Marantz 2275 idle current too high after transistor replacement

[Beamer302]

I would like to know why when replacing on a 2275 amp board H713 (which was a bad 2sd382) with a MJE15030G (suggested replacement) and H714 ( a good 2sb537) with a MJE15031G(suggested replacement) the idle current won't trim down to 10mV ? 10mV is what the service manual says to set it at. I can only get it down to 48.5 mV. I had this 2275 up and running for a few weeks till H713 blew.Idle current was fine before then. Do I need to add more resistance somewhere ? Are these suggested replacement transistors wrong? The components on the board show no sign of heat stress. Should I start checking resistor values ? Thanks.

 

[raidermc]

If memory serves me correctly diode h 710 is part of the bias circuit that I swapped out with (2) (1n----) diodes in parallel to solve that issue I had with a 1150 (same amp boards).That diode resides under the h713 transistor.
Make sure you use the insulator from the old diode and place the new ones in the same place (temp sensing for biasing).
That mod will get your adjustment back.

 

[Beamer302]

Thanks, I like the plan.I know where H110 (S3016R) is. Last year I spent a few hours looking for it on another 2275. I was hoping I wouldn't have to replace it. I have no idea what to replace it with. It is to be replaced with two diodes in parallel ? To replace a S3016R varistor what would be a usable diode set up ?

 

[raidermc]

H710, I went to radio shack a purchased a pack of assorted 1N diodes.

Grabbed 2 that were close in (diode checker on my meter) value, parallel them and all was good.
Here is my Thread on it.
Marantz 1150 int amp idle current woes

 

[Beamer302]

I will try a 1N4148 diode. I will also test the original H710. Not sure if I will need 1 or two 1N4148's. Still not sure about wiring it in parallel or series. Thanks for the help.

 

[raidermc]

From what I understand, I needed less voltage drop across the diode to get proper biasing.
That's kinda how I remember it being explained to me.

 

[Beamer302]

Alright I'll poke around with it and see what happens.

 

[raidermc]

When in doubt bring it up with a variac or dim bulb tester.
You should be fine with it.
I must admit I was apprehensive as well.

 

[Beamer302]

I tried using one 1N4148 in place of the original S3016R (710) It raised the bias (idle current) to about 84.5 mV. This is going in the wrong direction. Should I try two 1N4148's in series ? I checked the original H710 and it tested as a diode or diode junction. forward voltage 64

 

[raidermc]

Parallel

 

[Beamer302]

Just tried two 1N1418's in parallel and I got the bias down to 54.3 mV. Seems Like this is a long way to get to 10mV's. Has anyone ever replaced the H713 (2sd382) transistor and with what ? Was bias an issue afterwards ? I am sure that the original S3016R is good. I am just spinning my wheels. If I had an original 2sd382 I don't think I would have to jump through these hoops.

 

[Steven Tate]

Just to be sure, you are using the corrected method of measuring idle current in the 2275?

From the Marantz service manual error thread:
"SM says measure 707-708, adjust R742 for 10mV. Do this instead: Meter set to read DC mV, connect from J701 to J702, set R742 for 10mV"

 

[raidermc]

Just checked the bunch of RS diodes 1n4001 is what I used. Parallel they read 607.

 

[petehall347]

did you test/change the driver transistors ?
is dc offset ok ?
is the 35v set correctly ?
any oscillation at the output ?

 

[raidermc]

Good point , the diff input pair could be the culprit

 

[Beamer302]

Thanks Steve., I am using pins J703 and J704 (yellow and a purple) The left channel adjusted fine. I am set on the 200 mV setting. I believe J701 and J702 correspond to the same pins.

 

[Beamer302]

I checked most of the transistors that were near H713 after it blew out. I did not check the two transistors I had put together with heatshrink H701 and H702. I checked H708 and H705. I checked outputsH001 H002. I did not check H704 and H703 or H701 and H702. Looks like I have some checking to do. To be clear are H701 and H702 the differential pair ? Thanks guys.

 

[raidermc]

Yes

 

[petehall347]

h713 is a driver .it blew out for a reason . might have taken other things with it such as an output or resistor or 2 . h709 is the bias transistor ,
h701 702 are indeed the diff pair .
713 may have blown because of a bad output transistor or bad connection around it .

 

[petehall347]

look at the schematic and you will see various voltages to check . checking these might well reveal what is going on here .