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Author Topic: Collins 75S-3 muting with 32S-3 grief.....  (Read 5111 times)
W7GIF
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Posts: 122




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« on: August 10, 2012, 01:06:31 PM »

I hope someone can help me understand how muting the 75S-3 is supposed to function. I have a 75S-3 that performs beautifully on it's own, and a 32S-3 that also performs perfectly on it's own. But, configuring the two for transceive (or even separates with the muting cable installed) is a disaster. Whenever the 32S-3 is keyed, the 75S-3 fails to mute, and suffers signal overload. The 32S-3 K1 and K2 relays are functioning correctly (muting contact operation and antenna switching confirmed good), but absolutely NO muting of the 75S-3. All tubes check OK, and absolutely no other malfunctions of either piece, or visual evidence of damaged components on either piece.  What SHOULD the 75S-3 be seeing at the "MUTE" input, or at the 32S-3 "MUTE" output for muting? BTW, the receiver is a non-suffix 75S-3 (not an "A", "B", or "C").

I'd sure like to get these gems back on the air. Thanks for any help......
« Last Edit: August 10, 2012, 01:11:36 PM by W7GIF » Logged
AC5UP
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Posts: 3834




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« Reply #1 on: August 10, 2012, 01:24:03 PM »

Spend a little time with the documentation here:    http://www.collinsradio.org/     Then double check the interconnect cable.

A crossed pair, broken connection, or pilot error could be all that's wrong.    Cool
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W7GIF
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Posts: 122




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« Reply #2 on: August 10, 2012, 10:30:53 PM »

Thanks for the tips. The one that really paid off was "pilot error"! Duhhhhhhh......there's one sentence in the preface of the instructions for setting up transceive operation: The mode switch must be in the "STANDBY" (NOT "OPERATE") position to make use of the muting feature of the 32S-3.

But, I learned a lot about the 32S-3 and 75S-3, and found and cleaned up and adjusted some oxidized/intermittent contacts on K1 in the process of getting my head screwed on straight...and CAREFULLY/THOROUGHLY reading the instructions.

THANKS!!
« Last Edit: August 10, 2012, 10:32:32 PM by W7GIF » Logged
AC5UP
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« Reply #3 on: August 11, 2012, 04:39:03 AM »

As Montgomery Burns might say:  Excellent!

Good to hear it was a simple fix and now you're good to go. I also appreciate that you took the time to follow up with a reply. You wouldn't believe how often advice is given with no thanks and no response until someone needs more help.........  Thanks to your response there are now dozens of OM's who learned about the standby switch thing even though they may never need it!    Wink
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W7GIF
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Posts: 122




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« Reply #4 on: August 11, 2012, 06:27:04 AM »

It just goes to show that a guy's never too old or too smart to learn something new. The un-energized contact sets on K1 of the 32S-3 sure had me going. The "make' pressure of those contacts is very low, and it doesn't take much in the way of oxidation or contamination of those contacts to prevent circuit continuity. And since the mute signal required is an OPEN CIRCUIT (not too conventional), it masked the ability to receive in the transceive configuration with the 75S-3 in the "STANDBY" mode.......the receiver acted just as it would in the un-paired transceive configuration. So.......32S-3 owners: read every word of the instructions, and check actual circuit performance of of the K1 relay, especially the contact sets that are supposed to "make" with the relay unenergized.

Thanks again for the help!
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KE5GFJ
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« Reply #5 on: March 29, 2013, 07:42:39 PM »

I have exactly the same problem with the 75S-3 not muting when the 32S-3 is keyed. All the cables and connections are correct and the receiver switch is on Standby as required. But the mute circuit does not mute the 75S-3. The relays in the 32S-3 are working. However, the negative voltage coming from the 75S-3 is extremely low...,02 volts. I tested all the resistors in that circuit and they appear to be OK. Anyone have any advice on what to check next?
Thanks,
John KE5GFJ
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W7GIF
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Posts: 122




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« Reply #6 on: March 30, 2013, 10:52:51 AM »

I have exactly the same problem with the 75S-3 not muting when the 32S-3 is keyed. All the cables and connections are correct and the receiver switch is on Standby as required. But the mute circuit does not mute the 75S-3. The relays in the 32S-3 are working. However, the negative voltage coming from the 75S-3 is extremely low...,02 volts. I tested all the resistors in that circuit and they appear to be OK. Anyone have any advice on what to check next?
Thanks,
John KE5GFJ
John,
Are you actually getting audio of the transmitted signal when the receiver is supposed to be muted? Or, is it just that the needle on the S-meter  deflects when "muted"? (which is not abnormal). The contact tension on the 32S-3 relay is very light, so it doesn't take much in the way of contact oxidation or contamination to prevent a good "make" of the contacts. You might try logging on to the Collins collectors listserve on line, if you're still stumped.  Lots of very capable and experienced Collins help there. Here's the address for the Collins Collectors group:

http://www.collinsradio.org/

This will at least get you into the site where you can subscribe to the listserve for collectors (click on "REFLECTOR" to get started and subscribed to the group.......which is free).
« Last Edit: March 30, 2013, 11:22:05 AM by W7GIF » Logged
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