Ondrej,
Note where the pots R863, R1226 and R1228 are and turn them back and forth. One or more may have a open due to not ever being moved and turning it restores contact. Check for B+ at places that got to a supply voltage, e.g. H3 and H4. Some other contacts short/go to to ground, e.g. G1 on <7>. See if those are going to ground. The relay mentioned earlier could have dirty contacts in it. Another part that can give problems are 151-0367-00 (selected from 3571TP). These usually are leaky from C to E. Later ones that have a blue face are alright. Black face ones are very likely leaky. I have replaced them in scopes and 7B time bases with KSB10U. The pinout is different for these, BEC. The leakage was a problem, for me, at the higher sweep speeds and was right after I replaced the transistors.
Mark
