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That component was originally named "TS1" - throttle solenoid? In the diagram from the manual that I posted it is called "CR1" and the parts list describes it as "Relay, enclosed, 12v DC, single-pole, double-throw". However, the circuit diagram does not show a relay coil, there is no wiring for any contacts, and the "relay" has no item number in the parts diagrams.
The SCRs are shown as being rated at 8.5 Amps, but the solenoid is described as "12 volts DC 20 Amp". That current draw does seem excessive, but maybe Miller thought that the SCRs weren't up to the job so they interposed a relay, but did not fully document the change.
Ah thanks, I should've read the parts list 
I think/assume the contacts are the 2 parallel lines that look confusing like a capacitor symbol in the high-side of TS1 path.
There's also a note in the manual you posted about if you strike an arc, or come out of auto idle mode while the engine is slowing down, it's possible to trip breaker CB1 so it's safe to say that's an area of overcurrent weakness. Without the relay you just hope the breaker pops before the SCRs
I think/assume the contacts are the 2 parallel lines that look confusing like a capacitor symbol in the high-side of TS1 path.There's also a note in the manual you posted about if you strike an arc, or come out of auto idle mode while the engine is slowing down, it's possible to trip breaker CB1 so it's safe to say that's an area of overcurrent weakness. Without the relay you just hope the breaker pops before the SCRs
chrismac
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While I sit here in the back ground letting you electrical or electronic guys do your thing, please see the reply from Miller on the change, I sent an email asking for an explanation if possible about the modification.
The purpose for CR-1 was to move the higher current of the TS-1 off the board its self and drive the coil of the relay instead, The board driving the coil of the relay is of a much lower current draw that over time extends the over life and reliability of the board its self, When CR-1 activates the contacts of the relay handle the higher current and not the board.
The purpose for CR-1 was to move the higher current of the TS-1 off the board its self and drive the coil of the relay instead, The board driving the coil of the relay is of a much lower current draw that over time extends the over life and reliability of the board its self, When CR-1 activates the contacts of the relay handle the higher current and not the board.
chrismac
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So I have been trying to get my head around the wiring, getting there, testing continuity to ground for any faults in wiring, one thing I have picked up is the solenoid positive and negative side terminals have continuity to ground with no wires connected, I am wondering if this could give me my fault of the solenoid being energised when in weld mode continuously, should the solenoid be giving this reading https://www.amazon.co.uk/gp/product/B07DQK9SVY/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1
Thanks
Thanks
Well, that doesn't sound right. I wouldn't expect either of the 2 terminals to be connected to chassis ground given the circuit diagram we've been discussing so either the solenoid is faulty or the wrong part. Or there's expected to be some insulating material between the case and the chassis (but I find that unlikely).
One more thought - How are you measuring continuity? There is a chance that only one of the terminals is connected to the chassis, but both seem like they are due to the low resistance of the solenoid coil confusing whatever continuity tester you're using. In these situations you need to accurately measure the resistance between each terminal and ground. One would be near zero, the other the same as the coil resistance as measured across the 2 terminals.
However, even if you had such a solenoid, I refer you to my previous answer - it's either the wrong part, or it somehow needs electrically isolating from chassis ground.
However, even if you had such a solenoid, I refer you to my previous answer - it's either the wrong part, or it somehow needs electrically isolating from chassis ground.
This picture shows the pos and neg connections on the solenoid:
www.fridayparts.com
buy 1502 Series 20 Amp 12 VDC Pull/Hold Type Solenoid 106977 replace Miller
1502 Series 20 Amp 12 VDC Pull/Hold Type Solenoid 106977 replace Miller Replace Part Number:106977 Specification:20 Amp, 12 VDC Application:Fit for Miller
chrismac
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Typical the image from my amazon purchase list has the end cap covering the terminals, wires 40 & 41 connect to the terminal's, when I check from the positive terminal to the body of the solenoid it give a continuity reading, also the buzzer goes off, the same when I check the negative side, this is with the wires disconnected, just the bare unit bolted in place.
Still waiting for the diodes to arrive, the first lot were too large in physical size.
I'd still guess that the -ve is connected to the case and the +ve isn't, it's just that continuity buzzers are not discerning enough to tell (because the solenoid coil has very low resistance).
Anyhow, we know the solenoid "works" as it pulls-in when in weld position and releases in power, so there can't be a dead short between the 2 terminals.
What is the solenoid fixed to? Is whatever it fixed to connected to chassis ground?
Anyhow, we know the solenoid "works" as it pulls-in when in weld position and releases in power, so there can't be a dead short between the 2 terminals.
What is the solenoid fixed to? Is whatever it fixed to connected to chassis ground?
prepman
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Sorry... but can you clarify your 1st statement and add the diagram as an attachment? I used to do lots of this for a living. Can't promise anything though.
Do you have a diagram of idle control board?
chrismac
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Hi, there should be diagrams visible in previous posts, if you can not see them then in this manual
https://www.millerwelds.com/files/owners-manuals/O412G_MIL.pdf,
Can you open that link?
what would you like clarified on in my first statement.
Thanks
chrismac
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Replacement diodes finally arrived home, fitted it and put the board back in, no change, when on weld mode high revs, flick weld/power switch to power revs drop, when on high revs I unclipped the negative wire and it stayed energised, stopped machine removed wire 41 which is connected to the negative side of the solenoid, wire 33 from the auto idle switch & wire 33 from pin J on the board, I cant see another earth on the wiring diagram that would come into play, expecting when I start it now in weld mode there can be a connection for the solenoid to be energised, I was wrong the solenoid still pulls in.
More investigation and understanding of how the circuit can be being made with what I thought was all the negative connections pulled.
Idle board
Untitled by chrismac2012, on Flickr
Solenoid
Untitled by chrismac2012, on Flickr
More investigation and understanding of how the circuit can be being made with what I thought was all the negative connections pulled.
Idle board
Untitled by chrismac2012, on FlickrSolenoid
Untitled by chrismac2012, on Flickrbased on what you said the other day about there being continuity between the solenoid pins and the chassis when no wires were connected to the solenoid - I'm convinced this is just grounding itself through the metal mounting hardware. I assume the battery negative lead goes directly to the chassis.
chrismac
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Yes correct, so looking like a possible fault with the solenoid, my next planned move I think is to remove the solenoid and test across pins, then remove negative wire and fix to the body and see what happens, the strange thing is this was all working correctly after my initial repair to the board.
chrismac
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Thats what I did insulated the solenoid from the chassis, no change, even removing the negative wire while in weld mode did not release the solenoid, I assume this could be partly to do with the pull and hold type of solenoid, starting to think this thread is not going to have the outcome I had hoped, very thankful for the help to date though.
I'm confused then. My understanding of the solenoid you have is that if you connect the 2 terminals to a 12V battery it will pull in. When you remove the negative terminal wire, it will spring return to its resting position. Because it's a spring return type, it's going to need to have a complete circuit + and - to keep it held in against the spring, unless it's mechanically sticking. But, we know it isn't mechanically sticking because it releases when cutting the positive to it using the W/P switch.
1. How did you insulate it when you tested and did you electrically prove it was isolated from the chassis with a meter? You see, I'm wondering what's underneath that black boot - maybe a metal plunger pin that may still have provided an electrical path to ground via whatever levers it's moving?
2. Did you try physically removing the solenoid from the engine but leaving the 2 wires connected, laying it on the concrete, then seeing how it behaves? I'm curious whether that works as expected.
3. Also if you entirely remove and disconnect the solenoid you could check it's behaviour just by connecting it to a battery, make sure it pulls and releases like we are all assuming.
4. And for a bonus experiment, take the 2 wires off the solenoid and connect them to a 12 lamp, use that to indicate what the control circuits are doing when in weld mode.
1. How did you insulate it when you tested and did you electrically prove it was isolated from the chassis with a meter? You see, I'm wondering what's underneath that black boot - maybe a metal plunger pin that may still have provided an electrical path to ground via whatever levers it's moving?
2. Did you try physically removing the solenoid from the engine but leaving the 2 wires connected, laying it on the concrete, then seeing how it behaves? I'm curious whether that works as expected.
3. Also if you entirely remove and disconnect the solenoid you could check it's behaviour just by connecting it to a battery, make sure it pulls and releases like we are all assuming.
4. And for a bonus experiment, take the 2 wires off the solenoid and connect them to a 12 lamp, use that to indicate what the control circuits are doing when in weld mode.
