Cossor CDU 130 Portable Scope Repaired faults and notes.

[bigfathairyvika]

Hi All,

Just thought I'd pop a few notes from the repair of a Cossor CDU 130 Oscilloscope on here.
If I've posted it in the wrong place, please say so.

This scope came in as not working at all and without power leads.
First thing to fix was a missing spacer holding the transformer and battery bay.
Not having this fitted meant that someone has tightened up the screws and forced the transformer past its own mountings breaking one of the primary wires.
Repairing this and the scope burst into life.
But.. It still would not work via battery or external battery supply.
The power is controlled by a rotary switch for External/Internal and Battery charge selection. This switch had high resistance across a few contacts, so a complete strip down and clean restored battery power.
But.. intermittently it would not switch on without coaxing from screwdriver.
Traced this to MR614 (1n4001) which had a dry joint, fixing the dry joint didn't fix the problem. Tested the diode as ok, but failed to work in circuit, so replaced with new one.
This fixed the battery supply.
Also replaced one 160uf Cap as it more leaky than a government department.

Points to note about this scope are:

1, Front and rear panel screws are 5/32 BSW not BA like all the other screws!
2, Front panel is a pain to remove as it made up of two panels, requires undoing the three trimmer access Allen bolts, removal of both BNC sockets, the cal and x-amp sockets, the ground post and all knobs. Note that two main PCBS will slide back and forth half inch for easier access.
3, Enlarging the BNC socket holes on the outer panel before refitting allow these sockets to be left fitted and wired up in future.
4, It is a good idea to push all the battery converter connector pins home with an insulated tool if disturbed.
5, The mains power socket is NOT a Bulgin miniature three pin, it IS a Belling Lee. The plug for the latter is much cheaper and available from JAB Electronics at a very reasonable price.
6, The external battery socket IS a Bulgin! Same as the old Weller soldering stations.
7, External battery voltage needed is 15v. ( there is space for ten D size cells in the scopes battery bay. )

Finally, no I don't have a manual or schematic. But all the wires are nicely labelled at each end.

Only thing I haven't managed to repair is the plastic shroud for the screen.
I am keeping my eye out for a bit of 3 and an 1/8 dia pipe.

Best regards and happy new year to all,

Mark