DF 1766 Regulated power supply problems.

Hello members.,
I have a DC Regulated power supply which is giving me grief. It has been used to drive some halogen lamps at loads up to 25 Amps.
The output stage consists of 2N3055 transistors which are awkward to get at.
Just a bit of what happens. At the moment the PSU supplies 13.8 Volts but as soon some load ( 1 Amp ) is applied, the voltage drops to almost zero.
The 3.6 Volts Zener was low at 3 volts so a temporary zener was made with a led , and some 4007 diodes.
Somehow I don't understand the logic how that Zener Z1 is doing anything as it feeds only into a Capacitor C8 as on the circuit.
The 12 Volts zener Z2 is ok and measures 11.97 Volts.
I replaced one faulty 9014 (Q8) transistor with a BC546.
The small signal diodes are ok. The other 9014 transistors Q6 and Q9 measure ok. Interesting is that they are quoted on the schema as 9013 transistors, so I have my doubts about the accuracy of the drawing.
I guess it is a type of overload kicking in but maybe the 3055 are suspect.
Hope anyone can give me some advice.
Thanks in advance.

There are several things about that schematic which just do not make much sense if you are trying to make a stable PSU.

Have you tried comparing the schematic with the real thing?

JimB

JimB said:

There are several things about that schematic which just do not make much sense if you are trying to make a stable PSU.

Have you tried comparing the schematic with the real thing?

JimB

Click to expand...

Hi Jim, that schematic was sent to me by the Chinese manufacturer to me, but I have the idea that it is riddled with errors.
On the small control board the 220 Ohm resistor had burnt out in the past. It used to be a 1/2 Watt R, now there is a 2 Watt R fitted away from the CCT board. The 3.6 Volts Zener was reading low and I fitted the temp Zener with an LED and one 1N4007 diode, and one blue 2V7 Zener to give me the correct voltage.