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Dustin, Mac Support Specialist
Category: Mac
Satisfied Customers: 12536
Experience:  Over a decade putting the missing byte back into Apple. Also worked in The US Army as A Network Switching Systems Operator/Controller
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Have been resetting PRAM and SMC every now and again when power

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Have been resetting PRAM and SMC every now and again when power switched off from wall plug, as iMac will not then switch on normally. So I thought I would change the motherboard 3v battery. Now, nothing. The usual resets do not get it to switch on. How do I reset the firmware to tell the smc to start up again??

I am assuming that firmware for the SMC has been "lost" by the removal of the battery?

Welcome To JustAnswer!

My name isXXXXX am one of the Experts who will assist you today!

So I can assist you.. What year, model and version of Imac do you have currently that is having this issue?


Dustin S.
Customer: replied 3 years ago.

Bought about mid 2011. 21.5"

Customer: replied 3 years ago.

Hiya Dustin. Not sure what model,,just the top of the range in 2011


I think it is an Intel Based machine.

Thanks for clarifying Logan.

As a test.. can you put the old 3v battery back in.

And then perform the SMC and Pram reset again . ( or at least attempt to )

Also, after we insert the older battery.. lets make sure that we completed unplug this from power, wait one minute.. and then plug it back in ..

Do we get any signs of life after trying this test?

Dustin S.

( please use the reply to expert button if this doesnt help at all , so that we can continue the conversation )

Customer: replied 3 years ago.

No difference. Can't do either of the usual resetting of PRAM and SMC as the computer does not come on at all.

At an Apple repair shop, a technician mentioned having to reset firmware.

This was my original question. How do I go about resetting firmware or re-installing it?



To be clear..

When you press power. absolutely nothing is happening..

No sound, no noise, no lights, no blink of the power indicator..

Customer: replied 3 years ago.

Yes, ever since I removed the battery, nothing!!!


Previously, unless one went thru the exact routine of unplugging, waiting 30-60 mins, then switching on , waiting about 5 seconds, then pressing power button,,the computer would also stay dead!!

Unfortunately, we cant reload, load, or reset the firmware without having power to the machine..

If you can find the serial number for this mac.. I should be able to help you locate the internal diagnostic leds.

So we can see if your power supply has failed, or if this is something else.. But its entirely possibly your power supply was failing for quite some time, and finally gave out.

Send a reply when you can locate a serial number, and we will continue form there Logan.

Dustin S.

Customer: replied 3 years ago.

Lets try:

Serial No ;CO2GJ56WDHJN

Am pretty sure it is not the power supply as the one support technician I took the machine to today, put in their power supply module and it also did not switch on

Question.. Did that support technician, did they put the power supply in before or after you replaced the battery?

( while your answrering that, im going to look up the serial number)

Thanks Logan,

Dustin S.
Customer: replied 3 years ago.

Right, am back.


After I changed the battery no resetting techniques worked.

I then took the computer to a supposed technician who only had a few minutes unfortunately , and he switched power supplies,,but with no success.

This should be the mac you have..

according to the serial code you sent..

Im trying to look up a spec sheet on it, to find the internal location of the LED status lights, so we can check those lights and see where power is failing.. ( at the power supply, or past it )

Customer: replied 3 years ago.

Yes, that is the Mac I have.


Ok.. Since your tech guy didnt have the time to go over these steps..

We need to go over them.. See the first post on this page..

It has pictures to show the location of the LED lights on the mainboard..

We need to know the status of those lights, so we can judge how to proceed correctly, instead of guessing..

So when you have the time, lets dissemble the mac and then check your LED status..

Dustin S.
Dustin and other Mac Specialists are ready to help you
Customer: replied 3 years ago.

Hiya Dustin,

Could not find any LED's on . That is with the screen removed and the power on. In fact could not actuallu locate the leds as there is a metal strip running the length of the computer where the ram is located.

Anyhow, getting late, so will pack up tonite and see my options tomorrow. The closest Apple service is 500 miles away,,plus they chance their arm and just charge you for whatever, even if it is just a resetting of something small.

Thanks for you help.




Your welcome..

If you want, we can go into this a bit further tommorow..

I may be able to find a better breakdown of where the leds should be.. ( they may be under something )

And most likely, the apple store isnt going to do any type of solid repairs .. They make more money off selling new equipment vs repairing equipment..

Customer: replied 3 years ago.

Good Day Dustin,


Seems like the power supply is faulty. Put in a test one and it booted up fine,, so have ordered a power supply.


Thank you



Those power supplies are expensive..

Happy to hear that you got it working though Logan, if theres anything else you need , please let me know.

Dustin S.