Another Fender Stage Amp 100 DSP Problem Please HEEELP.!!

[Ensoniq1176]

Hello, the extensive research on the net and the forum search unfortunately did not answer my problem satisfactorily, so I am asking the community for support. My Stage 100 DSP blows the main fuse. Shortly before that, an ultra strong hum can be heard, then the fuse blows. As a result, some TIP142 and 147 break.
The following work has been carried out so far.:
Rectifier diodes are OK, 3000mF capacitor OK, all Darlingtons TIP142/147 replaced. To save money at the moment only 1 pair in use.. D25/D26 tested OK. D23,D24 ok, D21 and D22 ok, Q12 Q13 replaced. Q10 and Q11 with 2sc3298 and 2SA1306 replaced the original Q11, Q12 (1236 and 1857not available here in Germany). If I disconnect the AC +/-45V connection, the preamp works. If I interrupt the +/- 16V on the R87 and R94, is the output stage seems stable and I measure +/- 45V on D25 and D26. ...I have the same loud humming when I apply +/- DC voltage from my laboratory power supply to the D25 and D26 instead of the internal 45V. So I shoot out the error in the power supply unit..... The .47 Ohm resistors checked ..ok I can't figure it out....The 7805 regulator is ok....Anyone have an idea.??? Any suggestion is very welcome.

[The Dude]

None of those designation numbers mean anything without a schematic. Can you please upload a schematic or schematic link?

[Ensoniq1176]

here we go....

[nosaj]

First off remove the speaker. we will not need it again till we ensure no substantial DC on the outputs.
Test q10-q19
nosaj

[Ensoniq1176]

Hi nosaj, thank you for the reply... I replaced all Q10 to Q19,and C86 C87 ....still have a huge hum but less than before on the speakers ...I switched the amp for about for 2-3 seconds the fuse this time did not blow.I tried to measure the ripple on the scope by touching the measuring tip on +45 V the hum becomes much quieter. The preamp Signal on the preamp "output "jack is clear and ok....feeding sinewave into poweramp "in "jackwe have stll loud hum.....

[nosaj]

Remove the speakers and measure for DC at the speaker connectors.
nosaj

[Ensoniq1176]

Dc 0,14v....ac 0,45 v

[Ensoniq1176]

soory now AC 0,8V. DC 2,8mV

[nosaj]

what is the situation of the amplifier? out of the the chassis on in the chassis?
If in the chassis I'd suggest reflowing the solder on the input jack.

Please let us know if you don't quite understand something(I assume english is your second language?)
nosaj

[Ensoniq1176]

HI,yes english is my 3rd language .... I am from Slovenija but live in Germany..OK. I unterstand what you are talking about... The amplifier is not in the speaker cabinet. The chassis is on my table. The board ground is connected to the ground of the chassis. It hums even without the plug being plugged in. I already said that the preamp output (send loop-in point) at the back of the chassis is clean. I connected it to the active loudspeakers at my measuring station.It is the Power Section.
I listen to the power amp at the LINE OUT, without a speaker. If I just touch Pin 2 OpAmp U7 (4560) with the measuring tip of my multimeter, the hum goes away. but this means that the resistors R110, R111, R112 start to glow.I'm an advanced amateur at electronics but this fender circuit is a bit beyond my knowledge. I have no experience with solid state guitar amps. As I said, I don't measure any DC at the speaker output. The hum is a very loud 100Hz signal
.

[nosaj]

Well some people take the pcb out of the chassis an that can make a difference(I just wanted to clarify the setup since we have no pics). The preamp out being clean means free of hum?
Do you have an oscilloscope or an audioprobe?
nosaj

[Ensoniq1176]

Yes I have an osciloscope...sorry what is a Audioprobe:??.....Do you mean audio signal tracker

[g1]

If I just touch Pin 2 OpAmp U7 (4560) with the measuring tip of my multimeter, the hum goes away. but this means that the resistors R110, R111, R112 start to glow.
.

Touching the input pin of that IC must be causing a high frequency oscillation. That is why the resistors are burning, you should not do it.
The amp is reproducing so much HF content above hearing range that you can't hear the hum anymore.

Have you inspected the solder joints at the main filter capacitors C86 and C87? Also check for broken pins or solder pads of those caps.

[Ensoniq1176]

Hi G1, thank you for the reply. Yes The C86 C87 are replaced and new. Double checked! Good Contact.!

[nosaj]

Yes I have an osciloscope...sorry what is a Audioprobe:??.....Do you mean audio signal tracker

Yes basically it is a signal tracker, just audio only whereas the oscilloscope is visual only.
Well since you say the issue is in the power amp you can start probing at the poweramp in jack checking for where the noise starts just follow the signal chain.
Also post the TP data (test points are in an oval circle with an expected voltage.)
nosaj