Marantz SR4300 Receiver Peculiar set of symptoms....

jiot

Member
2017-10-03 11:19 am
This unit has an issue with no/intermittent sound output.

Appreciate all who read this.

Here is the thing Im listening to stereo music on it as I write through the preouts front left and right...but it still has its problems...

When powering up there are no problems...display works..all buttons seems to do what they say...yet no sound.

The problem is no sound even via headphone or preouts or speakers.
But then sometimes if you select DIRECT and if you turn either the volume knob or adjust volume via the remote...up and down you hear clicking..then maybe a slight pop...then continue up and down...and then you can settle on a spot where the sound will suddenly start...and as long as you dont touch the volume anymore it will continue to push sound out. But further sometimes sound is out one channel only...it can change to the other channel..and rarely both channels sound outputs.

Also weirder.....sometimes you can hear via headphones quiet sound from one channel..but its coming through all inputs...no matter which one you select ..you can still here it quietly.!

Ive replaced the power filter caps...and gone over the main board looking for poor solder joints and reflowed where appropriate. But issue has not changed.

Started to wonder if its a bad Sound Processing/Volume Tone Chip ..which is a M61516FP. (ICS03)

I dont want to bin this old beast if I can help it...hoping someone with some knowledge or experience may make some sense of this.

Cheers and Thanks in Advance!
 

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Have you checked all the power rails are at the nominal voltages?


Otherwise it sounds like a job for an insulated poking-stick or a cold-spray to try and find a dodgy part of the circuit - things like hairline cracks and dry solder joints are often provoked by mechanical or thermal intervention - this may help localize the issue.


The other thing I can suggest is some sort of HF oscillation is taking place.


The defect switching channels though is distinctly odd. Good luck!
 
Two possibilities I can think of:
a) The IC's digital section is in fact knackered as suspected.
b) digital communication unreliable e.g. due to unstable DVDD, bad trace, bad solder joints, bad ribbon cable contact or shorted ceramic cap on the line. Some poking around with the multimeter and possibly a good loupe on the CPU connections may be needed.
 

jiot

Member
2017-10-03 11:19 am
Thankyou for your replies !

Solder joints checked... power rails.. it’s hard to check test anything on this unit.. the circuit boards are layered horizontally.. I’m sure I can work around it .. even if I solder some wires to useful test points and put it back together and test.

It is certainly an odd set of symptoms.. and it makes me suspect the vol/tone chip is bad. Will play some .. if I see a clean signal going into that chip but a nothing or crap coming out then that should rule in rule out the chip. Have to dust down my old oscilloscope for the job.
 

jiot

Member
2017-10-03 11:19 am
I wonder if the clicking and pop is a defective protection relay on the outputs, or one being switched intermittently.

Thanks Stuey
Not sure..for certain tho no physical clicking sound coming from the relays other than after coming on.Clicking is heard when you increment each volume dB step either with the knob or remote... also you can hear it audibly via the preouts. It sounds not unlike an old audio click you may hear from an old multi gang source selector input switch when switching between different source inputs.
 
I wonder if that clicking could be a problem with the rotary encoder, but I don't think it would explain all the symptoms such as channel imbalance.

I'd definitely go over the circuit looking for cold joints as suggested above, esp on the encoder since it moves and could cause stress to the joints (I'm assuming it uses an encoder, if not ignore me).
 

jiot

Member
2017-10-03 11:19 am
I wonder if that clicking could be a problem with the rotary encoder, but I don't think it would explain all the symptoms such as channel imbalance.

I'd definitely go over the circuit looking for cold joints as suggested above, esp on the encoder since it moves and could cause stress to the joints (I'm assuming it uses an encoder, if not ignore me).

Hi Stuey
Yep It does use an encoder...Ive removed it cleaned it with some lube/switch cleaner...and resoldered...clicking still remains atm.. This clicking also happens if you use the remote volume +/- buttons.

Its coming apart again :) will certainly be checking again for any joints I may have missed...and if none will be attaching some wires for test points so I can more easily test some critical points with the meter and scope.
 

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definetly need to look at the digital commands, I had issues in the past with a dried cap on the CPU power line, apparently the cpu was working but it was sending really strange looking signals. If you have a scope, fire a sine wave generator a a phone or pc , and trace it as much as you can, I know how bad it is to work on that design but with a few extended test points it is mangeable. It is an old beast but if you have the time it is worth saving. My first start would be to see if you get clean signal in the cip and if you get the clicks out of the chip eventualy if the clicks match something on the comm signal it gets or some matching noise on the power supply.

Could be as simple as a bad cap on the logic rails.
 

jiot

Member
2017-10-03 11:19 am
definetly need to look at the digital commands, I had issues in the past with a dried cap on the CPU power line, apparently the cpu was working but it was sending really strange looking signals. If you have a scope, fire a sine wave generator a a phone or pc , and trace it as much as you can, I know how bad it is to work on that design but with a few extended test points it is mangeable. It is an old beast but if you have the time it is worth saving. My first start would be to see if you get clean signal in the cip and if you get the clicks out of the chip eventualy if the clicks match something on the comm signal it gets or some matching noise on the power supply.

Could be as simple as a bad cap on the logic rails.

Thankyou Kytan for sharing your experience and knowledge.. gives me some more ideas of where and what to look for.. it is a nice sounding amp enough for me to try and also very much a good learning experience..no matter if it can be fixed or not. Cheers .. will update any progress.
 

jiot

Member
2017-10-03 11:19 am
Just had this marantz back on the bench again for another looksee..
No noise anymore ..no click no nothing . Voltages check out OK...the problem is isolated to the 'Digital Audio Board' and specifically signal is going into Chip M61516FP but not out.

So my options are few...you can get the chip on Ebay. However I wonder if are they exactly the same..and not particularly cheap.

Is it possible to bypass this chip ..input straight into the Amplifier??....wanting to prove at least the Amplifier board is working if nothing else...and perhaps then try it out as a 2 channel amp.

Any help most appreciated.

Service Manual SR4300
https://www.vintageshifi.com/repert...ge.php?pdf=Marantz-SR-4300-Service-Manual.pdf