A high quality receiver I bought for my parents some time ago developed some very odd noise through all speakers only on first cold power up. No other symptoms. The noises were very odd, sometimes a crackling sounds, sometimes almost like the sound of water dripping. Through some reading I found a post by a guy that obviously is on the level and indicated s specific regulator had too much ripple and powers an audio decoder IC so I assume the IC flips out due to dirty power.
I checked all the regs on the digital board and all of them but this one were on spec for the DC voltage and about 1mV rms of ripple. The suspect reg was a 1.8V reg and showing 1.5VDC with about 70mV rms ripple.
The recommendation was just to add another cap on that reg as the OEM cap is of a junk variety and known for issues. I decided to remove and replace the cap though. After replacement, the reg was showing a perfect 1.8VDC and about 1mV ripple.
So it seems this particular power supply issue is fixed but I am stuck wondering, why would this reg supply to a decoder IC causing these odd issues only on start up? Would seem to me this would be showing up at all times?
really not sure the issue is repaired. Only time will tell. have to get several cold restarts to know.
I checked all the regs on the digital board and all of them but this one were on spec for the DC voltage and about 1mV rms of ripple. The suspect reg was a 1.8V reg and showing 1.5VDC with about 70mV rms ripple.
The recommendation was just to add another cap on that reg as the OEM cap is of a junk variety and known for issues. I decided to remove and replace the cap though. After replacement, the reg was showing a perfect 1.8VDC and about 1mV ripple.
So it seems this particular power supply issue is fixed but I am stuck wondering, why would this reg supply to a decoder IC causing these odd issues only on start up? Would seem to me this would be showing up at all times?
really not sure the issue is repaired. Only time will tell. have to get several cold restarts to know.