[ICOM] IC-2720 Malfunction at the Junction

[D C _Mac_ Macdonald]

The six-pin control cable was plugged in between 
the CTRL cable socket and the MIC cable socket 
on the RF deck while 13.8V was hooked to the 
RF deck! That would give the cross connect that 
I have shown below if I didn't goof! 
 
It would appear that 13.8V was applied to the Mic
Up/Down circuitry. 
 
I did not realize that the CTL cable had only six
conductors so arrived at an erroneous conclusion. 
It's good to know that it is unlikely that the 8V
was even activated, but another message stated the 
7808 regulator was probably protected. 
 
I just received the rig today and will have to look 
for damages in the MIC U/D circuitry.
 
Owner described display as sort of going nutso after 
things were then hooked up correctly. 
 
~~ CTL ~~~~~~~~ MIC ~~
~~ PIN ~~~~~~~~ PIN ~~
 
 ~~~~~~~~~~~~ 8v ~~~ 1
 1 CTHV ~~~~~ MICU/D 2
 2 TDATA ~~~~ EXTMIC 3
 3 RDATA ~~~~ PTT ~~ 4
 4 GND ~~~~~~ MICE ~ 5
 5 MIC ~~~~~~ MIC ~~ 6
 6 MICE ~~~~~ GND ~~ 7
 ~~~~~~~~~~~~ MICIN ~8
 
I have not yet looked at the schematic to see where 
damage is likely to have occurred. 
 
* * * * * * * * * * * 
* 73 - Mac, K2GKK/5 * 
* (Since 30 Nov 53) * 
* k2gkk at hotmail.com * 
* Oklahoma City, OK * 
* USAF & FAA (Ret.) * 
* * * * * * * * * * * 
 
 
 

 

> From: hinton.ll at frontier.com
> To: icom at mailman.qth.net
> Date: Sat, 22 Dec 2012 16:06:38 -0800
> Subject: Re: [ICOM] IC-2720 Malfunction at the Junction
> 
> You may not be in as bad of shape as you thought. The six pin control cable
> would plug into the center 6 pins of the mic connector due to the locking
> tab. The plug will not fit into the socket any other way.
> 
> CTL MIC
> -----------8v
> CTHV-------MICU/D
> TDATA------EXTMIC
> RDATA------PTT
> GND--------MICE
> MIC--------MIC
> MICE-------GND
> -----------MICIN
> 
> There is no power to the control head, no power on CTHV and the mic cable
> cannot be plugged in for 8V. I don't see anything that could go wrong if I
> am assuming correctly that the ctrl cable was plugged into the control head
> properly and just plugged into the mic jack on the RF deck.
> 
> Larry
> K7YBZ
> 
> >Looking at the service manual, it would appear that doing that grounded Pin
> 1 of the MIC jack J2001 (+8V supply) to Pin 1 of >CONTROL jack J2006 (Mic
> Earth). I expect that this probably took out the 8V regulator IC2003
> (TA7808F). 
> 
> >Also connected would be the 13.8V (HV) from Pin 6 of J2006
> >(CTRL) and Pin 6 of J2001 (MIC) that is the Mic Hi line. 
> 
> 
> 
> ----
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