Electronics > Repair

Marantz SR5200 surround amp odd buzzing sound on all outputs

(1/4) > >>

poot36:
I have this strange issue with what I think is 60 or 120 HZ buzzing in all audio outputs on this amp.  I have confirmed that it still happens when the amp board signal input is disconnected from the rest of the unit.  I have looked at the output from the headphones and the speakers with a scope and for some reason the output with the noise is inverted between both outputs.  The output on the headphone has short almost square wave looking negative pulses that do correctly trigger off the line setting of the scope.  The speaker output has long positive going pulses but would be a mirror image of the headphone output if it were inverted.  The strange thing is the the buzzing sound does decrease if I dim or turn off the VFD on the front of the unit.  I have checked all the voltage rails and they look fine to me but I could be wrong.  The B+ rail has around 300mv of ripple and the B- has about 250mv of ripple on it.  The ripple is higher on the B+ rail due to some I suspect protection related circuitry being powered off it.  I know that the B+ rail does drop fairly quickly when the power is removed and the amp board is disconnected from the B power supply.  The negative rail does not do this.  All other rails are provided by linear regulators and are very smooth.  Other then this issue the amp plays clean and does not sound distorted.

coromonadalix:
schematics : https://www.dclabs.lt/dainiaus/wp-content/uploads/2017/09/sr5200_k2g.pdf

i would isolate all the possible sections, short their inputs to ground and follow  the buzz on the supply lines,   maybe some broken ground link(s)

as the schematic shows you have some star groundings on the psu section,  follow them entirely, 

do check  if this ground is the same for the power amplifier section, and if the continuity is near zero ohms

poot36:
Thanks for the reply.  I have checked all the grounds and they are provided from the 3 pin connector from the power transformer for the B voltage rails.  I have removed all I can from the unit and it still makes the buzzing sound.  I even removed and then grounded the volume board (this is where the amp board gets it's ground from) and I still had the buzzing sound.  I did try grounding out the outputs on the volume board to the amp board and it made no difference.  The solder connections on the bottom of the board look good.  The star ground is connected to the volume board in a bit of a round about way on the PCB but it is connected.  I do not have the original B filter caps in the unit as they were starting to bulge but the replacement caps were working fine in another amp that I scrapped due to the HDMI switcher chip being bad.  I have had no end of issues with this amp trying to repair it: https://www.eevblog.com/forum/repair/marantz-sr5200-amp-damaged-center-channel/msg5600771/#msg5600771.  I fix one thing and something else either breaks or I find another issue.

coromonadalix:
this maybe ?

https://www.avforums.com/threads/marrantz-sr5200-help.1519047/

https://www.devroom.io/projects/repair-marantz-sr5200/


try in direct as they say  and see if it sound okay, if not,    you have 2 ic's to change ??

in the past  many  receivers / sound system did had the dsp processor going bad, and in some cases  the board was not made available for stupid licences issues ??  solution was to transplant from another or dump them :(


this page   has some services bulletins   who could be worth to check

https://www.diyaudio.com/community/threads/marantz-sr7200-buzzing-noise.371020/

poot36:
I have been able to fix the issues that I had in the previously linked thread.  It was the DACs and ADCs that were causing that issue.  I am now dealing with this new issue.  The buzzing still happens even when the volume board is removed from the system (the amp board connects to this board and not the main backplane board).  None of the service bulletins seem to relate to the issue I am having.  I think I am going to try an external power supply to the amp board and see if that changes anything.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod