Laney LX65R Overdrive channel not working

[techno-rachit]

Hi,
I have a Laney LX65R and the overdrive channel of it is not working. I am getting a little bit of crunch with very less gain after switching on the overdrive channel.
I checked for dry solders or loose connections, there is no such problem. How can i fix this problem? Help would be appreciated coz i'm in need and i need this amp for a gig which is there in 2 weeks.

Thank u.

[Twist]

You may have an open pot. Sometimes if an amp falls over or something falls against a control it can cause a fracture inside the pot where the carbon trace is. The control may look fine but be an open circuit. There is no way to repair this problem other than replacement. In some cases the back of the pot can be pushed out allowing the pot to partially lose connection internally.

[techno-rachit]

thanks a lot.... what would you say about the clipping diodes? would they be fine?

[oc disorder]

Hi Techno-Rachit
re "what would you say about the clipping diodes? would they be fine?" um it doesn't
have any. It uses a CMOS Hex Inverter CD 4069 (U5) followed by the tone stack
then buffered by a TLO72 (U2 a+b)then on to the master volume.
Unless you have the tools and experience seeing you have a deadline to meet
I would suggest you take it to an experienced tech.
My guess would be the output buffer may be faulty .
This could be checked by looking on a scope at the outputs and inputs of the IC.
I would fit a IC socket so a replacement TLO72 can be easily fitted.
Likewise with the CD4069.
Another possibility for breakdown would be the fets they use for switching ,one at the input to the drive channel Q1 and the other at the output after the master volume Q2.
Q3 switches in the clean channel . All three are or should be 2N3819 and Q1 & Q2 are arranged to bypass the o/d channel when the clean channel is engaged.

Having said all that its possible its something simple like Twist suggested a broken pot
either in the tone stack or more likely in the dual ganged 100KA gain pot VR1.
I have found some of these dual ones don't track properly even new ones.
The pot is wired in between sections of the CD4069.
Its hard to diagnose at a distance without the unit .
Good Luck !

[techno-rachit]

Well thanks for making me realize that there are no clipping diodes!!
I really didn't notice that and asked the question coz i was tensed whether i will be able to fix the amp or not.
Thanks for the advice!
The amp's OD is working better!
I changed the Dual Op-amp IC(TL072).
And dnt worry. I'am a 9th grader and i am into soldering since i was in the 4th grade! So no problem about the soldering part.

Anyways Thanks a lot! You saved my gig!