34: Replacing N1 suppressor/snubber (PCB iss. 6)

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27-Oct-2019 02:49 PM

Fabian

Fabian

Posts: 102

Telling from the pictures I have seen, issue 7 of the Quad 34 PCB has only one major change over issue 6: The RC suppressor N1 (0,47µF+100Ohm) has been moved into a more accessible position. And now I know why. :P

The case of N1 cracked on the unit I am currently revising (didn't check my other Quad 34 yet). The crack is towards the power switch S10, so I didn't notice this first, although I thought I had inspected the board thoroughly. 

Unfortunately, this part is hidden under all the live and neutral wires to the power in and power out sockets. The massive copper wires have all been fed through the eyes of the contact lugs on the switch and the sockets, so unsoldering them looks like a tedious job. 

I think, removing N1 should not be a big problem. Fitting the replacement looks like a bit of an advanced tetris challenge, but I still think it is doable.

Has anybody done this and can confirm this a working approach? I just don't want to waste (even more) time on something that is pointless from the start. :)





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27-Oct-2019 05:10 PM

Marcel

Marcel

Posts: 21


Hi Fabian, I have done replacements of N1 suppressors in two Quads 34 and one in a FM4. It is indeed a tedious operation but worthwhile to do. I have removed all wires to the power in and power out sockets. Carefull not to burn/melt the wire insulation. I used a supressor with a higher voltage rating see:  https://nl.farnell.com/kemet/p409ce104m275ah470/cap-0-1-f-20-paper-radial/dp/2474610?st=p409

Good luck!

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27-Oct-2019 10:43 PM

Fabian

Fabian

Posts: 102

Hi Marcel,

Thank you for your first-hand experience. Your link points to a part with a lead spacing or 20,3 mm which would not fit without extra work. But I found another Kemet metalized paper X2 cap matching the exact values from a stock Quad 34:

https://nl.farnell.com/kemet/p409qm473m275ah101/cap-0-047-f-20-paper-radial/dp/2474607

Did you actually use the bigger part or smaller one from my link?

I had already ordered a RIFA PMR209:

https://www.farnell.com/datasheets/1244264.pdf

This one is “only” specified at 250VAC. That little extra margin of the Kemet P409 would have been really nice, but I think (or rather hope) that it’s not worth ordering another part just because of this.

I will still try to the broken part out without unsoldering the mains wires, but if I cannot get the new cap in, I know what to do.

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28-Oct-2019 01:44 AM

EJP

EJP

Posts: 1669

I've done this many times. You'll probably find it much easier to remove the entire switch with all connections intact and just lift it out of the way.

EJP

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28-Oct-2019 04:50 AM

Fabian

Fabian

Posts: 102

That sounds smart. 

Thank you, once again, EJP.

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28-Oct-2019 07:32 PM

Marcel

Marcel

Posts: 21

Hi Fabian, you are right with about the spacing of the leads. You have to adapt (bend) them in order to make it fit onto the board. The surpressor I used had been recommended by Joost Plugge. To me this was good replacement for the orginal suppressor. I understood the higher voltage rating (275 VAC) is important. I think 250 VAC will do as well.  

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30-Oct-2019 01:45 PM

Fabian

Fabian

Posts: 102

Job done. At least on the work-in-progress 34, I still didn’t check my second unit. This is the cracked suppressor.

https://abload.de/browseGallery.php?gal=sbcXGPbA&img=rifapmr209crackedo0k31.jpg

As required by specs, it failed gracefully and did not spread any debris when it failed.

This is the new one. Looks like I managed to pick the exact same part (RIFA PMR 209), so there is definitely no extra margin (even though 250VAC should do).

https://abload.de/browseGallery.php?gal=sbcXGPbA&img=rifapmr209oldnewfrontkakiv.jpg

I got a little tired of removing the front plate over and over again so I still tried to just bend the power leads carefully as much as possible and puzzled the new part into place. It did work out.

https://abload.de/browseGallery.php?gal=sbcXGPbA&img=newsuppressorn1mountedzj1r.jpg

A big thanks to EJP (as always) and to Marcel. 

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