Fender Frontman 212R Distortion

[g1]

Could you clarify, are the distortion issue and the hiss/pop always present together or 2 separate issues?
If they are always occurring together, it does sound like an oscillation issue.

[themusic]

No the sporadic hiss and pop are always there clean or distorted.
Now I'm back to distortion. My TP28 is 2.64vac . Another factor I noticed is if my hand grabs the chasis " I know not safe " while testing then
some test values go down. Example TP28 goes from the 2.64vac to 6.4mvac

[themusic]

No the sporadic hiss and pop are always there clean or distorted.
Now I'm back to distortion. My TP28 is 2.64vac . Another factor I noticed is if my hand grabs the chasis " I know not safe " while testing then
some test values go down. Example TP28 goes from the 2.64vac to 6.4mvac

Turn off waited 10min back on good . Correction on TP28 9.5mVac to 6.6mVac when touched... 5min back to distortion same numbers on TP28

[J M Fahey]

Sorry but still unclear.

You answer:

My bad U^ pin 8 -16.62vdc.

Is that a "-"(minus) sign?

If it's just the grammatical "separator" "-" sign, please don't use it just before a voltage number.

-16.62vdc

means minus/negative 16.62vdc

while plain
16.62vdc
or
+16.62vdc (which is preferred) means: plus/positive 16.62vdc

So, what do you measure on IC pin 8?
And on pin4 ?

Thanks.

[themusic]

Sorry about the confusion. U6 Pin 8 is plus16.45 vdc . Pin 4 is Neg17.8 vdc no input , speaker connected.
Amp ran normal for about 30min . Went to distortion for 5min then back to clean. Finally just distortion. Every 30sec or so
there will be a pop amp will go clean and then right back to distortion. Thanks for your patience.

[Jazz P Bass]

So the amp is switching channels?

[themusic]

No , distortion is on clean channel. Channel switching works fine...thanks

[g1]

Can you plug straight in to the power amp in for your tests. Are both faults still intermittent (distortion and hiss/pop)?
Is the hiss/pop a different pop than the 30 second pop that clears the distortion?

[themusic]

Yes, when plug into the power amp section still intermittent distortion,hiss,pop. Same hiss, pop that clears the distortion.
Today, ran for almost 3hrs normal. then started in on the hiss pop that finally ended up in straight distortion.
There doesn't seem to be any consistent failure. I've poked and prodded when amp is normal or when in distortion and
it doesn't seem to make a difference. Tomorrow I could turn it on and it would be in distortion or clean...?

[Jazz P Bass]

So we, once again, have verified that it is a power amp issue.

Seeing that there are about 200 parts in that circuit, finding the problem without a scope is going to be tough.

Although a mutimeter set to read Volts/ac 'may' get you there.
You may find a gross signal difference when the 'distortion' happens.
That may or may not lead you to the offending circuit.

Me, I would flip the board over & check the factory solder job.
If it looks bad, I would resolder the whole board.
But that's just me. (I love to solder)

[themusic]

Yes I have to agree. Like finding a needle in a haystack. It's just so darn frustrating when the darn thing won't hard fail or I can't make it fail with any poking or
prodding. I can't figure what component in the power section would just randomly just work or fail ?
Today it's been running great for about 6hrs. ? I'll pull the board like you suggest and check again for the 3rd. time.
I'll also try to get my hands on a scope...thanks for everybody's help ...Merry Christmas

[g1]

If you can also get a hold of some freeze spray it may be helpful.

[themusic]

I've heard of that. Would I spray the individual components in the power section when the amp is failing ? ...thanks

[g1]

It can be useful especially for the semi-conductors. It works both ways, when the fault won't show up, sometimes the freeze spray will make it go into fault mode. Or when the fault is occurring, freezing parts may make the fault stop.

[themusic]

Thanks I'll give it a shot....Thanks again Happy Holidays