it was not effective.
Thermal measurements of the driver case don't indicate that the lack of thermal compound is a problem, but I always apply it when reinstalling the device.?
In short, I haven't encountered enough driver failures on rigs that I knew how they were being used at the time, to have an opinion about what the root cause of the failure is and what the proper fixes are.??
I doubt that a resettable circuit breaker will trip fast enough to protect the circuit, but haven't looked at their spec's for years, so maybe some exist.
The HF and VHF PA's will have factory-applied thermal compound.
My two 7K's are about 12 & 16 years old and had fairly heavy use (until the past few years), mainly mobile and portable, HF-UHF.? I've only fixed my radios 3 times and all of the failures were due to problems external to the radio.? I've also replaced the HM-151 mic switches with similar better-sealed switched when the original ones failed and replaced the poorly designed ATC style fuse holders used on some power cables with automotive style holders that bite through oxidation on the fuse blades.??
Steve, W3AHL
Steve W3AHL