Test IC TL074 CN circuit, CC+ and CC-

[Coconuttopdrop]

Hi.

I'm repairing a AMEK mixing board but i dont have an extensor to power the channel's that i'm fixing.
What i'm doing is comparing some readings on a good channel with the bad channel.

The EQ section of the board as 4 TL074CN IC's, and some are busted, but i dont have a way to see wich are ok and wich are busted because i cant power the circuit.

So i need to do some kind of circuit to test the IC's.
The TL074 brochure has a audio amp circuit (fig.25) wich i can try to replicate, but i have some questions.

Using a DC power supply, should i feed 12V to CC+ and hook up the ground to CC- and feed 6V to ground?

Thnks

 

[FvM]

Mixing consoles are usually designed for +/-12 or +/-15 V bipolar supply. Depending on the circuit, you are possibly able to test it with lower voltage.

I can't imagine multiple OPs being damaged without a serious reason. It may happen with in- or output stages, if you e.g. inadvertently connect a speaker XLR cable. Defect power supply with massive overvoltage would be another (very unlikely) possibility and almost mean total loss.

A TL074 datasheet can give you and idea of a basic amplifier circuit, but not of parametric equalizers or differential input and output stages found in a mixer console. I guess, there will be an Amek service manual out there.

 

[Coconuttopdrop]

This is actually a big studio board.
It's has several power rails, the audio ones being +17.5V and -17.5V, 11V for light's...
I cant test the circuit with current, I have no way to feed the rails properly.

The OPs were damaged due to a 50nf cap that busted and was drawing to much current (burned a diode, then the preamp transformer and some ic's on the way)
The thing is that now i have several TL074 that are not working and i need to know what i can do to check which ones are ok and which ones are dead.

There is no service manual for the Amek M1000 on the web

 

[rohitkhanna]

Hi.

... as 4 TL074CN IC's, and some are busted, but i dont have a way to see wich are ok and wich are busted because i cant power the circuit.
....

Why can you not power the circuit ? Maybe using a known power source ?
Busted IC's will remain busted, and good ones good. So what's the concern ?

 

[FvM]

The OPs were damaged due to a 50nf cap that busted and was drawing to much current (burned a diode, then the preamp transformer and some ic's on the way)
The thing is that now i have several TL074 that are not working and i need to know what i can do to check which ones are ok and which ones are dead.

So you say the cause of damage is overvoltage of the +/-17.5V supply rails? In this case I would think about replacing all TL074 powered by the rails.

 

[Coconuttopdrop]

Changed all the IC's and the problem remains, i must have missed something. Thank u all for the help