FM4 Mains Capacitors

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30-Apr-2019 03:50 PM

BJ

BJ

Posts: 2

Hello guys,

I just finished my experiment upgrading my old Quad 34 using the DADA kit. All went well and it was fun to do. To my ears the 34 plays more punchy and open now. 

Meanwhile my FM4 was undergoing an expensive professional revision. I just got it back and opened the cover to look inside what was done.  

What I noticed is that the capacitors in the mains are replaced by much bigger ones that hardly fit in. This not only looks unauthentically. Their capacity is more than twice the capacity mentioned in the FM4 Service Manual.

C4 and C5 are 1000u. 

However the new fat replacement caps both are 2200u.

Apart from that C1 according to the manual is 47n which corresponds with my other FM4 having the PMR 209 100r 47n X2 with integrated resistor at C1.

In the revision it is replaced by a physical much bigger 100n 47r X2 thus capacity and resistance are interchanged.

My question is if these new caps can do any harm.

Google hits some posts about the use of superfluos capacity, but only within the tolerance of 20%. Nothing like 2,2 times higher.

Thanks in advance.

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01-May-2019 03:01 AM

EJP

EJP

Posts: 1617

None of this will do any harm, but changing the 1000uF capacitors to 2200uF is pointless. The one that feeds the audio is behind a 7812 voltage regulator, and the other one only feeds the display. The doubled/halved values in N1 don't really matter, just sloppy procurement.
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01-May-2019 08:21 PM

BJ

BJ

Posts: 2

Thanks EJP. 

That's a comfort. Today the company which did the revision pressed that Quad would have preferred capacitors with higher capacities but at that time those were too large to fit in the FM4 casing. And it makes a difference because the fat ones last longer.

It suggests Quad designed the casing before they designed the circuit. I tend to stick to your explanation. It makes more sense to me.




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02-May-2019 04:12 AM

EJP

EJP

Posts: 1617

Unconvincing. By that logic, they should also have replaced all the 470uF, 220uF, and 2.2uF capacitors with 2200uF. A physically larger capacitor is better than a smaller oneof the same capacitance value, but the increase in capacitanceneeds to be justified separately. Claims like 'Quad would have preferred' are unverifiable and contrary to Quad's practice in units like the 44 and 66 where there is plenty of room and they still used 1000uF. The FM4 PSU cage is plenty big enough for any imaginable practical value. And the need for a 2200uF capacitor upstream of a 7812 regulator with 470uF across its output remains undemonstrated.
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