not enough power?

[mischl]

hello all

i have a circuit with 230 VAC to 5 V DC regulation. see picture

now when i connect 7.5V DC from an external source at the input of the 7805, it works fine and need 90mA at the 5 V out.

but when i connect the transformator as drawed, the pic18f876a reset itself allways. the trafo output is 6V 1.0 VA.
the input ripple at the 7805 is a sine between 6.6V and 8.8V peak to peak which breaks down every 80 ms to about 5 V.
the outpt voltage at the 7805 is 5.0 V and breaks down every 80 ms to 3.6 V.

ok, the 80 ms result from power-up timer(72ms), start up environment and then ... ? probaply there is not enough power to generate the 5V 90mA with 6 V AC 1.0 VA or the bottom of the input ripple is with 6.6 V to less for the 7805...??
i've tried to turn off the mclr at the 18f876a, but can't found the fuse configuration...

thanks for any help