MTX TA 81001

[Perry Babin]

I'm not sure. The 11v has to be coming from the area of the op-amp since there is no voltage on the other end of it and nothing else except for one resistor is connected to it. The other resistor (R412) goes to ground (confirm).

It may be possible for the voltage to be higher than it should be if R412 is open or out of tolerance (check it) but I wouldn't expect it to be near -11v.

 

[S Merlington]

Im rebuilding that entire section of the amp since the op-amps were new and had nothing but problems with this amp..

D402 is marked D4 here are the readings i get on it


im using the top leg as leg 1


Legs 1-2:0.562
Legs 1-3:OL
Legs 2-3:OL

Probes reversed

Legs 1-2:OL
Legs 1-3:0.560
Legs 2-3:1.052

Does this appear to be good ?

 

[Perry Babin]

If 'top' means the leg on the side with only 1 leg, there is a problem because the two other legs are directly connected and any reading that you get from the top terminal to one of the bottom terminals should be the same as to the other bottom terminal.

 

[S Merlington]

The readings were taken with it out of the board Does that make a difference?

 

[Perry Babin]

http://datasheet.octopart.com/MMBD4148-Fairchild-datasheet-19910.pdf

It appears to be OK.

 

[S Merlington]

Heres the op-amps i orderd from future wil theese work??


NE5532AD8G | NE Series 9 V/us 22 V SMT Dual Low Noise Operational Amplifier - SOIC-8 | ON SEMICONDUCTOR - Future Electronics

 

[Perry Babin]

That looks like the correct part.

 

[S Merlington]

I just have to install 3 caps yet in that section and its all rebuilt..

Do i need to check for defects in the section behind the RCA jacks before i power this up ??

Only wondering since i dont wanna destroy anything i just did

 

[Perry Babin]

Nothing previous to the large caps in the output drive stage can harm the output drive stage except for a defective voltage regulator.

 

[S Merlington]

D104 and D105 are the voltage regulators? along with U102 (7805)

 

[Perry Babin]

The only time that a Zener will be a regulator by itself is when its terminals are directly connected to the power supply terminals of the component for which the voltage is being regulated. In most cases, a Zener is only a reference for a larger circuit that ultimately produces the regulated voltage. The 7805 is a standalone regulator.

Re-read the MTX 7801 page for descriptions of the voltage regulators used in the MTX amps for the op-amp power supplies.

 

[S Merlington]

Powerd the amp up still no output..

With the black probe on the ground terminal

1 Side of of R414:0.72

Other side just jumps all over the place

 

[S Merlington]

I replaced D201 and i dont get this amp..

1 side of R414: 0.70 volts

Other side is: -11.45 volts

I replaced both op-amps with new checked for solder bridges and found none..

Is there another section of this amp i should be checking ??

R412 one side goes to ground

The other side has -11.38 volts

 

[S Merlington]

Any ideas where to look next on this amp??

 

[Perry Babin]

Remove the op-amp to see if the voltage remains.

 

[S Merlington]

Removed op-amp

1 side of R414 is 0.72 volts Other side is 0 volts..

 

[S Merlington]

Replaced the op-amp again..

This time i get 0.72 volts on 1 side of R414 and 0 volts on the other side..

Heres what i have on the op-amp closet to the opto_couplers

Pin 1:-14.23
Pin 2:0.15
Pin 3:0
Pin 4:-15.55
Pin 5:-13.89
Pin 6:0
Pin 7:4.40
Pin 8:15.01


The other NE5532

Pin 1:0
Pin 2:0
Pin 3:0
Pin 4:-14.89
Pin 5:0
Pin 6:0
Pin 7:0
Pin 8:15.03

 

[Perry Babin]

You shouldn't have voltage on pins 1 and 5. It appears that pin 1 is where the problem originates since the voltage is greater there.

 

[S Merlington]

If i remove the op-amp i get no voltage on the pad for pin 1..

Ive replaced this op-amp 7 times already and still have voltage problems with it..


I dont think 7 op-amps could be bad

Is there anyway that the Opto-couplers could be bad causing this ?

 

[Perry Babin]

I didn't see that you replaced it. I thought it was still out. What were the voltages with the op-amp out?

Sometimes problems in the circuit can destroy every op-amp you install untill the problem is found. It's virtually impossible to have multiple bad op-amps (before installing them).