Aerial tuning unit

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Aerial tuning unit

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Aerial tuning unit

Postby toadette » February 5th, 2016, 10:31 pm

My A2 has a PRC 77 installed with the amp kit and AS 1729 antenna with the MX 6707 VRC aerial tuning unit. All are in good condition but the tuning unit has stopped responding to frequency changes and I have to manually adjust it. I changed the connecting cable and improved the earthing but no difference. I opened the MX 6707 and it looks clean and new with no signs of arcing or damp. Any ideas on what can be wrong and is this a common problem?
Bill
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Re: Aerial tuning unit

Postby kmam » February 6th, 2016, 3:08 am

Short of getting the wiring details and checking for the correct output on each pin I suggest you do an MX6707/AM2060 swap to determine which is faulty.

I guess you mean it is not responding to frequency changes on the AM2060, not the 77 set?

Howard
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Re: Aerial tuning unit

Postby toadette » February 6th, 2016, 4:17 pm

Howard,
Thanks for the suggestions and I was referring to the AM 2060 aerial tuner control.
My A2 does have a second MX 6707 mounted which I tried but no result which suggests that it might be the output of the AM 2060 unit.
I have a circuit diagramme of this so will go ahead with testing the pins but I not looking forward to it as they are so small and hard to identify.
Bill
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Re: Aerial tuning unit

Postby kmam » February 6th, 2016, 4:46 pm

Bill

Assuming that the AM2060 is powering the 77 set, check for 25 volts (or thereabouts) on the connector for the lead to the MX6707. It should be on pin A for 30-53 MHz and pin B for 53-76 MHz.

I don't have a decent circuit for the AM2060 bUT IF THE VOLTAGE IS NOT THERE AND THE 77 SET IS BEING POWERED OK HOPEFULLY THERE IS A FUSE THAT HAS BLOWN.

pARDON THE CAPS, MY TABLET HAS GONE STUPID AGAIN.

hOWARD
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Re: Aerial tuning unit

Postby toadette » February 7th, 2016, 1:30 am

Howard,
I have just checked the cable end voltages and pin A shows 24v (with band setting 30-53 mcs) and pin B 24v (with band setting 53-76 mcs). I did have to change the ae setting on the power supply to get the voltage readings. Seems as though power is getting through to the MX 6707 but it is not responding. Any further thoughts?
Bill
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Re: Aerial tuning unit

Postby kmam » February 7th, 2016, 2:10 am

Bill

The switch on the AM2060 that controls the tuner has two wipers. One handles the voltage to pins a and b while the other does the rest. On the second wiper the 24 volt supply goes to the wiper and also directly to pin n. Check that pin n has the 24 volt. If it does not the tuner will not switch and it is likely that the connection from the 24 volt supply to the second wiper has broken.

I suspect that is the most likely cause. However if pin n has 24 volt you need to check these:

PIN. SWITCH POSITION
D. 1 & 6
E. 2 & 7
F. 3 & 8
H. 4 & 9
J. 5 & 1

If pin n is OK and d to j are not I suspect the switch is faulty.

Hope this helps.

Howard

PS There is no fuse involved. If you are getting 24 volts on pins a and b then you should be getting 24 volts on the other pins. And when I say 24 volts, that is nominal voltage. It may vary from that a little.

PPS Just another thought. Check that pin C is at ground potential. This should not be a problem as the MX6707 should be grounded but it is a possible cause. Should all the pins show 24 volts as above, connect the MX6707 to a good earth and see if it operates.

H
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Re: Aerial tuning unit

Postby toadette » February 7th, 2016, 2:25 am

Howard,
I will check the other pin voltages in the morning- I am in Sydney. In the meantime could you explain what you mean by pin D 1& 6 (what is 1&6 )?
Bill
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Re: Aerial tuning unit

Postby kmam » February 7th, 2016, 3:02 am

Bill

It means the voltage on pin d when the antenna frequency control is in positions 1 and 6, i.e for frequencies 30 and 56. Through to pin j when it is in 5 and 10.

Howard
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Re: Aerial tuning unit

Postby toadette » February 7th, 2016, 9:13 pm

Howard,
I have checked pin 9 and all the others including ground C and all show the correct readings. I did reconnect using extra earth but no response from the MX 6707.
The MX 6707 looks as though it has not had much use was working when I first got the Mutt. Any thoughts?
Bill
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Re: Aerial tuning unit

Postby kmam » February 7th, 2016, 11:32 pm

Well that indicates the AM2060 is not at fault. I know it seems unlikely but it could be that you have two bad leads or two bad tuners. I suggest you find someone nearby with a working setup and test your cables/tuners with that.

Howard
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Re: Aerial tuning unit

Postby toadette » February 7th, 2016, 11:51 pm

Howard,
Thanks for all your help. I have a few ideas on who I can pester down here.
Regards,
Bill
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Re: Aerial tuning unit

Postby toadette » February 10th, 2016, 6:15 pm

Howard,
Thought you should know that I took the MX 6707 to a friend who owns these units. We stripped my unit down and found that the relay switches were dirty. After cleaning them up with solvent it is working perfectly. He believes that the rubber and plastic used internally tend to give off fumes over time which coat the switches. I am now about to clean up my second unit and hope it can also be made to work. Thanks again for your help.
Bill
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Re: Aerial tuning unit

Postby kmam » February 10th, 2016, 7:49 pm

Good news Bill. I bet you are relieved.

As an aside, you should reasonably frequently remove the drain screw from the bottom of the MX6707 to allow any moisture to escape. That may well have had some bearing on the deterioration.

Howard
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