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Old 6th Jan 2021, 9:18 pm   #81
Trevor
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Default Re: Armstrong 600 series tuners and receivers

I bet the same fault would not take Steve so long next time
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Old 7th Jan 2021, 9:12 am   #82
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Default Re: Armstrong 600 series tuners and receivers

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I bet the same fault would not take Steve so long next time
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Exactly Trev. I've been restoring vintage radios, TVs, videos and hi-fi equipment for around 45 years, and yet 'new' types of faults continue to appear. In this case missing PCB tracks that look like they're still in place! As I've always been open about, even though I'm an apprenticed, qualified electronics engineer from the age of 20, I struggle when circuitry is even approaching anything complex. But my 45 years experience tells me that a good 80% of the faults on most pieces of kit can be found by addressing more simple things like dirty pots and switches, wax capacitors, dry joints, likely/dodgy electrolytics, overheated/burnt components, signs of being 'got at', tapping components to check for intermittency, faulty valves, broken wires at junctions, etc etc. Oh yes, I have got a scope and I do use it!
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Old 12th Jan 2021, 7:04 pm   #83
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Default Re: Armstrong 600 series tuners and receivers

There are continuing faults on this set. I'm not too well at the moment, so I'm not terribly proactive in terms of working on it daily, but thanks mods for keeping it open.

One as yet unsolved problem is the action of the AFC button. Tune in to an FM station, all is fine, nice and clear, press the AFC button and it gets swamped in noise as if badly tuned.
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Old 16th Jan 2021, 3:30 pm   #84
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Default Re: Armstrong 600 series tuners and receivers

No-one has responded yet, just wondered if anyone may have any input on this afc fault or can comment on how well the facility works on their Armstrong FM receiver or tuner like this 626.
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Old 16th Jan 2021, 4:05 pm   #85
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Default Re: Armstrong 600 series tuners and receivers

Sometimes the button works opposite to what you expect. Try the button in both positions. Try tuning to near the correct point and see if the button pulls the station in or makes it worse. Haven’t worked on one of these for about 40 years so memory is a bit thin.
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Old 16th Jan 2021, 8:22 pm   #86
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Default Re: Armstrong 600 series tuners and receivers

The AFC button on mine works fairly well. It doesn't lock onto the station terribly well but it doesn't bring in stations it shouldn't do. I have read or seen somewhere that AFC problems can point to the alignment being out
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Old 16th Jan 2021, 9:17 pm   #87
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Default Re: Armstrong 600 series tuners and receivers

Thanks guys, both good answers, I'll check the action of the switch out.
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Old 17th Jan 2021, 4:30 pm   #88
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Default Re: Armstrong 600 series tuners and receivers

Right. I'm not sure if it's from an actual user manual, but an Armstrong document I found on the internet that describes the function of all the switches just says, "AFC: Automatic Frequency Control". So it does not say if it has to be 'up' or 'down' for AFC to be engaged. Now, I've used an AFC button enough times to (normally) be able to tell when it is operative or not, but in this case I'm really struggling, it's effect is so bad. A station's position is in a different position depending on whether AFC is actuated or not. So, it seems that FM alignment - or AFC circuitry - is not correct.

Before I go in that deep, I'm going to have another go to see if I can figure out when AFC is engaged; with the button up or pressed down. Is anyone with a working set able to clarify?
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Old 17th Jan 2021, 4:51 pm   #89
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Default Re: Armstrong 600 series tuners and receivers

From Jim Lesurf's site, Up is AFC off, Down is AFC engaged.
See FAQs here: http://www.audiomisc.co.uk/Armstrong/600/600faq2.html
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Old 17th Jan 2021, 5:13 pm   #90
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Default Re: Armstrong 600 series tuners and receivers

Yes, up is off and down is on. It deflects the needle on the tuning gauge more when on. I realise yours isn't working but you might be able to test the voltage across it.
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Old 17th Jan 2021, 5:22 pm   #91
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Default Re: Armstrong 600 series tuners and receivers

Quote:
Originally Posted by snowman_al View Post
From Jim Lesurf's site, Up is AFC off, Down is AFC engaged.
See FAQs here: http://www.audiomisc.co.uk/Armstrong/600/600faq2.html
Thanks Snowman. Although I've looked at that site many times I'd forgotten or overlooked that 'tuning questions' page. Having just had a good testing session with the receiver, I'd come to the same conclusion; afc is 'on' when the button is down. When down, the 'spread' of a tuned station is much greater when rocking the tuning knob, indicating that afc is allowing that off-channel discrepancy.

Notwithstanding that, clearly something is wrong as the position of stations is sufficiently different between when the afc is on or off that it is not usable unless you re-tune after having operated the afc button, rather defeating the object of it! Pressing afc causes it to lock on to an adjacent station, not the one currently tuned to when afc is off.

Is that an afc circuitry fault or an indication of poor FM alignment?
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Old 9th May 2021, 11:36 am   #92
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Default Re: Armstrong 600 series tuners and receivers

Having worked on this set for months and bought donor sets for parts etc, I am now - very nearly - ready to put the lid back on it. Of course as soon as I do that another fault will expose itself but that's another matter. Anyway, one niggling fault remains. The centre tune meter is off centre when optimum tuning is achieved. By optimum tuning I mean the chosen station is clear and free from the effects of stations either side of it. If I adjust the tuning so that the needle is centred, then I'm either very close to, or actually being affected by a nearby station.

Ay ideas how I can get the meter to centre for optimum tuning? As far as I can see there's no adjustment pot to tweak and the service manual just says "release AFC button and check tuning meter for centre tuning".
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Old 11th May 2021, 2:04 pm   #93
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Default Re: Armstrong 600 series tuners and receivers

It sounds from your symptoms like the FM discriminator alignment might be a bit off. I've never worked on a 600 tuner but looking at the circuit, both the AFC and tuning meter are derived from the discriminator output. This is a Foster Seeley and normally when a signal is correctly tuned in the centre of the IF passband, the DC output should be zero volts and the tuning meter will then be centred.

It looks like there are two adjustment cores in the final IF transformer but which one is the one you need to adjust (the secondary) I don't know - maybe someone else who has actually done this will! If you can inject an accurate 10.7 MHz into the IF amp it should just be a case of adjusting this core to centre the tuning meter, which will also normally coincide with maximum volume and minimum distortion. Then the AFC should work properly too.

I enjoyed reading down this thread; you are so very nearly there with repairing this unit! The missing track damage and burn mark on the chassis under the board is characteristic of lightning damage. I've seen this many times on transmitter site equipment when the mast has had a near miss.

Best wishes,
Alan
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