VM100 repeated T1 /T2 failure - second request for help!

Why am I having to replace transistors T1 and T2 for second time?

Is it possible that the spec of the replacement BC640 that I bought from RS Components is a problem? Vceo max =80V. Can this be too low?

In the RS Catalog there are two current ratings for BC640; 1A and 500mA. I bought the 500mA device. From what I can see in their datasheets Vceo max is 80V for both.

The voltage I measure (loudspeaker not connected) across the VM100 power rails is 81.5V!

I have already posted this question last week but I get no reply. Is there another method I can use to request help from Velleman?


The VM100 is an assembled and tested module. If it has gone defective, it is most likely due to user error such as use beyond the specs, poor connections or cooling issues. The voltage rating for the transistors is fine.
If you are unable to fix the circuit, you can return it for inspection/repair.
Please note that the main purpose of this forum is to allow users to help eachother. We simply do not have the means to treat every question individually.