Unusual behaveour of Marantz

[Gasho]

Does anybody have a simmilar problem with Marantz PM7200 output section.
Everything is working fine until I try to switch on loudspeaker ouputs (No speaker connected) , than the quiescent current on both channels rise and i must turn of the output binding posts before mad heat up.

I dont know what can go wrong by switchin on only output relays .
this only happends when class A mode is used. Help please. I am pretty pist off with that problem .

 

[Graham Maynard]

Hi Gasho,

This amplifier is known to run hot in class-A - it is meant to.
One friend fried a DAC that he had sitting on top !


Cheers ....... Graham.

 

[jan.didden]

Hi Gasho,

This amplifier is known to run hot in class-A - it is meant to.
One friend fried a DAC that he had sitting on top !


Cheers ....... Graham.

Indeed. And, if the heatsinks get too hot to touch more than a few seconds, they may still be less than 50 degrees Celcius. We don't really know what HOT means anymore

Jan Didden

 

[Gasho]

I understan that class A means hot heatsink , but this is too much . When I measure the voltage across emiter resistors (0.18 ohm) it is too high , about 490mV . That is not OK.

This only happends when I switch on the output relay for loudspeaker.

Somethig is very wrong here. I must run some tests to locate a problem wich is very srange.

 

[Graham Maynard]

Hi Gasho,

Does it do the same with a loudspeaker connected ?


Cheers ......... Graham.

 

[Leolabs]

Looks like a short circuit problem

 

[Gasho]

I solve a problem!

I cant belive it! It was the thing with outpur LCR filter. When I remove output coil , the rest of filter have too much of paralel capacitance (about 400nF ). I put the new paralel RC combination of 100nF +10ohm . Now everthig works fine.

 

[moamps]

.... Now everthig works fine....

Why did you remove output inductor?
Did you check amp stability with oscilloscope?

 

[Gasho]

Yes

Yes

 

[Graham Maynard]

Hi Gasho,

I'd love to hear what you think of the sound of this reasonably priced amplifier.

Reviews say that it has reasonable power, a decent phono input stage and useful pre-amplifier options.

Is it a good basic amp, and has removing the output choke improved it ??


Cheers ......... Graham.

 

[roba08]

My Marantz pm 7200 does not power up anymore and cannot get the amplifier respond to the remote. Could somebody send me the service manual for this amp ?

 

[kzsolt]

Manual

It possible to order from Marantz Service manuals - 5 euro per manual - Marantz, Philips, Denon, Quad, JVC, Akai, Revox, Studer, Sony, NAD, Harman Kardon, Sansui, Onkyo, Krell, Yamaha, TEAC service manuals, schematics, datasheets, diagrams, repairs, schema .
Remeber, some circuit in to protect speakers from deamge!