Slow blow or fast blow fuse?

[kaborex]

I have a mackie srm450 V2 speaker that suddenly stopped powering up (cut out at a gig). I found an internal fuse blown. Its rated 3.15A.

I am not sure if its slow blow or fast blow. Tried a fast blow and blew up straight away. There does not appear to be any damage to any of the components on the board. I will try and attach a schematic.

.

Any help is much appreciated.

Regards

JIm

 

[kaborex]

On the schematic it is written 3.15A SB. Does that mean slow blow???

 

[Arouse1973]

Hello

Yes I would have thought SB meant slow blow. If you still have the original fuse it may have some markings on it that tell you what type it is, that's if it is the original and someone hasn't replaced it with the wrong type. Some slow blow fuses will have a T at the end of the rating, to indicate time delayed fuse.

All that said, there must be a reason the fuse blew. This could be a fatigued fuse or faulty piece of equipment. The fact a fast blow fuse blew straight away could be an indication that there might be a fault. Just be carful!

Adam

 

[kaborex]

Hi Adam. Thanks for the reply. I tested with a brand new fuse from an already damaged speaker with the woofer and tweeter disconnected and it blew straight away again. Therefore the issue is definitely with the board. I read somewhere that to replace the board (effectively the amp) cost nearly as much as a new speaker. My workplace has 8 of those mackie srm450 and already two have had issues. They do not build them like they used to anymore.

Regards

Jim

 

[Arouse1973]

That's true Jim. You could take the unit apart and post some pics of both sides of the PCB here, and let us have a look. We might see something.
Thanks
Adam

 

[Martaine2005]

Hi Kaborex. If I may interject here?
I have four of these speakers with the same problem as you. Kept blowing the SLOW BLOW fuses instantly.
I had a neighbour take a look at one and he said it was the inverter side causing the fuses to blow. He is NO electronics genious, just way better than me!!!
Any way, he narrowed it down to a blue capacitor/filter next to the fuse that had shorted and gone high (Suppresion filter) maybe?
Or transient suppressor/filter, cannot remember. It was nearly midnight and after a few beers he pulled it from the board and the speaker worked perfectly. Only problem is when somebody puts the kettle on or turns lights on and off I get a click through the speaker. I have ordered the new parts and am going to try all four speakers.
Got to be worth a try £0.99 for ten!!
But do as Adam says and post a pic of the board so the experts here can take a proper look for you.

 

[Customj79]

I have a mackie srm450 V2 speaker that suddenly stopped powering up (cut out at a gig). I found an internal fuse blown. Its rated 3.15A.

I am not sure if its slow blow or fast blow. Tried a fast blow and blew up straight away. There does not appear to be any damage to any of the components on the board. I will try and attach a schematic.

.

Any help is much appreciated.

Regards

JIm

Look for the big black capacitors are any of them bulged if they are then replace them. look under them there might be a bad trace or gold looking strip burnt if it is take a wire and solder it to the 2 pieces that are not connected

 

[Harald Kapp]

@Customj79 : do you realize that you answered to an old thread from 2015? Unlikely that you'll receive a response as the op has never again been seen here since then.