Well, after a short pause, I'm here again. I have no time during vacation, so today I looked at the A7 current assy.
Based on advantages from ddrl, I checked circuits listed in contribution:
U23 and U28 were replaced before, they were burned (visible);
U53 and U48 were replaced today, because Z4 was hot during operation;
Q31, 32, 34, 35, 38, 39 were checked and they are OK;
all transistor mounted at aluminium heatsink were checked and they are OK;
CR24, 25 and 17 were checked and they are OK;
U31 was replaced preventively (because both 10R0 resistors located between K3 and K2 were smoking ago);
Z2 was repaired by mounting 40R/1% resistor (30W, TO220) as a temporary fix, I must obtain Z2 or some precision thin film resistor.
Besides that, following components were replaced - some of them was burned, some of them causes malfunction, just like 74HC374 which gives Err 104:
U19, U20, U21, R116, U16, U3, U4, U5, U43, RT2, RT3, E1, E2, K16, K20 (these relays were OK, but they had mechanical damage due to burning of E1 and E2) and CR18 (I hope I don't forget anything).
Situation is following:
330uA range, AUX output: OK (both AC and DC)
330mA range, AUX out: OK (AC/DC)
3A range, AUX output: NOK (8A permanent!)
20A range, 20A output: NOK (18A permanent!)
AUX voltage 0-7VDC: OK
AUX voltage 0-5VAC: OK (tested 50Hz and 1kHz)
Well, question is, if there is something, which has 3A range and 20A range in common or they are two independent faults. I'm working with schematics from 57lfc and 5500, but they are different. It takes some time, but it's on the good way, completely dead board, many faults were reduced to 2 also thanks to ddrl with good hints, which were helpful. Later I will also post some pics from A7 (and other boards).
ddrl, if you have something to tell about my problem, I will be very happy, I like happy endings