Thanks SG,
I'll contact support.
The clamp meter I used is not the most accurate one, once the unit had shut down for the day, it still showed 0.5A!?
It had a fixed range of 200A I could set it at - so there is a large uncertainty.

Attached another sound-track, since today was a quite day without much other noise.
You'll hear the first 15sec the regular sound (it's 11am, mppt is about 60V) at about 16s into the sound the DC volt drops to 40V and the buzzing starts, the buzzing is gone and DC volt returns to 60V (as the mppt, which remains 60V throughout).

Do you have a list of the TP located on the PCB and what one can expect to read?

If it is the FET, I can change it, just need to know the location and part number.

The drop to 40V indicates the AC inverter section is not in regulation. Changing the FET's in the AC side is not recommended as the CPU has a per board calibration for controlling the AC inverter section, changing any part in the inverter require calibration and is not a do it yourself task

The AC clamp on is measuring the VA, at low power levels your not measuring actual power but the reactive power caused by the capacitance in the RC output filter of the inverter.

http://en.wikipedia.org/wiki/AC_power

It's a sad thing to say, but I think this Suntie has had its day. I do have the schematics, but for liabilities reasons I can't give out advise, part numbers or instructions on how to repair - calibrate the inverter ... sorry

Well, I did get my order in with Xantrex for the GT2.8 for $999 under the loyalty program.
Do not know exactly when they gonna ship, they say there is not stock cause some parts they need are not available....

In the meantime I have changed the fan and it seems to improve a little - at least the unit is not making so much noise any more.

Also, an update the the electrical bill and it does average about 6kW/day I am missing. I do not remember the last time I was in that "high" tier bracket...

That's good you could the the discounted price for the GT2.8, you will really like the GT. One suggestion, read up on the input voltage requirements and pre-plan how you want to change your strings connections, likely, parallel to a single series string, but best to have this figured out ahead of time

Not to get too much off this topic, but is the efficiency of the GT better at higher voltages?
Is there a graphic showing the efficiency vs. input voltage.

You should run the Xantrex string calculator , short answer is I suspect you will only have one option, when I've changed out ST2.5's , I just wire-nutted all the strings in series in the BOS ( balance of systems box, AKA the wiring compartment of the GT inverter ). If your conduit is to large for the BOS, add one of those grey PVC work boxes from home depot and do the wiring in there and they send the single string to the GT

http://www.xantrex.com/support/gtsizing ... p?lang=eng

This is the users manual

http://www.affordable-solar.com/admin/p ... 120951.pdf

And more about string voltages

http://www.xantrex.com/web/id/2671/docserve.aspx

Got the replacements and installation was done within a couple of hours.

Now I want to connect the RS232, Is there a max length of the cable from GT to the PC?

Good to hear your installation has gone well, I have used a full roll of cat5 cable ( 500ft ) without issue, I just soldered on DB9 connectors on each end