Strange sound from Marantz 2250B

[mikerm]

I recently bought a Marantz 2250B and have been using it for a month or so without any issue. The last couple of days when I first turn it on, I can hear a very soft "rumbling" sort of noise from the speaker. It almost sounds like a hungry stomach rumbling, or maybe soft wind against a microphone. First time I heard it I thought it was my imagination, but I listened closely today and it's definitely there. It seems to go away after a few seconds (maybe 5-10?).

Any idea what could be causing it? The receiver was supposedly rebuilt by the previous owner and I've got a giant list of parts that were replaced. Peeking inside I can see it's definitely had considerable work by someone very skillful with a soldering iron.

Thanks.

 

[fernarias]

We need more information. Is it one channel or both that make the noise? Is it limited to one source (am or fm or phono or aux) or all sources? What work was done (recap only, recap and new transistors, recap, new transistor and rectifier/diodes, etc.)? Do you have other gear (used to test preamp vs. amp)? Do you have a dmm and some electronic knowledge?

I've noted this in the past but a recap only is insufficient. When someone sells a recapped unit the person who receives it buys it to used on a frequent basis and definately tests (high volume, long usage) the unit. It's been my experience that other components, that are as old as the caps that were replaced, start to fail. The last 2230 I sold had everything replaced except for the things that are no longer available (yes, even in the am/fm boards).

 

[elnaldo]

That Marantz uses some transistors that get noisy, I've fixed one a year ago. Try to post the transistors replaced in that last service.

 

[mikerm]

It doesn’t seem to matter which source. I do have other gear and can do additional testing. Will need to check if it was one channel or both, but it seemed like it might be only one.

The seller listed the following work. I have more documentation at the office and will see if there were more details.

• All New Lighting and Filters Throughout
• Power Supply Board Fully Rebuilt and Recapped
• Power Supply Protection Relay Replaced
• Main Amplifier Boards Both Fully Rebuilt and Recapped
• Main Amplifiers - 1% Matched High Gain Differential Pairs Installed
• Main Amplifiers - Bourns Multi-Turn Sealed Potentiometers Installed
• Phono Amplifier Board Fully Rebuilt and Recapped
• Pre/Tone Amplifier Board Fully Rebuilt and Recapped
• Removed and Replaced Thermal Paste on ALL Original Output Transistors
• Complete AM & FM Tuners Both Peaked and Fully Aligned
• ALL Service Manual Calibrations Completed to Factory Specification
• Complete Internal and External Cleaning with Ultrasonic Detailing and Polishing
• ALL Controls Cleaned and Professionally Lubricated
• And Much More as Described in this Listing...Over 100 New Parts!!

 

[slimecity]

Second a small transistor failing. "Fully rebuilt" could mean anything.

I bet you are getting this noise only thru one speaker.

 

[fernarias]

If it's only one channel then it's not the power supply. Use another unit to check the amp and the preamp. Use an rca cable with the main in (connect a preamp to test the amp) or the pre out (connect an amp to test the pre amp).
Again, transistors, diodes/rectifiers are starting to fail (soon the transformer, some already have) and should be replaced. On working units, I have measured low hfe (below specs) on output transistors (to-3 mostly) that I replaced.

 

[mikerm]

Just thought I'd update this -- I called the seller and he was more than happy to do any additional repairs it might need. He mentioned changing some transistors and other work, not just caps. Anyway, the receiver hasn't made this sound again since back in March, and I use it on a daily basis. Not sure if this is significant -- can some problems spontaneously resolve themselves? Or maybe it was picking up interference from some other nearby electronics?

 

[elnaldo]

Some transistors starting to fail that I faced, did more noise after a cold winter night. It could be your transistors at hotter temperaure stay silent.

Of course an external source is possible too.

I'd use it until the problem develops again.