Laney RB9 Bass Head

[Groove Harder]

Looking for a bit of advice for what is more than likely a really noob question...?

I am a bedroom player first and foremost and have always used combos and have never had the need to mess about with heads/cabs, etc. I picked up a Laney RB9 head for a song but when I plug the 1/4" speaker cable from my RB9 speaker out jack into a cab there is no sound whatsoever. When I connect the RB9 to a Marshall MB30 via the FX send/return I can control the sound coming through the MB30 speaker using the RB9 unit. 

I know that the cab works as I can connect it to another practice combo speaker output that I have lying around via the same speaker cable.

Would it be that both the speaker outputs jacks need replacing on the RB9 or maybe a fuse?

I hope this rambling makes sense to somebody because it doesn't to me 

Cheers,

GH

[Mottlefeeder]

You've checked the cable, you've checked the speaker cab, Working back upstream, the chances of both speaker jack sockes developing the same fault is fairly remote, so my starting point would be inside the amp casing. The internal mains wiring and terminals should be insulated, but if you are not competent to work out whether that is true in your case, don't go there.

a) There is a relay that does not connect the amplifier to the speakers until all the switch-on surges etc have been and gone. It may be inhibited by a fault, so listen for the click a second or so after you switch on. That will tell you if it is trying to connect, or not. If you do not hear a click, it could be due to (b) or (c) below.

b) One of the fuses connecting power to the amplifier circuit may have blown, so check for blown fuses in holders on the pcb. If you find one, there is an obvious question to ask - why did it blow?

c) You will find four or six transistors bolted to a heatsink that the fan is blowing air at/though. Check if the fan is working, and the fan grill and heatsink are clear of fluff/dead mice/etc. A clean heatsink and a working fan are good signs, but the fan may not operate until the temperature rises, so this is not a definite tick in the box. A well-designed amplifier should shut down undamaged if it overheats, but it is possible that yours doesn't, and a thermal fuse has blown.

I've had two amplifiers with faulty outputs, and both were due to faulty output relays, so I'm slightly biased.

David

[Groove Harder]

Hi David, thanks for the reply. The fan kicks in as soon as the amp is switched on so in all probability it probably is a blown fuse. I'll have a look inside the amp later on. If it's not that then I will more than likely just knock it on the head as it probably wouldn't be worth pursuing.