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ic-151 protection diode fix
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. nothing could be further from the truth. measurements show that the surface temperature of ic-151 is low, even after 4 hours of continuous operation. our service technicians do not see any discoloration of the circuit board or the deformation of parts that are the symptoms of overheating. as stated above, protection diodes have been shown to resolve the issue and no heating calculations are needed. icom america service records show that the failure rate of this part has been reduced to 1/10th of the previous value.
since february of 2003, this circuit change has been installed on every ic-746pro that has been repaired at icom america. our authorized independent service centers have also been asked to install this modification.
if your ic-746pro is sn 3351 or higher, you already have the factory installed protection diodes. or if your ‘pro’ has been serviced by icom america in the last year, the protection diodes have been installed and you should enjoy years of trouble free service from your transceiver. (if it has been serviced by an independent service center, please contact them to determine if the protection diodes have been installed.)
if your radio does not fall into any of these three categories, do not worry. icom america’s standard repair policy is to offer all technical updates free-of-charge to any icom america radio still in production.
please keep in mind that external forces may cause failure to rf equipment. some precautions to take during the installation and operation of the radio are as follows:
recommendations made by the arrl and polyphaser include the addition of lightning protection. this includes disconnecting and grounding the antenna feed line when the radio is not in use.
it is also necessary to ensure that the antenna has a low vswr.
use a transistor buffer circuit to key a non icom linear amplifier. this will prevent damgage to or sticking of the send relay contacts in the radio.
do not use the radios internal antenna tuner when using an external antenna tuner. with a linear amplifier use an external tuner after the amp and leave the internal tuner off.
if running multiple transmitters or antennas be sure to keep antennas spaced far enough apart to prevent rf overload to the receiver front end.
keep all accessory cables as short as possible especially when using a linear amplifier. shield cables that are too long and ground the shield at both ends to prevent rf feedback. a ferrite bead around the cable may help if shielding the cable is not an option.
icom is committed to your satisfaction.
