The relais (use one w/o free wheeling diode) must be mounted on the top side because there’s not enough room underneath (metal sheet cover of the tuner).
Also, be very cautious with the three printed flex cables.
For removing the CONTROL UNIT one has to de-solder both SO-239 connectors from the PCB. Remove the top lid, detach the speaker cable and remove a second internal shielding lid. The best place for this patch-relais is directly on the CONTROL UNIT. For here a tiny reed-relais can add up several tens of dB decoupling. adding a short circuit for the ports in off-conditions. But there’s also a fourth method iv) that is both most effective and simple:Īs known from VHF/UHF antenna relais technique one can achieve huge decoupling values when earthing unused pins, i.e. Their cure effect, and worse their side effects too, are hard to estimate. A third method iii) is to increase the input damping of the final amp (there’s already a 3R-pi input attenuator). Two alternatives curing this ICOM implied design flaw are i) replacing the antenna relais and ii) replacing the decoupling diode by a better one. Even the antenna tuner changes the phase relation and can cause several go/no-go situations. When one of the attenuators is on (for sure not the default for 6m!) the decoupling might be ok. Depending on part tolerances the IC-756 oscillates on 6m or does not. On 6m the decoupling of both the antenna relais and the decoupling diode D131 is no more sufficient. Hereafter the RX path joins the TX small signal route via IC151 to the final amp. This is caused by a loop-back from the antenna relais (TX/RX decoupling) via the RF board, passing the persistently switched input attenuator (2 relais) and the RX/TX isolator diode D131. Some IC-756PRO (-2) tend to oscillate on 6m. 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: New Kenwood TH F6/7 Mod:Service Menu switch!
Icom IC-756 PRO (IC 756 PRO IC756PRO) transceiver mods reviews software manuals and diagrams
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