How to test a Toroidal Transformer?

[Fabrizio]

Hi , I would like to know the procedure of How to test a toroidal Transformer out of circuit.
I attached the picture of the transformer .( It is from a A70 Harke Bass Amp).

Thank You

[Helmholtz]

What is known about transformer voltages?
Is this an amp repair? If so, what are the symptoms? And please post a schematic.
Does it blow the mains fuse?
Do you have a bulb limiter?

[Fabrizio]

[QUOTE=Helmholtz;557515]What is known about transformer voltages? Primary 220v secondary 31.7 V

Is this an amp repair? Yes It is , to be precise it is a old repair that I left a few years ago and now I want to resume it .

If so, what are the symptoms? Short shown on the lamp limiter


Does it blow the mains fuse? Yes if without a lamp limiter

Do you have a bulb limiter?Yes

I would like to troubleshoot the transformer first then I will start again with the amp if transformer is good.

Thank You

[Helmholtz]

Did the PT produce any secondary voltage with the bulb limiter?

Is there an older, related thread you could link here?

With the PT out of the amp, does it blow the mains fuse (correct type and value) with only the primary wires connected to the amp, making sure that all secondary wires are disconnected and not touching anything?

[Fabrizio]

[QUOTE=Helmholtz;557643]Did the PT produce any secondary voltage with the bulb limiter?

Yes 34.34

Is there an older, related thread you could link here?
Yes : https://music-electronics-forum.com/...ad.php?t=42352

With the PT out of the amp, does it blow the mains fuse (correct type and value) with only the primary wires connected to the amp, making sure that all secondary wires are disconnected and not touching anything?

No It doesn't blow the fuse. and the lamp limiter is not lighting up.

[Helmholtz]

No It doesn't blow the fuse.

If this is without the bulb limiter, your PT is most probably ok (no signs of a winding short).

Is there a schematic of the power supply which shows secondary voltages? If so you could verify winding voltages without the limiter (bulb limiter lowers all voltages).

I don't suspect your PT.

[Fabrizio]

Thank you

I have a schematic of the amp in the attachmentharke A70_SCH.pdf.

The voltage on the secondary is 34.5 V without a bulb limiter . Fuse Ok

[Helmholtz]

Ok, unfortunately the schematic does not show transformer and power amp voltages.
Your PT has 3 secondary wires, meaning one winding with a center tap (CT) to support +/- supplies.
Between which of the wires do measure 34.5 VAC? Is it like 34.5-CT-34.5, meaning that you have 69VAC between wire 1 and wire 3?

One more transformer test:
Mount the PT back into the amp, connect only the primary and check again for blowing the mains fuse and secondary voltage (without limiter). Reason: There is a slight possibility the pressure exerted by the mounting screw might cause a winding short.

If everything is fine, your PT is ok and the rest will be an amp repair. I recommend to start a new thread for this.