Hello !
I need an advice for a faulty Quad FM3 :
This tuner has a problem : the signal is weak. I can hear the stations in my hearphones, but when the tuner is on a station, the signal is a lot more weak than the noise between the station (with the trimpot on OFF). And the voices seems to be also with some saturation. The two tuning lights are not "progressive" on a station, they light together or they don't. On ONE station, the stereo lamp lights, with more noise in the signal than between the stations.
I asked on a Quad specialist forum, and the answer was that this tuner needs realignment. It's possible, it's even sure, but before sending this unit for servicing (and I have to find a technician before !), I would like to be sure that it is nothing else... The tuner have only genuine parts and components, I could compare with pictures of the same issue. And really, it doesn't looks like someone tried to tweaks something in.
But the schematic give very few informations about the voltages. So, is somebody in this forum knows enough this tuner to tell me some control points, to be sure that the ONLY thing I can do is to send it for a realignment ?
I had the same symptoms on my FM2 valve tuner, it was just 2 resistors out of tolerance, and a dry joint. That's why I ask...
Thank you, and a nice sunday to everybody ! I post the tuner schematic, too.
I need an advice for a faulty Quad FM3 :
This tuner has a problem : the signal is weak. I can hear the stations in my hearphones, but when the tuner is on a station, the signal is a lot more weak than the noise between the station (with the trimpot on OFF). And the voices seems to be also with some saturation. The two tuning lights are not "progressive" on a station, they light together or they don't. On ONE station, the stereo lamp lights, with more noise in the signal than between the stations.
I asked on a Quad specialist forum, and the answer was that this tuner needs realignment. It's possible, it's even sure, but before sending this unit for servicing (and I have to find a technician before !), I would like to be sure that it is nothing else... The tuner have only genuine parts and components, I could compare with pictures of the same issue. And really, it doesn't looks like someone tried to tweaks something in.
But the schematic give very few informations about the voltages. So, is somebody in this forum knows enough this tuner to tell me some control points, to be sure that the ONLY thing I can do is to send it for a realignment ?
I had the same symptoms on my FM2 valve tuner, it was just 2 resistors out of tolerance, and a dry joint. That's why I ask...
Thank you, and a nice sunday to everybody ! I post the tuner schematic, too.
The schematic with better resolution is here:
http://www.saturn-sound.com/images - cct dia/quad fm3 - stereo fm tuner - cct dia'.jpg
The reason must be the IF amplifier and demodulator TAA661B itself or the parts arround it.
This IC from SGS-ATES (now ST) I have never see before.
Unfortunately the datasheet about
TAA661B ... - Datasheet Search Engine Download
shows only page 1. Thus you need the associated databook from SGS-ATES to get the whole datasheet.
http://www.saturn-sound.com/images - cct dia/quad fm3 - stereo fm tuner - cct dia'.jpg
The reason must be the IF amplifier and demodulator TAA661B itself or the parts arround it.
This IC from SGS-ATES (now ST) I have never see before.
Unfortunately the datasheet about
TAA661B ... - Datasheet Search Engine Download
shows only page 1. Thus you need the associated databook from SGS-ATES to get the whole datasheet.
By 'weak' do you mean:
1. the tuner is deaf and doesn't receive weaker stations at all,
2. the audio level is low,
3. the audio is noisy.
1 or 3 probably mean a front-end problem (circuitry around Tr1, Tr2) while 2 probably means a discriminator problem (IC1 or L6). An alternative is a squelch problem.
1. the tuner is deaf and doesn't receive weaker stations at all,
2. the audio level is low,
3. the audio is noisy.
1 or 3 probably mean a front-end problem (circuitry around Tr1, Tr2) while 2 probably means a discriminator problem (IC1 or L6). An alternative is a squelch problem.
Hello DF96 !
Yes, the audio level is low, a lot lower than the noise between the stations. I receive stations, but I have to augment really the lever on my amplifier to her them, they are much lower than the noise between them. But the tuner, at least, has a reaction when he meets a station ! ;-) On only one station, the "stereo" lamp light, and here the signal is really noisy, with a noise level higher than the noise between stations.
The last thing : the 2 lamps for the tuning light together or not, they are not progressive at the approach of a station.
All that is described with the "mute threshold", at the rear of the tuner, on "OFF".
All the tuner are different, but this one is not the most complicated. The problem is that, on the schematic, just very few informations are present, about the voltages for example. And as I wrote, all the parts in are genuine, it is exactly this one :
Quad
And on mine, even the two yellow trimpots in the IF are in the same position than on this picture ! Really, I don't think someone tried to tweak something in...
So, is there a way to be sure that there's nothing else than a realignment ? Can a tuner be completely misaligned without a dead component, just because of his age ?
Yes, the audio level is low, a lot lower than the noise between the stations. I receive stations, but I have to augment really the lever on my amplifier to her them, they are much lower than the noise between them. But the tuner, at least, has a reaction when he meets a station ! ;-) On only one station, the "stereo" lamp light, and here the signal is really noisy, with a noise level higher than the noise between stations.
The last thing : the 2 lamps for the tuning light together or not, they are not progressive at the approach of a station.
All that is described with the "mute threshold", at the rear of the tuner, on "OFF".
All the tuner are different, but this one is not the most complicated. The problem is that, on the schematic, just very few informations are present, about the voltages for example. And as I wrote, all the parts in are genuine, it is exactly this one :
Quad
And on mine, even the two yellow trimpots in the IF are in the same position than on this picture ! Really, I don't think someone tried to tweak something in...
So, is there a way to be sure that there's nothing else than a realignment ? Can a tuner be completely misaligned without a dead component, just because of his age ?
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One of the tuning lamps LP1 just indicates that the squelch has opened - that means that there is insufficient interstation noise - which shows that you have tuned to a station. The other tuning lamp LP2 may also be a crude indicator of signal strength; I am not sure.
It is difficult to do remote diagnosis on an FM tuner.
It is difficult to do remote diagnosis on an FM tuner.
I understand that it's not easy to follow and to imagine the kind and the look of a signal in the different steeps of a tuner...
I'll try to check the components around IC1, I suppose the problem is before the multiplex decoder, because the light balance of the tuning presents a problem. I'll check all the voltages I can check, and I'll see if I find a trouble.
I suppose, I have the intuition that the tuner is not misaligned : it is not so old, and all look untouched inside. That's why I'll begin with checking the components, and the joints in the RF and IF section.
If someone with a knowledge of this specific tuner read these lines, or someone with the knowledge of some tricks I can use, he's welcome !
Thank you for your help DF96 ! All your advices are welcome !
I'll try to check the components around IC1, I suppose the problem is before the multiplex decoder, because the light balance of the tuning presents a problem. I'll check all the voltages I can check, and I'll see if I find a trouble.
I suppose, I have the intuition that the tuner is not misaligned : it is not so old, and all look untouched inside. That's why I'll begin with checking the components, and the joints in the RF and IF section.
If someone with a knowledge of this specific tuner read these lines, or someone with the knowledge of some tricks I can use, he's welcome !
Thank you for your help DF96 ! All your advices are welcome !
Hi, and happy New Year!
I have got hold of a nice FM3, central MHz legend, n° 5902.
It produces no sound, no hiss, nothing.
The +/- 14 V are correct, the dial light works and the right tuning beacon is constantly lit.
The transistors and ceramics all test fine (unsoldered of course) and the mosfets have been replaced but to no avail.
I tried a new TAA661 and if I inject a signal at the input of the stereo decoder, it gets out fine.
I have absolutely no clue. The tuner was last seen by Quad Huntingdon in '96, but apart from the factory sticker, I don't know what they did.
Thanks for any leads!
Jacques
I have got hold of a nice FM3, central MHz legend, n° 5902.
It produces no sound, no hiss, nothing.
The +/- 14 V are correct, the dial light works and the right tuning beacon is constantly lit.
The transistors and ceramics all test fine (unsoldered of course) and the mosfets have been replaced but to no avail.
I tried a new TAA661 and if I inject a signal at the input of the stereo decoder, it gets out fine.
I have absolutely no clue. The tuner was last seen by Quad Huntingdon in '96, but apart from the factory sticker, I don't know what they did.
Thanks for any leads!
Jacques
You don't by any chance happen to know what the Technician did to realign it do you?
What are the symptoms of your Quad FM3 that would suggest that it is out of alignment? Which version do you have? The serial number will tell you the version.
The version difference is significant in terms of what needs adjustment. The oldest version with the serial number 5884 and older will be the most complicated as it uses coils in its multiplex decoder IC. The later version uses the PLL.
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