Marantz CD-400B Repair

[Stiffgriff]

Hi All,
Having trouble with my Marantz CD-400B demodulator. Two big issues.

1. Loud buzz occurs when in direct out two channel mode. I’ve tried daisy chaining the turntable ground from cd-400 to receiver with no luck. Also, when Cd-400 is not hooked up, and the turntable and receiver are hooked up to each other alone I have no grounding or buzzing issues.

2. When playing a Cd-4 record in 4CH mode, the radar button does not light up and it sounds more like it’s just playing double standard stereo between the four speakers. My cartridge is a relatively new AT-VM95ML.

I’m almost 100% positive I have it all hooked up correctly and I think it’s the unit alone. Without it in the system my turntable (Marantz 6200) and reciever (Marantz 4270) worked perfectly when paired only with each other. I’m using brand new RCA cables when trying to use the CD-400B.

Im not very skilled at working on this old equipment in general but if there is someone I could ship this to for repair or if anyone knows of someone in the Chicagoland that could help I would appreciate it. Thanks!

 

[Sonik Wiz]

Hi All,
Having trouble with my Marantz CD-400B demodulator. Two big issues.

1. Loud buzz occurs when in direct out two channel mode. I’ve tried daisy chaining the turntable ground from cd-400 to receiver with no luck. Also, when Cd-400 is not hooked up, and the turntable and receiver are hooked up to each other alone I have no grounding or buzzing issues.

2. When playing a Cd-4 record in 4CH mode, the radar button does not light up and it sounds more like it’s just playing double standard stereo between the four speakers. My cartridge is a relatively new AT-VM95ML.

I’m almost 100% positive I have it all hooked up correctly and I think it’s the unit alone. Without it in the system my turntable (Marantz 6200) and reciever (Marantz 4270) worked perfectly when paired only with each other. I’m using brand new RCA cables when trying to use the CD-400B.

Im not very skilled at working on this old equipment in general but if there is someone I could ship this to for repair or if anyone knows of someone in the Chicagoland that could help I would appreciate it. Thanks!

Here's a shout out to @J. PUPSTER who can probably point you in the right direction...

 

[Stiffgriff]

Here's a shout out to @J. PUPSTER who can probably point you in the right direction...

Thanks!

 

[J. PUPSTER]

Hi All,
Having trouble with my Marantz CD-400B demodulator. Two big issues.

1. Loud buzz occurs when in direct out two channel mode. I’ve tried daisy chaining the turntable ground from cd-400 to receiver with no luck. Also, when Cd-400 is not hooked up, and the turntable and receiver are hooked up to each other alone I have no grounding or buzzing issues.

2. When playing a Cd-4 record in 4CH mode, the radar button does not light up and it sounds more like it’s just playing double standard stereo between the four speakers. My cartridge is a relatively new AT-VM95ML.

I’m almost 100% positive I have it all hooked up correctly and I think it’s the unit alone. Without it in the system my turntable (Marantz 6200) and reciever (Marantz 4270) worked perfectly when paired only with each other. I’m using brand new RCA cables when trying to use the CD-400B.

Im not very skilled at working on this old equipment in general but if there is someone I could ship this to for repair or if anyone knows of someone in the Chicagoland that could help I would appreciate it. Thanks!

Please check out this thread; hope it helps-

https://www.quadraphonicquad.com/forums/threads/marantz-4140-happy-ending.35608/#post-760943

 

[Stiffgriff]

Please check out this thread; hope it helps-

https://www.quadraphonicquad.com/forums/threads/marantz-4140-happy-ending.35608/#post-760943

Thank you!

 

[Sonik Wiz]

Thank you!

Do let us all know how this pans out. CD-4 is not for the timid.

 

[Stiffgriff]

Do let us all know how this pans out. CD-4 is not for the timid.

Will do! I gave those J&T Electronics Repair guys a call today but no answer, I’ll try again tomorrow. I’m hoping I can bring my CD-400B down to them in Nashville because I have an install trip for my job down there next month. We’ll see! I’m so close to getting CD-4 to work! Hopefully the final step… I’ll keep ya posted.

 

[Doug G.]

Usually, the input to the demodulator would be connected directly to the direct output jacks through the switch without going through any other circuitry. I have never had a Marantz demodulator but there would be no reason to have it any other way. Direct output means the input is connected directly to the direct outputs. That's the way my SH-400 is.

So, if you have loud hum,it has to be a bad ground someplace. Is it in both channels?

A double stereo situation and no radar light means the demodulator is not entering four-channel mode. Almost all demodulators are made so that if it isn't in four-channel mode, it outputs 2 channel stereo to both front and back speakers.

Not entering four-channel mode means either the demodulator isn't receiving the 30kHz signal from the turntable/cartridge or the front end of the demodulator, itself is faulty. There is circuitry which picks off the 30kHz signal from the composite signal entering the demodulator and triggers the demodulation circuitry to do it's thing. This also lights the radar.

Doug

 

[Stiffgriff]

Thanks Doug!

Yes, connected 2ch direct out does work without the demodulator turned on, but I do get feedback/buzz out of both channels. However like I said, when connecting just the same turntable and reciever together I get no feedback/hum.

Not so sure about the 30kHz situation but for some reason it’s either not switching to 4ch mode even when the button is pressed or something is wrong with how the demodulator is reading what’s supposed to be getting picked up by my cartridge.

 

[MidiMagic]

Could be the power supply capacitors aging from 50 years of existence.

 

[Doug G.]

Do you have a way of recording the buzz/feedback?

Doug