[ICOM] 756ProII Reset on TX Fixed...maybe

[Ted Wright]

Hi Frank
Good to hear that your Pro is back up & running..
Ted
n3zrx

Frank N. Haas wrote:

>
> I finally had a chance to work on my 1.5 year old 756ProII Saturday 
> night. I believe I have corrected the problem myself.
>
> To review: Any attempt to transmit would cause the radio to instantly 
> and completely shut down and turn back on. This occurred even if the 
> RF power output was set to its lowest level. The symptom occurred in 
> all modes and with any type of transmit key (CW keyer, SSB VOX and 
> front panel Transmit button.)
>
> Icom tech support recommended swapping the power supply (PS-125) and 
> many of you suggested I look over the fuseholders.
>
> The PS-125 powered other 100 watt radios without any problem so I 
> concluded the problem was NOT the power supply.
>
> There are NO external fuseholders connected with either the power 
> supply or the rig. I didn't open the power supply but inside the 
> 756ProII I did see a 5A power supply in what I believe is a DC to DC 
> converter circuit.
>
> The Fix:  I looked over the 5 amp fuse and didn't see anything 
> unusual. No corrosion and no deformation of the fuse element. The 12 
> volt power leads from the Molex connector on the rear panel of the rig 
> are screwed to inverted U shaped metal pieces securely soldered to the 
> circuit board in the center of the top inside of the radio. I 
> unscrewed each of the power connections (noting that they were tight 
> to begin with) and examined them. Nothing unusual seen so I screwed 
> them back down securely. A second set of positive and negative 12 volt 
> leads run to the aforementioned DC to DC converter from the vicinity 
> of the center circuit board as the input leads. This second set of 
> leads are also screwed down to inverted U shaped metal pieces that are 
> securely soldered to the circuit board. I unscrewed them (again noting 
> that they too were tight to begin with) and saw nothing unusual. I 
> reconnected them securely.
>
> After doing all of this, I powered the radio, connected a dummy load 
> and attempted to transmit. To my joyous delight, the radio did NOT 
> reset itself. Even with full output, the radio now seems to be working 
> well again.
>
> Conclusion: I didn't see any corrosion or even any dirty contacts 
> anywhere. I suppose it is possible that one of the screwed down 
> connections may have not been good. It is also possible that a stray 
> bit of solder (from the Icom repair shop effort in January 2004) may 
> have found its way into a circuit which didn't appreciate its 
> presence. It is possible that the process of opening the radio may 
> have dislodged the bit of solder ending whatever circuit anomaly it 
> was causing or my re-tightening the hardware actually did some good. I 
> don't know which.
>
> The radio has returned to its dominant position on my operating desk 
> where it seems to be working happily. We'll see if it can work for 
> more than one week in a row.
>
> 73,
>
> Frank N. Haas KB4T
> Florida
>
>
>
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