magnum transistors voltage

[mariusz]

I can't get 11v an 5v6 on power supply unit I think it could be transistors fault any ideas ? I v'e got only 3v7 an 2v And 11 instead 14 v on connection between baterries and pcb

[Carl]

>I can't get 11v an 5v6 on power supply unit I think it could be transistors fault any ideas ? I v'e got only 3v7 an 2v And 11 instead 14 v on connection between baterries and pcb


Just got back from travel. I don't know if you've solved this problem but here is a possible solution.


The design of the reference circuit in the Magnum is flawed. The zener diode is biased off of the reference output (11.2v) so the reference has to get started in order to turn on the zener, but the zener has to turn on in order to get the reference going - it's a catch-22.


Instead of connecting R45 to the 11.2v side of TR9 connect it to the 18v side (the emitter). Now the zener will bias regardless of the state of the reference. Also, you can increase R45 to 10K instead of 2.7K so it draws less current.


Hope this does it.


- Carl