Need help with Yamaha RX-500. CD input stuck on and DC voltage on CD RCA inputs.

Thread Starter

002

Joined Jun 11, 2022
3
Hello!

I have an old Yamaha RX-500 receiver that I am trying to repair. The symptoms are as follows:

  • Unit powers up OK and I hear a relay click inside. The LED for the 'CD' input on the front of the unit is always lit, irrespective of my current input. For example, if I select 'Video', the 'Video' LED is lit and the 'CD' LED is also lit but it is a bit dimmer. If I press the 'CD' input button, it lights up as per normal and the previously select input's LED turns off as you would expect.

  • If I plug my phone into one of the inputs (e.g. Video), I can play sound but it is very low volume and does not sound healthy - furthermore, if I choose another input while plugged into Video, I can still hear sound coming out of the speakers.

  • The last symptom is that I am measuring 7 volts DC on the CD inputs at the rear of the unit. I found this out when I initially got the unit and tried to plug my smartphone in to play some music, I chose the CD input and my phone switched off immediately (I guess it was protecting itself, thank goodness). I measured the other inputs and they don't have this high voltage - nowhere near it.

The service manual is on ManualsLib here: https://www.manualslib.com/manual/1287625/Yamaha-Rx-500.html#manual I have also attached it. I had to .zip it as it was too large to attach otherwise. The schematics begin on page 14. I currently have the whole unit taken apart as I was testing the capacitors with an ESR meter and can't find any bad ones so far. I have access to an oscilloscope, DMM, and an ESR + LCR meter...all the gear, and no idea perhaps? :oops:

If anyone can suggest some troubleshooting steps for me, that would be most appreciated.
 

Attachments

abrsvc

Joined Jun 16, 2018
117
I would check the voltages on the LC4966 ICs. These are the input switching ICs and any fault here could cause what you are seeing. Start there. The voltages are listed in the manual. IC202-IC204.
 

Thread Starter

002

Joined Jun 11, 2022
3
I would check the voltages on the LC4966 ICs. These are the input switching ICs and any fault here could cause what you are seeing. Start there. The voltages are listed in the manual. IC202-IC204.
Thank you for your reply. In fact before I took the whole thing apart I did notice that there are voltages on both of those chips that do not match the service manual. There were definitely pins that were reading 7V instead of 0V but would it be the chips themselves that are faulty would you think?
 

Thread Starter

002

Joined Jun 11, 2022
3
I finally got around to this one today and can confirm that swapping out the LC4966 IC's (202, 203, 204) has solved the problem.
 
Top