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Old 2nd October 2012, 01:04 PM   #21
jaycee is offline jaycee  United Kingdom
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Good to hear you have the unit working!

The important part is that the capacitor should have an X2 rated dielectric for use on the mains line. From what I can tell, the WIMA FKP2 series is not rated as such. I would replace it with the right part simply to ensure safety. The voltage rating itself would otherwise be fine.
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Old 3rd October 2012, 06:09 PM   #22
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by Tristo View Post
A big thank you to everyone who helped with my issue.

On Sunday I replaced C405 with a new one purchased from Maplin (N38CN / 89p)and unit fired up perfectly. The original cap look fine and had no obvious signs of damage, but when tested, was only reading 6.6nF and not the stated 22nF.

The new capacitor is rated for 1250V, a lot higher than the 630V specified.
Do you guys recommend that I change it again for one of the correct rating, like the one linked to by Jaycee in an earlier post?
I will have to get this capacitor mail order, which Is why I went for the Maplin one originally.
Good to know you fixed it.

I can't really discover from the schematics or the BOM if this cap really needs to be X2-rated, nor is there the usual exclamation mark inside a triangle printed near C405 (when deviation from original is not allowed for safety reasons).
Look at C410 in the schematics and BOM, there's no doubt about that one...

If the original was X2-rated, then yes, otherwise keep the one you have in now.
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Old 3rd October 2012, 06:47 PM   #23
jaycee is offline jaycee  United Kingdom
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Quote:
Originally Posted by jitter View Post
Good to know you fixed it.

I can't really discover from the schematics or the BOM if this cap really needs to be X2-rated, nor is there the usual exclamation mark inside a triangle printed near C405 (when deviation from original is not allowed for safety reasons).
Look at C410 in the schematics and BOM, there's no doubt about that one...

If the original was X2-rated, then yes, otherwise keep the one you have in now.
It should be X2 rated because this is required as a safety feature for capacitors used in this fashion, to couple line voltage. X2 rating guarantees that the capacitor will fail open. You can imagine how nasty it would be in this circuit if the capacitor were to fail short.
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Old 3rd October 2012, 06:58 PM   #24
jitter is offline jitter  Netherlands
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When we're talking safety, I'd agree. But if failure of C405 would only lead to the destruction of some resistors, semiconductors and a fuse without any further risk to human life, I doubt that X2 is required. Yes, the circuit would have become a mess, but what would that matter to health and safety people? Of course, personally I'd try to avoid the mess and apply an X2-rated cap, but my argument is theoretical.

I would not expect Yahama to disregard rules and regulations, so if X2 were required, then the one pulled from the amp should be just that and would I strongly recommend to use nothing else.

Last edited by jitter; 3rd October 2012 at 07:05 PM.
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Old 4th October 2012, 11:57 AM   #25
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Im not really sure if the original was X2 rated or not.
I have attached a couple of pics for reference.
Attached Images
File Type: jpg Cap.jpg (305.5 KB, 55 views)
File Type: jpg Cap 2.jpg (798.9 KB, 52 views)
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Old 4th October 2012, 04:54 PM   #26
jitter is offline jitter  Netherlands
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Your's doesn't seem to be, so wether or not you'd like to go for that extra bit of safety is up to you.

X- and Y-rated caps should be clearly marked as such and will probably carry approval body's stamps (such as UL, VDE, etc.).
Below are images of safety caps, and it's clearly visible that the blue ones are Y1-rated and the gray one is X2-rated.
Attached Images
File Type: gif Image2.gif (5.1 KB, 51 views)
File Type: gif Image4.gif (60.9 KB, 46 views)

Last edited by jitter; 4th October 2012 at 04:58 PM.
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Old 4th October 2012, 04:58 PM   #27
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Whatever the choice taken by the manufacturer and the rules require as a minimum, I would use the X2 rated part regardless when mains is about, if it fits the board without difficulty or lead stress. That way, you cover all bases.
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Old 4th October 2012, 05:02 PM   #28
jitter is offline jitter  Netherlands
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If you're going for a safety capacitor for C405, do it also for C409 as this one also connects directly to mains. I see no point in changing C405 to X-rated and leave C409 as is.
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Old 7th November 2012, 06:42 PM   #29
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Hi sorry for the late reply, but just want to say thankyou to everyone who took the time to reply...............and in my case it was the same cap out of range.
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Old 7th November 2012, 07:36 PM   #30
jaycee is offline jaycee  United Kingdom
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As a follow up on this for anyone who reads the thread after...

The reason for this complicated jiggery, is that it is what Yamaha calls a "green standby supply". The flipflop based circuit acts a bit like a light dimmer, only allowing some AC into the transformer, just enough to keep the capacitor C411 topped up. It is a bit odd because normally a triac is used in such a situation, and Yamaha have used a MOSFET.

The flaw is that C405 should have been an X2 rated part. These have a self healing dielectric that will survive spikes on the mains (as well as being safer, failing open). Apparently the Yamaha designers never tested the design properly with 220-250V and the higher peak voltage, coupled with normal line spikes, ruins the standard metallized film capacitor they used.
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