Hi

I have a strange issue where the amp of my sound system (NAD T758) goes into protection mode for no apparent reason. I sent it in for repairs, only to have it going into protection mode again. When the repair shop test the amp at their premises, the amp works fine.

So after a few time back an forth, the repairer asks me if I run my system off an inverter, and that this is likely the issue. I have a Sunsynk 5kw inverter. The amp ran fine for the last 2 years it was on the inverter, first time now giving the issue.

Has anyone measured the power output "quality" of Sunsynk inverters? Do they usually give clean and proper sinewave output?

How can I check this on my inverter. Doe a normal electrician have access to an oscilloscope to check?

Anyone else experienced something similar before?

What state is the inverter in when this happens? Is it happening when power is supplied from the battery or the solar panels or is happening even when power is supplied from the grid?

The inverter is only backup power, no solar.

Strange. So I bypassed the inverter, and amp still went into protection mode.

So it must be something else in the power supplied that causes this.

Any ideas what to look for? I measured the voltage and it is around 220 volts which seems ok.

3 hours ago, Leonb said:

How can I check this on my inverter. Doe a normal electrician have access to an oscilloscope to check?

Anyone else experienced something similar before?

Normal electricians only have access to multimeters, screwdrivers and insulation tape. You need an instrument that can measure harmonics. I have had it that lights flicker when heating elements are used with diodes. Typically the inverter should have less than 3% Total Harmonic Distortion on its own.

So who can solve a problem like this....?

1 hour ago, Leonb said:

Strange. So I bypassed the inverter, and amp still went into protection mode.

So it must be something else in the power supplied that causes this.

Any ideas what to look for? I measured the voltage and it is around 220 volts which seems ok.

What happens when you disconnect the grid at the main switch, and run solely off the backup inverter on its own 230V sine wave?

1 hour ago, Leonb said:

Strange. So I bypassed the inverter, and amp still went into protection mode.

So it must be something else in the power supplied that causes this.

Any ideas what to look for? I measured the voltage and it is around 220 volts which seems ok.

From this, I would get a second opinion, in regards to the amp repair.

Then also, there is this? Sparkies will probably be able to answer the question better when it comes to voltages https://powerforum.co.za/topic/1379-what-voltage-are-you-running-220v-230v-240v/

1 hour ago, Leonb said:

So who can solve a problem like this....?

Your more advanced solar installers should have access to power loggers with harmonic recording capabilities.

43 minutes ago, GreenFields said:

What happens when you disconnect the grid at the main switch, and run solely off the backup inverter on its own 230V sine wave?

Just tried this. No differences. Still go inuo protection.

26 minutes ago, Leonb said:

Just tried this. No differences. Still go inuo protection.

Here is another test. Disconnect all the speakers. Boil a kettle and switch on the receiver while the kettle is on.

Edited March 3, 20251 yr by frivan

2 minutes ago, frivan said:

Here is another test. Disconnect all the speakers. Boil a kettle and switch on the receiver while the kettle is on.

Speakers and all other cables already disconected. Only power cable.

Why the boiling kettle?

If there are harmonics in the house, the kettle may draw some of them down.

You have an inverter for backup. Do you have any non-backed up plug circuits on the property? If so, run an extension lead from the non-backed up socket to the NAD.

If the NAD is happy then we must consider that the sunsynk is introducing harmonics or causing some other condition that makes the NAD unhappy.

On my property the outbuildings are not backed up. The washing machine is in the outbuildings. I have put one of these clever plugs on it. It provides surge protection and it has LEDs that can indicate various error conditions. When we have grid and the washing machine is plugged in as usual, the LEDs in the plug show no error. When we have load shedding and I use an extension lead to get power to the washing machine, the LEDs change state. The washing machine still runs OK, but the LEDs change state.

My inverter is not a Sunsynk, but I am not sure that the AC output from an inverter is the same as grid power.

Thought: get one of those Ellies error detecting / surge protecting plugs, fit that to the NAD and use the same plug socket. See what condition it reports.

Poor or floating ground connections can lead to voltage imbalances and noise, which might cause the amplifier to shut down to prevent damage.

Nearby switching inductive loads could cause voltage instability. Why don't you remove the amp and go and test it at a family members or friends premises that is in a total different area.

Is the NAD plugged into a wall socket directly or is it going through an extension cord or multi-plug adapter?

Edited March 4, 20251 yr by TheMac

11 hours ago, frivan said:

If there are harmonics in the house, the kettle may draw some of them down.

Kettle trick did not work.

48 minutes ago, TheMac said:

Is the NAD plugged into a wall socket directly or is it going through an extension cord or multi-plug adapter?

Directly into wall. And I tried many differnt wall plugs just to test.

2 hours ago, TaliaB said:

Why don't you remove the amp and go and test it at a family members or friends premises that is in a total different area

I second this. It will narrow the search.

Edited March 4, 20251 yr by TheMac

2 hours ago, TaliaB said:

Why don't you remove the amp and go and test it at a family members or friends premises that is in a total different area.

I'm taking the amp back to repair shop today. Want to see with my own eyes if it powers up normally.

If it does, I have mny questions they need to answer, i.e. whar components did they replace the first time round and why.

Ok, so at the repair shop the amp also went into protection mode, so either:

1) the power at my house is damaging a component every time I bring the amp back from the repair shop, or

2) the repair shop is not playing open cards

It is the NAD authorized repairer in Cape Town, so not a round the comer repair shop.

They are having another look at the problem now.

There are many posts online about the NAD protection mode and how many times faulty or even sub-par components had to be replaced. I wonder if your device has a similar issue with sub-par components on their way out.

Edited March 4, 20251 yr by TheMac

Yes. Ive seen some posts on the Nad issues. Just strange that something new pops everytime the previous component is replaced. It had no issues for 10years. And quite expensive to replace unit, about R35k new. So I hope to get to bottom of root cause.