[ICOM] Icom 706 Dead on Tx and Rx (Again)

[Jim Miller]

AL, I have used Matt Adrian KD8ZB several times at least for my ICOM repair
guy for several ICOM radios HTs and my 706 as well.  I recommend him to our
clubs here and I know several who have also used him.  His prices are
reasonable and his fixes are just that, fixes.  

He is an authorized ICOM repair center and does excellent work.

Matt Adrian KD8ZB
1792 Nash Drive
Sat Joseph, MI 49085
269-429-2334

73, de Jim KG0KP

-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Al Waschka
Sent: Thursday, August 01, 2013 5:55 PM
To: ICOM Reflector
Subject: [ICOM] Icom 706 Dead on Tx and Rx (Again)

Seveal months ago I posted on here about a problem with my IC-706 (Mk I). 
After finding and replacing a damaged cap, the radio got well and stayed
well for several months, but the problem has now returned.  The replaced cap
is fine.
 
Symptoms are no transmit output and severely degraded (40 dB) receiver
operation on HF.  Based on output Rx noise, the attenuator and preamp appear
to be working fine.  I can hear the noise at three distinct levels depending
on whether the preamp or attenuator are selected.  On strong injected
signals, the relative levels of the three options appear correct.  VHF works
fine.
 
I have instrumented the radio with test points and traced signals through to
the main board.  It appears that the filter unit is working normally. 
Signals injected on all HF bands pass through the filter unit and appear
unattenuated at the input to the main board.  After the receive signal is
routed to the main board from the filter unit, it passes through a high pass
filter consisting of C3, C5, C7 and L4, L5.  The output of this filter does
not look right.  Either some of the diode switching is malfunctioning or
components in the filter have changed values.  Instead of the 3.9 MHz signal
I'm injecting, the filter is passing only high order harmonics, and those at
attenuated levels.
 
Has anyone seen anything like this, and if so, was a cure discovered?  I'll
continued to troubleshoot, but I thought I'd poll the group to see if there
might be a shortcut.
 
Thanks,
 
Al K5TAN
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