I need help.
I have 2kw Elenos transmitter. It has a problem of output power cant go above 750watts. I have checked power supply voltage is 31volts when output power is below 500watts and 28volts when power is 750watts this is not normal. Normal operating transmitter has voltage ouput which varies between 31 to 50volts depending on output power.

Bad powersupply unit, swap all electrolytics and if no help, swap psu unit.

I had a problem with the same transmitter that you have. It would ramp up to about 500w like you said, and flicked on the flashing fault LED and drop down to 200w and keep fluctuating between 200 and 500w even though we had target set at 1300w... We purchased a new power supple unit from Elenos after like EFR said, re-capping the PSU, but it didn't make a difference, even with a new power supply unit the TX would never hit target power, we ended up shoving it into a suitcase and booking a flight to Italy, and arranged a time to meet Marco at the Elenos facility, (by the way a very great respectful lad), After their checks they had again found the PSU to be at fault, they replaced it in front of my eyes but no fix, then he started messing about with bias voltages but nothing worked. I ended up giving them the unit and getting the older style ETG1KW from them, which since has suffered 3 lightning strikes and after a few IC's its back up and running, This was my 2nd experience with their newer indium models, but from what I have heard and experienced myself these newer Elenos units just aren't as tough as the older ones.

I'd say for you your best bet is probably replacing the caps, and if there isn't a fid then email Elenos, They will take some event logs from the TX's internal data logger and could provide better assistance, I would have known the newer model Elenos TX's inside out if it didn't fail on me in less than a year in use!

Did you get any response from Elenos what was the main fault on old tx, or did they toss it to the garbage bin?

I had one of those on the bench last year. Close examination showed some poor solder joints in the PSU, which would only show as faulty when the board got hot. Application of freezer spray and a hair dryer showed up the fault. It took a couple of days on the bench to discover the poor joints - we re-flowed the whole area, and added more solder to some of the big tag connectors, and bench tested it for three days. It held up at 1400W for three days, so we assumed that it was OK.

It was freighted to its owner, and tested on their site. It worked fine for about a week, then died again! Unfortunately, this was due to a nearby lightning event. Luckily, the station has a valved back-up (which they don't like to use because of the exorbitant price of the replacement bottles) which could do up to 2 kW, so they used that. As far as I know, they've got rid of the Elenos box, and replaced it with a Bext box they got from the 'States (from a station that went bust). The Bext has given perfect service since it was installed.

Info from one group:

Run it lid open, and use thermal camera to take quick look at the output stages, there has been bad fets on these.

EFR is right, but I'd also look for hot spots in the power supply too!

These have some fets that will start leak at higher voltages -> current rises and fet heats more.