Imac A1312 - Blown Diode, Need Inverter Schematic?

[reessi]

iMac 27-Inch "Core i7" 3.4 (Mid-2011):

First off I have the Imac Schematic but only for the mainboard, does anyone have the inverter one or a similiar one from another for better understanding?

Searched all over for one!

All voltages to the Inverter are correct:

(12v in, 3.3v Enable and PWM Approx 3.0v).

Output was 12v and moved a little but Inverter was obviously cutting off as D1 was SHORTED.

After replacing this the IMAC works for 1 week exactly and dies again. When working the output was correct at 42v. Before repairing the Inverter I tested the LEDs one by one in the display with a multimeter in diode mode and they light. I also tested the strips when out of the display on the Inverter and all lit as normal!

I just confirmed the same Diode was Shorted. I had replaced with the exact type from RS electronics (V10P10), Datasheet attached.

There are 2 others on the board which are still fine. The Inverter works without it but as I do not understand how the circuit is fully working I'm not sure if it is a good idea to leave it out!!

There are 3 sets of Inductors so are they sharing the load so if it is left out are the other 2 sets running at higher current?

So any ideas as to why it has blown 2 so far!

I have annotated the pictures please have a look.

Cheers.

[mon2]

Re: Imac A1312 - Blown Diode, Need Inverter Schematic?

For this year, the inverters are cheaper than dirt on Ebay. Perhaps consider to purchase a replacement inverter board? Should be $20 or less for a confirmed working board.

Just confirm that your p/n matches the replacement.

For example, V267-604HF, etc.

See a listing of a reseller on Ebay @ $12 USD and he currently has 8 of these boards available. Seller is repairgig.

[reessi]

Re: Imac A1312 - Blown Diode, Need Inverter Schematic?

I know that mate, but I am trying to learn board repair.

Cheers though.

[reessi]

Re: Imac A1312 - Blown Diode, Need Inverter Schematic?

I've now got the Inverter hanging over the front of the display on a cloth and still all connected.

The board is getting very very hot. If I put screen brightness down to minimum it goes cold.

Output ranges from 28v to 36v on the LEDS when changing brightness.

Could the LEDS be faulty but even if they went short isn't that not a problem since the Inverter is current limiting them anyway as all LEDS have to be current limiting.

I've attached a pic of what seams to be hot but it is all over alot.

Inductors, MOSFETS and especially Resistors are very HOT!

Voltages on the 3 diodes circled in green of which the top I replaced are:

95v Top Replaced!
95v Middle,
110v !!! Bottom.

The diodes are rated at 100v yet the bottom is higher but not overheating!

Cheers.

[reessi]

Re: Imac A1312 - Blown Diode, Need Inverter Schematic?

Forgot to update this, was in another forum as well for it.

This turned out to be a the LED Strips. Well the left strip to be precise. I replaced that and all is well! Before I did that I tested the voltage across each LED while on to find anomolies as all LEDs appeared to be working. Some on the left strip had a bigger voltage drop across some of the strings and hence was pulling more current and overheating the Inverter which blew the Diode.

Seams a very bad design that the inverter cannot limit the current in this situation and instead just overheated and blew the diode. The Imac has been working ever since!

Had to get second hand from Aliexpress!

Cheers.