Now the description of the problems.
the scope arrived with signs of having been opened before:
it lacked screws from top and bottom plates, and one from power supply on the back.
The psu had some connectors bent like if it was extracted not too gently.
The internals are very clean, and there were some wires unsoldered on the back, these
came from the connectors of probes power supplies on the back.
I put these wires in a safe position, changed the voltage range to 220V, inserted
a new fuse and fuse cap that were absent and powered up.
The graticule lighted up at max but not responded to the regulation pot,
and the cooling fan was silent. Powered down and started reding the service manual.
First thing I checked the psu voltages: +-50V and 5V were ok and very well regulated,
but +-15 were almost zero. Powered down and waited for the input capacitors to
discharge and measured the dual 15V rails with an ohmmeter and they were dead short to ground.
Started disconnecting the cables, beginning from the psu, and the short went away once
disconnected the cable that was going to the readout board.
At this point tried starting without this connector and the fan started (in it is loud!)
now the graticule illumination responded to the pot and the voltages were all ok.
I gained access to the readout board on the side and here it was showing some signs
of precedent working, two capacitors were bent down and two pots had signs of
fused plastic from soldering iron. The wires that were desoldered came from this board
and the pads have the signs of (dirty) desoldering process.
The funny thing is that once removed the board I tried mesuring the 15V rails and the
short simply wasnt there. I reconnected the board to the scope and the scope started
with all the voltages ok. I only reseated two caps with hands and nothing else.
This is the readout board, tektronix partnumber 670-8622, it's different from the
one in the R7103 service manual but the detailed schematic can be found
in the service
manual of the 7934 scope in the final part of the service manual, section MANUAL CHANGE INFORMATIONS,
probably because is a more recent unit.
Now I don't know if there are other problems, and I dont like the fact that
the rails problem disappeared with apparent self healing.
My other concern is the tube, given the
long shipping and all the movement it was subjected during the delivery.
Now I'm waiting for two plugins, probably they will arrive next week,
I bought a pair of generic ones: 7A26 and 7B92A, if the scope will come
back to life I'll start searching info about suitable probes, and will
try to complete the setup with a 7B15 7A29 7A29/opt04,
and another 7A26 for high impedance work.
If there are ways to test the tube without the plugins let me know.
Fabio.