# need help Repairing a jman 300 cnc mill

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#### fixinstuff

##### New Member
I am working on a cnc mill. The thing wont power up. This may seem obvious . First I replaced the DC power supply for the cnc. I powered it up,and nothing happened! Then I went to the main power transformer. I checked the power, this is what I got. There are five outputs. #1-200v, #2-200v, #3-75v, #4-68v, #5-115v. The schematic says that they should be #1-89v, #2-82v, #3-75v, #4-68v, #5-115v. The two first leads are obviosly higher than specs. I think it blew the DC power supply again. Would this cause this to happen? Is the only course of action to replace the transformer and the dc power supply? I checked all the fuses none are blown. This is another perplexing thing to me. Any help would be appreciated.

#### lavenatti

##### Member
Are you sure you have the correct diagram of the transformer? I find it pretty unusual the two windings would go bad and end up at 200V. If this is really the case, and the transformer can still put out any current (check the voltage on all the leads when it's hooked up and turned on. You probably fried the power supply. If the voltage on the two bad transformer windings drops to zero or a very low voltage you may not have ruined the new power supply and the old one may be ok as well. Just the transformer is bad.

#### fixinstuff

##### New Member
More Questions

Thanks for the reply lavenatti, the problem is that it raises more questions. Are you saying that a burnt out transformer wont short across the windings and therefore send too much voltage? That is what I was thinking. I am just learning how these electrical and electronic parts work. therefore I am confused about the transformer. I have never had to deal with a bad one before. I am a machinist in a shop and I got threw into this repair thing. I have been doing some intense study on the subject though. I have learned a lot. I have also found that I enjoy the electronics repair field. I really dont know how to tell if I have a bad transformer. The power supply was getting the correct amount of voltage comming in (115v AC). It also has serveral outputs sending from 5v DC to 24v DC to the computer componants (I think). The supply is dead in all output leads exept for one (a 5v lead). I sent it off to be repaired originally. Then I beleived that was all that was wrong with it. I mounted the rebuilt power supply in the machine and nothing happened. Then I started doing some research and that lead me to the power transformer. This is the first component in the power circuit besides the fuses and they checked out allright. I checked it out today and the DC power supply is giving the same readings as before also the transformer has the same specs on the plate on top of it. Therefore Im pretty sure the specs are correct. You should also know that the machine has not worked in a few years, another man whom does not work there anymore was running it and I`m not sure what was happening before it went down. thanks for your help!

#### olly_k

##### Member
How are you measuring the transformer outputs might I ask? From what you are explaning, It sounds as if the transformer is stepping up instead of stepping down the voltage??? Assuming you have measured correctly, is the mains input connected to the correct terminal of the transformer? i.e. if you connected the 115v input to the 89v output you may get 200v at the primary of the transformer? I would have thought the transformer would have died though but you never know...
Can you supply a schematic of this setup?
Also what is the 89V supply line used for?
I have never heard of a transformer acting like this before unless a, it's connected up wrong or b, it's designed to step up in the first place!
Transformers normally burn out plain and simple!

#### fixinstuff

##### New Member
thanks for the reply OLLY_K. I will be at work tomorrow July 7. I will get you the needed information to analize the questions you have raised.

thanks,
fixinstuf

#### fixinstuff

##### New Member
here is the drawings

I think this is all you need to answer my question. two drawings are attached.

thanks
fixin stuff

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#### olly_k

##### Member
Also did you look to see if it possible that the supply is linked up to the wrong winding - it might seem unlikely but you never know!

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