Re: Dc power supply in cnc not working
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Re: Dc power supply in cnc not working
In case you didn't see post #20 after my edits:
- Make sure your 42V consumers aren't shorted... TOP PRIORITY as this is the TOP reason for needing to do the following replacement:
- Replace U1 (LM338) on the board, make sure resistors aren't open (infinity ohms) after you remove the LM338 to make it easier to measure them.Comment
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Re: Dc power supply in cnc not working
Hi eccer
Thank you that does sound logical
Maybe ill try ordering the u1 and replace it...if part isnt obsolete
as you said its probably the most common failure part on the board.
It say LM338 is 1.2v to32v...which i am getting about 1.4v at the output terminals
My circuit is 42v...so maybe need upgraded part? Higher than 32v?Last edited by shelby5041; 08-28-2021, 12:32 PM.Comment
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Re: Dc power supply in cnc not working
It is going to be a challenge to find a regulator that goes higher 36 voltsComment
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Re: Dc power supply in cnc not working
You don't need to get a better regulator as long as there are no and never a short(s) on the output to ground even for a short duration.
If there's a short, expect to toast the device pretty much instantly.
If you need a 42V regulator that can withstand temporary shorts, you'll pretty much have to design your own.Comment
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Re: Dc power supply in cnc not working
Ok thanks ill buy same part...one note...when this loss of 42v happened at same time a 10a fuse blew near the machine main ac input
I replaced the fuse and has not blown again
At the time i was working on a diff area of the machine...trying to install a potentiometer on a diff board to control rpms of spindle...when i installed the pot and set it at 0rpms the spindle was turning fast...i was like what the heck...so i powered off machine...rechecked pot wires and powered on again and main fuse blew...along with losing my 42v output.
Maybe this is all related.Last edited by shelby5041; 08-28-2021, 01:04 PM.Comment
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Re: Dc power supply in cnc not working
No i do not know what caused main fuse to blow but it has not blown again
..if i replace the lm338 maybe it will blow main fuse again...its a cheap part so ill try it
Or maybe wires shorted out while i was working on machineComment
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Re: Dc power supply in cnc not working
mouser ... backorder
digikey ... not in stock
... unobtanium?Comment
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Re: Dc power supply in cnc not working
Try this LM338T
https://www.digikey.com/en/products/...YaAhVXEALw_wcBComment
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Re: Dc power supply in cnc not working
ThanksComment
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Re: Dc power supply in cnc not working
hmm that looks like it's on backorder too, but probably easier to get that way than mouser.
Seems you can only get the TO204 version in stock at the moment which sure wouldn't fit...and costs $ARM$LEG ...
Ah here might be an option. https://www.jameco.com/z/LM338T-Nati...or_192284.html Would be a pain if it truly was unobtainable, but I'd not be surprised if they become more and more difficult to acquire as time goes by...Last edited by eccerr0r; 08-28-2021, 09:31 PM.Comment
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Re: Dc power supply in cnc not working
I will have to get some it looks like they are becoming obsolete and will be really hard to getComment
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Re: Dc power supply in cnc not working
The spindle has a separate speed controller board called cheetah-sm-2hp
I was just hooking up a manual potentiometer to control speed...and i connected it per manual.Comment
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Re: Dc power supply in cnc not working
i know ebay is known for many fake disguised parts but since this machine will only be used once in a while as hobby i was thinking of just buying cheap chinese LM338 off ebay
or is that a bad idea??
i have bought many cheap fake electronic component parts off ebay and have had no issues but most of what i buy goes into items i dont use often
does anyone have first hand experience buying cheap fake parts off ebay straight from china?Comment
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Re: Dc power supply in cnc not working
If it's just for home use and don't care it prematurely fails, go for it.
Due to its similarity to LM317, I suspect that fakes would be based off this much lesser part. Need to really do testing to ensure you don't have a fake...Comment
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Re: Dc power supply in cnc not working
what you may find cheap on ebay or ali-express is the older ones that arent lead-free.
those cant be comercially used in most country's so surplus isnt worth much.Comment
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Re: Dc power supply in cnc not working
yeah im sure they are fakes and not to specs but since its just home hobby use and i wont use it often ill just buy a 10pack of LM338T fakes/non spec for $3 shipped lol straight from china
in no hurry
on the other hand when i bought my sanyo stk amplifier chips i bought from a guy who had 25year old stock..real..all the stk amplifier chips that say sanyo on them now are fakes since sanyo is not a company anymore nor has it been for many many years....sanyo is just a name that chinese bought and market as crap products today...when sanyo was a company they made decent products...this is same with polaroid..zenith..rca..bell howell...these are not actual companies anymore ..just names bought by chinese and put on POS products.
you can tell by the weight and the type of print on the front...i wanted real becasue i wanted to keep my classic fisher receiver original
Last edited by shelby5041; 08-29-2021, 11:02 AM.Comment
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