Fender Pro Tube Series Twin Amp Problem

[shortfuse]

Hey guys been away for a few months.  Finally got my job completed, the owners moved in and the heck out of KC and back to the sunshine (hotter than hell) state.
I have a 2005 Fender pro tubes series Twin Amp.  Played it one day everything just fine turn it on the next day and flip the stand by switch on and it howls and make and ungodly noise. 
The only diagnostics I have tried so far are;
If I flip the power cut back switch to 1/4 the noise subsides and you can play the guitar through he amp and it makes noise.  A bit edgy on the gain Chanel but still can play the guitar and here it through the speakers.  Does that rule out a OT and tubes?  The tubes work fine in another amp. 
But if the amp is on full power and i flip the stand by switch on it almost seems like a surge across all the power tubes and there is a subtle blue glow at the base of all the tubes that flashes with the surging type noise.  Wish I could explain this one better.
Could it possibly be a bad cap?     Stumped and need guidance as to where I might look first.  This is a PCB type tube amp and I have had very little experience with them.

[shortfuse]

  There is a lot going on inside this amp.  7 12xx7's, 1 12at7, and 4 6l6gc's for a total of 12 tubes, 7 beyond what I have messed with so far.  I like single Channel turret or PTP amps 
Found the schematic but is was more than 800kb so I will attach the link to the PDF until I can split the pages up and post them.
Nothing looks burnt on the PCB by visual inspection.  Although there are several solider joints that do not look factory at the PCB.  I paid close attention from the PT to the B+ at the OT.  Am I starting in the right place?  With he power tubes out the indicator lights in the back glow green when the stand by switch is placed into the on position.  With the tubes in it does what was stated in the 1st post and the4 indicator lights glow red stating the tubes are bad but the tubes work just fine in the JCM 900. As stated above when the 1/4 power switch is on the noise is way less and I can actually play through the amp. 
Would voltages with the tubes out help?  Or i could get readings with it in 1/4 power mode but would they be correct?  Never messed with power cut back switches befor but looks straight forward in the schematic.
Here is the link to the schematic http://support.fender.com/schematics/guitar_amplifiers/Twin-Amp_schematic.pdf

[kagliostro]

Here the splitted file as 4 png

Kagliostro

[shortfuse]

Wow 57 views and no comments?  Did I not give enough info?

[phsyconoodler]

No,you didn't do anything.Like changing out tubes with known good ones first.Go figure the most common problem with a tube amp is the tubes,eh?

[shortfuse]

No,you didn't do anything.Like changing out tubes with known good ones first.Go figure the most common problem with a tube amp is the tubes,eh?

Well I guess I could have stated that the 1st thing I did was spend $154.00 and replaced all 12 tubes and it did the exact same thing as it did with the old tubes.  But seeing as though I stated that the tubes work fine in the JCM 900 I thought that was irrelevant.  It does howl like a bad power tube though.  I guess I could have got 4 bad brand new tubes but that never crossed my mind.  Any other suggestions.

[DummyLoad]

divide an conquer. electronics repair credo. what are the PS voltages? - you have a schematic - there's a place to start: are ALL power supplies working? SECOND most trouble w/ tube amps - the power supplies. is the bias supply working? do you have the correct bias voltage at pin 5 of every 6L6? you don't have to have the tube installed to check that.

start with the preamp. pull the power tubes, feed it a sine wave. work your way towards the output stage. build a probe to tap signal - feed signal to another working amp - stop when you find stage causing issues.

--DL

[shortfuse]

You guys are right I need to go to the basics.  Looking inside that chassis is very intimidating to a beginner like myself.  I guess I will just try to break it down into several small sections and divide and conquer as DL stated and ask questions about the things that don't make sense.  I guess I was hoping for the tube replacement to make it all go away.  Turn it on one day and it is fine and the next its messed up.

[shortfuse]

Finally had a little bit of time to look at some basic stuff this week and spent a few hours messing with it tonight.
I was able to get the amp on with the stand by switch on tonight.  I rolled everything to zero and turned it on and it gave a loud noise like a amp cranked up and the guitar jack got jerked out.  I noticed in the back the effects loop was on and the levels on the send return pots were 5 to 6 on each pot.  Turned those to zero with loop by passed and I was able to flip the standby switch on and the amp now had a loud hissing noise.  I did plug a guitar in and you could play it on full and 1/4 power.  Although it was hissing i was able to start checking some voltages.  Power tubes and pre amp tubes seem normal (reset bias and balanced to 60ma) and within the range of the voltages given on the Fender schematic.  Not to sure about the trem and reverb circuits as I have really never built or messed with these before but the 12AX7s seemed normal and the 12AT7 a bit lower on the readings.  Wrote them all down and will post tomorrow but I dont think the problem lays there.
This is what I did find going on.  Everything rolled to zero and it hisses.  Surprising enough the clean channel much nosier that the gain channel.  Place everything on 1.5 to 2 and hissing still there but not near as bad.  Effects loop send and return pots seem to be acting like a master volume in bypass and when the loop switch is engaged it goes berserk unless rolled to zero.  Trem is on all the time and it can not be controlled speed nor intensity.  I do not have a foot sw for the amp but the diode light D220 in the FTSW circuit on the PCB is always on if I plug a mono jack in the FTSW jack the light goes out but the amp does nothing different.  It seems like something in the FTSW / trem / Effects Loop circuit is causing the problem.  I am afraid that this one may be beyond my capabilities if it is getting into IC's and Jfet's.  
If any of you know anything about these foot switch circuits please look at the bottom left of the schematic page titled pre amp it shows the FTSW and the D220 which is a light and and how it ties to the FX loop, trem, and chanel sw.  And if any thing I stated above makes sense with this.
Phsyconoodler and Dummyload thanks for your previous posts it forced me to stop looking at the whole big picture which was very intimidating to me and break the amp down into little areas to try and pinpoint the problem which I think I may have done but not real sure how to nail it down from here.

[shortfuse]

Ok I went around the world the long way on this one.  I would like to blame it on the meter but I believe it was operator error.  The problem ended up being 2 bad caps C206 & C207 which feed the pre amp, fx loop, reverb & trem.  Replaced them and fixed the broken shielded wire found on the board at WJ10A and WJ11A which is on the send side of the fx loop.  The amp played fine and was quieter than it ever was before.  Played the amp for 30 minutes had dinner went back and played again after dinner and 15 minutes into playing there is now noise (hum, open circuit kinda noise) when you stop playing on the gain channel.  Clean channel is fine and dead quiet.  All grounds appear to be connected and I checked all the shielded wires again.  The input jack is my gut feeling as to what is wrong but it only happens on the 1 channel.  It mounts on the pcb and seems fine could it be intermittent and only effect the gain channel?  Noises on the gain channel go like this: nothing plugged in a little noise, cord plugged in more noise, guitar plugged in volume turned up lots of noise and does it with all guitars.  I tried swapping tubes between V1 clean and V2, V3 & V4 PI no change.  Could this be another cap going bad should I have just replaced them all?  Or am I going the wrong direction again.

[LooseChange]

I had a feeling it was that effects loop. Got it fixed. Nice job!

[shortfuse]

LC thanks for the advice.
Now tonight I play it and it is dead quiet on both channels.    Black Forest Gnome's????  It will do it again its just a matter of when.  Very frustrating.

[OVNIPR]

I know it is an old post but I want to know if you had more problems with the amp after changing the caps?