Recommendation for an amp repair technician in or near London

[Colin151]

Posted this on another forum, but was wondering if someone here might have some different advice.I
I have a couple of NAD 208 solid state amps that are quite a complex design, and notoriously difficult to repair. They were NADs best ever power amp and quite a no compromise design compared to their usual stuff. They use 14 MOSEFTS per channel. I have spoken to a few people who didn't want to touch them and NAD themselves don't exist in the UK anymore.

Has any got any recommendations for a very skilled an knowledgeable repair person who might be able to take these on? Any suggestions would be greatly appreciated.

When working these are wonderful sounding amps for a very powerful solid state design. One alone is capable of 600 watts into 8 ohms on transients peaks, and up to 1 KW into 2 ohms. Way more if you use them in bridging mode! They have a cult status amongst audiophiles in Sweden apparently. The downside is that they can be unreliable. Hence why I have two dead ones on my hands!

Cheers,
Colin

[istari_knight]

Whats wrong with them ? I've had a look & they honestly don't look that complicated at all.

The most common problem with NAD gear is flakey component quality leading to early failure.

[Colin151]

Thanks for replying. They don't turn on! External and internal fuses seem OK.

Like I say I think better parts were apparently used in this amp than other NAD gear. They do have a reputation for being unreliable though. I read before that often people disable the extra rail to make them more reliable and to get better sound quality. The service manual is online but doesn't mean much to me!

Cheers,
Colin

Whats wrong with them ? I've had a look & they honestly don't look that complicated at all.

The most common problem with NAD gear is flakey component quality leading to early failure.

[istari_knight]

Okay, just to clarify: By "don't turn on" you mean there is no power present whatsoever, nothing lights up, no mechanical clicks are heard just stone dead ? Looking at the service manual shows there is one fuse on the transformer primary and five fuses on the transformer secondaries... You say that you've checked them all.

In most cases *no power* faults are some of the easiest to rectify so I'm surprised no one wanted to know... Basically it can be either: Fuses, short/open circuit transformer, open circuit thermal fuse inside transformer, short/open circuit rectifier diodes, short circuit power supply capacitors or a faulty power switch simple as that.

[Colin151]

Hi There. Many thanks for looking. Yes I mean stone dead, on both amps. I have visually looked at the fuses. There are 7 inside the amp, and 2 where the power lead plugs in. The latter 2 are definitely Ok and the others looked OK visually, but I will also check with a multimeter when I have a minute.

One of the amps was working Ok recently and suddenly stopped working the other day.
Thanks for the info on possible causes. The only thing I can really do myself is test the fuses. I do know a local guy (who will remain anonymous) that could repair them but he charges a lot. The sort of guy that would charge you £400 even if it was a very simple problem. Like a dodgy car repair guy! Hence why i was asking for recommendations for an honest repair person.


Cheers,
Colin

Okay, just to clarify: By "don't turn on" you mean there is no power present whatsoever, nothing lights up, no mechanical clicks are heard just stone dead ? Looking at the service manual shows there is one fuse on the transformer primary and five fuses on the transformer secondaries... You say that you've checked them all.

In most cases *no power* faults are some of the easiest to rectify so I'm surprised no one wanted to know... Basically it can be either: Fuses, short/open circuit transformer, open circuit thermal fuse inside transformer, short/open circuit rectifier diodes, short circuit power supply capacitors or a faulty power switch simple as that.

[istari_knight]

Fair enough, I'm not particularly keen on being ripped off either !

Definitely check those fuses for continuity, if they check out OK [which they probably will] I suspect a fault in the switch on delay circuit as you've two with the same problem. Most likely an aged electrolytic capacitor or open circuit resistor... I've seen it before on large Marantz amp's of similar age.

I've sent you a PM with more information.

[PaulStewart]

Hi Colin,

I have a technician who does all my stuff both solid state and valve, we are in west London North side of Chiswick.

Send me a PM if you want us to take a look

Cheers

[Colin151]

Thanks a lot have replied to your PM. Am going to check the fuses will report back later!


Fair enough, I'm not particularly keen on being ripped off either !

Definitely check those fuses for continuity, if they check out OK [which they probably will] I suspect a fault in the switch on delay circuit as you've two with the same problem. Most likely an aged electrolytic capacitor or open circuit resistor... I've seen it before on large Marantz amp's of similar age.

I've sent you a PM with more information.

[Colin151]

Many thanks, Will keep in mind, but am doing OK myself so far as two of the internal fuses have blown!

Cheers,
Colin
Hi Colin,

I have a technician who does all my stuff both solid state and valve, we are in west London North side of Chiswick.

Send me a PM if you want us to take a look

Cheers

[Colin151]

Ok in the amp which stopped working the other day, internal fuses F901 and F902 have blown. They look just fine, but no continuity on a multimeter! So I suppose the first thing to do is to replace these. They say T250mAL on them. I guess they must be fast blow?

Will check the other amp and report back.


Fair enough, I'm not particularly keen on being ripped off either !

Definitely check those fuses for continuity, if they check out OK [which they probably will] I suspect a fault in the switch on delay circuit as you've two with the same problem. Most likely an aged electrolytic capacitor or open circuit resistor... I've seen it before on large Marantz amp's of similar age.

I've sent you a PM with more information.

[JohnJo]

No they're not fast blow. T = time delay, F = fast blow. The L = low breaking capacity. Just replace with the same type and see if the fuses hold.

http://http://www.thefusewarehouse.com/pages/learn_fuse_markings.php (http://www.thefusewarehouse.com/pages/learn_fuse_markings.php)

[Colin151]

Cheers for the info! Sorry for the ignorance should have looked it up!

When this particular amp stopped working the other day it was driving a 2.75 ohm Magnepan ribbon tweeter I was running in pretty much directly (just a single 10 uF cap in between), which a friend of mine tells me is too low impedance for continuous operation. Lots of amps can't handle it. Should have used a 1.5 ohm resistor in series too to bring the impedance up to around 4 ohms. Hopefully no real damage is done and just those two fuses blew as a result.

I had a look at the other dead 208 amp I have and that has different problems. All the fuses measure ok, but it still does not switch on.

Cheers,
Colin

No they're not fast blow. T = time delay, F = fast blow. The L = low breaking capacity. Just replace with the same type and see if the fuses hold.

http://http://www.thefusewarehouse.com/pages/learn_fuse_markings.php (http://www.thefusewarehouse.com/pages/learn_fuse_markings.php)