[ICOM] IC765 - no rx, no tx

[Bert Almemo]

Thanks Jim and Larry,

I've forwarded the info to my friend. Tomorrow I'll join him for some
trouble shooting if time permits and hopefully come up with some
conclusions. I'll keep you posted.

73 Bert, VE3OBU

 

-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Jim Hargrave
Sent: Monday, February 25, 2008 11:51 AM
To: ICOM Reflector
Subject: RE: [ICOM] IC765 - no rx, no tx

Bert,

I don't have a 765, but your description of the problem points possibly to
the filter circuits.

I assume that you have tried to modulate in the SSB modes and also tried to
key in the CW mode. If this does not result in any power output, then I
would look in the area around the filters. Most radios use the filters in
both receive and transmit, so that would be a good place to look.

 More comments below

> -----Original Message-----
> From: icom-bounces at mailman.qth.net
> [mailto:icom-bounces at mailman.qth.net]On Behalf Of Bert Almemo
> Sent: Monday, February 25, 2008 9:53 AM
> To: 'ICOM Reflector'
> Subject: [ICOM] IC765 - no rx, no tx
>
>
> Hi guys,
>
> Now I have received some more details about my friend's 765. Some of 
> previous info was not correct. This is info from my friend's measurements.
> Here goes.
>
>
>
> No Receive
> No Po on Xmit in CW/LSB/USB but full carrier output in RTTY

 That might eliminate the RF circuits. In RTTY mode the radio is frequency
shifted by the FSK Keying circuit, and is normally full output. Have you
actually checked the frequency of this output. Is it at the right frequency?
This would insure that all the transmit mixers are functional. I assume that
you have tried to transmit CW using a key and used a mic in SSB modes.

The problem could be in the filter area, since the filters are used in both
Transmit and receive. So the switching circuits around the filters could be
suspect.

While in SSB transmit, have you tried to place an audio tone into the acc
connector? This would help isolate where the transmit audio is failing. Also
have you checked for audio output from the acc connector while in receive?
This would be a fixed output level irrespective of the Audio gain setting.

> Audio Gain Control works to change hiss from speaker but not strong.
> Mode change makes no difference
> No popping sound switching from Tx to Rx Turning RF Gain moves S meter 
> up scale as normal.
> No S meter movement in RX or TX position - needle in left 
> position/normal, not pegged

I assume from this statement that you are using an external power meter when
you say that RTTY mode is full power output. Is this true on all bands?

> T/R relay clicking when switching from RX to TX - seems to be OK
>
> RF board - D47 voltages OK except when trying to measure the anode in 
> TX shuts the radio down.
> Cathode of D47 is 13.8 in TX but when I touch DVM to anode it shuts 
> down every time.
> Anode of D47 is OK in Rec 9.2 and cathode is 8.4.

The shut down could be normal.  Any time you place a test lead on an RF
circuit, it can change the match of that circuit and also it can act like an
antenna. This may be the SWR loopback circuit shutting down. Voltages in RF
circuits should be measured using RF isolated probes. Also be careful using
digital voltmeters, RF can wipe out the internal ICs in the voltmeters


* 73's Jim - W5IFP *


>
> I hope this info will help you to help me. Thanks!
>
> 73 Bert, VE3OBU

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