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QUAD FM4 Power supply repair

MikeMA

MikeMA

pfm Member
My QUAD FM4 keeps blowing the internal fuse. I believe this is a fairly common problem and is usually down to failure of the RIFA capacitor in the power supply. I've checked it out and it's definitely bulging slightly and has leaked and smells like it's burnt out! I've sourced a replacement together with a new memory back-up battery which I'm going to replace at the same time. It looks like a simple enough job, but I'd be interested to know if anyone else here on pfm has done it, whether they had any problems, and if there is anything I need to watch out for.
 
No, it is ...just as very simple as you have assessed.

You can just remove the old Rifa snubber cap (the block internally is 47nF+100r in series; the paper-based capacitor part fails precipitously with age), and without, the FM4 will work - just fine!

It's not an essential part in any sense - just a nice-to-have. Other suitable parts are available!

(eta: I've something suitable in the bits box - drop me a pm with postal address, and it's yours FoC :) )
 
martin clark said:
No, it is ...just as very simple as you have assessed.

You can just remove the old Rifa snubber cap (the block internally is 47nF+100r in series; the paper-based capacitor part fails precipitously with age), and without, the FM4 will work - just fine!

It's not an essential part in any sense - just a nice-to-have. Other suitable parts are available!

(eta: I've something suitable in the bits box - drop me a pm with postal address, and it's yours FoC :) )
Click to expand...
Thanks Martin, that's interesting. I hadn't realised it wasn't essential - I'm no expert and just assumed that everything that's there needed to be there! - but it's cheap enough so I may as well finish what I started and replace it. And thanks for your kind offer - you have pm, or will in a moment !
 
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The Rifa capacitor is sacrificial to absorb mains spikes. While the FM4 will work without it, the mains transformer might fail in the long term
 
One thing I would check carefully is for any corrosion around the battery, and if found deal with it properly with white vinegar, isopropyl and finally conformal coating. It likely has leaked and speaking as a geek into old computers etc once PCB corrosion starts it needs to be stopped or it can keep eating into tracks some distance away from the original leak point. Don’t assume any mess on the board is benign or static, it is likely still an active chemical reaction. FM4s have a reputation for suffering this kind of corrosive battery damage though I’ve never worked on one myself.
 
Well, the replacement battery and snubber arrived today. I've swapped out the snubber and it's all working well.:)

I've not swapped out the battery because it seems to be fine. The original was replaced by QUAD about 10 years ago with one encapsulated in a little plastic wax filled tank, there's no sign of leakage, and it's holding a charge of about 1.5v - it may not be fully charged yet - and the presets are working. I can't imagine the encapsulated battery leaking, so I'm inclined to leave things as they are until such times as it fails.

I was going to take photographs as I did the job and post them here, but given the way this forum works it would have taken me longer to upload the photos and link to them than to do the actual job, so I gave up!

Thank you to everyone for the helpful advice and comments.
 
Well done then. :)
But after all this time the battery should be replaced. Otherwise presets will be lost quite quickly, in a matter of a few weeks if unused.
 
I buy my components from them. Cheap with low P&P to France (€5) where I live.
That snubber cap is an ubiquitous component and any outlet will stock it, in different guises.
 
Hi all, just getting started on this electronics game and looking to restore a few Quad pieces. I noticed the link to the Mouser site was for 0.47uF capacitors but the Quad FM4 RIFA is rated 0.047uF. There doesn't seem to be such a thing as a 0.047uF capacitor so I assume I'm misunderstanding something ?
 
Just serviced a few of these :)

Suppressor: Ebay item 133953985335
Backup battery: Ebay item 294614352451

You don't want to be in the same room when the RIFA suppressor fails - lots of stinking smoke. If you're lucky the fuse blows before that happens :)
 
Richard Lines said:
@mikehut - you need to change the parameters - I changed to a 0.047uF/ 275VAC with 15mm pitch and then selected 'In Stock' items.

Regards

Richard
Click to expand...

Thanks - I was thinking the link was supposed to be to the actual RIFA cap being discussed. I also looked up a list of cap values and the smallest seemed to be 0.1uF so 0.047uF confused me. I did try to reply to this before but cannot reply to posts with links in yet apparently so had to delete it from the quote.
 
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