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Old 11th Jul 2020, 5:33 pm   #1
Vintage_RC
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Default Quad FM4 tuner blowing fuses

My friend's Quad FM4 tuner has started blowing fuses after about two hours use. I suspect it will be heading my way for investigation, is this a well known issue? and what should I be looking out for?

Thanks, Alan
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Old 11th Jul 2020, 5:46 pm   #2
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Default Re: Quad FM4 tuner blowing fuses

Have a look at the RIFA cap in the power supply and you may as well recap the power supply whilst in there
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Old 11th Jul 2020, 7:31 pm   #3
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Default Re: Quad FM4 tuner blowing fuses

Thanks, I haven't got the unit yet but as soon as it arrives I'll take a good look around the PSU.
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Old 11th Jul 2020, 7:31 pm   #4
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Default Re: Quad FM4 tuner blowing fuses

I had a mains transformer go on my FM4 - might be worth checking for signs of deterioration.
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Old 11th Jul 2020, 9:15 pm   #5
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Default Re: Quad FM4 tuner blowing fuses

My FM4 started blowing fuses a few years ago. I thought it was the mains transformer and fitted a new one but it turned out to be the RIFA. If it does turn out to be the transformer I have a spare.

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Old 11th Jul 2020, 11:51 pm   #6
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Default Re: Quad FM4 tuner blowing fuses

I'll check the RIFA first. When they have failed are they always cracked?
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Old 12th Jul 2020, 12:29 am   #7
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Default Re: Quad FM4 tuner blowing fuses

Yes, but you might not see the cracks at first on some. When they finally go they blow their guts all over the place and produce the most god-awful stink.

I've even had one inside the metal can of a Schaffner mains filter blow a hole through the can.

You don't even have to use them to get them to degrade, the crazing and cracks form without need of electricity, but they are ready and waiting for it.

I was fixing the boss' pet Tek 4265 and guess what it was. So I didn't want that brand again, so I carefully selected an alternative brand in stock at Farnell. Guess what turned up.... another golden olfactory chronometer.

David
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Old 12th Jul 2020, 12:38 am   #8
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Default Re: Quad FM4 tuner blowing fuses

I change the blasted things on sight now. I chanced it once or twice and regretted it as soon as I'd stopped coughing...
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Old 12th Jul 2020, 4:27 pm   #9
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Default Re: Quad FM4 tuner blowing fuses

I had several RIFAs split open just sitting in a drawer, they don’t need power. In German hifi circles they are known as “Knallfrosch” which translates to firecracker!
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Old 12th Jul 2020, 4:31 pm   #10
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Default Re: Quad FM4 tuner blowing fuses

Does anyone know what the C and R values were in the original RIFA device? is it critical? I have found 0.1uF plus 100ohm and 22nF plus 100ohm on eBay.
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Old 12th Jul 2020, 6:51 pm   #11
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Default Re: Quad FM4 tuner blowing fuses

avoid them like the plague a lot are NOS and will fail very soon try CPC/Farnell https://cpc.farnell.com/evox-rifa/pm...a%20capacitors
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Old 12th Jul 2020, 8:22 pm   #12
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Default Re: Quad FM4 tuner blowing fuses

Whatever else it may do, it shouldn't blow the internal fuse.
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Old 12th Jul 2020, 10:07 pm   #13
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Default Re: Quad FM4 tuner blowing fuses

Odd. No X-class capacitor at all in that diagram, Bill. Just two capacitors on a single low voltage secondary, and across a pair of zener diodes at that.

I always associate that generation of Quad stuff with big fat Rifas straight across the incoming mains... Am I thinking of the preamps?

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Old 12th Jul 2020, 10:25 pm   #14
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Default Re: Quad FM4 tuner blowing fuses

Looks to me that there is a suppressor cap just after the mains switch and marked N1
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Old 12th Jul 2020, 10:55 pm   #15
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Default Re: Quad FM4 tuner blowing fuses

Quote:
Originally Posted by AC/HL View Post
Whatever else it may do, it shouldn't blow the internal fuse.
I wonder if the schematic is incorrect, wouldn't be the first time.
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Old 12th Jul 2020, 11:37 pm   #16
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Default Re: Quad FM4 tuner blowing fuses

Could be, but 'N1' made me think it was a mains pilot neon with series resistor. But no, that doesn't make sense, it's upstream of the on/off switch. It must be the Rifa.

Either way, whatever it is, it's upstream of the fuse and would therefore have difficulty blowing it.

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Old 12th Jul 2020, 11:42 pm   #17
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Default Re: Quad FM4 tuner blowing fuses

When the tuner arrives here I will check how the switch/neon/RIFA are actually configured.
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Old 13th Jul 2020, 12:38 am   #18
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Default Re: Quad FM4 tuner blowing fuses

N1 is the suppressor, Quad part no. NPMR20A, our joint favourite bĂȘte noire.
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Old 13th Jul 2020, 8:20 am   #19
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Default Re: Quad FM4 tuner blowing fuses

Be aware that the diagram in post 12 shows the voltage selector in the 120 volt position.
The primary winding's are shown in parallel.
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Old 13th Jul 2020, 10:10 am   #20
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Default Re: Quad FM4 tuner blowing fuses

Hi!

I thought myself it the symbol for N1 was a pilot neon myself but not so it seems!

If you post a pic of the original I can confirm what to buy for replacement purposes!

Full S.M. if you need it:–

https://www.google.com/url?sa=t&sour...=1594631513860

. . . complete with circuits in authentic P.W. sloping lettering!

If you have the VFD version the power supply shown in the small extract applies, whilst the alternative with an additional secondary and VM18 rectifier applies to LED display tuners.

D.I.L. bridge rectifier units of he "VM" type are a bit unreliable so I recommend replacing them both as a start, followed by a check of the mains transformer primary current, which should be no more than 40–50 mA, see alignment/test pages in manual for a guide!

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Last edited by Chris55000; 13th Jul 2020 at 10:27 am.
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