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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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13th Jul 2020, 10:23 am | #21 |
Hexode
Join Date: Jun 2018
Location: Buckinghamshire, UK.
Posts: 387
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Re: Quad FM4 tuner blowing fuses
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20th Jul 2020, 10:31 am | #22 |
Heptode
Join Date: Sep 2018
Location: Twickenham, London, UK.
Posts: 539
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Re: Quad FM4 tuner blowing fuses
Time for an update. I now have my friend's FM4 with me. Externally it looks very clean and tidy and on removing the cover the internals also look in good order with no signs of tampering. First thing to note, whatever the circuit shows, the RIFA device is definitely after the fuse so if it fails to a low impedance it will blow the fuse. This is a late model (made 1992) with the fuse holder integrated with the mains socket so perhaps the earlier variant with the separate fuse holder was different.
There was a faint smell of burnt electronics in the PSU area so I removed the RIFA. On inspection it has not split open but it is slightly swollen and the encapsulation shows signs of crazing. It does appear to be the source of the burnt smell. I have ordered a replacement device and will power the unit up and soak test once it is fitted. The electrolytics look OK so I will leave them at this stage. Inspecting the battery shows it is the later style fitted in a plastic holder, there is a slight white deposit at the negative end but no leakage. It is still holding a charge (measured 5V on meter) but I might replace it. Does anyone know what holds it in the plastic holder? surely not just the leads. I will report back after I have fitted the replacement RIFA and soak tested.
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Alan G6PUB, BVWS |
20th Jul 2020, 12:08 pm | #23 |
Dekatron
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,675
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Re: Quad FM4 tuner blowing fuses
Lucky you caught it before the firework stage!
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22nd Jul 2020, 9:35 pm | #24 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,603
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Re: Quad FM4 tuner blowing fuses
Found a reference to the Quad N1 NPMR20A suppressor being a RIFA 0.047uF 100ohmx2 PMR209MB 40/085/56 (same as Post 21), which I think is metalized paper.
Ensure replacement is an X2 rated Polypropylene snubber of sufficient AC voltage. David |
23rd Jul 2020, 7:03 pm | #25 |
Heptode
Join Date: Sep 2018
Location: Twickenham, London, UK.
Posts: 539
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Re: Quad FM4 tuner blowing fuses
I have sourced and fitted A RIFA PMR209 and the unit has been running all day without blowing the fuse. The transformer is mildly warm but you can easily keep you finger on it so I think that the RIFA was the only problem.
One more question, I am considering replacing the battery before returning the FM4 to my friend. This is a later unit with the battery in a plastic box (see photo at the beginning of the thread). Does anyone know what holds the battery in the box?
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Alan G6PUB, BVWS |
23rd Jul 2020, 8:44 pm | #26 |
Dekatron
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,675
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Re: Quad FM4 tuner blowing fuses
Mine was potted with some sort of inert goo. The box is just there to stop the battery's innards from spilling onto the board. As the original processor is now obsolete, Quad, bless 'em, make a kit to replace it with a more modern device which doesn't need a back-up battery at all.
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23rd Jul 2020, 9:20 pm | #27 | |
Heptode
Join Date: Sep 2018
Location: Twickenham, London, UK.
Posts: 539
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Re: Quad FM4 tuner blowing fuses
Quote:
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Alan G6PUB, BVWS |
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25th Jul 2020, 7:59 pm | #28 |
Heptode
Join Date: Sep 2018
Location: Twickenham, London, UK.
Posts: 539
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Re: Quad FM4 tuner blowing fuses
The FM4 is back together and ready to return to my friend. As already mentioned the fuse blowing was the RIFA device (no surprise there), while I had the unit and it was on the bench I decided to go ahead and change the battery. A few notes may be of interest, this is a later model with the battery housed in a plastic tub. A suitable battery is a Varta Mempac 4.8V 150mAh NiMh. It is held in the tub by a low melting point wax so heating with a hairdryer will soften the wax adequately for removal. The wax can be softened again with the hairdryer for insertion of the new battery. To carry out the battery change the plastic tub is best removed, it is held in place by a self tapping screw.
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Alan G6PUB, BVWS |