Stuff comes and stuff goes. Time Owned: more than 12 months. Totally Love, Owned Multiples.
Ic 746 Pro Manual And Documents
Carefully remove two small SMD 0 ohm.Manual and Documents : Many (probably all) of these documents are also available from the Files page for the IC746 Email Group at YaHoo. Remove the bottom cover of IC-746PRO. AES recently dropped the price of this radio to $1300, and for that price, I think it’s the best deal on the market.Icom IC-746 PRO (IC 746 PRO IC746PRO) TX modification. Never had a moment's trouble with any of them.I really want an IC-746PRO. Currently on my 3rd 746 purchased on the used market in late 2020.
Many hams point to the difference in the two circuits. 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.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. Some IC-746PRO owners say that IC151 gets hot, causing it to fail prematurely. Both cause the rig to quit transmitting.The first problem seems to be a thermal problem. Summary of Contents for Icom IC-746 Page 1 INSTRUCTION MANUAL VHF/HF ALL MODE TRANSCEIVER.At least it would be if not for that nagging IC151 problem.There actually seems to be two problems with IC151.
The Icom America website has a page titled, IC-746PRO – IC-151 Protection Diode Fix states,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. 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.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. 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. OZ2M also shows on this page various heatsinks that some hams have designed and installed in attempts to keep the chip cooler.K5LXP also experimented with heatsinks, but he took his fix a step further. This will, of course, keep the part much cooler.
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.It also appears that there’s more to this ESD problem than meets the eye. ICOM America service records show that the failure rate of this part has been reduced to 1/10th of the previous value.Note that they don’t say that the fix eliminates the problem completely. 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.
Changing the supply line to IC151 will have no effect on this since the surge is coming down the receiver line and damaging the outputs in IC151. Theses other components will cause the receiver to be noisy. Not only will IC151 of the RF unit be bad but also D21,D22,D24, and Q25 of the Tuner control unit. The message quotes someone at Burghardt, who says,“Most of the cases when we see IC151 bad is due to static discharge.
AES recently dropped the price of this radio to $1300, and for that price, I think it’s the best deal on the market. Current production units already have the ESD protection diodes installed, and if IC151 does fail, I’ll apply K5LXP’s VCC fix.I really want an IC-746PRO. He also reminded me that at $1300, the IC-746PRO is a really great deal, and the cost of the modifications is very small.In the end, I have the feeling that I’m going to bite the bullet and buy the IC-746PRO. He noted that hams have a long tradition of modifying gear, and while modern rigs are certainly more complicated than the older stuff, these modifications are not impossible to do.
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