Marantz 2275 P700 Diode Questions

[richiem46]

I am in the process of restoring a Marantz 2275 and I noticed that on the P700 amp boards there are two red/green "diodes" installed across J703 and J709 and J704 and J707. Two other 2275's I restored did not have these "diodes". I looked online at various pictures of the P700 and yes, some have the "diodes" and some do not. The blue arrow in the picture below points to the components in question.

I was wondering of anyone was familiar with why they are on some boards and not others? This board is working fine but I was wondering:

1. Just what are these devices?

2. if I should remove these diodes if I replace the Fairchild output transistors with onsemi MJ21193/94 outputs?

3. What purpose do they serve where they are installed?

Thanks for any help!

Rich

 

[petehall347]

fly-back arrangement for some reason . i dunno . maybe to stop speaker pop at power up /down . just a wild guess

 

[ocdecio]

fly-back arrangement for some reason . i dunno . maybe to stop speaker pop at power up /down . just a wild guess

Most definitely flybacks and they should not be messed with. They help protect the amp against reactive speakers.

 

[richiem46]

Thanks for the information, I will leave them in place. It also sounds like I should add the flyback diodes to any 2275's I restore. Any suggestions on what type of Diode I should use? They are not in the schematic or parts list.

 

[ocdecio]

Thanks for the information, I will leave them in place. It also sounds like I should add the flyback diodes to any 2275's I restore. Any suggestions on what type of Diode I should use? They are not in the schematic or parts list.

1N4003-1N4007 any would work. 1N4003 is listed for the 240 120WPC amplifier so it stands to reason it would work across the board.