XPS2 blown fuses becoming a pain

blythe posted:

I just returned from 10 days holiday and having powered down everything, I turned on my equipment, one by one, slowly, to allow the capacitors to "fill".
As always seems to be the case when turning on after a prolonged power-down, the mains fuse inside the XPS2 popped.
So, I dragged my rack out, removed the XPS2 to gain access to the fuse cover, only to find that the fuse glass had popped too.
This of course meant the end caps of the fuse were still inside the machine.
In trying to remove the end caps of the blown fuse, one cap dropped inside the XPS casing, so, armed with Hex head (Allen) spanners, I had to remove the case to find the fuse end cap...
I then inserted the replacement fuse, placed the XPS2 back in the rack, turned it on and guess what? It blew the fuse AGAIN!
It was however a case of 3rd time lucky. This time, the fuse held!
The XPS has always done this during my ownership (over 10 years) and has recently been serviced by Darran at Class-A.
Firstly, I'm getting a little tired of changing the fuse virtually EVERY time I switch on the XPS2 and secondly, surely the fuse shouldn't be rated so closely that the fuse should blow so easily?
Do any other XPS2 owners have the same problem?

I have an XPS that is now 7 years old and for the first 5 years of ownership no fuse would survive more than 4 or 5 power ups. Then a couple of years ago I started to keep a log of how long each fuse actually lasted. In August 2015 I fitted a new fuse following a fuse failure on power up, this particular fuse survived 25 power ups before failing on the 26th. I asked the question if there had been any change in the supply or manufacture of these fuses. Richard Dane advised that I must have acquired a 'lucky fuse' that was running on the high end of the manufacturing spec and as such was tolerating my power up current better than most. The fuse I replaced my 'lucky fuse' with has so far achieved 6 power ups. I hope in posting this I haven't jinxed this fuse. 

If you search the archives you will find for some this has been a common problem with XPS's and has been talked to death on many previous occasions with no defining statement as to why other than this is stated as the best design for sonic reproduction. To me this is still an unacceptable answer and as I have said many times before if this was a persistent fuse failure on a Mercedes or a Bentley car an engineering resolution to the problem would have been found.

Ken

Another reason for upgrading to a 555 or 555DR.

So now you can justify the expense!

Huge posted:

Another reason for upgrading to a 555 or 555DR.

So now you can justify the expense!

Huge,

I have thought about that more than one or twice in the past but sadly now I am retired I cannot justify the cost 

Ken

 Thanks for your comments and input. Sadly a 555 is not on my shopping list !

 I remember speaking to Naim about it some time ago but like you say, if it were a persistent issue in a car or something, it would have been rectified by now...

The XPS2 is a bugger for eating fuses. Mine would go through them quite happily, such that I always had a bag of spares to hand. Pushing the switches slowly was not recommended to me. I was advised to push fast and firmly. I've had one 500PS fuse go. 

SWS, are you using the exact same fuses specified by Naim? It may be worth a word with Steve Hopkins to see whether he can send you some. 

FWIW my own XPS2s only blew a fuse once and that was down to me not having the mains lead connected all the way in to the IEC socket. Worth checking there's no arcing going on in there...

The size of fuses used in XPS & other psu units was questioned with Phil Harris 2 years ago,  it was not followed up on.

https://forums.naimaudio.com/to...44#46478588386706144

@mike-b - I think it might be fairer to say that [@mention:1566878603985147] did not respond further, to that direct question, about fuse ratings vs PSU types. I suspect he might be between a Rock and a Hard Place on this issue. An earlier repons pretty much confirms this - (quote) - ''The fuse spec is as large as we are allowed to *LEGALLY* provide / use and that is laid down by the safety testing houses ...'

Evidence (?) on this Forum suggests that the XPS2 has a higher reported  failure rate for its fuse, in apparently 'non-fault' conditions - compared to other Naim boxes. I might suggest that the 'Classic' 250 is a more distant 2nd place, in this respect.

My own 2nd hand XPS2 seems one of the 'better ones and blows fuses occasionally - much as my Classic 250 used to (but has not done for ages now).

Spare Fuses seems to be the way to go......  

Mike-B posted:

The size of fuses used in XPS & other psu units was questioned with Phil Harris 2 years ago,  it was not followed up on.

https://forums.naimaudio.com/to...44#46478588386706144

 

Hi Mike,

The fuse ratings are determined by the inrush currents and the physical construction of the transformers as to what constitutes a maximum permissable safe current through them however ultimately it was a bit of a vague question which - looking back at the thread now - seemed to be pretty much covered by the next reply.

The VA rating of the transformer itself does not determine the fuse rating.

Cheers

Phil

[@mention:1566878604014594],  might well be so with the Naim ‘test houses’.   However I used to be involved in type approvals & compliance to TUV BSI & US stnds for my old company & the fuse ratings we ended up with did contain a certain logic wrt surge power draw.   

@mike-b - I will defer technically to @Phil Harris on this. He knows his Onions. And he gets paid to know....

I suspect both inrush and steady state current matters - but one or other will 'size' the fuse. The nature of Naim PSU's seems to be that they exhibit high inrush current. Fuses are also in finite ratings - design might (ideally) suggest a 2.73A fuse, or some such odd value - but the engineer needs to pick a size. Better 'safer', with a risk of some failures, I guess....    

Ian, it goes a bit further than that - the fuse rating has to be selected such that it passes safety testing. As you say, one size may be safe but right on the edge of tolerance, while moving up to the next size up, the unit is no longer safe. Part of this test involves the equipment being powered up and then having the transformer sawn in half. If the fuse doesn't blow immediately then watching the resultant transformer fire (scary) will soon reinforce the importance of the right fuse rating.

Richard Dane posted:

Ian, it goes a bit further than that - the fuse rating has to be selected such that it passes safety testing. As you say, one size may be safe but right on the edge of tolerance, while moving up to the next size up, the unit is no longer safe. Part of this test involves the equipment being powered up and then having the transformer sawn in half. If the fuse doesn't blow immediately then watching the resultant transformer fire (scary) will soon reinforce the importance of the right fuse rating.

I can't imagine how you would go about conducting a test like that - did you have to draw straws, or did you volunteer with your chainsaw?!

I still have the same fuse in mine for 18 months. Never had a blown fuse. Powered down a few times but my kit is powered up permanently. Probably jinxed it now. 

ChrisSU posted:

Richard Dane posted:

Ian, it goes a bit further than that - the fuse rating has to be selected such that it passes safety testing. As you say, one size may be safe but right on the edge of tolerance, while moving up to the next size up, the unit is no longer safe. Part of this test involves the equipment being powered up and then having the transformer sawn in half. If the fuse doesn't blow immediately then watching the resultant transformer fire (scary) will soon reinforce the importance of the right fuse rating.

I can't imagine how you would go about conducting a test like that - did you have to draw straws, or did you volunteer with your chainsaw?!

It's not done at the factory. I was told about this when I spied some transformers in R&D that had been sawn in two. I'm told it's one of the tests that can be carried out at the specialist testing centres. 

I’ve been using Naim since 1983 all my boxes have been exceptionally quite and I’ve only ever changed one fuse that was this year, generally carry out a power cycle 3 or 4 times a year must be a lucky boy.

I loaned an XPS2 once and it blew an internal fuse on power up. I had to resort to the spare one on the back panel. Otherwise it would have meant an eighty mile round trip to my dealers.

Richard Dane posted:

ChrisSU posted:

Richard Dane posted:

Ian, it goes a bit further than that - the fuse rating has to be selected such that it passes safety testing. As you say, one size may be safe but right on the edge of tolerance, while moving up to the next size up, the unit is no longer safe. Part of this test involves the equipment being powered up and then having the transformer sawn in half. If the fuse doesn't blow immediately then watching the resultant transformer fire (scary) will soon reinforce the importance of the right fuse rating.

I can't imagine how you would go about conducting a test like that - did you have to draw straws, or did you volunteer with your chainsaw?!

It's not done at the factory. I was told about this when I spied some transformers in R&D that had been sawn in two. I'm told it's one of the tests that can be carried out at the specialist testing centres. 

Phew! That does seem like a rather extreme way to test a bit of HiFi equipment, I'd have thought maybe spilling a cup of coffee over it would be more like it. Clearly, I have led a sheltered life!

Richard Dane posted:

SWS, are you using the exact same fuses specified by Naim? It may be worth a word with Steve Hopkins to see whether he can send you some. 

Yes, the fuses are those supplied by my Naim dealer and have also received fuses via Steve in the past, made no difference.

FWIW my own XPS2s only blew a fuse once and that was down to me not having the mains lead connected all the way in to the IEC socket. Worth checking there's no arcing going on in there...

The power supply is via a Powerline firmly plugged into a 10mm dedicated spur and i always check the line is pressed home at the IEC end.

Harry posted:

The XPS2 is a bugger for eating fuses. Mine would go through them quite happily, such that I always had a bag of spares to hand. Pushing the switches slowly was not recommended to me. I was advised to push fast and firmly. I've had one 500PS fuse go. 

Nothing to do with pushing the switch in my opinion. A brand new fuse never blows on it's first power up, that cannot be coincidence.

Southweststokie posted:

Harry posted:

The XPS2 is a bugger for eating fuses. Mine would go through them quite happily, such that I always had a bag of spares to hand. Pushing the switches slowly was not recommended to me. I was advised to push fast and firmly. I've had one 500PS fuse go. 

Nothing to do with pushing the switch in my opinion. A brand new fuse never blows on it's first power up, that cannot be coincidence.

"A brand new fuse never blows on it's first power up"?
Mine did !

Richard Dane posted:

SWS, are you using the exact same fuses specified by Naim? It may be worth a word with Steve Hopkins to see whether he can send you some. 

FWIW my own XPS2s only blew a fuse once and that was down to me not having the mains lead connected all the way in to the IEC socket. Worth checking there's no arcing going on in there...

As the originator of the thread, perhaps you were asking me about the exact same fuses specified by Naim?
When I bought my last box of fuses (yes, I buy them buy the box full) I spoke to Naim who advised the correct rating and then, I bought them on-line.
It's possible of course that my source of purchase was subject to on-line vagaries and begs the question, was I actually buying the correctly rated ones...?
Richard, are you able to post the correct rating for the 240v XPS2 unit here?
By ordering a batch from a reputable supplier such as RS Components, that'd help me rule out "dodgy under specced fuses".
Thanks, Martin.

I perhaps should add, I always leave my Naim kit powered on, unless going on holiday or working away for a week or more.
With reference to an earlier post above, my 3 x "Classic" 250's have never blown fuses on power-up.

blythe posted:

Richard Dane posted:

SWS, are you using the exact same fuses specified by Naim? It may be worth a word with Steve Hopkins to see whether he can send you some. 

FWIW my own XPS2s only blew a fuse once and that was down to me not having the mains lead connected all the way in to the IEC socket. Worth checking there's no arcing going on in there...

As the originator of the thread, perhaps you were asking me about the exact same fuses specified by Naim?
When I bought my last box of fuses (yes, I buy them buy the box full) I spoke to Naim who advised the correct rating and then, I bought them on-line.
It's possible of course that my source of purchase was subject to on-line vagaries and begs the question, was I actually buying the correctly rated ones...?
Richard, are you able to post the correct rating for the 240v XPS2 unit here?
By ordering a batch from a reputable supplier such as RS Components, that'd help me rule out "dodgy under specced fuses".
Thanks, Martin.

Blythe, best get Naim's recommendation on this.  I'm a bit reluctant to post here, mainly because it's an international forum and specs are different depending on where you are and the local voltage supply, and I would hate to be wrong.  With that in mind, from memory, the UK supplied 230V XPS2 uses a 2.5A T fuse from The Littel Fuse Company, but I would recommend double checking with Naim on this.  I don't know whether Naim test their batches or not, but may be worth finding out.

Hi,

If your XPS is continually popping fuses then I'd get your dealer involved and get them to check it out - it could be that it has developed a fault and actually is correctly blowing fuses.

Best

Phil