Amplifier relay problem

[fantasmical]

I have a Marantz SR7000 amplifier (240V / 50Hz) that has recently developed some problems.

Normally when powering up the amp, there would be an initial clicking sound, a pause of 3-4 seconds, followed by a second click when the amp would start outputing amplified sound. In April 2024, when powering up the amp, it started taking more than the usual 3-4 seconds for the relays to click into place. Once powered up, the amplified audio was perfect and there was no hum or crackle. I disconnected the amp and put it aside for a few months.

When I powered up the amp this morning (it's 12°C / 54°F indoors), it took a full 40 seconds before the second relay clicked and amplified audio started coming out. However, after a minute or so, there was another click and the audio stopped. A bit later, the relays clicked again, and a quiet 200Hz hum came out as well as a momentary white noise/crackle which disappeared after a couple of seconds. After turning the amp off then on again, the audio was perfect, however after a few minutes it stopped again, only to restart after half a minute or so.

Apart from the speakers and AC power, the amp is connected only to a TV using a TOSLINK optical cable - nothing else is connected.

The amp is is powered through an IEC male plug with no earth pin. It's currently winter, but in the summer it gets very humid.

Service manual

User guide

I have attached photos of the IC connected to the mains plug and some schematics of the same board from the service manual.

 

[petehall347]

could be cb54 470uf.. blow some warm air on from a hairdryer and see if it powers up quicker .

 

[Dswankey]

I see this your first post so welcome to AK and here's hoping you enjoy your time here.

A couple of things

What you have is an Audio/Video receiver which has an amplifier inside it but it's not a stand alone "amp" or "amplifier"

I have a Marantz SR7000 amplifier (240V / 50Hz) that has recently developed some problems....Apart from the speakers and AC power, the amp is connected only to a TV using a TOSLINK optical cable - nothing else is connected.

If its been sitting dormant in the cold environment "(12°C / 54°F indoors)" it might just need to warm up

 

[Sandman1221]

In second pic there is a black box on the right side with a blue diode just to the left, I would try replacing that relay (LB52 next to it on first schematic). Relays are moving parts and from my limited experience are the first component to go in a well made unit. There is a coil inside that power runs through to creat a magnetic field that then moves a lever to open and close the relay, maybe it has a crack in the fine wire and closes with applied current and heat buildup. But overtime the crack is getting bigger, and so takes more tine/heat to close. Looks like a standard 8-post relay. The 8-post relays in my 25 yr old NAD are identical to a brand new one.

 

[RalphRaccooN]

C866 looks like top is budged in second picture.
But it sounds like the power supply is working, I would measure DC offset, I would also measure the speakers and wires.
If the amplifier is healthy and the protection keeps triggering maybe target the related capacitors in the protection circuit.

 

[fantasmical]

UPDATE: The hum/intermittent audio is exactly the same when headphones are connected, i.e. it still takes a long time for the relays to click into place and for audio to be heard. The same hum heard through the speakers is also heard through headphones.

 

[Dswankey]

connected only to a TV using a TOSLINK optical cable - nothing else is connected.

Regarding the hum, have you tried a different source other then the TV? have you checked the TVs audio output settings?

 

[fantasmical]

Regarding the hum, have you tried a different source other then the TV? have you checked the TVs audio output settings?

The hum is present on all inputs, even when the amp is muted, or is "between" inputs. The hum is ever so slightly louder on the analog inputs.

 

[krautmaster]

From what I can see in your pics, it looks like one capacitor is bulging and two others have vented--time to have them replaced;

 

[Buck Rogers]

Time to replace all six caps in this picture.

Smaller caps are always more problematic.

Also between the two blue resistors on the left side, Something does not look right.

This is called the "Protect circuit" and they are a very common problem.