Adding external fuses to a amp

[newlash09]

So I was listening to music late night at low volume, and went to the balcony for a smoke.

And when I returned back, I found the stabilizer's fuse blown, the next in line spike gaurd blown and finally the devialet amp switched off. I really don't know what happened.

So I dismantled the devialet and pulled out its power board. There are two surface mounted fuses on the board that have blown as checked by my multimeter.

Don't want to send it to devialet , as they will replace the entire power board and charge me a bomb. And iam unable to find these slow blow ceramic fuses of 6.3A 250V in my place.

So I was wondering if it is advisable to remove the fuses and solder a straight wire on the power board. And then install two normal replaceable fuses of the same rating on the power cable.

Is this safe

Maybe there is more damage to the devialet than just the power fuses, but I will only know how deep the damage is, after getting these fuses sorted to check if the devialet atleast powersup.

 

[insider9]

If you have a blown fuse it may be because a fault developed. I'd advise caution.

 

[Gray]

If you have a blown fuse it may be because a fault developed. I'd advise caution.

Wise words Insider. With any luck (and from his description) it will be an external surge rather than any internal fault that's caused the blown fuses.

 

[Gray]

Hello Newlash

You say you can obtain replacement fuses of identical rating, something like these:

http://cpc.farnell.com/siba/70-007-65-6-3a/fuse-20x5-ceramic-slow-blow-6/dp/FF02850?st=slow%20blow%20fuse%20%206.3A%20250V

If so, it would be a good idea to temporarily connect them accross the blown fuses by (carefully) using crocodile leads while you power up the amp.

If all is OK, make the replacements permanent on the PCB by adapting a couple of these:

http://cpc.farnell.com/bulgin/fx0321/fuse-holder-20x5mm/dp/FF02908

with insulating covers:

http://cpc.farnell.com/bulgin/12760/cover-insulation-pcb-fuse-holder/dp/FF02909?MER=sy-me-pd-mi-acce

I would keep the fusing internal if I were you.

 

[insider9]

Can you get any similarly rated fuses? Even if they're not slow blow. Just to test out? I'd try a 5A fast blow i guess these should be more common and see if it works. Your amp should not blow a 5A fuse under any conditions anyway.

The idea to solder a straight wire with fused power cable is a recipe for a disaster. I know that's what dad's do, but I wouldn't do it myself.

 

[Gray]

Can you get any similarly rated fuses? Even if they're not slow blow. Just to test out? I'd try a 5A fast blow i guess these should be more common and see if it works. Your amp should not blow a 5A fuse under any conditions anyway.

The idea to solder a straight wire with fused power cable is a recipe for a disaster. I know that's what dad's do, but I wouldn't do it myself.

No harm in trying a 5A F type - to see whether it blew. But if it did blow, you couldn't be sure that it wasn't just the amp's normal power-up surge that took out the F type.

 

[insider9]

But with Class D power stage I really wouldn't know how it could ever draw over a kilowatt. I'm sure there is a reason why they went with 6.3A slow blow, but it could just be that someone placed a wrong order

 

[lindsayt]

Double check that 6.3 a slow blow are the correct type for your model of amplifier and replace with the exactly correct fuse type.

Try powering your amplifier on again - possibly connected to 8 ohm resistors and not your speakers and see if the fuses blow again.

If they do, investigate.

Does make you wonder if the previous owner was aware of an intermittent fault and that was the reason for them selling it?

 

[Vladimir]

Post photos of the power board, including both sides.

You can use a free photo hosting service like https://imgbb.com/ and post us the links or pics.

 

[Vladimir]

Does make you wonder if the previous owner was aware of an intermittent fault and that was the reason for them selling it?

The most common problem with s/h amps. Repaired to work just enough to get it to sell, then never answer the phone to the buyer few weeks later.

The fact that the amplifier fuses blew together with the voltage stabilizer means there was excessive current draw in the amp, not prior. The biggest indicator of short circuit is large current draw.

Amp shouldn't be powered on without a lightbulb in series to limit the current draw. Absolutely NO speakers attached when doing this. If the amp powers on and the bulb doesn't shine bright from excessive current draw, then measure DC offset on the speaker terminals. If its above half a volt it may cook the tweeters. Anything above 50mV DC means there's something wrong with the amp and it should be sent for repairs.

 

[Andrewjvt]

To hear this
We did warn you of the terrible reliability of devialet.
Hope you can do a pirate repair and not reward the manufacturer with more money.
Good luck

 

[insider9]

Let's hope it's not what Vlad says. I've tried and failed to fix a Magnum Class A amp recently. My mate bought it from ebay. It worked for a minute or two and failed with a flash. Killing one of the drivers in the process. I suggested he contacts Colin Wonfor who designed it but he wasn't sure if he should put any money towards it.

When I opened it up it was exactly like Vlad says. Inside it looked like someone tried to fix it and did a poor job. It was so bad that my soldering skills were actually far superior to whomever did it. There were a couple of blown fuses and two rectifiers loose inside the case. How bad do you have to solder that rectifiers come off? Power board looked fried from before and other mods were noticeable.

I worked without a schematic so soldered replacements and replaced fuses. All to no avail. Got a lovely flash of light on every power up. Now it may actually be going back to the designer. If it's salvageable it could be a great amp.

 

[Vladimir]

Best not to mess with it and just take it to a professional electronics repair service that knows how to fix laptops, tablets, phones and basically anything with small format component level repairs (because there is likely to have SMD fixes involved).

 

[insider9]

He got a full refund and seller didn't bother having it back. So not really risky. Colin Wonfor who's design it is, is happy to look at it. It was a long shot I'd be able to do anything other than fault find. I can only guess where the issue is and not exactly what it is.

But agree on the whole. Best to leave it to someone who knows what they're doing. You could do more damage if you're not careful. Considering how much you've paid it's not worth the risk.

 

[Vladimir]

Let's hope it's not what Vlad says. I've tried and failed to fix a Magnum Class A amp recently.

The problem with Class A is you need tight tolerance matched components, otherwise the amp may go into oscilation and thermal runaway even if the components and soldering are perfect. The original manufacturer bought buckets full of transistors, resistors etc. and matched them closely before installing, which is highly unlikely whoever messed with that amp bothered doing.

Such amps also may have some hard to find components or scratched off codes so the 'receipe' remains a secret. Close replacements will not do as well. Imagine what fakes would do.

Buying a used class A amp off ebay is simply asking for trouble.

 

[Vladimir]

Most of the time only feasable repair is lowering the biasing untill the replaced components stop failing. It may no longer be a class A amp, but at least it wont end in the bin.

I wouldn't call it risk free. What if it blew an expensive driver or unobtanium vintage driver?

 

[insider9]

True! It did blow a driver on a pair of near impossible to get QLN speakers. Luckily driver used is easy to get to. It's a little too complicated for me at the minute. Maybe if it was my amp I'd put more effort in *secret*

 

[Blacksabbath25]

Sorry to hear this bad news i hate it when things go wrong its not nice but it happen's to all of us at some point but better to have it fixed at a dealer network then doing it your self as there must of been a reason to blow amp fuses in the first place .

I hope you get it sorted out soon or a refund *smile*

 

[CnoEvil]

Colin Wonfor who's design it is, is happy to look at it. It was a long shot I'd be able to do anything other than fault find.

On a side issue (which you probably know), Colin Wonfor was (as I understand it), instrumental in designing Telurium Q - but after some internal acrimony, which I don't fully understand, ended up being pushed out of the Company. He was not happy about it.

http://www.hifianswers.com/2018/06/colin-wonfor-sets-the-record-straight/

 

[newlash09]

There have been lots of meaningful and well suggested advises so far. And that got me thinking further. I was only considering the fuse blow as a simple occurence, and really did not give it the serious thought you all have mentioned.

Maybe it would be of help to know, that during that evening, i had the devialet placed flush and standing on the wall. I was fluffing with the placement of the umik-1 for some room measurements. And did not notice the devialet sliding down the wall. And the music was not playing now as i had paused it on the CCA, though the amp was still on and running. And then the amp fell on the ground with a thud.

1. Even after the fall, the amp was still powered on and did not shut down.

2. I immediately resumed playback to test, and there was clear lovely music coming out of the speakers. I kept playing for like 10 seconds, and then decided to take a smoke break. And by the time i came back after 5 mins, the deed had happend.

3. I immediately opened the amp, and kept sniffing for any burnt smell. However, there was none. I also looked at all the internals carefully, but couldnt find anything amiss.

4. When i started hunting the power board, found the two fuses marked F1 & F2 in the below pics, not showing any continuity with my multi-meter. And since the amp was still running after the fall, I presumed that the fuses could have been blown by a power surge.

Please find attached pics of the amp internals :

https://ibb.co/kbbq8z
https://ibb.co/gktFae
https://ibb.co/cd3WFe
https://ibb.co/kGoL8z
https://ibb.co/n5b7oz
https://ibb.co/iEtWFe
https://ibb.co/kvyL8z
https://ibb.co/h6zSoz
https://ibb.co/gDk08z
https://ibb.co/mz1wgK
https://ibb.co/nm508z
https://ibb.co/dQKhMK
https://ibb.co/nfzGgK
https://ibb.co/dSwwgK
https://ibb.co/b16wgK
https://ibb.co/iUP5ae
https://ibb.co/kZdnoz
https://ibb.co/haCDTz
https://ibb.co/jxBkae

As suggested, Iam trying to find someone to check what's wrong. The last shop is due for a check up tomorrow. Everyone I;ve been to so far, has been too petrified to even touch it with a barge pole

Thanks in advance for any suggestions, regarding anything else i can check from my side, to ascertain if it is a simple fuse blow in a surge or there is component damage down the line.

And i have been playing this amp for almost 3 hrs everyday for the last one month, witout issues. So i dont think the seller sold me a lemon. And when i opened it, everything looked in pristine condition, as it still does in those pics

 

[insider9]

 

Please find attached pics of the amp internals : 

https://ibb.co/kbbq8zhttps://ibb.co/gktFaehttps://ibb.co/cd3WFehttps://ibb.co/kGoL8zhttps://ibb.co/n5b7ozhttps://ibb.co/iEtWFehttps://ibb.co/kvyL8zhttps://ibb.co/h6zSozhttps://ibb.co/gDk08zhttps://ibb.co/mz1wgKhttps://ibb.co/nm508zhttps://ibb.co/dQKhMKhttps://ibb.co/nfzGgKhttps://ibb.co/dSwwgKhttps://ibb.co/b16wgKhttps://ibb.co/iUP5aehttps://ibb.co/kZdnozhttps://ibb.co/haCDTzhttps://ibb.co/jxBkae

 

 

[newlash09]

For the clickey

 

[lindsayt]

...As suggested, Iam trying to find someone to check what's wrong. The last shop is due for a check up tomorrow. Everyone I've been to so far, has been too petrified to even touch it with a barge pole ...

That's the trouble with an amplifier that's more like a computer motherboard than a traditional amp.

The lack of smell is a good sign. But there's plenty of components that may have failed without burning. Fingers crossed for you that it's a cheap repair, or even as simple as replacing the fuses and carrying on...

 

[insider9]

Looking at this

Not sure it's not be tampered with. I hope I'm wrong.

 

[newlash09]

Looking at this 

Not sure it's not be tampered with. I hope I'm wrong.

I checked that link. And that is the component with the two surface mounted fuses that has failed to the best of my knowledge so far.

My electrical knowledge is limited to multimeter skills learnt from YouTube vids. So can you please elaborate if you think there is anything else wrong on the power board. Thanks.