the power supply in 890 C is base on UC3842, then i measure on Vcc
(pin 7) the voltage is rising slowly, it take minutes to rise to 16 V,
where the PSU start. if PSU is unloaded Vcc (pin 7) drop down to 12 V
and the psu keep running.

If PSU is loaded the Vcc (pin 7) drop down to below 10 V and UC3842
switch off the psu.

the load is'nt to big everything Work fine if i use externaly power
supply.

i have tried to change the capacitor on Vcc (pin 7).

Any other suggestion