Marantz 2325 P700 Unknown Diode...

[OFrank]

There is a diode from J708 to R749 (positive power supply rail) and another from J702 to R750 (minus power supply rail) on both amps. These are not on the schematic and not in the parts list of the service manual. I do have an earlier model (s/n 2181). Therefore I assume (I know) that this must have been a modification at some point in time. I have not found any service bulletins for the 2325. Does anyone know what are the spec's on these diodes? They are at least twice the size of the 1N4148's.
Thank you in advanced. O. Frank

 

[wlhd1610]

Pretty sure those are the flyback protection diodes that were added later in the production run by Marantz.
Highly recommend that they be retroactively installed on any 2325 not having them.

Bob

 

[llwhtt]

Those are flyback diodes to protect the output transistors from inductive loads. Something along the specs of an 1N4004 would do.

Bib types faster than me!

Craig

 

[wurlyman]

Could someone please post a photo of them on the board? I'd like to compare it to mine.

 

[OFrank]

Here is a pic of mine after restoration (replace caps,etc).

 

[wurlyman]

Thanks Ofrank, but not a very clear photo. I was hoping for a close up of the actual diode showing where it is connected. I kind of see it but not clear about it or the orientation.

 

[OFrank]

I'll post a better picture when I get home.

 

[tonebells]

Looks like the left hand side next to the dual resisters.

Tony

 

[OFrank]

her are some close up pictures. I hope that they are clear.

 

[wurlyman]

Thanks, Those will be very useful!

 

[wurlyman]

her are some close up pictures. I hope that they are clear.

It looks like diode 2 is mounted in the opposite direction of diode 1, correct? The cathode of number 1 goes toward the resistor and cathode number 2 goes toward J702?

 

[OFrank]

Yes. One is on the positive power supply rail and the other is on the negative power supply rail.

 

[Jflijohn]

Is anyone aware if this also true for a 2275. H719 is on the boards but not in the service manual schematic version that I have, also possibly the fly back diodes?