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Old 18th Sep 2018, 1:32 pm   #1
Michael Maurice
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Default Quad FM4

Well it seems I'm not having much luck with radios at the moment.


Perhaps someone can help me with this Quad FM4.


I have changed the 220uF and 1000uF capacitors in the power supply can, also the 0.047uF cap across the mains.


I have also replaced the back up battery, it was in its own box and there was no sign of leakage anywhere.


The radio does work, sort of, tuning is difficult with the tuning frequency jumping around all over the place.


I'm not sure where to start looking, when it does lock it sounds very nice, but it doesn't stay lockede for long.


I've also replaced C11, 100uF/10V
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Old 18th Sep 2018, 2:02 pm   #2
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Default Re: Quad FM4

This any help?https://www.diyaudio.com/forums/anal...-quad-fm4.html
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Old 18th Sep 2018, 2:29 pm   #3
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Default Re: Quad FM4

Thank you, that will certainly help me
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Old 18th Sep 2018, 6:36 pm   #4
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Default Re: Quad FM4

I've had the frequency jumping around and an inability to tune over the whole frequency range due to a dry joint on L20 in the local oscillator.

Keith
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Old 19th Sep 2018, 7:54 am   #5
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Default Re: Quad FM4

I have 3 at the moment with various faults
1: no display radio ok
2 : unable to tune in 12v rail down to 7.5 v
3 : unable to tune 12v rail ok
I have been retired for 20 months and still have not had time to look at these ( busy building workshop, extension on house ,garden ) all those roundtoit jobs whilst at work had no time . On the upside I have lost 1 1/2 stone due to hard work ( can I please go back to work for a rest )
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Old 19th Sep 2018, 10:14 pm   #6
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Default Re: Quad FM4

Quote:
Originally Posted by KeithsTV View Post
I've had the frequency jumping around and an inability to tune over the whole frequency range due to a dry joint on L20 in the local oscillator.

Keith
Keith, I can't find L20 either in the diagram or on the PCB though it is in the parts list.

I've done most of what's been suggested in the link that PJL has suggested but it makes no difference.

D24 has been replaced by a circuit board which I can't find reference to in the Quad manual. I'll change it to an 1N825 tomorrow.
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Old 19th Sep 2018, 11:26 pm   #7
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Default Re: Quad FM4

L20 is the ground return for the local oscillator varicap tuning voltage as shown on the attachment. From memory it was the ground connection on my tuner that was dry jointed. It's possible that there are other dry jointed components as I've experienced several dry joints in my FM4 and 44.

Keith
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Old 20th Sep 2018, 12:35 am   #8
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Default Re: Quad FM4

Thanks Keith, but on my diagram it's L8 and its not dry jointed.

Mine is the early version, Serial No: 2003
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Old 20th Sep 2018, 8:11 am   #9
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Default Re: Quad FM4

Mine must be a later version. The circuit extract is from the Issue 3 circuit.

Does the tuning vary on manual tuning, preset tuning or both? If it varies on both then it's probably the tuning reference diode. If it occurs on preset tuning only then it could be an issue with the D-A converter.

Keith
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Old 20th Sep 2018, 8:34 am   #10
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Default Re: Quad FM4

I have had a number of dry joint problems with QUAD equipment over the years.
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Old 20th Sep 2018, 8:39 am   #11
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Default Re: Quad FM4

Quad, although part of the Chinese IAG group, still have their product service function in Huntingdon. Could be worth giving them a call http://www.quad-hifi.co.uk/our-story.php?id=19 .

Craig
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Old 25th Sep 2018, 8:39 am   #12
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Default Re: Quad FM4

Replaced Diodes D21 and D22 with 1N4148's as the original 1S929/921's are not available and so far it's working.
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