Incomprehensible industrial schematic

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?
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.
Is the triangle within a square symbol some sort of odd representation of a transistor? And the "arrow thing" that feeds them? Ideas?
Help!
Thanks,
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DaveC
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: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? : :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. : :Is the triangle within a square symbol some sort of odd representation of a :transistor? And the "arrow thing" that feeds them? Ideas? : :Help! : :Thanks,
Not even LM Ericsson x-bar schematics use such nondescript symbols, and their symbols took some getting used to back in the 60's.
I'm afraid you are going to have to trace out the wiring while comparing it with the schematic and that way you should be able to work out what each of the nondescript items with the triangle symbols are. My guess is that they indicate some sort of active semiconductor function block. There may be additional schematics detailing what is in each block but if that were so then one would expect to see some identifier number written inside each block but I don't see this information either.
Good luck!
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repost to de.sci.electronics perhaps
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net /
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Thanks.
--
DaveC
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:> repost to :> de.sci.electronics : :Thanks.
Your query seems to have the contibutors on de.sci.ing.elektrotechnik just as baffled as the rest of us here Dave....
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The transformer feeds a block with a triangle symbol, so my hypothesis is that this represents "rectifier" and it's a full-wave bridge, especially as it says 42V= (42VDC) underneath. The block on the left with three inputs at the top could be a three-phase rectifier, and the small blocks with three terminals could be silicon controlled rectifiers. Your mystery block must be something which flips into one of two positions.
Dave W
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In the US, a triangle is usually a symbol for a gain stage -- most-often an op amp. But it can also be a driver, which is likely what the triangles you think might be transistors are.
But... I've never seen a schematic like this. Whoever drew it seems to be using one symbol to represent different devices.
I would trace everything out, starting from the side of the transformer on the "flat" side of the triangle. As you find parts that match the schematic symbols, you might be able to start unscrambling the symbols' meanings.
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DaveC wrote:

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.

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

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

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finger to keyboard and composed:

Maybe this particular clutch requires a higher frequency than 50Hz or 60Hz ???

I'd say it's probably an NPN transistor (plus associated components ?). I suspect that the rectangular block immediately above the two chopper transistors (?) is probably an oscillator or multivibrator.
Having said that, I can't follow the current path. It appears to flow into the transformer's centre tap and then out via either end of the primary winding. It must then flow through the "transistors" into the "oscillator" because the side paths are blocked by reverse biased diodes. But the remaining terminal for the oscillator is also blocked by diodes ...
It seems to me that your circuit is some kind of hybrid block diagram.

- Franc Zabkar
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On Wed, 10 Dec 2008 11:41:45 +1100, Franc Zabkar

Sorry, I didn't read bud's post properly. It appears that he has already come to the same conclusion.
- Franc Zabkar
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a
I believe you will find "the arrow thing" will be an astable multivibrator.
I suspect the following stage are time delay relays modules. Note they are controlled by 24 VDC yet they are controlling AC... after all, you need AC to run a transformer.
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DaveC wrote:

That's a perfectly normal Euro standard symbol for a transformer.
The thing with an arrow it feeds is obviously a bridge rectifier which makes me wonder if the arrow symbol thingies with 3 connections might be SCRs.
But the rest is extremely odd.
The ?? might be a panel mounted SPCO switch.
And yes, the clutch is in black because it's inductive.
Graham
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DaveC wrote:

The rectangle with double-headed arrow *might* be a center-tapped inductor/choke. If the two items underneath it that you marked 'transistors?' are actually SCR's, then a center-tapped inductor could be used to commutate them. When one fires, the sudden rush of current through that half of the inductor produces enough induction to stop/reverse the current through the other side and commutate (shut-off) the other SCR. In a slightly different form this sort of circuit used to be used in power inverters.
So the two SCR's would pulse each end of the center-tapped primary of the transformer. But I'm not sure of the rest since it looks like +24V is feeding the choke/SCR and the center-tap of the transformer primary is also +24V. Where does match-mark 'A' go off to?
daestrom
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To the coil of yet another logic relay (d71). It energizes the relay coil.
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DaveC
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