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. If you can't find out the version of your 756-PRO (#02 or #03), look at the topside of the box. Trouble to find the diode-row ? It's about 1/2 inch located under the CPU. R R R I I I X X I I X X I X X X after version "2" mod. R R R I I I X X I I X X X X X X after version "3" mod. R R R I I I X X I I X X I I I X diode-row IC756-PRO version "#03" When you have a version "#02" : remove diode 3751, 37 ! You have to remove 3 small diodes located on the left side of number "3751" (diodes 3752, 37) when you have a version "#03" Icom IC756-PRO. You can see on the right of the row the number "3751", that diode is already missing, hi. You have lift the dsp-box (with care !) out of the mainboard.Īfter removing the dsp, you can see a row of diodes with some spaces. When you removed the cover and you have the backside of the 756-PRO facing you, you can locate the dsp-box on the left-side (the shiny-box). You have to remove the bottomcover of the 756PRO. You need a very fine solderiron to remove the 3 diodes from the mainboard! Icom IC-756 PRO (IC 756 PRO IC756PRO) technical specifications Icom IC-756 PRO (IC 756 PRO IC756PRO) technical specifications : Icom IC-756 PRO (IC 756 PRO IC756PRO) Expand tx-freqeuncy Icom IC-756 PRO (IC 756 PRO IC756PRO) CW Filter Shape Selection Icom IC-756 PRO (IC 756 PRO IC756PRO) Eliminate an adjacent channel noise problem (QST mod) Icom IC-756 PRO (IC 756 PRO IC756PRO) 6M oscillation problem
Mods for Icom IC-756 PRO (IC 756 PRO IC756PRO) : Schematics for Icom IC-756 PRO (IC 756 PRO IC756PRO) :
PDF Adjusments Procedures Manual with schematics for Icom IC-756 PRO (IC 756 PRO IC756PRO) : PDF User Manual for Icom IC-756 PRO (IC 756 PRO IC756PRO) : Icom IC-756 PRO Instruction Manual
Programming software for Icom IC-756 PRO (IC 756 PRO IC756PRO) : Programming interface schematics for Icom: