Carvin x100b head amp...

[plec.22]

Has anyone came across is odd fault...

when you use a an effect's unit and plug in to the effect's loop on the rear of this amp it doe's not want to turn the effect off via it's own foot pedal? it channel selects ok changes the reverb ok but does not cut the effect unit off.mmm this unit as xlr foot pedal connection 1 chan switch 2, effect(1) effect(2).. there's white red,green, black and screen cable's... I've checked the switch's there ok...

the only way to cut this is use the baypass on the effect's unit to cut in or out...the on line guide say's you plug your effect unit from the sent out to your unit then back via the the return and using it's own 3 way foot pedal will turn the effect on/off but it's not doing so...

thanks for any help..

[plec.22]

I've even looked at the diagram from carvinservice.com and it show's how the effect's loop works....

[Jazz P Bass]

Carvin X100 Schematic

Verify that the FET Q9 is functioning.
IC A6 controls it.
If that is switching properly check Q10, Q12 & IC A3 B.
Here is the schematic.

[plec.22]

cheers for the diagram I will be checking around that part of the circuit soon and see what's going on..

Thanks again..

[plec.22]

After rechecking and replacing the switching ic op amps and fet's it's still the same..when using the foot pedal and plunging an effects unit into the sent and return as the service guide state's, it still will not 'switch' out the effect's... even after rechecking the foot pedal...it switch's between channels reverb on off but still refuses to switch out the effect!!

any comments...

[plec.22]

Xlr pin connections are white wire pin 1 red wire pin 3 and green wire pin 2 and black ground... unless there's a mod to get it to switch the effect's on and off?

all foot pedal's switch's and led indications are connecting on and off within the foot...

[52 Bill]

Did you replace A6? Check for voltage on each of the three xlr pins coming from the amp. It looks like there should be +15 vdc on each one. Switch each of the 3 footswitches. What happens to the voltage?

Now check the voltages on the pin 4 of A6. Pin 4 is the control pin for the FX loop. How much voltage is there? Now switch the footswitch. What happens to the voltage at pin 4?

[plec.22]

I've replaced ic 6 and things are still the same even the switching fet's plus the 2n550 transistor in the line up and things are still the same!!

[plec.22]

will recheck voltages...thanks for the info bill...

[Jazz P Bass]

IC A6 pin 5 is the footswitch input.
What is happening at Pin 5 & Pin 4 voltage wise when you depress the footswitch?