Marantz 2270 late model factory modifications

[MBuras]

I was recently working on a Marantz 2270 that is very late production, from October 4th, 1975. Serial number is #U462378. We all know there were a few service bulletins issued on this model but I've never seen pics of the mods.

First up is service bulletin one which changes the temperature compensating transistor from the round 2SC984 to a flat 2SC496. Here is a picture of the factory custom bracket to mount the new transistor and include the bias diode alongside.



And next up isn't a service bulletin, at least that I'm aware of, but is a common good practice on some of these older units. Many of them didn't come with flyback diodes from the factory. This late production model did have flybacks installed and best I can tell they were either factory or early service center work.

They were installed as follows to each amp board:
cathode to J753, anode to J754. cathode to J760, anode to J761.

 

[thxdave]

What does a flyback diode do? (in layman's terms) ;-)

 

[MBuras]

The way I think about them is a a one way road with an entry gate. During normal operation it allows voltage (traffic) to flow to the outputs. If there is a failure of some sort and a voltage spike tries to go backward and take out the output transistors it clamps down and says nope, can't go this way. Later on these were built in the circuit designs.

 

[Dearslayer]

That's the best explanation I've heard for a rookie like me.

 

[avionic]

The way I think about them is a a one way road with an entry gate. During normal operation it allows voltage (traffic) to flow to the outputs. If there is a failure of some sort and a voltage spike tries to go backward and take out the output transistors it clamps down and says nope, can't go this way. Later on these were built in the circuit designs.

Actually. And energized relay coil is a "field". When the relay denergizes .The "field" collapses. A collapsing field across and inductor(relay coil) causes a high voltage spike. The flyback diode controls that spike and safely dissipates it.

 

[Steven Tate]

I posted this in another thread a few days ago. Someone mentioned a flyback diode, so I hit Google to try to see what it was. Found this pretty simple explanation that even I could somewhat understand.

http://www.douglaskrantz.com/ElecFlybackDiode.html