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Marantz 2270 - Sound at start but then protection relay kicks in after a while.

DomPal

DomPal

New Member
Hello folks,

I have a Marantz 2270 that I bought from ebay. When I first got it and connected everything, plugged it in the the power socket, it sounded great and everything worked. Then after maybe 2 hours of listening I heard a click from the relay then there was no sound. The music came back on it's own after maybe 50 sec to 1 min. Same thing happened the next day. everything is fine at the start til the relay kicks in.

Then as the day goes by, I try to turn it on again to listen to music, but this time, the relay doesn't kick in at all and I can't play music. so i unplugged it. I took the unit to work the next day so that I can have equipment to diagnose it. I plugged it in to the power socket and turned it on. This time everything is fine and the relay clicks fast as usual and I can listen to music. I checked the Voltages on the P800 Power supply board and i am getting

AC:
J804 to J805 74 VAC
J804 to G 37.01 VAC
J805 to G 36.99 VAC
DC:
J802 to J803 35.06 VDC
J802 to G 35.04 VDC
J801 to G 12.88 VDC
J806 to G 38.76 VDC
J807 to G 48.6 VDC
H803 to G 14.06 VDC

What do you think is the fault?
 
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My offhand guess would be amp board transistors, probably the differentials. Does your 2270 have the old (silver cylinder) bias transistors or the new (flat black rectangle) ones? They’re attached to the heat-sinks on the inner side. The silver ones need replacing.
 
Hello Thank you for the tips. I checked the ac signal on the speaker output terminals and I am getting different amplitude values with tha same volume level. I am feeding in a 1kHz sine wave signal.

Then I measured the Vdc on the terminals and left channel is at 43mV while right channel is at -50mv.

Do you have a specific component number for the differential transistors so that I can look it up on the schematics?



Left Channel.jpg
Left Channel

Right Channel.jpg
Right Channel
 
Then I bypassed the preamp and conencted the signal generator directly to the main in to test only the power amp circuit. and I got equal amplification.

This points to the conclusion that my imbalance is in the preamp. any idea on what to do next?
Left.jpg
left ^
right.jpg
right ^
 
Two things - thorough cleaning of RCA connectors and selectro switch, as well as push buttons on the front. And full rebuild of preamp. That's one reason a full restoration is the only thing that can give you peace of mind.
 
Yes I will do this. thank you for your suggestions. Can this be the reason why the protection circuit and the relay keeps cutting power to the speakers or is this just another problem?
 
I suspect the differential pair is bad on one channel, and that the bias is off (not offset, current flow through the outputs at idle).

If it were me, I'd consider an overhaul -- well aged capacitors and transistors known to fail with age will all need to be replaced, probably need to check carbon composite resistors for drift as well.

The differential pair can cause bias problems, and given the symptoms (goes into speaker protection after warming up) I think the basic problem is there. Won't be a bad idea to replace the electrolytic caps in the PS and probably the rest as well.
 
Make sure the balance pot is centered! If so, then...

The preamp side may be off just due to the volume pot. They're not all that great at tracking. Lower the sig gen level a lot, turn the pot all the way up, and bring the sig gen level up enough to see the waveform. This effectively bypasses the pot and see what the levels are like amplitude-wise.
 
Thank you again guys :D really helps a lot. I tried adjusting the bias to to specification and I noticed that at step no.3 on the service manual where I connected my voltmeter ono pin terminals J753 and J754. the readings was 50Vdc for both channels! the manual said it should be at just 5 mVdc. And when adjusting the trimmer pot R763, the values just changes at a maximum of 1V. impossible to get dowm to 5mVdc. Do you think it is a dead capacitor somewhere?
 

Attachments

There are two methods depending on your serial number. The one you seem to have used is for units under serial number 3901. Try the lower one using pins J754 and J756 and adjusted for 10mV.
 
My dumbass found out that the reason I have different amplification between left and the right is because I have the balance pot turned a little to the right channel so that explains it. So I am back to square one to finding why my protection relay keeps being tripped after a while of listeninng and sometimes not clicking at all on start up when the amp has been connected to the mains supply for a while. any thoughts?
 
Measure DC at the amp outputs (at the relay is usually the easiest place). If high DC levels it will certainly trio the relay. Otherwise you are looking at a faulty protection circuit.
 
Replace all small signal transistors here.
The diff pair is always on it's way out, and the preamp ones have given me issues here and there.
 
It could be the cap for the timing of the power on relay release, C807 = 220uF at 10V. All of the caps on the power supply board are really ready to be replaced if not already done.
 
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