Dc power supply in cnc not working

[shelby5041]

Hi
I hsve a cnc mill that uses a dc power supply that outputs 12vdc and 42vdc

Last time i used machine no issues..about 1yr ago

I used it today and i somehow dont have 42v output from ps...the 42v output is only measuring 1.4v

12v output is good

Can someone assist me?

Due to design im not able to remove ps currently

See photos...i have 3 machines use same ps i posted 2 pics for better views

[eccerr0r]

Re: Dc power supply in cnc not working

Well, you'll need to do some tracing.

Do you get voltage across the big capacitor at least?
Looks like wire colors are reused quite frequently making it tough to trace wires without having the device in hand...

[shelby5041]

Re: Dc power supply in cnc not working

I havent tried
Would i just multimeter to test at the red black wires at the screw terminals going to the large blue cap?

Like i said i have 3 diff machines with exact same ps configuration so comparing will be possible during troubleshooting

Just the 1 machine is not getting 42v anymore

[eccerr0r]

Re: Dc power supply in cnc not working

Can only guess there's some sort of switch on the other side of that pcb but without data, no idea.

[petehall347]

Re: Dc power supply in cnc not working

i only see one bridge rectifier so guessing the 12v is derived from the 42v . says to me it might be simple like a poor connection . or a short .

[stj]

Re: Dc power supply in cnc not working

remove the screws holding the board to the cap and flip it over

[shelby5041]

Re: Dc power supply in cnc not working

I will test voltage across the large cap and then maybe try remove board if i can tomorrow

The thing is im not comfortable with large capacitors and electronics in general...so i may not try and remove it....there is,really nothing much on other side of board from what i can see ..though.there are 3 transistor looking components that are mounted to aluminum heat sinks

As i said the 12v output is ok
Just no 42v output as it should be...measures only 1.4v

[eccerr0r]

Re: Dc power supply in cnc not working

Sorry we need to see what the items on the other side is so we can reverse engineer it, unless you can find the schematics to your device... What may look like a transistor could be an IC.

[shelby5041]

Re: Dc power supply in cnc not working

I understand..ill see what i can do

Schematics not avail..machine proprietary and 25yrs old

Compsny was bought out no info avail from new compsny

...thank you

[sam_sam_sam]

Re: Dc power supply in cnc not working

Does the output from the transformer go to 42 volt board first or does it go to the 12 volt board first

Because I noticed that the 42 volt board has diodes in the upper right hand corner I would check those diodes first

Second where is the 12 volts coming from is from the 42 volt board or somewhere else

[shelby5041]

Re: Dc power supply in cnc not working

Thanks..the 12v and 42v both output on the board with the huge cap

Everything starts at the large donut shaped transformer

[sam_sam_sam]

Re: Dc power supply in cnc not working

Does it have two separate winding on 12 volts and one for 42 volts if it does then look at diodes for the main filtering capacitor on that board because if you do not have any voltage on that capacitor then this would be the first place to check but make sure that your 42 volt winding has ac voltage on the secondary winding

[shelby5041]

Re: Dc power supply in cnc not working

hi samsam
i do not know sorry

i will check the voltage on the large blue cap today

if you look at the large donut transformer it has multple wires coming out of it..the yellow and orange go to the 12v side of the capacitor board and the red black goes to the 42v side of the cap board ..im not into electronics but to me it seems the large transformer is outputting 2 diff voltages..is this possible?

i guess if i get good voltages from the cap the issue will be on the cap board..if i get no or low voltages from the large cap then i would imagine the issue could be with the transofrmer or rectifier?

[sam_sam_sam]

Re: Dc power supply in cnc not working

hi samsam
i do not know sorry

i will check the voltage on the large blue cap today

if you look at the large donut transformer it has multple wires coming out of it..the yellow and orange go to the 12v side of the capacitor board and the red black goes to the 42v side of the cap board ..im not into electronics but to me it seems the large transformer is outputting 2 diff voltages..is this possible?

Yes this is possible and it done all time thanks for letting me know that it does have two different winding for each voltage

Like I said earlier I would first check and see if you have ac voltage on the 42 volt winding from the transformer if you do then check the diodes with a volt meter on diode test and make sure that you do not have any open or shorted diodes for the main filtering capacitor input if you have voltage on the capacitor then you need to trace where the voltage goes from there on that board and figure out where you lost the voltage

[shelby5041]

Re: Dc power supply in cnc not working

Maybe good news...i have 45v at large cap so that means trans and rectifier good

[shelby5041]

Re: Dc power supply in cnc not working

Here is pic

[stj]

Re: Dc power supply in cnc not working

that board looks almost new! even the molex pinstrips are the latest type!

[sam_sam_sam]

Re: Dc power supply in cnc not working

Now the question is where are you losing the 42 volts at you need to trace the circuit on the board and see where you lost the voltage at

[shelby5041]

Re: Dc power supply in cnc not working

Lol...not new but high quality made in usa board

25yrs old

Its an old school board so im pretty confident its repairable

[eccerr0r]

Re: Dc power supply in cnc not working

It looks like at this point all of the "transistors" on the board are indeed ICs. The 12V is using a 7812 IC and 42V *appears* to be regulated by a LM338 - which like the LM317 is actually limited to 33-ish volts. So this IC actually being operated out of range though it's valid to run it this way.

So since the red and black wire terminals on the big blue capacitor is getting the 45-ish volts, you probably need to replace the LM338. These die readily when operating above 30V.

That is if you don't have a short somewhere else which caused the LM338 to die in the first place. This is your #1 priority, then replace the LM338. Goes without saying, make sure the resistors didn't fuse but they should be allright.