21.5" iMac (Mid-2011) won't power on

[omnichad]

I'm working on an iMac that has been through a thunderstorm and did not work again after power came back.

I took off the glass and screen and none of the four diagnostic lights are lit. If I unplug power for a few seconds and plug back in, Diagnostic LED #1 (Trickle power detected) soon lights up for a second and then shuts off.

I took a multimeter to the power supply pins. Pin 4 is showing 12V (11.99V) and pin 6 is showing a little over 4v (4.62V). This is even after the diagnostic LED shuts off. I can't find a single reference for this model as to what power should be showing on the pins on standby.

Customer would probably rather replace the whole computer if it's anything more complicated than the power supply since it's 5 years old. Is there any reason to think that replacing the power supply will do anything or is the logic board fried? My current guess is that the surge probably came in via Ethernet.

 

[trevm999]

I can't remember what I used to get for voltage, but it is right that there are only two pin with voltage readings when it is off. Test the pins on the logic board. If you're not getting voltage all the way through it could be an issue with the cable or the logic board. However, even if you don't get voltage on the logic board pins, it could still be (and is probably still more likely than cable of logic board) the PSU.

When I worked on Macs I would always test the pins, but the solution was pretty much always swap out the PSU.


**Just thought, which pins on the power supply are you referring to, power in or power out?

 

[omnichad]

I haven't taken the logic board out, but I just found what looks like the solder points for the connector on that end. I get 12V on one of the pins. Nothing else, but I'm not sure the 4.62V goes to the logic board or if it goes elsewhere.

I was definitely referring to the power out pins on the PSU. The solder joints on the back of the connector is where I tested.

I'm just wary of ordering a PSU for a 5 year old computer that may do nothing. I would have expected the LED to at least light up to indicate that there is power there, since there's no load for a bad PSU to cause problems on that. But I don't deal with Macs very often at all.

 

[Markverhyden]

Have you looked though the service manual for this?

 

[trevm999]

I know what you mean. Here's what I would do. Source the PSU and the cable to the logic board from somewhere that would allow you to return it. Tell the customer it is either the power supply or the logic board but there is no way to know for sure unless you swap out the parts. Power supply is most common and least expensive so that's why you start there. Tell them how much the cost would be for an unsuccessful repair (bill your time and cost of shipping) as well as a successful repair. Let the customer decide if it is worth it to try. Alternatively you could suggest they take it to an Apple store or an AASP who might have better access to parts.

 

[trevm999]

Have you looked though the service manual for this?

I can almost guarantee what the service manual will say for this. No diagnostic LEDs staying on - check cables for damage - no damage = swap PSU

 

[trevm999]

You've already done more troubleshooting than an Apple store would do, your problem right now is easy access to parts.

I would never physically inspect the cable though. That's a lot more work than swapping the PSU. I would just order the PSU and I had a cable on hand just in case.

 

[trevm999]

I know what you mean. Here's what I would do. Source the PSU and the cable to the logic board from somewhere that would allow you to return it. Tell the customer it is either the power supply or the logic board but there is no way to know for sure unless you swap out the parts. Power supply is most common and least expensive so that's why you start there. Tell them how much the cost would be for an unsuccessful repair (bill your time and cost of shipping) as well as a successful repair. Let the customer decide if it is worth it to try. Alternatively you could suggest they take it to an Apple store or an AASP who might have better access to parts.

OR you could think of it like a laptop battery. 99% of the time it is the battery and not the charging circuit, so you order the battery, The one time that it's not the battery, you just absorb the cost of the part-you've already saved that much in time by not testing the charging circuit of everything that looks like it has a bad battery.

 

[omnichad]

I did look at the service manual. It definitely says swap the PSU and if that doesn't work, replace the logic board.

Thanks for all the advice. I haven't moved to full time business yet (2 more weeks), but I guess it's time to start being more prepared to absorb this kind of cost in exchange for speed and sanity. It's different right now, because I literally have nothing else competing for my time - I need to start developing better habits.

 

[Markverhyden]

Yep, people don't plan to fail, they fail to plan. A very important part of running a successful business is to put a $ value on your time and ALWAYS consider that in your decision making processes. That way if you are going to do something that is marginal in terms of revenue and/or profitability you will have forced yourself to evaluate that decision and what kind of impact it may have.

 

[trevm999]

It's different right now, because I literally have nothing else competing for my time - I need to start developing better habits.

It's easy to see parts as worth money so you spend more time so you don't need to pay out as much money when you're starting out. But even at this stage your time is worth more. That's time you can spend working on growing your business, developing a marketing strategy, creating procedures. All which should end up with you making more money.

You should also plan to have to absorb costs sometimes. Guys who "do their customers a solid" by charging parts at cost are not doing their business a solid. I consider parts markup as kind of a buffer for when things go wrong. I also think a good rule of thumb is that you want to try to just absorb costs in parts and equipment, not labour if you can help it. Not that you should be telling customers there is a fee for everything, for example if you did a Windows reload and the customer calls you back with a small request you shouldn't necessarily tell them there will be a charge, but the original amount you charged for the Windows reload should have taken into account that this might happen.