Quad FM4 tuner blowing fuses - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Trigon. · 13th Jul 2020, 10:23 am

Quote:

Originally Posted by Vintage_RC

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.

The one I just removed from a 33 is marked 0.047uF+100ohm, RC Unit PMR209M.

Cheers

Vintage_RC · 20th Jul 2020, 10:31 am

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.

Ted Kendall · 20th Jul 2020, 12:08 pm

Lucky you caught it before the firework stage!

DMcMahon · 22nd Jul 2020, 9:35 pm

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

Vintage_RC · 23rd Jul 2020, 7:03 pm

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?

Ted Kendall · 23rd Jul 2020, 8:44 pm

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.

Vintage_RC · 23rd Jul 2020, 9:20 pm

Quote:

Originally Posted by Ted Kendall

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.

How did you get the battery out of the goo?

Vintage_RC · 25th Jul 2020, 7:59 pm

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.

20th Jul 2020, 10:31 am	#22
Vintage_RC Heptode Join Date: Sep 2018 Location: Twickenham, London, UK. Posts: 538	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. Attached Thumbnails __________________ Alan G6PUB, BVWS

20th Jul 2020, 12:08 pm	#23
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: Quad FM4 tuner blowing fuses Lucky you caught it before the firework stage!

22nd Jul 2020, 9:35 pm	#24
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,600	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
Vintage_RC Heptode Join Date: Sep 2018 Location: Twickenham, London, UK. Posts: 538	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? __________________ Alan G6PUB, BVWS

23rd Jul 2020, 8:44 pm	#26
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	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.

25th Jul 2020, 7:59 pm	#28
Vintage_RC Heptode Join Date: Sep 2018 Location: Twickenham, London, UK. Posts: 538	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. __________________ Alan G6PUB, BVWS