Recent content by MojoAmpGuy

Update. Contacted Phil Jones support in USA. Came back saying that this is not a common fault with this amp type. Generously provided me with a schematic. Well done PJ! Traced the fan circuit, which is temperature controlled. Fan is Not on, until temp rises. Connected Fan to external bench...

As an amp tech UK based, I’ve been passed a M300 that has reported to have completely lost sound on gigs, on three occasions. Both channels silent when it occurs. Recycling the power brings back sound. Suspect it is being triggered into protect? Any ideas? Is this a known fault? Amp is...

I’ve just repaired one. Same issue. LED used to light up, now DIM or not visible (effects still present). Fact. This pedal was originally expecting a ACA supply = 12v DC unregulated supply. Most people are unaware and plug 9v Power supply. This WILL work, but there is a diode and resistor in...

As I previously said. I’ve checked the mute circuit. Transistor Q33 is the transistor that needs to be switched ON, to MUTE. 0v on CSD is shutdown condition. CSD needs to float to <5v to enable oscillation. Not as you thought. I believe the pull up voltage is internal to the irs209257s device...

It’s a surface mount 10uF cap. It measures 10uF with my Cap tester. Can’t get an ESR reading wit my test equipment. I may just change it

I have done. Mute circuit is design to pull this signal to 0v. But this circuit is NOT doing that.

I have repaired this new version to the point where it powers up fine, fault light out, but now audio output. This is due to IRS20957s not starting up oscillation. Voltages appear good, except for CSD which sits at 3.2v. It needs to be above 5v to operate. Mute circuit checks out fine. any...

I own a GP12 300W combo that I use at a weekly jam session. Stopped working yesterday. I’m an amp tech also. Looked that the amp this morning and I’m little stuck. As you raise the o/p volume the output (connected to a dummy load) shows a 160 KHz oscillation. With or without input signal. This...