Yamaha RX-V475 HDMI audio distortion - Page 1
Forum section: electronics / repair

author: dammert89
author_rank: Contributor
timestamp: August 11, 2020, 07:36:40 am
content: Hi everyone.So I picked up another dead receiver (just needed to be reset). This one is an older model, a RX-V475. Got it all connected and updated the firmware and set up all the basics.I have 2 issues with the receiver, if anyone has some input it would be much appreciated.Issue 1When I use HDMI as the input source for audio it is distorted, but when I use the AV analog as input (Same source) the sound is perfect and there is no distortion whatsoever (I have tried multiple sources as well). So my thinking (correct me if I am wrong), is that the digital input signal is not correctly getting processed to analog by one of the chips on the HDMI board (The DIR / DAC or ADC)Any advice?Issue 2All of the channels of the receiver are working correctly except the Front left channel. The front left channel sound quality (when using AV) is good and there is no distortion of any kind, the issue I have is that the actual output volume is very low(not amplified). Yes, I have done all the necessary test to eliminate speakers, wire, source etc. and have come to the conclusion that it is definitely the amp channel. Could it just be the power transistors that have failed (1 of the pair or both?). The amp also does not enter protection mode.Any advice on this issue?Perhaps Issue 2 is the cause of Issue 1? or vice versa.Thanks in advance.

author: dammert89
author_rank: Contributor
timestamp: August 11, 2020, 03:21:16 pm
content: Hey there. So after some diagnosing and reading up on it.The hdmi does output sound. There is just this distinct hum. Not actually distortion, more like a constant switching frequency playing at all times. Don't exactly know how to explain it.That got me thinking, maybe it's the caps on the HDMI board. How often do these fail and if they do, what are the symptoms.

author: dammert89
author_rank: Contributor
timestamp: August 12, 2020, 07:34:58 am
content: So I realised that I can troubleshoot further through process of elimination.If I am reading the block diagram correctly. HDMI audio goes from HDMI (any input port) to IC1, the SII9573CTUC, from there the signal is transmits to IC61, the PCM9211PTR, and then to the DSP.Optical follows a similar route (except that it does not go through IC1).Analog goes to IC201 and then to IC61 in DSP mode otherwise straight to the amp section in Direct mode.I unfortunately don't have an optical cable lying around to test at the moment. When I find one I will test it asap.This leads me to believe that IC1 and/or circuitry around IC1 is faulty?

author: mzacharias
author_rank: Frequent Contributor
timestamp: August 12, 2020, 12:19:10 pm
content: Rule #1 (in the Thundering Voice of God)Thou Shalt Check Power Supplies!For example, there could be some power supply noise affecting the digital audio circuits.Don't rely only on a multimeter, although a noisy line may read a bit low; use an oscilloscope.

author: dammert89
author_rank: Contributor
timestamp: August 12, 2020, 12:33:38 pm
content: Don't have a oscilloscope, maybe i should get myself one.I will see what I can find around here.

author: dammert89
author_rank: Contributor
timestamp: August 12, 2020, 02:22:00 pm
content: I just tested the HDMI passthrough in the service menu. That works 100% (output from tv).If it was a power supply issue would the analog not be distorted too?I am going to try with my bench power supply now and see if the hum/buzz still occurs.

author: mzacharias
author_rank: Frequent Contributor
timestamp: August 13, 2020, 12:34:02 pm
content: Quote from: dammert89 on August 12, 2020, 02:22:00 pmNot necessarily - not by a long shot.

author: elecdonia
author_rank: Frequent Contributor
timestamp: August 14, 2020, 12:41:22 am
content: Quote from: dammert89 on August 12, 2020, 02:22:00 pmThere are numerous different power supplies and power supply regulators inside these AV receivers. Almost too many to count.I suggest downloading a service manual, either for your exact model, or for one that is similar. There are a huge number of different Yamaha model numbers for their AV receivers, but many of them are rather similar in internal circuit design.I've recently fixed several, but none had the exact problem you are reporting. I haven't traced the entire "flow" of digital audio signals inside the receiver. I do believe that most of the digital audio action takes place on the "digital" PC board. This is the board that carries all the HDMI jacks.-E