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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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29th Oct 2020, 12:32 pm | #1 |
Nonode
Join Date: Dec 2002
Location: Coulsdon, Surrey, UK.
Posts: 2,130
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Quad FM3 -stereo not working properly
Just looking at an FM3. It seems to basically work and sounds excellent EXCEPT that I'm not getting any stereo information. When first switched on if the tuning is moved there is a burst of stereo and the light comes on. It then seems to switch into mono and the light goes out. ( background noise drops at this point)
Once this has happened, no amount of retuning will bring the stereo light back on or any stereo information. I will admit that I'm using a pretty naff internal dipole aerial to feed it, as it's all I have since my rooftop aerial blew down. Not sure whether the circuitry is arranged to force to mono if the signal strength is low and hence maybe there is no fault ? Any thoughts welcome. Andy |
29th Oct 2020, 1:13 pm | #2 |
Heptode
Join Date: Nov 2009
Location: London, Ontario, Canada
Posts: 675
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Re: Quad FM3 -stereo not working properly
Hi Andy,
Do get the service manual from here: https://www.manualslib.com/manual/407333/Quad-Fm3.html Depending what is the serial number there are different circuitry. The latest models do use the MC1310 stereo decoder and CA3089 FM-IF/decoder IC, earlier models use more obscure ICs. The service manual also gives alignment instructions. Regards, Peter |
29th Oct 2020, 5:56 pm | #3 |
Dekatron
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,982
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Re: Quad FM3 -stereo not working properly
OK - there are three generations of the FM3. Which one do you have?
Best alternative is look at the type of decoder chip fitted. Craig |
29th Oct 2020, 5:59 pm | #4 |
Dekatron
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,982
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Re: Quad FM3 -stereo not working properly
There was a recent thread on this forum about this issue with a third generation one. The guy had replaced the decoder twice, the IF chip once. A bunch of resistors and capacitors. With zero change - short period of stereo and then bosh - just mono.
It turned out in the end to be the transistor that is used to force mono not being a good transistor any more. Do a forum search and ferret the thread out. Craig |
29th Oct 2020, 6:16 pm | #5 |
Heptode
Join Date: Mar 2003
Location: Waiheke Island, New Zealand
Posts: 503
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Re: Quad FM3 -stereo not working properly
I Had one with the same problem. I just changed the electrolytic next to the decoder IC then it was fine again.
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29th Oct 2020, 8:25 pm | #6 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,326
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Re: Quad FM3 -stereo not working properly
You mentioned a naff aerial. Are you sure you have enough signal to make it switch to stereo? Low signal will revert to mono which is how you described it.
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29th Oct 2020, 9:24 pm | #7 |
Dekatron
Join Date: Jan 2003
Location: Bradford on Avon, Wiltshire, UK.
Posts: 3,310
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Re: Quad FM3 -stereo not working properly
I had a Grundig tuner with exactly that problem. A squirt of freezer on the decoder chip would restore stereo for a few seconds. It is was over 25 years ago so I have no idea now what the chip was.
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29th Oct 2020, 10:42 pm | #8 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,845
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Re: Quad FM3 -stereo not working properly
I had a Rotel with these symptoms too, a new decoder ic curing it.
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29th Oct 2020, 11:37 pm | #9 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: Quad FM3 -stereo not working properly
This is the thread Craig is referring to and your symptoms sound quite similar so I would check this first. https://www.vintage-radio.net/forum/...d.php?t=170997
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9th Nov 2020, 2:43 pm | #10 |
Tetrode
Join Date: Nov 2020
Location: Edinburgh, Scotland, UK.
Posts: 89
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Re: Quad FM3 -stereo not working properly
I sold these when new - they weren't the most sensitive of tuners and you do need a good strong signal to get them working at their best .
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10th Nov 2020, 12:13 am | #11 |
Nonode
Join Date: Dec 2002
Location: Coulsdon, Surrey, UK.
Posts: 2,130
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Re: Quad FM3 -stereo not working properly
I appreciate all the helpful ideas from this thread. The difficulty is that I cannot access a decent aerial, so I have no way of knowing whether this is a 'real' fault, or simply the tuner doing as expected. I'm reticent to look for a fault that might not exist !
Andy |
10th Nov 2020, 10:46 am | #12 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,326
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Re: Quad FM3 -stereo not working properly
Have you tried using an aerial amplifier to see if that improves the stereo switching.
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10th Nov 2020, 10:51 am | #13 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,831
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Re: Quad FM3 -stereo not working properly
Hmm. The amount of times I have tried using signal boosters to improve FM performance. Usually resulted in more signal + more interference (multipath etc).
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10th Nov 2020, 11:43 am | #14 | |
Tetrode
Join Date: Nov 2020
Location: Edinburgh, Scotland, UK.
Posts: 89
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Re: Quad FM3 -stereo not working properly
Quote:
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10th Nov 2020, 11:48 am | #15 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,326
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Re: Quad FM3 -stereo not working properly
I was suggesting the aerial amplifier as a way of checking whether it switches to stereo. I agree that a proper aerial is always best.
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