Strange schematic [Englisch]

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 passive components.
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?
I can say from experience that other machines of this same manufacturer (Polar) use a voltage derived directly from the 3-phase input to drive the electromagnetic clutch. Why use a switched voltage, I cannot understand.
Is the triangle within a square symbol some sort of odd representation of a transistor? And the "arrow thing" that feeds them? Ideas?
Help!
danke,
--
DaveC
snipped-for-privacy@bogusdomain.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It's the block diagram symbol for an amplifier. So presumably, your transistors somehow go there.

No idea on that one. Some kind of "alternating switch" or such, the entire circuit looks like a voltage inverter, so maybe it is switch-driven by some kind of mechanical feedback to keep it in synch?
--
cheers, J"org .-.-. --... ...-- -.. . DL8DTL

http://www.sax.de/~joerg/ NIC: JW11-RIPE
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
DaveC schrieb:

Yes, I think too the symbol marked with the "??" is an oscillator and the two triangles within a sqare are the power stages. As Joerg said, this are symbols for amplifiers, but where used very broad in this kind of plans. So they can mean anything, from a single transistor to a complex amplifier.

It looks that this is done for galvanic isolation of the clutch circuit, may be for safety reasons.

See above, but it looks to me that there is an error at the symbol at the secondary side of the transformer, which is similiar to the amplifier symbol.
There was a block-diagram symbol for a rectifier in this plans, a diode without the "pins" inside of a square: |----------| | __ | | \/ | | -- | |__________|
Probably the author just forgot the small line at the tip of the diode.
The circuit on the left of the plan is for the safety light barrier, LDRs with the well known amplifiers. But the big symbol is of course not only an amplifier, it must have some and-logic built in. It shows how crude the use of this symbols is.
Please be very careful when you try to repair this machine, there are a lot of safety arrangements and if you fuck them up somebody may loose a hand or two. Many years ago I once worked with such a machine and the boss told me to act very carefully with it. Not necessarily because it was dangerous: The machine had an emergency break which was able to stop the heavy knife almost immediately. If it was triggered once it meant a very expensive repair to get the machine up and running again.
Jörg.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.