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2275 stumper

tarior

tarior

Dirty pool, old man?
Subscriber
Alright, this thing is driving me crazy. I can't get it to stop emitting a small "pfftht" when powering off. The mute relay just won't open fast enough. So far, on the relay/power supply board, I have replaced every electrolytic cap, H805, 806, 807, 812 with the proper replacements. I read 1.35v on the bas of H806, and .018v on the base of H805. I get 23v at the cathode of H812. Voltage between J804 and J805 is dead nuts 35v. DC offset is ~.5mv, bias is dead on at 10mv (let's hear it for those Bourns pots!). All of the resistors associated with the relay are within 5%.. The relay coil is supposed to be 560 ohms, and it is dead on.
The power down pop isn't loud, I just know it's there, maybe I'm just being too picky?
 
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tarior said:
Alright, this thing is driving me crazy. I can't get it to stop emitting a small "pfftht" when powering off. The mute relay just won't open fast enough. So far, on the relay/power supply board, I have replaced every electrolytic cap, H805, 806, 807, 812 with the proper replacements. I read 1.35v on the bas of H806, and .018v on the base of H805. I get 23v at the cathode of H812. Voltage between J804 and J805 is dead nuts 35v. DC offset is ~.5mv, bias is dead on at 10mv (let's hear it for those Bourns pots!). All of the resistors associated with the relay are within 5%.. The relay coil is supposed to be 560 ohms, and it is dead on.
The power down pop isn't loud, I just know it's there, maybe I'm just being too picky?
Click to expand...

Sometimes there is a diode used in the relay driver cicuitry to discharge the timing capacitor more quickly on power off. Possibly if your circuit has one and the diode is open the circuit would work OK but be slower to turn off the relay.

Lefty
 
dr*audio said:
Got a schematic?
Click to expand...
Yes, and I replaced H812 which is the diode which shorts the relay coil when power is removed. I understand that when power is removed, C808 discharges and forward biases H805, grounding the base of the Darlington pair of H806/807. It just seems a little delayed, maybe I need to widen the scope of my investigation?
 
H812 does nothing of the kind...it is there to protect H807 from inductive kickback when the relay opens on power down. Replacing it is still a good idea.

This scheme has no AC voltage sense...most protection circuits have a single diode, cap, and resistor allowing forward biasing of the relay driver transistor. On power down, it is designed so that this holding voltage falls very quickly and forces the driver transistor to shut off, opening the relay. On the 2275, Marantz has relied solely on the load provided by the relay to suck the tiny 10µf 50V C807 capacitor dry on power down to prevent turn off thumps.

If you used a bigger cap than 10µf for C807, there's your problem. If not, then the relay may simply need replacing.
 

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EchoWars said:
H812 does nothing of the kind...it is there to protect H807 from inductive kickback when the relay opens on power down.
.
Click to expand...
Yeah, I guess it would be tough for the anode to get more positive than the cathode here. I did use the exact value cap for C807, but it wouldn't be the first time I've had a brand new component be less than good. I'll swap it out for another and report back. BTW, how exactly does a relay get lazy on opening? When this one closes, it does it with authority, quick.
 
There's a spring just behind the pivot point on the relay which pulls it open by mechanical force once the coil is de-energized. It may be weak.

Your 10µf cap would have to read high by at least 100% to cause what you're seeing. Check to see that you replaced it with the proper value, and then I'd just replace the relay (they do wear out, and are a source of a lot of distortion once the contacts get a little pitted).
 
EchoWars said:
There's a spring just behind the pivot point on the relay which pulls it open by mechanical force once the coil is de-energized. It may be weak.

(they do wear out, and are a source of a lot of distortion once the contacts get a little pitted).
Click to expand...
I was wondering if the coil somehow became capacitive, essentially latching itself (very briefly).
I guess I'm gonna be shopping for a relay.
Funny thing, it was giving a power down thump when I first fixed it, so I replaced C808 (again) and the trouble went away for two or three days, then it came back today. Replacing C808 now has no effect, same with 807.
 
Hello,

replace C807 with 4,7 uF. This will make the relay fall off faster.
Maybe you have a worn power switch and/or a bad noise suppresion capacitor across the switch.

Helmut
 
ruesselschorf said:
Hello,

replace C807 with 4,7 uF. This will make the relay fall off faster.
Maybe you have a worn power switch and/or a bad noise suppresion capacitor across the switch.

Helmut
Click to expand...
Replacing C807 with a 4.7 uF did make the problem go away. I am a little concerned in that it appears to be the filter for H811. I doubt the DC needs to be really "clean" here, I just don't want it to affect longevity in a negative way.
 
sssmokin99 said:
these relays just arent worth guessing about or trying to fix. I say, replace 'em!
Click to expand...
Yeah, I hear ya', I just hate waiting for my order to come in.
 
''Replacing C807 with a 4.7 uF did make the problem go away. I am a little concerned in that it appears to be the filter for H811. I doubt the DC needs to be really "clean" here, I just don't want it to affect longevity in a negative way.''

H811 and C807 sole porpose is to supply the relay circuit with an extra DC current that will vanish as soon as AC power is switched off, so the relay falls off fast. So the Marantz engineers did some thinking when they designed this circuit - they could have saved 2 diodes and a capacitor by supplying the relay from H808/ C801

B.t.w. the later 2285 had that same circuit, 10uF cap. on the manual, but usually 4,7uF on the pcb.

Helmut
 
ruesselschorf said:
B.t.w. the later 2285 had that same circuit, 10uF cap. on the manual, but usually 4,7uF on the pcb.

Helmut
Click to expand...
Well, with that in mind, I guess I'm not gonna sweat it.
The 2275 is running very nicely, and seems to be totally quirk-free now.
Thanks again to everyone for the ideas.
 
Using a 4.7µf cap is a decent solution...it should be able to handle the ripple current of the relay with little problem.

Be aware that the Omron relay coil of the MY2-02-DC24 is about 640 ohms. I don't know what the original coil is, but in the end it might require an adjustment of R815 to install the new one.
 
The original is 560 Ohms, Allied just happens to stock one.
I feel even better about the solution since you OK'd it.
Thanks
 
tarior said:
Well, with that in mind, I guess I'm not gonna sweat it.
The 2275 is running very nicely, and seems to be totally quirk-free now.
Thanks again to everyone for the ideas.
Click to expand...
Hello, how's that cap solution working out for you? I have the same issue with my rebuilt 2275 - small pffft sound with woofers popping a little bit when I power off. Thanks!
 
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