memphis st1500

[timwebb]

i switched probes. on my old one the button was loose and wasnt locking in place
i used the r762 resistor. and i read 0 ohms from the 3 pins.

 

[Perry Babin]

I'm working from photos but I think R762 connects to the outer secondary terminals. Use the secondary center tap.

You should not read the same thing from all 3 terminals. If I'm not mistaken. the end terminal is ground and should read 0 ohms to the secondary center tap. The other two are positive and negative 15v, if I'm not mistaken. Confirm by following the traces from those pins to the power supply pins 1 and 6 of the LM361.

 

[timwebb]

is this the right card?

 

[Perry Babin]

It's probably the right board but it's different than the photos I have. This is a PAS127-34. The photos I have are of the -32. I would think that the pin configuration would be the same.

The B52 is the LM361.

 

[timwebb]

I'm working from photos but I think R762 connects to the outer secondary terminals. Use the secondary center tap.

You should not read the same thing from all 3 terminals. If I'm not mistaken. the end terminal is ground and should read 0 ohms to the secondary center tap. The other two are positive and negative 15v, if I'm not mistaken. Confirm by following the traces from those pins to the power supply pins 1 and 6 of the LM361.

they connect to the pins 1 and 6. the center connects to pin 9.and the first pin connects to pin 11. with the black probe on ground i get -6.3v on pin 1.and -18.88v on pin 6. of the lm361

 

[Perry Babin]

Pin 1 of the LM361 should have +12/15v. Is your 12/15v regulator working properly?

Don't use the ground terminal. Use the secondary center-tap of the transformer.

 

[timwebb]

ok my 7812 was shorted. the 7912 is putting out -16v is this to high for the regulator?

 

[timwebb]

ok i lifted the leg of a cap connected to it and the voltage went down to -14v.

 

[Perry Babin]

Did you measure the voltage with the black probe on leg 1 and the red probe on leg 3?

 

[timwebb]

that way its still at -16.4v

 

[Perry Babin]

16v from a 12v regulator indicates that it's defective but I don't think that's causing your problems.

 

[timwebb]

could the lm361 be defective?

 

[timwebb]

pin 4 of the lm361 has a very good signal. pin 3 has a distorted signal i traced it back going under the tl074c

 

[Perry Babin]

Do you see a square wave on pins 9 and 11 of the LM361?

Do you have positive and negative supply voltage on pins 1 and 6?

 

[timwebb]

Do you see a square wave on pins 9 and 11 of the LM361?
no

Do you have positive and negative supply voltage on pins 1 and 6? yes

i think think the tl074c is shorting or bad. its to hot to touch.

 

[timwebb]

i put a negative regulator in and i get -12v now but the opamp on the card is burning up.

 

[Perry Babin]

If the voltage across pins 4 and 11 isn't significantly more than 30v, the op-amp may be defective.

 

[timwebb]

pin 4 12.3v pin 11 -12.6. would that cause the problem im having?

 

[Perry Babin]

No.

If you think it's defective, replace it.