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How does the portable make 12 VDC from a 6VDC battery?
- Thread starter uniserver
- Start date
There is a boost converter with a rather large inductor. L7, C6, C3, VR1, D1 Form the boost converter. Check the Diode, and obviously C6 and C3 have to be replaced as well. Also, pull the datasheet on the linear technology boost regulator and check it against what it should be via datasheet. you will find your fault this way.
Datasheet:
http://pdf1.alldatasheet.com/datasheet-pdf/view/70296/LINER/LT1070CT.html
Take a peak at the first page, it has an example 5v to 12v circuit based around the LT1070 which is what the portables use. Start here...
Note: since its a boost configuration, if it was not oscillating/running, your v-out would be V-in minus a diode drop. So, it minimum your output voltage would be roughly a volt below the input supply. So if it was 6v, it would be around 5v. Now since yours is sitting around 1v, you need to make sure your output isnt shorted or heavily loaded, which it appears to be, the regulator will shutdown in overcurrent protection, and your D1 would heat up really fast. But at the same time, the LT1070 can also be shorted and give you the same result, and it will also heat up really fast. Something is getting hot. For sure. Too heavy of a drop from Vsupply.
Datasheet:
http://pdf1.alldatasheet.com/datasheet-pdf/view/70296/LINER/LT1070CT.html
Take a peak at the first page, it has an example 5v to 12v circuit based around the LT1070 which is what the portables use. Start here...
Note: since its a boost configuration, if it was not oscillating/running, your v-out would be V-in minus a diode drop. So, it minimum your output voltage would be roughly a volt below the input supply. So if it was 6v, it would be around 5v. Now since yours is sitting around 1v, you need to make sure your output isnt shorted or heavily loaded, which it appears to be, the regulator will shutdown in overcurrent protection, and your D1 would heat up really fast. But at the same time, the LT1070 can also be shorted and give you the same result, and it will also heat up really fast. Something is getting hot. For sure. Too heavy of a drop from Vsupply.
HDD? SCC, audio, FDD, and some other little things
I recapped a Mac Portable a few days ago but it's having power issues on the +12 volts line. All SMD caps have been replaced, the radials and axials too.
It works but not from a fully charged rebuild battery. However when I plug in the power adapter, together with the battery, it does boot.
When checking the battery level indicator under OS 6.0.8: it's full with the power brick connected, however when I unplug it, it goes to empty in 1 minute and automatically shuts down, while the main battery still has 6.5 volts on it.
In my other Mac Portable, the same battery yields at least another 2 hours, so the battery is not the issue.
When I test the +12 volts line at the FDD connector or on C3 ( 220uf 25v ) I measure only 11.6 volts, which is too low. On my other Mac portable, that's 12.05 volts.
I think this is the culprit of the problem. I have tested D1: ok, C6 and C3, VR1 are replaced, L7 checks fine for continuity.
Even with the bare board and power adapter connected, on my bench, I only get +11.6 volts on C3, which is too low.
I hope someone has encountered this problem and can pinpoint me to the solution.
11.6V does not strike me as all that out of line, it's low by less than 5%. I don't have a schematic of the boost converter to look at, but usually regulation is accomplished by monitoring the output of a voltage divider made of a pair of resistors between the output and ground. The regulator compares the output of the divider with an internal reference voltage and varies the duty cycle accordingly. If the resistor values are a bit off, the output will be off as well.
I think your problem is elsewhere. Even if the 12V were way low, the machine should still operate to some extent.
I think your problem is elsewhere. Even if the 12V were way low, the machine should still operate to some extent.
It does operate to some extend but is unstable, does not work from battery power only and shuts down with a fully loaded battery if I unplug the adapter.
So I guess the PMU is monitoring the +12 volts line as reference for it's battery level indicator and shutdown when it becomes too low but it's way off now.
So I guess the PMU is monitoring the +12 volts line as reference for it's battery level indicator and shutdown when it becomes too low but it's way off now.
