Where are the Diagnostic LED's on a EMC2105 iMac?

I have a iMac emc 2105 20" model that will not power on. I have removed the case cover and am trying to locate the diagnostic LED's . There does not appear to be any LED's just to the right of the ram slots visible.

Where are the Diagnostic LED's and what do I have to remove to locate and see them ? I have found numerous references to other models and the diagnostic LED's but not this model.

I have found what might be a LEd on the "bottom" of the unit to the right of the RAM slot, but this is what might be a single LED, certainly not a row of 4 of them are present.

My real problem is that the machine will not power on and I am trying to diagnose whether it is the power supply or the motherboard.

Does this model have a SMC reset button ? If so, where?

Does this model have a internal power on button. If so, where ?

I was hoping to reset the SMC before I went any further -- how do I do that.

There is NOTHING glowing anywhere that I can find. I have not removed the back cover, only the front bezel and screen. I have replaced the backup battery ( Cr2032 on the motherboard). I have tried cmd+option+shift + pwr button reset -- -to no avail.

A pointer to a previous thread that answers this question and provides diagnostics for THIS model would be helpful.