AV receiver has no sound, trips PROTECT or won't power on — what it means

You switch the receiver on, «PROTECT» flashes on the display for a moment, a relay clicks, and the unit drops back into standby. Or the sound is fine but the TV shows no picture over HDMI. Or only the right speaker stays silent. These are not random symptoms. Each one points to a specific section inside the receiver, and getting the diagnosis right is already half the repair.

An AV receiver is not just a stereo amplifier. On top of the output stage it carries an HDMI switching board with HDCP handshake, multichannel processing, and a separate protection circuit that shuts the whole unit down the instant something on the output goes wrong. These are exactly the sections that fail most often — we see it regularly in Denon, Marantz, Yamaha, Onkyo, Pioneer and Sony receivers. This article is organised by symptom: find yours and understand what is happening inside.

Receiver trips PROTECT or clicks off after a few seconds

This is the most common symptom. The unit powers on, runs for a few seconds or the display lights up, then a relay clicks and «PROTECT» appears (or «PROTECTOR», depending on the maker). After that it either falls silent in standby or the cycle repeats.

PROTECT is a protection circuit that watches the output stage. It trips in three main cases:

• Short in the output stage. A blown output transistor or output IC in one of the channels. The protection reads an illegal current draw and cuts everything to keep the speakers safe.
• DC offset on a channel output. A healthy output sits at almost 0 V DC relative to ground. As the output stage starts to fail, DC voltage appears at the terminal — the protection treats that as a threat to the speaker and shuts down.
• Overheating. If PROTECT shows up not immediately but 20–40 minutes into a film, the cause is most likely temperature rather than the output stage (covered in its own section below).

There is one important check you can do yourself: disconnect every speaker wire from the back of the receiver and power it on with no load. If the unit no longer trips PROTECT without speakers and stays on, the problem may not be in the receiver at all but in a short in the speaker cable or in the speaker itself (a frayed strand touching the chassis behind the cabinet). If PROTECT still appears with no speakers attached, the fault is internal — in the output stage or the power supply — and that is bench work.

No power at all — standby supply and fuse

A different case: no display, no standby indicator, the button does nothing. Here the protection is not involved — the problem is in the power supply.

A receiver has two supply sections. The standby supply is a small auxiliary circuit that feeds the microcontroller and the front panel even while the unit is in standby. That is exactly what lets the receiver respond to a button or the remote. If it has died, the unit is completely «blind». The main supply, with the large mains transformer, only starts after power-on and feeds the output stage.

Typical reasons a receiver won't power on at all:

• Blown mains fuse. The simplest case, but a fuse rarely blows «on its own» — most often it is the result of a short in the power supply or the output stage. Replacing the fuse without fixing the cause means the new one blows straight away.
• Faulty standby supply. A dried-out electrolytic capacitor or a shorted switching transistor in the auxiliary circuit. A classic on older units.
• Voltage surge. The mains in older Riga apartment blocks can dip and surge, especially during the heating season when the load is high — these often hit the supply input section first.

Here is a line you must not cross yourself: in the power supply, the large electrolytic capacitors hold a dangerous charge even after the unit is unplugged from the wall. Changing the fuse on the outside of the chassis you can still try, but everything else in the supply belongs to the service centre.

Sound is there but no HDMI picture (or no sound over HDMI)

This is almost the signature AV-receiver fault, one a stereo amplifier simply cannot have. Inside the receiver sits an HDMI switching board that routes several HDMI sources to the TV and performs the HDCP handshake — the authentication «handshake» between source, receiver and TV. When it starts misbehaving, the symptoms are characteristic:

• the picture does not reach the TV through the receiver (black screen or «no signal»), even though sound from the receiver speakers is fine;
• or the reverse — there is a picture but no sound from the receiver;
• the picture «flashes» and disappears, flickers, or only appears after switching the source several times;
• one HDMI input port is dead while the rest work.

Before thinking about a repair, check the simplest things first, because the HDMI handshake is finicky:

1. Restart the whole chain: switch off and unplug the TV, receiver and source, wait a couple of minutes, then power on in the right order — source first, then receiver, then TV.
2. Try a different HDMI cable and a different HDMI input on the receiver.
3. Connect the source straight to the TV, bypassing the receiver — if the picture is there that way, the problem is in the receiver's HDMI path.

If there is still no picture after that, the fault is in the HDMI board itself — most often the switching chip or the HDCP section. This is a typical, repeatable failure, and it is fixed on the board rather than by replacing the whole unit. One note: sound over HDMI ARC between the TV and the receiver is a different story with its own settings — covered in detail in no sound over HDMI ARC.

One channel mutes or distorts — the output stage

Every other channel plays but one — the right speaker, the centre or a rear — stays silent or plays with hiss and distortion. Here suspicion falls on the output stage of that particular channel.

Before blaming the receiver, rule out the speaker and the cable — you can do this yourself in five minutes:

• Swap the speakers over. Move the «dead» channel to a different speaker (or the other way round). If the silence travels with the speaker, the speaker is to blame, not the receiver. If the silence stays on the same receiver channel, the fault is in the unit.
• Check the speaker cable and terminal. A frayed or oxidised strand, a loose terminal, a broken contact in the speaker all give exactly the same symptom.
• Check balance and channel assignment in the menu. It sounds trivial, but sometimes the cause of the silence is a wrong balance setting or a channel marked «None» in the menu.

If the speaker and cable are fine, then the output transistors or output IC on that channel are shorted or degraded. Important: a faulty output transistor often produces not just silence but also a DC offset — and then the unit does not mute one channel but trips PROTECT instead (see the first section). So a single live symptom — a dead channel or PROTECT — often leads to the same section.

Overheating and shutdown (dust, fan, bias)

The receiver starts a film fine but after a while suddenly shuts off or trips PROTECT, and the case is unbearably hot. This is thermal protection — it trips not immediately but once the heatsink reaches a critical temperature.

Causes by frequency:

• Clogged heatsink and fan. Years of dust build-up «choke» the heatsink fins and the heat stops escaping. In receivers with a fan, it sticks and slows down. Baltic humidity and the dry, dusty air of the heating season in Riga flats speed this up.
• Dried-out thermal paste. The output transistors are clamped to the heatsink through thermal paste — over many years it dries and crumbles, heat transfer worsens, and the unit overheats even with a clean heatsink.
• Poor ventilation. The receiver is built into a closed TV-cabinet niche with no air gap, with other equipment stacked on top. Before blaming the unit, give it air — at least a couple of centimetres above and to the sides.
• Drifted output-stage bias. Too high a quiescent current in the output transistors means surplus heat even in silence. That is a bench adjustment.

The first two you can partly address yourself — an air gap and blowing dust out from the outside both help. Cleaning the heatsink inside, replacing the thermal paste and adjusting the bias are service-centre work.

Self-checks versus the bench — where to draw the line

Some things really are worth trying at home before you bring the unit in. But there is a clear line beyond which high voltage and test instruments begin.

What is safe to check yourself (receiver unplugged from the wall, lid closed):

• Disconnect all speaker wires and check whether PROTECT disappears with no load.
• Inspect the speaker wires and terminals for frayed strands or a short.
• Swap speakers over to find out whether the speaker or the receiver is to blame.
• Restart the HDMI chain, change the HDMI cable and input, connect the source straight to the TV.
• Check the audio output, balance and channel assignment in the menu.
• Give the unit air and blow dust out from the outside.

Where to stop and bring the unit to the service centre:

• PROTECT remains even with no speakers — an internal fault on the output or in the supply.
• The unit won't power on at all — power-supply and fuse diagnosis with the lid off.
• A blown fuse — that is a symptom, not the cause; the new one blows straight away if the cause is not found.
• No HDMI picture after checking every cable and input — HDMI board repair.
• One channel mutes, speaker already verified — output-stage repair.
• Thermal-paste replacement, internal heatsink cleaning, bias adjustment.

The simple rule: anything that needs the lid open, soldering or voltage measurement is bench work. The supply electrolytics hold a charge and can injure even after the unit is unplugged.

Symptom → cause → action