Post #5 shows the measurements.
The positive 15V regulator works fine but the negative 15V regulator has a problem causing an output of only -5.24V.

Yes!

As i mentioned in an earlier post, i now have a working unit also, with a 15VAC supply

Measured the pins in that unit
Pin4: -15.18V
Pin8: +15.18V

So i would need to replace the 7915 regulator in my faulty unit.
Should i replace them both, or no need?

It's strange that these regulators are not made for the voltage it's running on... but, they work this way so

 

Hello,

The regulators need some overhead (dropout voltage) to be able to do the regulation.
See the datasheets for more info.

Bertus

 

Since the -15V is too low then you have a defective 7915, a defective rectifier diode or a defective filter capacitor.
Measure the input to the 7915 to make sure it is -17VDC or more produced by the diode and capacitor.

Maybe the -15V is overloaded by something?

 

Since the -15V is too low then you have a defective 7915, a defective rectifier diode or a defective filter capacitor.
Measure the input to the 7915 to make sure it is -17VDC or more produced by the diode and capacitor.

Maybe the -15V is overloaded by something?

Thanks for the picture explanation
I measured with both PSU voltages, just for curiosity.

15VAC PSU:
7915 input: -7.8V
7815 input: +24.6V

12VAC PSU:
7915 input: -5.5V
7815 input: +17.9V

Seems like it's not the regulator anyway then, because of the low voltage input..
I have checked the diodes in circuit earlier, but it might be faulty anyway i guess.... or a capacitor.. need to pull them to check then

It's hard to say if something is overloading. it's such a small current i can not feel any component generating any heat at all, event it has stayed on for longer periods..

 

Remove the regulators and check it's input voltages

 

Remove the regulators and check it's input voltages

Without the regulators in place voltages are:

7915 input: -12.8V
7815 input: +26V

 

The diode and/or the filter capacitor is/are bad.

 

The capacitor connected with 7915 is bad.

But regarding the two diodes, checking them in circuit, they give about the same value.
So i will assume they are ok, and only try to replace the capacitor

 

Maybe the original capacitor was wrongly connected backwards? Make the + wire to ground and the - wire to the anode of the diode and to the input of the 7915.

 

Maybe the original capacitor was wrongly connected backwards? Make the + wire to ground and the - wire to the anode of the diode and to the input of the 7915.

No i don't think so, this has been working for years untouched.

I got new capacitors today.
Installed the capacitors and measured without the voltage regulators, +25.6V And -25.5V to the inputs.

Installed the regulators, measured pins on opamp +15V and -24V
Regulator 7915 has the same input and output voltage. Guess i have to replace this also...

 

Hello,

Keep in mind that the pinouts of the 7815 and 7915 are different:

On the 7815 the gound is the middle pin.
On the 7915 the ground is on a side pin.

Bertus

 

I know Bertus, thanks

Finally got new regulators from ebay.
I replaced both 7815 and 7915.

Now it works like it should.

However there is a bit of voltage difference between + and -
+15.04 and -15.30 on the opamp and regulators
Regulators have the same input voltage, so i guess it might be a bad quality regulator, or is this difference within the tolerance?

I don't know if this means anything in this circuit, as long as it works like it should?

 

Hello,

The output voltage are within range.
See these snippets from the datasheets:



Bertus