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.
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.
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.
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.
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.
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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.
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.
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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.
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.
Different Model Same Fix
Although this thread is a bit old I just wanted to say that it helped me fix my Yamaha HTR-5840. Symptoms were the same - it seems like the power supply is common across many Yamaha models. Replaced C405 (0.022uF in my case) and it came back to life. Like others befor me the schematics gave me a headache so I really appreciate the help provided here.
Although this thread is a bit old I just wanted to say that it helped me fix my Yamaha HTR-5840. Symptoms were the same - it seems like the power supply is common across many Yamaha models. Replaced C405 (0.022uF in my case) and it came back to life. Like others befor me the schematics gave me a headache so I really appreciate the help provided here.
Same problem with my 12-year old DSP-AX750SE amp, intermittent start-up for a few days, then wouldn't start up at all. Same solution - replaced C405 (which is nice and easy to get to, no need to remove the PCB 
) with X2 part recommended by jaycee, and it now works fine. Many thanks to everyone who contributed to this topic, especially jaycee and percival007. Thanks also to CPC, who currently have a summer promotion of no minimum order to get free postage - must have cost them more to send the replacement capacitor than I paid for it!
UK readers should note that the UK version is the 'B' model in the service manual, not the 'G' model, which is the European version (not that it makes any difference for this fix!).
Unfortunately, the link to the service manual provided by jitter no longer works, but it can be found at Yamaha DSP-AX750SE Manuals
) with X2 part recommended by jaycee, and it now works fine. Many thanks to everyone who contributed to this topic, especially jaycee and percival007. Thanks also to CPC, who currently have a summer promotion of no minimum order to get free postage - must have cost them more to send the replacement capacitor than I paid for it!UK readers should note that the UK version is the 'B' model in the service manual, not the 'G' model, which is the European version (not that it makes any difference for this fix!).
Unfortunately, the link to the service manual provided by jitter no longer works, but it can be found at Yamaha DSP-AX750SE Manuals
DSP-AX750SE Switching On/Off Randomly
Folks,
I have the same Amplifier, Yamaha DSP-AX750SE.
Although it switches on fine it began powering itself off & on continually
after a random period of time !!
You can hear what appears to be a replay click off & on.
It may be after 1min,1hour,10hours .
I brought it to an AV repair guy who returned it not finding any fault but i suspect it simply behaved over the time he had it switched on and he didn't spend too much time fault finding. Unfortunately it started the same behaviour that very evening.
In desperation I located the service manual for this model online and
performed a factory reset which hasnt helped.
Has anyone any insight as to what could be going wrong here as id love to get it back in reliable action !
Thanks
Folks,
I have the same Amplifier, Yamaha DSP-AX750SE.
Although it switches on fine it began powering itself off & on continually
after a random period of time !!
You can hear what appears to be a replay click off & on.
It may be after 1min,1hour,10hours .
I brought it to an AV repair guy who returned it not finding any fault but i suspect it simply behaved over the time he had it switched on and he didn't spend too much time fault finding. Unfortunately it started the same behaviour that very evening.
In desperation I located the service manual for this model online and
performed a factory reset which hasnt helped.
Has anyone any insight as to what could be going wrong here as id love to get it back in reliable action !
Thanks
Hi folks,
Just wanted to say a massive Thank You to everyone who's put this post together - I've got exactly the same Yamaha DSP-AX750se amp and had exactly the same problem. Working perfectly since purchase in 2004 and then suddenly wouldnt power up at all. Really good amp and would be a shame to see it gone.
Tested with multimeter and found 13A plug and sub-trans PCB fuses both OK, no voltage seen leaving the sub-trans PCB via the click-on terminal output to the main transformer.
I'm reasonably good at electronics with an HND somewhere in the dim and distant past, but it was really great to get the advice above on the most likely cuplrit - C405. When I tested the existing C405 cap removed from the PCB it was open circuit, showing no charging using standard multimeter to test it so seemed like this would indeed be likely to be the fault.
Bought the replacement for a whopping 77p using the link from Jaycee above , 10 mins with the soldering iron and the amp is fixed - result! Hopefully it'll run for another 20 years..
Thanks ever so much people, its really appreciated.
Cheers
David
Just wanted to say a massive Thank You to everyone who's put this post together - I've got exactly the same Yamaha DSP-AX750se amp and had exactly the same problem. Working perfectly since purchase in 2004 and then suddenly wouldnt power up at all. Really good amp and would be a shame to see it gone.
Tested with multimeter and found 13A plug and sub-trans PCB fuses both OK, no voltage seen leaving the sub-trans PCB via the click-on terminal output to the main transformer.
I'm reasonably good at electronics with an HND somewhere in the dim and distant past, but it was really great to get the advice above on the most likely cuplrit - C405. When I tested the existing C405 cap removed from the PCB it was open circuit, showing no charging using standard multimeter to test it so seemed like this would indeed be likely to be the fault.
Bought the replacement for a whopping 77p using the link from Jaycee above , 10 mins with the soldering iron and the amp is fixed - result! Hopefully it'll run for another 20 years..
Thanks ever so much people, its really appreciated.
Cheers
David