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Old 22nd Mar 2018, 12:28 pm   #1
Brettski
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Default Roberts RM40 tuning issue

Hi all, I am hoping to restore an RM40.

I've not been inside yet, but when powered up it has a very strange tuning fault . Medium and Long wave no issues. Amp section appears to be fine too.
But VHF is odd. I can tune into a strong local station and within a couple of seconds it will drift and try to retune its self to the next station along . Very much like a TV looking for analogue stations when tuning and storing as it goes along. Would this be an AFC issue ? Any thoughts before I get stuck in please ?

Also, does anyone have the pinout for the AUX socket so I can run my CD101 through it please.

As ever any help is always most appreciated.

Brett.
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Old 22nd Mar 2018, 12:33 pm   #2
Nuvistor
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Default Re: Roberts RM40 tuning issue

Is it a varicap tuner, if so I would check the stability of the tuning voltage supply.

I have just checked and the VHF is varicap with the tuning voltages taken from the stabilised PSU. There is a switch to disable AFC which is probably on the front panel so that is easily tested as the cause.
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Old 22nd Mar 2018, 12:48 pm   #3
dazzlevision
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Default Re: Roberts RM40 tuning issue

Another possibility is that the VHF tuning potentiometer has poor contact between the wiper and track. A squirt of suitable switch cleaner and lubricant should resolve that.
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Old 22nd Mar 2018, 1:17 pm   #4
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Default Re: Roberts RM40 tuning issue

Quote:
Originally Posted by Brettski View Post
Also, does anyone have the pinout for the AUX socket so I can run my CD101 through it please.
Socket,
Pin 2 chassis.
Pins 1,4 output
Pins 3,5 input.

Make sure your CD player doesn’t overload in the input.
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Old 22nd Mar 2018, 1:34 pm   #5
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Default Re: Roberts RM40 tuning issue

Brill, thanks everyone, I will give these ideas a go. And thanks for the pinout too. I might run a Bluetooth receiver( and use my phone and spotify) through the radio if input overload may be a problem.

Many thanks .

Brett.
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Old 23rd Mar 2018, 6:35 am   #6
julie_m
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Default Re: Roberts RM40 tuning issue

If the input signal is too strong for the amplifier, it's simple enough to fix, with just three resistors. 100mW ones will fit right inside the plug, even.
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Old 23rd Mar 2018, 3:11 pm   #7
Brettski
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Default Re: Roberts RM40 tuning issue

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Originally Posted by dazzlevision View Post
Another possibility is that the VHF tuning potentiometer has poor contact between the wiper and track. A squirt of suitable switch cleaner and lubricant should resolve that.
That's it !!

I got a few mins last night to take set out of its box. And went straight to the pot and gave it a little deoxit . And the tuning stabilised .

I reckon another little blast and leave the set running for a few hours should see it back to its best.

Really pleased. Thanks for the help .

Brett.
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Old 23rd Mar 2018, 5:04 pm   #8
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Default Re: Roberts RM40 tuning issue

Excellent, it’s a nice looking Radio.
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