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  1. #1
    The manual has been translated from German but patently not by a Brit.

    The name of the game is persuading LED b20 to light show the guards are in place and allow the hydraulics to come on.

    The manual says, "Magnetic read-contact on safety grid of the safety gate, activated by a magnet mounted to the stationary mould platen".

    Do you reckon "read-contact" should be "reed switch"? If so I am good to stick my multimeter up it's yarris.

    It is one, or more, of 3 sensors that is kaput.

    #2 looks common or garden mechanical.

    #3 is built in to a "Rexroth hydraulic interruptor". Sounds a bit Dr Who but has a little Perspex window and I can see what looks like a contactor going up and down. Hoping it isn't that one, too many screws for comfort.

  2. #2
    m_c's Avatar
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    Reed-switch would fit the context.

    However, if you're wanting to be careful, I'd do it with the machine powered up and using a voltmeter to see if it's working or not. That way you're less likely to blow up your multimeter, or any bits on the machine, provided you don't short anything out while probing!

  3. Hi Robin,

    I agree that sounds like a reed-switch...

    #3.. The BOSCH Rexroth website has a handy multi-language media search and a quick browse suggests that a 'hydraulic interruptor' is in fact a float switch - I would guess to check the level of hydraulic fluid - or it could possibly be a pressure switch. They all seem to be conventional contact switches so I doubt you'll do any damage by probing with a multimeter.. I would guess its a series connected 'AND' gate of switches...

  4. #4
    I hear what you say about measuring volts rather than resistance, sounds very logical.

    The hydraulic interruptor looks like an afterthought because it doesn't wire to the little distribution board which does the rest of the guard switches. According to the hydraulic circuit diagram it diverts any oil sent to the platen closing ram straight back to the reservoir. I presume they used the electrical switch on it simply because it was there. It seems to do exactly the same job as the "read-contactor".

    After much reeding of the manual, I have found a reference to an optional, "pneumatic safety gate" which I don't have. I believe it locks the guards shut while the machine cycles but the manual is vague. There is a socket where an "auxiliary control box" plugs in and the manual says, "Jumper plug in b41/b42 if control box is not connected. Without plug in b41/b42: no mould closing". Off the top of my head, I can't remember there being a plug in it, this could be fun to try and recreate without a circuit diagram if it isn't there. OTOH it would be nice to think that wiring and sensors are all present and correct.

  5. #5
    There's another idea out the window, I don't have the aux socket, it's blanked off. Everything seems to work fine, except it doesn't.

    To understand it I took the guards right off and found 2 more gadgets to stop me cycling it with the guards open. A switch and an interlock that physically blocks the platen if all else fails. This machine is seriously paranoid.

    It all comes down to one box of tricks with a 12 wire connection that covers most everything and I will need help to buzz it out, I haven't got enough hands.

    With the guards off I went around all the bits and pieces figuring out what they do. It's much easier to fix something if you know how it works and the manual is not friendly. Now I understand it everything looks bleedin' obvious.

    I was surprised to find the fixed platten isn't fixed at all, which explained why it has pipes connecting to it, it's got grease lines. If it moves before it should, the machine assumes something didn't eject properly and it would be a bad idea to insist.

    Next. disassemble the box of tricks, buzz it out to the controller, make sure the guard switches are connected. It has 8 switches going to 12 wires, how hard can it be?
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  6. #6
    Still no reason why LED b20, guards closed, doesn't light. I took the control box apart and found a mess of TTL, this thing doesn't have a microprocessor. The control box has an input labelled b20 which lights the LED and does nothing else.

    There must be another circuit board to nobble b20 somewhere in the cabinet which is an absolute rats nest of wiring. However, I now know which pin on the monster plug control box plug goes to b20. Armed with that I should be able to find this mystery board and see which of it's inputs is failing to light b20 and enable the hydraulics.

    When I plug/inplug the shorting link on the optional core retract guard socket I can hear a relay click, so I am probably looking for a board with relays on it.

    I shall keep posting, I know you lot can't help but somehow it makes me feel less alone

  7. #7
    Hmmm!

    Found the safety guard circuit relays and they are truly unwell. I'm looking at 6A 3 pole c/o relays and only 2 out of 9 normally closed contacts actually buzz through.

    Close up piccy shows they are full of gunge, probably plastic residue.

    This isn't arcing causing the problem, most of the nc contacts aren't even used. These 6A relays drive nothing more than other relays or LED's.

    Next problem, they are archaic, not listed by RS, Farnell or Rapid. Do I try and clean them or bodge in equivalents???
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  8. Quote Originally Posted by Robin Hewitt View Post
    Hmmm!

    Found the safety guard circuit relays and they are truly unwell. I'm looking at 6A 3 pole c/o relays and only 2 out of 9 normally closed contacts actually buzz through.

    Close up piccy shows they are full of gunge, probably plastic residue.

    This isn't arcing causing the problem, most of the nc contacts aren't even used. These 6A relays drive nothing more than other relays or LED's.

    Next problem, they are archaic, not listed by RS, Farnell or Rapid. Do I try and clean them or bodge in equivalents???
    These are open chassis relays??? Otherwsie how did they get gunged? If the contacts are ok, I'd go for cleaning them. Can you swap to another contact pair? What relays are they?

  9. #9
    Not open chassis but still gunged. The second board has 2 similar relays, different make... 2 out of 6 contacts connect on that one.

    I wonder if there are any on e-bay? I will have a look tomorrow.
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  10. #10
    Found the relays on ebay but then I drew out the rest of the circuit.

    I've never dissected a commercial guard controller before, curious stuff.

    There are 4 switches tripped when you close the guard, they pair up and close 2 relays. When both relays are shut the guard is accepted as shut.

    A third relay closes when you open the guard, this relay has to stay closed for normal operation.

    As the other two relays close they cut the third relay back to a holding current. If any guard switch opens momentarily relay number 3 lets go. If the switch should close again the holding current isn't enough to reset it.

    Basically, lose any guard switch and you have to open and close the guard before you can restart the machine.

    The circuit is dependant on the holding current so changing relays seemed like a bad idea. I had to clean the contacts.

    If it plays up again I will rework it and drag it in to the 21st century.

    While tracing the circuit I noticed one of the solenoids on the hydraulic valves had had it's connection broken off, probably in transit. Bummer. Luckily the wires are still visible so I should be able to patch it.

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