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 and 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.

 

That schematic shows the power supply circuit, not the actual amplifier. Those relays are mostly to protect the speakers from DC voltage damage in the event of an amplifier component failure that wold send a DC current thru the speakers and burn out the voice coils. So it is not a protection relay problem, it is an amplifier fault problem. And without the actual circuit schematic there is no way that we can research what the failure might be.

 

Full schematics are in the service manual link in my original post.

 

Full schematics are in the service manual link in my original post.

The "full schematics are not readable without joining the organization. What I see is just fuzzy enough to be useless.

 

Open the link, click the green "Download" button -> Get Manual -> Download PDF. The PDF contains vector drawings that can be scaled cleanly and easily. No need to join/subscribe to anything.

 

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 and 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.

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.

 

Looking at the second photo, CB66, the large capacitor in the middle at the bottom of the PCB appears to be bulging on top, so is definitely suspect!

 

Looking at the second photo, CB66, the large capacitor in the middle at the bottom of the PCB appears to be bulging on top, so is definitely suspect!

Replacing that capacitor, or at least testing it, is a good choice. Thanks to SarahM for the sharp-eyed inspection.

 

At some decades, all large electrolytics ought to be replaced. Extended power off time with aging can also stress caps from power on surges.