Thanks a lot for your suggestions, MJMP.
Following you i checked around and the 8031 and i saw that pins from 1 to 8 has 180mv ca. from ground and pin 9 has 220mv ca. from ground.
Between pin 20 and 40 there are 4.80v ca.
Other, i made the battery mod, to make it changeable easy and changed C4 with 22uf (this i had..) and C1 with 10k (it was 5k originally).
After that i turn on the machine and a strange thing happened, it started with leds on from overdrive to effects loop and four strange digits on the display (something like G with missing elements).
After that no more life on it.
What do you think?
Also what rnolan says it's a good option, i'd like to do it by myself but i'm a little skilled only on tube. If i'll not be able to fix it, and you're agree, i can send it to you. In case we'll speak through personal messages.
Thank a lot to both.
Bye!