Please check your winding orientation. You may have terminated the windings incorrectly otherwise the unit will work with a new RM8 transformer. I don't know exactly what to change because the attached trf spec is different from the original RD-194 (referring to secondary windings), and there is no schematic. Try interchanging the secondary winding termination, or please send the schematic for further checking.

Hello,

thank you for suggestion, I've solved the problem: the device entered in OVP,
because the bias winding was slightly higher than the other transformer.

I'll rewind the transformer with a lower bias voltage or use a zener with higher clamping voltage.

 

Thank you Sir

I'm now testing the driver with a triac dimmer. There's a lot of low-frequency noise (I think 100Hz) coming from the driver (with the original RM8 transformer the dimming was "silent"). Have you any suggestion about this?

Thank you!

Try to varnish the other transformer if the original RM8 trf you have has varnish. Other components especially the EMI filters may contribute to audible noise as well when you dim with leading-edge triac dimmers due to large current spike once the triac fires.

The original transformer isn't varnished, while the new RM10 transformer is varnished, so it's quite strange this behaviour!. Further, the bulk capacitors C2-C11 are metal film type (Panasonic ECQ series).

I think could be useful to increase the value of R13 or C6-R12: what do you think?

Have you other suggestions?

Thank you

Please check that the new transformer does not saturate. This could explain why it is even noisier despite having varnish.

Or perhaps the core materials are different. Try better core materials, because if the peak currents are similar, then it should have the same noise level. 

If it's not related to the transformer, you can try to reduce the value of the passive bleeder C11 or C1. You can increase R13 value but check thermals and efficiency. Also verify dimming performance if you change these components.