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'92 Mits DWC110-SZ - puts cutting power to the head as soon as "ready" is pushed.

Wade C

Stainless
Joined
Jul 21, 2004
Location
Wiggins CO. USA
'92 Mits DWC110-SZ - puts cutting power to the head as soon as "ready" is pushed.

Been fighting an issue with my 1992 Mits DWC110-SZ where upon pressing the "ready" button, it comes to life as expected, but then after about 1 second it shows almost 150V on the volt meter and the wire spool will wind up the wire, pull it out of the head, and will not shut off with the "pre-tension" switch turned off. I do not know what else it may or may not be doing as I didnt feel comfortable tinkering around with 150V to the head that I cant shut off without hitting the Estop or full power down. Checked it with a DVM and am getting 144VDC between the head and the table.

I was told there are supposedly 3 different safeties in the system to keep this from happening. It was suggested to me to swap out the two main power units in the back half of the cabinet, then if that didnt work, the DC unit directly below it, and then if that didnt work, the card rack with the SIFA, MNTA, and MRAA boards. I have tried all the above and it still does it. But the parts I swapped in, though they were supposedly good, I dont have verification of that. (they are from a donor parts machine I have). Though I would find it odd to have a second parts machine that has the exact same issue as mine is having.

Im sort of out of ideas of what to try shy of calling in the tech so he can do some one on one time with the machine. Any thoughts of something that may be the culprit here? I have a decent amount of spare cards, racks, and units from parts machines - so there is at least a chance I have a spare on hand, if I knew what I should swap out.

Any thoughts or advise is appreciated.

Thanks!
 
Hi Wade C,

The only thing that can supply that kind of voltage is the Power PCB'S as Main Units or Sub Unit. I've got one time this issue on FX that only pushing power it has 150 VDC between head and table.
My recomendation is to disconnect Main units completely (all connections): Firstly disconnect one Main Unit and measure against head and table, if no voltage you have found your trouble, if still have voltage try with the second Main Unit and connect the first one. After this test if it is not solved disconnect the Sub Unit and try again. One of them must be faulty, is true that SZ is an old machine and I don't have all the info but also could be the DC unit that is a litle it different from FX series.

Best Regards.
 
Are you meaning disconnect all connections going OUT of the main power units? (only the wires going to the machine from the power unit) Or also disconnect the inputs to that same unit? (so that there is no connection on the main power unit at all)

Just want to be sure I understand.

Obviously, which ever way I go, I would need to insulate/protect from shorting the disconnected wires with potential voltage...

I have already swapped out the two main power units (the two Main Switching Units as per the drawing attached), checked it, still had voltage, then the DC unit (as per drawing), tested, still had voltage, and then the Machine Control unit rack (as per drawing) and still had voltage. I did not try swapping the Sub Switching unit.

I do have two different sets of "spare" Main Switching Units and the Sub Switching unit - though the spares are not confirmed good.

SZ_rack_locations.jpg
Thanks again for your time!
Wade
 
Hi Wade C,

Disconnect from one MAIN UNIT INPUT and OUTPUT and of course isolate the inputs. Then try to turn on ready and measure between head and table. If not do the same with the second MAIN UNIT and connect the first one that you tested.
If the main Units seems to not be the problem try with SUN UNIT.

Best Regards.
 
Thanks for the suggestions. I did as you described and came up with the following:

Disconnected inputs and outputs of the Main Switching unit (MSU) located in the center of the back cabinet (middle rack top row of right hand pic I posted previously). Wire Pretension switch is OFF and no wire around the pulleys to the upper head.

Powered up, Released Estop, hit "Ready". Few normal clicks from the control cabinet, wire tension/brake roller was spinning, and after 1-2 seconds I got +144.8VDC to the head as per my Fluke 87 (upper head + to table -), about that on the meter on the panel.

Hit Estop, powered down, breakers off. Reconnected the middle MSU and disconnected the second MSU (left side).

Powered up, hit ready, few normal clicks from the cabinet, wire tension/brake roller was spinning, and had -3.136VDC on the DVM and panel meter showed a tiny bit of movement that would equate that I would guess.

Hit Estop and powered down. I have not reconnected that MSU yet.

I figured better to touch base with you prior to doing anything else. But it seems that at least there is something pointing to either that left hand MSU, or what ever controls it.

I have, I think, 4 other MSU's from parts machines, two of which were in the machine when the issue first appeared (original to this machine since Ive owned it). So I have more units I can swap in to try if that is the next move. I should also have 2 other Sub Switching Units available in unknown condition. I would suspect the tension/brake roller being a separate issue - maybe caused by the voltage issue, but otherwise not related?

Thanks again for taking the time to offer assistance and suggestions.

Wade
 
Hi wade C,

I see with the second MSU out there's no voltage of 150 VDC, so this MSU is not ok, must change it.

About the spinning of wire/tension brake roller, you mean main tension roller? If that, is spining as it has to do?, I mean in the same direction that the wire goes? or is it going to the inverse direction? That's another problem apart from MSU UNIT, maybe some AVR is not OK or one transistor is faulty.. I must look on documentation.

Best Rergards.
 
Ill swap that one out, with one of the others I have and check.

On the tension roller, I think thats what its called... Ill dig around and see if I can verify the technical name in the parts book. The wire goes from the spool to a couple plastic pulleys, then around this roller once, around two more pulleys, back to this roller, and then on to a few more pulleys before it goes in the upper wire guide at the top of the Z column.

I think it was spinning in reverse - as if it were to try and wind the wire back up onto the spool.

When I test out another MSU - hopefully today, Ill try and get a video and post it so you can see things.

Thank you very much for the help!

Wade
 
Update:

Changed out the suspected MSU - no longer have +144.8VDC from head to table. I guess one of the spares that I had also had the same issue as the original - so when I swapped them out at the advice of my tech, and still had the same exact problem. I dont know that I would have suspected that. Sure, could have seen it been bad - but with the same problem is surprising. I now have -3.130 VDC between the head and the table with both MSU's completely connected and in the ready state.

So, now what is left is the tension Roller/Motor spins constantly (yes checked the parts book and is called the tensioner roller and motor) - in reverse - as soon as the ready button is pushed. I want to say I think the card that controls that stuff is the MNTA card - which I dont think I have a working spare of... The original burned out a few years ago, and replaced it with the one from the parts machine I had at the time. Then when this whole voltage mess happened, I changed that again, after swapping the MSU's and the DC Unit - and it did the same thing. So I would presume that the voltage to the head could have fried the same part of the wire control card on the swapped one - either when the previous owner had it with the same issues or upon me installing it here while trouble shooting.

I have a couple videos if you want to see them, but they really dont show anything other than what I typed above. I took them more in case something new happened so I had record of it.

Im going to let my tech know this as well in case he has a suggestion on the tension roller being on constantly. I suspect he'll say "oh its ____ card - replace that and you should be good" - which I bet will leave me looking for a card I dont have a known good one on hand.

Thanks for the trouble shooting process on the MSU's! Any additional thoughts or suggestions you may have are welcomed.

Wade
 
Hi Wade C,

Good to know that MSU issue was solved !!. OK going to the second issue, I've attached some few info I have about MNTA PCB, please check the input voltages and transistors marked in red, I think some AVR or transistor is faulty. If not I think MNTA is not OK.

Let me know.

Best Regards.MNTA.jpg
 
Ill check the input voltages, but I am not all that knowledgeable on testing a lot of electrical gizmos. Ill do a search on how to test transistors and see what I find.

Thanks
Wade
 
Test Results - I have three different racks with transistors on them, but just checked two of the three.

Fluke 87 meter - set to "diode" test
Rack 1 (93-90SZ)

Positive lead on "B" - Negative lead to E & C
TR1-B to TR1-E = .733
TR1-B to TR1-C = .615


TR2-B to TR2-E = .728
TR2-B to TR2-C = .615


TR3-B to TR3-E = 2.302
TR3-B to TR3-C = 2.303

Negative lead on "B" - Positive lead to E & C
TR1-B to TR1-E =1.237
TR1-B to TR1-C = OL (open loop)


TR2-B to TR2-E = 1.202
TR2-B to TR2-C = OL


TR3-B to TR3-E = .656
TR3-B to TR3-C = .656


Rack 2 (93-110SZ)

Positive lead on "B" - Negative lead to E & C
TR1-B to TR1-E = .746
TR1-B to TR1-C = .620


TR2-B to TR2-E = .737
TR2-B to TR2-C = .617


TR3-B to TR3-E = 2.497
TR3-B to TR3-C = OL

Negative lead on "B" - Positive lead to E & C
TR1-B to TR1-E =1.322
TR1-B to TR1-C = OL


TR2-B to TR2-E = 1.255
TR2-B to TR2-C = OL


TR3-B to TR3-E = 1.149
TR3-B to TR3-C = .659


Voltage at the MNTA Card (rack installed)
-12 to +12c and +12d =11.45v
-12 to 0V = -.544v
-12 to P24 = 21.63v
0V to +12c and +12d = 12.00v
0V to P24 = 22.17v

And now, to add the confusion to the mix...
I took the rack out and pulled the MNTA card to get to the transistors for testing. When I put it all back together after testing the transistors, and powered up to check voltages - the tension roller/motor are NOT spinning and so far things seem to be working. :confused::toetap: So, in typical fashion, I bet I have something thats going to go again, but I dont know what.

Thats what I know for now. Need to do a couple things and then will try and do a test cut on it and see if everything works as it should.

Wade
 
Got a chance to try and set up for a cut.

Some things are not working. I suspect they are related to the MNTA board?

- Wire Collection Motor/Rollers will not turn on. I threaded the wire manually, and that all worked as expected. But pressing the wire feed or align wire button makes a click in the air solenoid box, but no roller movement - doesnt even wiggle when the wire feed button is pressed.

- The DI resign pump is not turning on in automatic. I can manually turn it on and it runs just fine, but will not turn on in the auto position (where machine controls it) Had an LR error and showing 60, and went down to 42 over about 5 minutes of being manually turned on. It usually kicks off the pump at 13 or 14 and turns on around 15-16 if I remember right - when in auto mode.

So obviously I cant align the wire or TaperZ, or test cut.

I do have a couple extra SIFA boards on hand that were sold to me as "good with a DOA warranty" but the time frame for the DOA warranty has lapsed, but the only extra MNTA and MRAA boards I have were already in this machine - so if the voltage to the head caused these other things as well, then I likely dont have a working spare to try of those two cards. I have been keeping my eyes open for MRAA and MNTA boards but no luck yet - at least not in the price range Im willing to take a gamble on without knowing that I do need either card.

Thats what I know for now. Guess Ill move on to another project until I get some brilliant idea to check something.

Thanks again.
Wade
 
215.0 - 216.1 - 217.2 at the machine circuit breaker.

Im on a 240 Delta service going into a Mits transformer tapped as low as it will go (panel says 214 out on the transformer)

My service to the transformer is 246-247 in - leg to leg.

Wade
 
And your tapped on the 220 on the machine transformer correct? Assuming it has 180/200/220..

You seem to have lots of electrical & board issues?!
 
Youre meaning the one in the cabinet? yeah its feeding in the 220 lugs. It only has 220 and 200 on it.

Guessing maybe she is starting to show her age?
 
Thought I'd ask, only time I had issues with boards was when I was running a bit over with voltages. Learned my lesson to keep things within spec.

Hope you can figure everything out!
 
Thanks for asking... it did make me go check and verify - which is never a bad thing.

I hope so too... When I got the FX I thought "I can sell the SZ or keep it and see if I can't crank through some stuff and get caught up first, and then decide if it was handy enough to have to be worth keeping" Guess maybe I should have sold it then, and started thinking about adding another more current one after I had saved up some. Though, while it was running, it sure was nice to have both going. And in the process I had added a few higher dollar spares to the shell for those bad days (monitor, floppy drive, and a set of good X,Y,Z servo and U/Vstepper drives). Having one chugging through low tol batch work on a fixture loaded with 12 parts and use the other for the more important and one off stuff. Has me feeling like whether this SZ lives or dies, I will probably start saving for a replacement for her. Just a matter of whether she goes to machine heaven or in operating condition. Gotta pay off the new to me but essentially new Okuma Genos lathe that made its appearance here in April - first though. Management (aka SWMBO) might look at me funny throwing down for another newer machine in such a short time frame. :D

Wade
 
Got a new to me MCU rack (MNTA, MRAA and SIFA. And things worked!
Tried making a cut and it breaks the wire as soon as it touches metal.
Did some research and got to talk to the tech for a minute, and found out there are versions of the main switching units. I had one with no sticker, and one with a yellow/white sticker. Read a thing about the versions and the oscillator board having to be different too. So dug into the parts from the other two Mits SZs I have... grabbed another yellow/white sticker switching unit, and the Oscillator board from that machine.

First, checked the MSU to make sure I wasnt swapping in the original problem. Nope, good... no voltage at the head when the ready button is pushed.
swapped out the OSBB board. Fired er up. Everything that had not been working - to this point, was still working. Wire collection, threading, DI pump on auto, etc.

To check, I threaded the wire, filled the tank, turned on flush, then wire feed, and then "machining on" just to see before I threw material in to try a cut. Pressed machining on and immediately tagged the volt meter, as I realized it, and was looking back to turn it off, there were some loud pops and I think a spark or two that came from somewhere around the upper head/in tank area - but I was looking away to kill machining or hit estop so was not really looking. Unded with a U700 alarm (power supply)

Thought maybe the wire shorted and popped, but wire was not broken. Checked fuses, and that is when I realized, the MSU I put it, someone had taken a little rectangle fuse out, so only have one of two. I found this, as I was ohming fuses. Ends up, the 3 of the 4 - 0.5 rectangle fuses were popped, and the 30A fuse on each MSU was blown.

Replaced ALL fuses that were missing or bad. Powered up (but no way in hell was I going to turn machining on - just checking other stuff), hit ready. No more alarm, wire feed, collection rollers, di pump, etc all were working. So there is at least a little good news.

Ive been over connections again and again, making sure I didnt screw up a wire somewhere.... (thinking the E and W wires on the back of the MSU that go to the machine primarily since they are a little awkward to deal with) Nope, all good. So Im perplexed, and have not heard anything back from my tech yet. So figured I would update this post in hopes I might run into a suggestion for a fix, sooner than later.

Im guessing maybe the problem is the MSU that I swapped in? But also nervous to swap in another and have the same thing happen (fear of damaging something else in the process.

On a side note, if things dont go well.... Ill have a SZ and remnants of two other SZ machines worth of parts, available for sale before too long :/ I dont know if all wires are like this or if its just Mits - as Ive only ever owned Mits wires, but I have never had so many issues with any other machine Ive had since 2005 (Okuma and Fadal) and I have likely been spoiled by the tech support from Okuma and the Fadal places out there... and of course then there is Mits's "hey, pay us 1500 buck so we'll talk to you and you can buy parts from us" fee for each machine you own. Makes me wisk Okuma made wires.
 








 
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