[ICOM] IC-746Pro Audio/Receiver Cut Out Issue

[Mark K3MSB]

OK.    The T/R Relay looks to be RL4 on the CTRL board, part number NR-HD
(12V) AE5343.   Available from at least one supplier in China if not from
ICOM USA.

>From the service manual,  I've located the board and RL4.    Are they any
particular problems removing the board and desoldering the Relay ?

73 Mark K3MSB

On Wed, Nov 16, 2016 at 1:58 PM, Bert Almemo <balmemo at sympatico.ca> wrote:

> Hi Mark,
>
> When the audio signal drops in the speaker, internal or external, does the
> signal strength on the S-meter change too? If so, the T/R relay, I don't
> know the RL number, is your best bet. I don't think you have a "weak" 14V.
>
> This is quite a common problem on transceivers with T/R relays.
>
> 73 Bert, VE3NR
>
>
>
> -----Original Message-----
> From: Icom [mailto:icom-bounces at mailman.qth.net] On Behalf Of Mark K3MSB
> Sent: Wednesday, November 16, 2016 12:37 PM
> To: ICOM Reflector
> Subject: Re: [ICOM] IC-746Pro Audio/Receiver Cut Out Issue
>
> Good Afternoon All
>
> Thank you for your replies.
>
> A resistance test on the SEND output show no change when the Transmit
> button is enabled.  This indicates RL781 or related components is toast.
> This occurred several weeks before the current audio problem manifested
> itself.
>
> The External Speaker (and Internal Speaker) are controlled by RL740,  which
> may be marginal.
>
> The only common item between RL781 and RL740 is the 14V line,  and I
> haven't had the time to trace that through the service manual.
>
> Even if the 14V line is not strong, that would not account for the complete
> failure of RL781.   However, a weak capacitor on the 14V line would account
> for what we're hearing on the audio.   It would also account for
> intermittent operation of RL781 if it were alive.
>
> A problem in my comments is that the schematics show both RL781 and RL 740
> in the receive configuration;  If so,  then how does the audio signal
> "PAFO" get to the external speaker (or internal speaker) ?     It almost
> seems like RL740 needs to be closed in receive and open in transmit,  just
> the opposite of RL781.
>
> So, might it be that the radio has two problems - RL781 and a weak 14V line
> ?
>
>  73 Mark K3MSB
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