Quattro 48/5kVA unstable output frequency

I experience quite unstable output frequency issues with an older (and repaired) Quattro, where the frequency fluctuates 48.2 to 51.4 Hz - sometimes even more extreme - under normal (non-load, non-battery full etc.) conditions.

Compared to other Quattros, MultiRS etc. we have (and which remain in narrow frequency bands 49,8-50.1) this is significant. Ist that some indication of HW failure, some configuration quirk or what could be the cause?

HW is 2658 FW is 496. I tried to install the PV assistant in the hope it would gain more control over output frequency, but that was completely without effect.

There is a microgrid inverter (old 230W Involar) connected to this Quattro and it keeps shutting off frequently when AC-IN is off. It works well when the Quattro is connected/synced to grid/ac-in.
The problem is not the microinverter itself, the frequency oscillates even when it is detached, it seems the Quattro itself is the cause.

Any guesses what the reasons or how to remedy?

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Alexandra ♦ commented · May 29 at 08:58 AM

@PetaJoule

As a guess, assembly assuming the repair was done the usual way which is board replacement.

Check all the comms cables internally are seated well. Maybe a good old unplug and plug.

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petajoule Alexandra ♦ commented · May 29 at 11:48 AM

Yes, replacement. And by board it was the power unit (the one with lots of transistors and aluminum heatsink) as well as the connection unit (the one where the connectors go, as well as where the relais are). The only thing that remained original was the case, the transformators and the CPU unit.

Will schedule some downtime and try the inspection on/off thing, but seems like a far shot.

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