Roadking fx loop problem

[AMiGO]

My first post here. I hope you can understand my english=)

Yesterday i've bought Used Mesa Roadking V.1, my first mesa and the service warranty isn't valid any more. The amp sound totally
awsome but when i turn on the Fx Loop main switch (not the ones on the channel strips, loop1, loop2) The sound
gets very weak. Although i increase the value on the master and output wheel.

The bass frequency is reduced by 30-40% and the amount of gain is slightly less and the treble has increased a little.

Nothing is connected in the loops. ive tried straight guitar cables but the same problem.

I've tried all different settings on the fx loop wheels. The mix wheel doesn't do much but send level increases/decreases
the volume.

The sound with the loop on/off is like day and night.

Do you have any idea what could be wrong?

I have also called the swedish dealer service person. He said after a short look on the schematics that it could be the
V4 preamp tube, cause the other components probably wouldn't have the bass reducing effect.

Could it be a bad soldering?

Thanks for any help you might give me=)

/ Kim Wiklund

 

[disassembled]

I would swap the tube in V4 for V3 or V2 and see if that makes a difference.



Greg

 

[AMiGO]

Im gonna try that when i come home=)

/Kim

 

[123thefirst]

Tjena AMiGO! and welcome to the forum.

I'd guess that the problem is that the RK expects you to have effects wired into the loop whenever either the FX Loop 1 or FX Loop 2 switch in the channel settings is turned on. Otherwise there isn't a connection between the send and return.

Yes I agree, the RK is an awesome machine.

 

[AMiGO]

Tjena Tjena=)

The thing is that none of the loops i activated in the channelstrip or by the pedalboard.

only the "Main" switch that activates the whole loop/output/solo circuit is activated.

/kim

 

[123thefirst]

Okay, then it sounds most likely to be a marginal preamp tube or two as disassembled suggested. It could be that the previous owner put some really old tubes there and kept the newer ones for himself.

It could be that something is bad on or around the circuit board too. I have a strange problem where the slave out produces no sound. The amp is nearly new but it's not worth bringing the unit in to have that fixed IMO.

Someone else in the forum had a very similar problem to yours recently:
http://forum.grailtone.com/viewtopic.php?t=17506&highlight=loop

 

[AMiGO]

I've tried some more now. The difference seems to be smaller now. Maybe my ears where tired yesterday.

I changed the v4 tube but that didn't do anything.

How much difference should it be between loop cricuit on/off?

where can i find some schematics of the circuits? like service manual?

/kim