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Marantz 4300 won’t come out of protection after amp rebuild

C

Chris boyd

New Member
I have a Marantz 4300. I used it for a while before I started getting a crackle in the left channel that wouldn’t go away no matter what I did. I then switched the amp boards around. And the problem followed the amp board. I purchased a rebuild kit and replaced all the transistors varistores and capacitors on the left amp board now the receiver won’t come out of protection on dim bulb. What should I check first?
 
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That's the peril of kits. They are not meant to replace everything rather they give you everything you need in case you determine something is broken - particularly and especially transistors. I for one don't recall having replaced a single varistor. Crackle in the amp board is usually related to the differential pair (two transistors close by). I would have started the troubleshooting there. If it isn't too late I would carefully return everything as it was in the beginning taking great care not to damage the board which is very delicate and start troubleshooting area by area starting with the diff par. You also need to run it in quad mode so you can determine if the issue is on one amp or both.
 
ocdecio said:
That's the peril of kits. They are not meant to replace everything rather they give you everything you need in case you determine something is broken - particularly and especially transistors. I for one don't recall having replaced a single varistor. Crackle in the amp board is usually related to the differential pair (two transistors close by). I would have started the troubleshooting there. If it isn't too late I would carefully return everything as it was in the beginning taking great care not to damage the board which is very delicate and start troubleshooting area by area starting with the diff par. You also need to run it in quad mode so you can determine if the issue is on one amp or both.
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That makes sense in hindsight I should have just done the differential pair and be done with it. But to late now. I have most of the components I removed still. Also how would I tell which amp has a problem in quad mode if two amps are on one board and it won’t turn on with it in?
 
Chris boyd said:
That makes sense in hindsight I should have just done the differential pair and be done with it. But to late now. I have most of the components I removed still. Also how would I tell which amp has a problem in quad mode if two amps are on one board and it won’t turn on with it in?
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You need to measure the DC value at the signal output. If memory serves me they show up at the very top of the relay board so you could compare each one of the four connectors voltage against ground and I suspect one (or two) will have way too much DC. Do that under a 100-150W DBT to be on the safe side.
 
ocdecio said:
You need to measure the DC value at the signal output. If memory serves me they show up at the very top of the relay board so you could compare each one of the four connectors voltage against ground and I suspect one (or two) will have way too much DC. Do that under a 100-150W DBT to be on the safe side.
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The highest watt dim bulb I have is 60. Does that work? Would it be the 4 terminals labeled jn01 2 3 4? At the top of the relay board?
 
Yes. You may need to get a 100W or 150W or at least two 60W. I got mine on Amazon.
 
If you get no voltage the relay is not engaging due to lack of enough voltage. 60W is low for this receiver.
 
ocdecio said:
If you get no voltage the relay is not engaging due to lack of enough voltage. 60W is low for this receiver.
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I figured it out! I put in one of the differential transistors backwards. my understanding is that I need to set the bias voltage and idle current anything else?
 
Chris boyd said:
I figured it out! I put in one of the differential transistors backwards. my understanding is that I need to set the bias voltage and idle current anything else?
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Great! Bias and idle current is the same thing. You need to adjust dc balance and I'd do that only in quad mode so you can adjust the amps separately
 
Chris boyd said:
Thanks. Is the info for that in the service manual?
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Yes it is all there. Bias you can measure on the sides of the big dual resistors at the bottom there are loops to place mini grabbers. You can check DC at the relay board.
 
Thanks I got it all set but I still have a tiny bit of noise. I had put back most of the original transistors and I may have to put the new ones back in.
 
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