[Icom] 756PRO rx audio

Mon, 25 Mar 2002 20:32:28 -0500

Hi George!

I see in the block diagram what you described below. It takes about 11-13
minutes for the audio to "Arrive at the speakers" :)  It must be on holiday
in one of the semiconductors. I am trying to figure out the ground on the
headphone jack. Looks like inserting the headphones drops out a stage of
amplification somewhere. That is probably where the problem is.

73

Bob

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of George, W5YR
Sent: Monday, March 25, 2002 12:12 PM
To: [email protected]
Subject: Re: [Icom] 756PRO rx audio

Thanks for the info, Bob. The ACC1 receive audio comes from an almost
totally different path within the radio than does the speaker audio. So,
that helps to pin down at least the area of the problem.

I understand from what you are saying that your headphone jack works
properly and only the internal speaker and audio available at the
rear-panel speaker jack remains off for ten minutes after you first turn on
the radio.

The headphone circuit is wired logically in parallel with the speaker
wiring. Electrically, however, there are several components between the
headphone jack connection and the internal speaker and speaker jack. For
what it is worth these are shown on the schematic as

D351 (DAN222)
Q351 (DTC114EE)
RL351 (AHY103)

Any or all of these could account for what you are observing, or the
driving signal to the switch transistor Q351 could be delayed. The actual
connection of the speaker circuitry to the circuitry that feeds the
headphone jack is the relay RL351. Its coil is driven by Q351 and D351 is a
snubber diode pair. The relay could be defective in some manner or the
driving signal to Q351 (SPS) could be delayed.

At this point, Bob, I think that you need to refer to the service manual
for more ideas and/or contact Icom Service about the problem.

Sorry, I can't give you more specific direction, but this is one that
probably means opening the box and doing some looking around.

The PRO is quite a complex little black box, isn't it?

73/72/oo, George W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 #02437

All outgoing email virus-checked by Norton Anti-Virus 2002

Bob Marzari wrote:
>
> Hi George,
>
> Everything works but audio out to the internal speaker AND the 1/8" audio
> jack on the rear panel.
> The audio from the ACC jack I use for PSK works fine also. Any ideas?

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