The message quotes someone at Burghardt, who says, As one message to the IC-746PRO mailling list mentions, Burghardt Amateur Center is preparing a more comprehensive ESD fix. It also appears that there’s more to this ESD problem than meets the eye. It is OZ2M’s opinion that the fix may indeed prevent some units from failing, but that the fix does nothing to prevent thermal failures. Note that they don’t say that the fix eliminates the problem completely. ICOM America service records show that the failure rate of this part has been reduced to 1/10th of the previous value. As stated above, protection diodes have been shown to resolve the issue and no heating calculations are needed. Our service technicians do not see any discoloration of the circuit board or the deformation of parts that are the symptoms of overheating. Measurements show that the surface temperature of IC-151 is low, even after 4 hours of continuous operation. There are rumors on the Internet that the circuit around IC-151 is incorrectly designed causing overheating of this part and that the protection diode fix is an attempt to mislead customers by ICOM. The Icom America website has a page titled, IC-746PRO – IC-151 Protection Diode Fix states, The second problem is an ESD problem, and Icom claims that if there is a problem it is an ESD problem, not a thermal problem. He suggests that perhaps you don’t need the heatsink with the VCC fix, as this modified circuit is similar to the circuit in the IC-756PRO, which does not seem to have an IC151 problem. What he did was find an 8 VDC line that was switched on only during transmit and used that to power IC151. In addition to adding a heatsink to IC151, he also found a way to switch the VCC to the chip. K5LXP also experimented with heatsinks, but he took his fix a step further. OZ2M also shows on this page various heatsinks that some hams have designed and installed in attempts to keep the chip cooler. This will, of course, keep the part much cooler.
OZ2M, an electrical engineer by training with five years of experience with Motorola as a Senior RF Design Engineer, points out on his IC-746PRO web page that in the IC-756PRO, the VCC line is switched on and off, with the IC only being powered when the rig is transmitting. Many hams point to the difference in the two circuits. What’s even more confusing, or dismaying, is that the IC-756PRO uses this same IC in the same application, but IC-756PRO owners don’t report anywhere near the number of failures that owners of the IC-746PRO do. If you read the IC-746PRO reviews on eHam, it looks as though quite a high percentage of the units fail, and many fail more than once. Some IC-746PRO owners say that IC151 gets hot, causing it to fail prematurely. The first problem seems to be a thermal problem. There actually seems to be two problems with IC151. AES recently dropped the price of this radio to $1300, and for that price, I think it’s the best deal on the market.Īt least it would be if not for that nagging IC151 problem.
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