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Speaker fuses popping and distorted channel

L

LukeHamm0

New Member
Hello,

so I've got a Rotel RA-400 and recently the left channel has started to sound distorted and it keeps popping speaker fuses. Just wondered if anyone else has had these issues and how you fixed them? from what I've seen online recapping the amp might be the way to go but before I try and figure out how to do that I wanted to see if there was a simpler fix.

If you need more information just let me know and thanks for any help! :)
 
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Have you tried swapping the speakers? Right to left and left to right, to make sure it's not a speaker?

What does it do with the speakers disconnected?

Does that amp use an output power pack? Are the emitter resistors outside the pack?

Rob
 
LukeHamm0 said:
from what I've seen online recapping the amp might be the way to go but before I try and figure out how to do that I wanted to see if there was a simpler fix.
Click to expand...
Welcome to A.k.
Simpler fix? No. the unit is circa 1972. And don't play it anymore as blowing speaker fuses is serious.
I assume you have little or no experience stating how to figure out how to do a recap? You'll also need to clean the pots and perform general inspection for aged solder joints and visual inspection.

manual and service manual here:
https://www.hifiengine.com/manual_library/rotel/ra-400.shtml
 
Robisme said:
Have you tried swapping the speakers? Right to left and left to right, to make sure it's not a speaker?

What does it do with the speakers disconnected?

Does that amp use an output power pack? Are the emitter resistors outside the pack?

Rob
Click to expand...

Hi,

Yes, I've tried swapping the speakers and i even used another amp on the speakers and they work fine.

I cant really see a difference in the amp with the speakers disconnected.

and no the amp just plugs straight into the wall I'm pretty sure the amp is from the 70s/80s

Cheers
 
Binkman said:
Welcome to A.k.
Simpler fix? No. the unit is circa 1972. And don't play it anymore as blowing speaker fuses is serious.
I assume you have little or no experience stating how to figure out how to do a recap? You'll also need to clean the pots and perform general inspection for aged solder joints and visual inspection.

manual and service manual here:
https://www.hifiengine.com/manual_library/rotel/ra-400.shtml
Click to expand...
I'm not totally new to soldering I more meant figuring out what capacitors to get really.

Thanks for the service manual though!
 
LukeHamm0 said:
more meant figuring out what capacitors to get really.
Click to expand...
I looked at the SM. and there is no parts list for caps so you'll have to go with what is in the unit. if there are any low voltage rated caps e.g. 6-10v up the voltage but keep the uf rating.
 
LukeHamm0 said:
Hi,

I cant really see a difference in the amp with the speakers disconnected.

and no the amp just plugs straight into the wall I'm pretty sure the amp is from the 70s/80s

Cheers
Click to expand...

Did you try it with the speakers disconnected? Does the fuse still blow?

The power pack I mentioned is the output section of the amp. Some use transistors and some use power packs.

Rob
 
Robisme said:
Did you try it with the speakers disconnected? Does the fuse still blow?

The power pack I mentioned is the output section of the amp. Some use transistors and some use power packs.

Rob
Click to expand...

Hi, Sorry for the late reply Christmas and all that.

but I tried the amp without speakers plugged in and so far no fuses have popped.

I'm not 100% on when the fuses pop sometimes it's when music is playing and sometimes it's when I turn the unit on could it be that my speakers are drawing too much power?

something else I noticed that was probably causing the distortion is the fuse for the left channel hadn't completely broke and it had only blacked the wire inside the fuse.
 
LukeHamm0 said:
Hi, Sorry for the late reply Christmas and all that.

but I tried the amp without speakers plugged in and so far no fuses have popped.

I'm not 100% on when the fuses pop sometimes it's when music is playing and sometimes it's when I turn the unit on could it be that my speakers are drawing too much power?

something else I noticed that was probably causing the distortion is the fuse for the left channel hadn't completely broke and it had only blacked the wire inside the fuse.
Click to expand...

so i just tested the amp again and even with a new fuse the left channel is still distorted so it wasn't the fuse causing the distortion
 
LukeHamm0 said:
Hi, Sorry for the late reply Christmas and all that.

but I tried the amp without speakers plugged in and so far no fuses have popped.

I'm not 100% on when the fuses pop sometimes it's when music is playing and sometimes it's when I turn the unit on could it be that my speakers are drawing too much power?

something else I noticed that was probably causing the distortion is the fuse for the left channel hadn't completely broke and it had only blacked the wire inside the fuse.
Click to expand...

I also checked if the speakers are suitable for the amp as well and they should be fine they recommend an amp that supplies 20 to 74 Watts and the amp supplies 22 Watts per channel. The impedance is also fine, the speakers have 6Ω and the amp has 4-16Ω with the way I'm using it.
 
Recapping an amp is not a cure-all. You need to do board level diagnosis or take it to someone who can do that. Hence, the service manual...
 
Check the DC voltage at the speaker terminals with the speakers disconnected. Should be zero volts.
The right channel can also be used as a reference when checking voltages on the bad left channel.
Most likely a fried output transistor and / or related circuitry. There is no crystal ball with electronics !
 
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