Fender princeston 112 Plus Distorted clean channel

[blindboybenton]

Hi All

I posted a thread on here about a week ago about this amp . friend said the vol on clean channel was either on or off

Anyway i checked it out and it was and fitted a audio taper 50k which seem to of done the trick

I noticed when i was testing it that the clean channel was like the overdrive channel distorted
while testing it further the TIP142/147 blow. Ive replaced them and it back working again. but still distorted
Supply voltages are correct + 42v and - 42v

Using the signal gen and scope ive found the signal going output stage area is correct, ( C34 ) But at pin 3 it don't look right

http://elektrotanya.com/fender_princ.../download.html

at C34

at pin 3 of mc1436p1

at pin 6

at the output to dummy load

I may be wrong but it looks like the Mc1436p1 is faulty. Can anyone help

Bassman

[Enzo]

On the output to dummy load, is that baseline at zero volts or is it elevated DC? The output of the IC looks like half a sine wave, but the amp output looks more like just peaks.

If you had blown outputs, then check the 0.47 ohm ballast resistors for opens, check all eight diodes between the bases of the outputs.

You may have +/-40v. but to you have +/-25v at the IC itself?

[blindboybenton]

Thank you Enzo

Ive just checked and one of the 0.47R is high. I will change it in the morning. I'm learning slowly. Ill let you know the outcome

Bassman1965

[52 Bill]

And if you are not familiar with that type of amp from Fender, do not run the amp without having the output devices correctly heatsinked or they will overheat and short out.