murex transmig 140 fault

[NotANormalCoder]

Hi Stephen. If you still need tech info, please PM your email address and I'll send it to you. The contactor is powered from some transistors on the PCB, so it's unlikely that they are the problem. The relay is for motor control and not directly related to the contactor. Note that if the contactor is not an original one, it may have been replaced with an AC version and as I have found out to my cost, they never work correctly. However, please throughly check all the soldered joints, especially those where the pins for the multiway connectors are attached to the PCB. Final thought, as I explained previously, one coil lead to the contactor is supplied via a normally closed contact on the top of the contactor. Find this and make sure that it is very low resistance (<5 ohms??) when at rest, If this contact is mucky, it may well hamper the coil operation. Also check continuity of the contactor coil as I have had these with a break in the coil wire to terminal fault.
Good luck - Dave

 

[Stephen Curle]

Hi,
Still not got this resolved, although to be fair I haven't looked at it for a while. (Busy / broken leg etc)
View media item 9916A2 & A3 are the normally closed terminals. When the contactor is in I get 25v DC across these.
A1 & A2 are the coil connections. When I pull the trigger I get 3v DC across these. I think I should be expecting either 12v DC or 25v DC.
If I put a 12v DC car battery across A1 & A2 it works perfectly.
Could anyone help re suggesting why I'm only getting 3v DC across A1 & A2 and how to resolve this?
Ps coil lead is showing 6 ohms

Thanks

Stephen

 

[Stephen Curle]

A couple of photos to show the coil voltage and the NC terminals (21 & 22)
View media item 9907 View media item 9918

 

[bwservices]

That is an AC coil,it sounds like you need a dc coil

 

[NotANormalCoder]

You do indeed need a 24Vdc Contactor. I know from bitter past experience that AC contactors do not work in these machines. It is also vital that you understand the weird way the contactor is wired up. I believe that I sent you a circuit diagram a while ago, so you need to study and understand this, fit the correct contactor and wire it up as shown in the diagram. It is not as simple as other machines that just need a 24V supply to the contactor coil, as the voltage is supplied to the contactor coil through a normally closed contact that by-passes the gas solenoid valve, allowing full (24VDC) voltage to be applied to the coil for long enough for the contactor to energise. When it energises, the normally closed contact opens, putting the gas valve coil in series with the contactor coil, with just enough current to hold them both in the operating state. It is also possible that fitting the wrong contactor has damaged the transistor network that provides the supply (TR105/106 & 107) but as you stated you are seeing 25 Volts in the circuit, it may be that these have survived. Also note that R113, D113 and C117 are for surge/spike protection but should be checked for correct functioning, especially the diode, as if this is shorted, you'll lose all the voltage to the contactor coil.
HTH Dave

 

[Stephen Curle]

Thanks Dave,
You are a star! Yes you did send me the circuit diagram (a year ago)! This is me just getting round to looking at it again.
That's the coil that was fitted to it when I bought it (second hand) 20 years ago. It's not had that much use though so it may have taken a while to develop issues. I'll get a 24v DC coil for it. Can anyone recommend the est place to source one? http://www.scatts.co.uk or would this do the trick https://uk.rs-online.com/web/p/contactors/3927835/

Could D113 be the reason that I am only seeing 3v Dc across A1 & A2?

Thanks again

Stephen

 

[Stephen Curle]

Ok
A wee update. Gave Dave a call (very helpful) I have a new 24v contactor ordered. Disconnected the exciter wire from the coil and am getting circa 30v DC so hopefully the PCB is ok. Was only seeing 3v DC when connected.
I'll feed back once I have the new contactor fitted.

 

[Stephen Curle]

The new 24v DC contactor is pulling in perfectly but the gas is now not coming on! The gas solenoid is ok as I tested it by refitting the old contactor and it worked ok.
I'm starting to think someone may have swapped wires about when they fitted the AC contactor.
Does anyone have a wiring diagram showing the cable numbers or a photo of the contactor wired up correctly?
Thanks

 

[mike 109444]

Something in this lot may have the info.
Note these are for the 130 and 160 so use with caution