Hi, I plugged in the mains lead into the back of my OC250 while the lead was still plugged into the wall socket and live. The fuse next to the socket on the amp blew. I got a suitable replacement but no luck, the new fuse has not blown but the amp has remained off.
I know the fuse in the mains plug has not blown because it’s a Hydra lead and the other 4 boxes connected to the same plug still power up
Are there any other fuses in the case that I need to replace as well, or do I need take it to a dealer? Thanks
Best wishes Amer
Thoughts:
1- did you use the replacement fuse that was in the back of the 250? – as there should be a spare one in the unit? Reason I ask is that these fuses can be incredibly difficult to see if they’ve blown and are ‘good’. Plus you’ll need the correct type for the 250.
2- are you 100% sure you have the fuse in the correct holder – as there are 2, one for the ‘live’ fuse and one for the replacement (furthest away I think).
3- you may want to leave the kit for a few hours and then try again, as it could just be you’ve activated a protection circuit inside the 250 - unlikely.
Other than that, it sounds like a dealer call, and see what they suggest.
Simply hooking up a live lead shouldn’t do damage from what I know - i.e. it not far different from when the power lead isn’t all the way in and it’s powered-up, which can blow the fuse. This is all assuming you didn’t somehow cross the pins when inserting the cable, which is exceedingly difficult with an IEC.
Of course, the golden rule is always ensure the front button is ‘off’ when playing with the power supply.
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My money’s on this. 
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I’m holding my breath waiting for the happy ending too 
Thanks HappyListener, no I didn’t know there were two fuses, I’ll check that out. The fuse I replaced was blown, so thought that was the only one to consider. I’ll investigate further and report back. Best wishes Amer
To be 100% clear, the fuse holder which you pull out (adjacent to the IEC input) should house 2 fuses (unless the replacement has already been used). Only one of these is ‘live’, the one furthest away as you pull the plastic out, is the (spare) replacement (as I understand things).
These fuses are also directional (but not essential it seems?) – but good luck with that, as my ageing eyesight couldn’t detect the markings when I had similar issues!
There is a spare fuse in the holder back of all naim power amps.
My Dealer told me Naim in fact select from a specific supplier fuses that although they show the same nominal rating as other possible replacements in fact have higher surge-rating capacity and ‘sound’ better - and the Dealer has a stock of these. When mine occasionally blow every few years I get these for free as part of Dealer after-sales service.
In any case try to get the Naim-approved version ahead eventually.
Once mine did blow and I replaced then the amp (NAP500DR) did sound a lot better with the new fuse so think it had been slowly hanging-on with the old fuse about to blow for a while. I’m now aware of the process of fuse degradation but it will be linked to how many times the amp is turned-on.
I hope you get it all sorted to satisfaction! 
DB.
The Naim recommended fuses come from the Littel company. It’s important to buy slow blow fuses, as specified next to the fuse holder. A normal fuse will blow immediately on switch on, even though there is nothing amiss with the amplifier.
Huh???
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Indeed. There is a lot of such belief in Naim-world.
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Apols – let me re-phrase. There are recommended orientations of the case fuses, as per the link attached:
Equipment Fuses - Frequently Asked Questions - Naim Audio - Community
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Hi thanks for all your helpful comments. Unfortunately it seems I will have to return the 250 to the dealer as the replacement fuse has not worked.
I bought the 250 ages ago as an ex-dem unit and enjoyed it for years. I had it fully serviced by Naim when it was upgraded to the DR spec. It came back sounding so much better in every aspect of it’s sound, but it seems the service did not result in it being provided with a spare fuse as well. I can see the space for the fuse, but it’s not there.
Probably a good time to have another full service from Naim. Maybe they will also be able to solve the problem of the tempramental on/off button - it worked for a few months after the last service, then just wouldn’t switch off - I tried the strategy suggested by Richard Dane in another forum thread to ‘ping’ the switch to latch again, but to no avail. As leaving the amp on 24/7 is not the end of the world I hadn’t bothered to have that repaired.
Thanks again for al your comments.
Best wishes Amer
Let us hope your Dealer can fix it for you. Fingers crossed, its something simple… 
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