now i don't know the setup internally on the inverter, but often there are mosfets paralleled and if one or more should open up and just lay dead this would possibly explain the cool nonrunning side and lower output. is it possible sg as you know more of its layout?

here the recording of the buzzing sound, it gomes and goes.
Cannot get the hole recording, size is too big.
(there is a short hammer noice in the middle, thats a construction going on next door...)

I also replaced the fan in the meantime.
the source I found for a 230V is Grainger, PN: 2RTE1 for $35
With 117cfm has a little more air flow as the original.

Sounds normal for the Suntie, the inductors were always a bit buzy and with age I'm sure it would get worse

All happened at once, from one day to the next that:
- the unit started this buzzing sound, before it was not noticeable at all (for all the years)
- the display started showing only 50% of the performance
It has been almost a full month now and I guess the truth will show up in the next utility bill, which should come next week.

without better diagnostic equipment, one will never know exactly whats gone wrong. Your clamp on AC shows ~1160 watts ac with the dc watts ~1600 ... big difference from what the unit is reporting. Also you would need to check both legs and use a oscilloscope to check out the wave forms.

Could be one of legs has a failed FET on the AC section ( right side heat sink ), if this happened, it would mess with the wave form and the inductors would probably be stressed and make the buzzing sound.

Regardless, there is no options for repair, only replacement. Xantrex had a program to offer at discount a GT2.5 for 999.00 to Suntie owners, call support and see if they can help. Usually, one can just take the strings of solar panels and instead of being in parallel, run them in series ( change at the inverter , I just wire nut to strings that went to the Suntie combiner board), you would have to check the voltages of course.

Good luck!

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.