Repair Notes, October 2019

The camera Marconi Mk IX

Brian Summers writes :-

Marconi MkIX restoration notes

Main CCU crate
Mains input filter X caps failed were replaced, a tedious but necessary job.
See Page 21

Main CCU PSU(s)
Second one tried worked, hint of hum?? The first PSU was found the have an open circuit resistor across the base emitter junction of one of the camera inverter transistors. The PSU still did not fire up so the said transistor was removed (unplugged from it's socket, for examination). It looked to be good so I put it back and the PSU sprang into life?? It must have been making poor contact.

Coder B-110-3267-01  serial 510 mod state 16.
IC Z17 replaced in subcarrier section, broken wire fixed. Relay RLA replaced. Note there are 3 of these relays on the input section switching between Bars or Picture. They are known to be problematic, on this particular coder all 3 have now been replaced. Best to use an IC socket.

Camera PSU B-105-3266-01 serial 213 mod state 3
The +50V was missing on the test point on the front of the PSU, as was the fuse, not blown! just not there! (FS1 160ma.).

Camera body
The main frame is very similar to the MkVIII camera but there is a different top cover. The pivot points were it hinges back and detaches from are “improved” in the MkIX camera and “improved” again in the MkXIb. Three versions so not altogether a successful hinge point.

Camera #182
The fan driver card for the camera fan was faulty. An open circuit decoupling choke on the +15v rail and a short circuit Tantalum capacitor was found and replaced. I did the -15v rail for good measure.  The Green tube socket was making poor contact, a reseat fixed it for now.