Noisy Valvestate 8040 repair

[IvanMan]

Hello everybody.
I'm a newbie in amplificators repair, but hungry to learn.
My (little) experience is more on tube amps, but now I'm working on a Marshall valvestate 8040 that is an hybrid machine (attached the schematic).
If I attach any cable to the input, also without signal, the amp become very noisy, not a specific frequence (more around 350-500Hz, I've analyzed using an app on the phone), growing when I raise the volume / gain.
I cleaned all, controlled tracks, but no results.
Surely the problem is in the pre-amp part and I concentrated my attention to the TL072 op (IC3 in the schematic) and particulary to the IC3a part.
The power is correct (-12V/+12V to pin 4/8), but with no signal the pins 1/2/3 are all aroung -11.5V, while on the other side pins 5/6/7 are 0V.
I don't know about OP but it seems strange to me, also thinking on how works a tube seems an internal shotage?
What do you think about? May be an issue of the TL072? To be substituted or before I've to check something other?
Thanks in advance, guys.

[Stevem]

D.C. Voltages seen on pins of a opamp where only audio should be seen ( AC voltage) if there is signal being pumped in is a sure fire sign of a bad Opamp.

You will only get one shot at unsoldering that chip from the board if it's a two sided board before messing up the circuit traces and having to do repair and jumper wires and so forth, so if you do not have a vacuum desoldering station you might think twice about doing this repair yourself!

[IvanMan]

Thanks for suggestions, Stevem.
What do you think about cutting the pins on the component side and solder the new OP to them
Any other suggestion about what can generate this strange Vdc on pin 1/2/3?

[pompeiisneaks]

That is one way I've seen it done, also another thing that is smart to do at that point is to buy and insert a socket into the board so swapping/replacements in the futuer for the opamp would be just a chip removal/replacement. I've seen many do what you're suggesting, snip all the leads to the opamp at the chip itself, and then carefully just quickly pull each pin on it's own quickly. Then you don't have to heat the entire 8 (or 16) pins. You can also replace the op amp again if you find something else is bad causing the op amp to fail, and it fails a second time etc.

~Phil

[IvanMan]

Successfully substituted the TL072 and the amp works quite good. There's a residual hum using the high channel, but playable in any case.
I wondering if there is a simple way to protect the op from overvoltage/spikes that may be generated by the insertion of the jack on the amp input.
Any suggestion?