DaveC wrote:
This is a partial wiring diagram for an early 80's (West) German guillotine
paper cutter:

http://freefilehosting.net/show/42l0i

The goal of this circuit is to energize an electromagnetic clutch coil (m27)
that takes rotational energy from a flywheel to do a task (bring down the
knife blade). This circuit is currently not working.

This machine has no ICs. There are some monolithic rectifier bridges and
discrete transistors (the common symbol for which I cannot find *one* in the
diagram), and plenty of passives.

The transformer (m) primary center tap is connected to 24vdc. Do I interpret
this correctly that the primary is run by a switched dc voltage? (This on a
machine that runs on 3-phase 245vac.) Why?

Looks like the transformer must run switch-mode. The clutch is 42V while
the rest of the circuit is 24V - may be why a transformer is used.

I don't see any connection that can get to ground on the transformer
primary. Everything looks like it goes to 24+. Could be the
"Transistors?" mount on, and connect to, a grounded surface - not shown.
(That would give the "Transistors?" 4 leads.). "??" is the switch-mode
drive? Would think it also would need a ground - maybe not shown?

Where parts are about all identified it seems strange the blocks with
triangles and "??" have no identification at all.


I can say from experience that other machines of this same manufacturer use a
voltage derived directly from the 3-phase input to drive the electromagnetic
clutch. Why use a switched voltage, I cannot understand.

The manufacturer may want all of the control to be low voltage?


Is the triangle within a square symbol some sort of odd representation of a
transistor? And the "arrow thing" that feeds them? Ideas?

My dipsiht news provider apparently no longer allows crossposting. Not
knowing which newsgroup the OP watches this is posted on all 3
newsgroups. Sorry.