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Luxman R-800 no FM (or very very weak)
Luxman R-800 no FM (or very very weak)
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Old 9th September 2020, 05:08 PM   #1
Depaj is offline Depaj  France
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Default Luxman R-800 no FM (or very very weak)

Hello,

I'm having some issues with a luxman R-800. When I got it the symptoms were : no fm reception and popping/crackle noises when fm selected accompanied by wild movements of the two meters (centre and signal strength). The auxiliary inputs work fine so it's not the preamp. I replaced two transistors in the front end portion (q102 and 103) with 2n5770 as q103 was an infamous "flying saucer" and actually had a gain of 1 when tested. Now I still haven't got any reception (that is unless I directly connect an fm signal generator to the antenna with its output at max and I only just get enough deflection on the signal strength meter to actually notice it, and with fm muting on it stays dead silent) and the popping sounds are still there although a lot less perceptible. I don't really know where to start although I can already say that the +12v rail is present even if rather at 13.2v.


Thanks in advance for your help
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Old 11th September 2020, 09:49 PM   #2
duncan2 is online now duncan2  United Kingdom
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"Popping/crackle while some would think audio I am well aware of as being related to RF problems particularly the RF input section ,having said that I have never worked on cpu controlled household receivers with all sorts of "bells & whistles ".
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Old 13th September 2020, 01:31 PM   #3
Depaj is offline Depaj  France
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The input section really only consists of a dual fet and two small signal transistors.
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Old 13th September 2020, 02:11 PM   #4
as_audio is offline as_audio
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Have a look at dirt and shorts in the tuning capacitor
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Old 13th September 2020, 04:56 PM   #5
Regenpak is offline Regenpak  Netherlands
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Quote:
Originally Posted by Depaj View Post
I don't really know where to start
Always start at the end. In this case this is the Foster-Seeley discriminator (D204/5), driven by Q204. Touch its pin #6 (input). You should hear some noise. Better yet, set your generator to 10.7 MHz, modulate with 1 kHz, and inject with a small capacitor on pin #6 (or R215). Move to the front of the IF strip (Q203, -2, -1) until you lose signal/gain. Reduce signal level as needed. Popping sounds are worrying. Check DC levels at these four devices. They are marked on the schematic.
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Old 16th September 2020, 06:13 AM   #6
Depaj is offline Depaj  France
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Sorry for my late answer, I didn't get the usual notification.
I'll do these tests probably tomorrow and let you know. Is it possible the actual dual fet is the problem here because there is nothing measurable on the output of the front end ?
I did already clean the tuning capacitor (with a dry brush and some compressed air, and put a drop of deoxit on the ground contacts.
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Old 16th September 2020, 11:44 AM   #7
Regenpak is offline Regenpak  Netherlands
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That MOSFET is at the beginning, not at the end. Those devices are seldom bad.
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Old 16th September 2020, 11:56 AM   #8
lcsaszar is offline lcsaszar  Hungary
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See the other Luxman thread:
can someone please advise on a problem with my Luxman tuner?
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Old 16th September 2020, 12:07 PM   #9
Depaj is offline Depaj  France
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What I meant by "frontend" is the part in the enclosure directly mounted on to the tuning capacitor.

Lcsaszar, did you ever get a return from this person to know if changing the dual fet changed the problem ?

I don't actually get any reception whatsoever unless I connect my signal generator directly to the antenna input but it does move the tuning meter and only gets through when I'm dialled onto the correct frequency.
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