68kMLA Classic Interface
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| Click here to select a new forum. | | Mac Portable, Dead Battery, Compatible AC Adapters | Posted by: techknight on 2013-07-18 10:19:38
Keep in mind the pinout. I havent looked in the datasheet. So I dont know if the LM part will drop in place of the LT part
Also the diode package type isnt correct
| Posted by: uniserver on 2013-07-18 11:57:05
ok i will keep an eye on that.
It would be much less of a hassle to spend more money and get the right part, instead of making something else work.
Its not like there is a %90 price difference ether, its 50% less expensive, and has 2 amps less power output as well.
I know the diode package is not like what is on there.
looking closer at the pads, I think this one might fit.
| Posted by: techknight on 2013-07-18 12:41:40
Give it a shot ;-)
| Posted by: uniserver on 2013-07-18 13:16:19
i'll make sure to start with the m5126 that has a completely dead 12v rail. 🙂
| Posted by: James1095 on 2013-07-18 15:06:47
Linear Technology parts do tend to be a bit on the spendy side. If you ask them nicely though, they will usually send you a couple of samples free of charge. I've used the LM257x parts as well, originally National Semiconductor and now cheaper clones are made by TI. They work very similarly to the LT parts but do double check the pinout and current rating.
The inductor is really not all that critical. They only come in a handful of standard values and most of these integrated switching regulators will work fine over quite a wide range of inductances and in this case a similar application recommends 150uH so I would expect anything from 100uH to 200uH to work just fine and a much wider range is likely to work to some extent. If you are trying to optimize efficiency then you want to get the value a bit closer to ideal, but here you are just trying to diagnose and I am betting there is nothing wrong with the existing inductor.
Same with the diode, it's not critical. Any Schottky diode of equal or greater current and voltage ratings will work fine, although if the diode tests ok out of circuit then it's highly unlikely to be bad.
There is just not much to this circuit, and most of the parts are easily tested. There is no need to shotgun it and replace everything.
| Posted by: techknight on 2013-07-18 17:30:12
All I can say is order up the parts and try it.
First thing is first though, test all the traces that connect the regulators circuits all together. Follow the datasheet, its example circuit diagram is what I would follow as its likely the same.
Also, check any resistors it may have to form the output voltage.
oh and last but not least, check the shutdown signal. if engaged, thats why no 12V. and the 68HC05 is responsible for that.
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