HI, I have a Marantz PM6004 amp which has developed a problem. It was working fine until I went away and turned it off for a few days, when i switched it back on things went wrong.
The output through the speakers was now at a low volume and heavily distorted, i checked the headphones and the output was the same. I checked the input and discovered that the input from the CD could also be heard at a lower volume when changing the input selector to any of the other inputs, i.e. I could hear the CD through the AUX input. I changed the input to say the Phono input and could hear that through all the other inputs.
I thought it may be the input selector chip at fault but couldn't find any shorts across the pins.
Any suggestions as to what to check next?
The output through the speakers was now at a low volume and heavily distorted, i checked the headphones and the output was the same. I checked the input and discovered that the input from the CD could also be heard at a lower volume when changing the input selector to any of the other inputs, i.e. I could hear the CD through the AUX input. I changed the input to say the Phono input and could hear that through all the other inputs.
I thought it may be the input selector chip at fault but couldn't find any shorts across the pins.
Any suggestions as to what to check next?
Hi check the plus and minus DC supply rails on U3501 LC78212 input selection IC.
Pin 19 plus 15V, Pin 15 minus 15V.
If okay replace U3501.
Pin 19 plus 15V, Pin 15 minus 15V.
If okay replace U3501.
Hi, really appreciate the response. There is no minus 15V supply to the chip. I have 18V AC coming into the board and positive 5, 12 and 15 but no negative coming out of U8102. Would that be at fault or something else between the input and output voltages?
sazgaz
The system protection system monitors the plus and minus 15 volt supply rails and if they are low or missing the Amplifier would switch to protection mode.
Connect your multImeter negative probe lead to the negative speaker terminal binding post on the rear and then recheck the voltage on each of the pins of U8102.
The system protection system monitors the plus and minus 15 volt supply rails and if they are low or missing the Amplifier would switch to protection mode.
Connect your multImeter negative probe lead to the negative speaker terminal binding post on the rear and then recheck the voltage on each of the pins of U8102.
It would be a bit odd if a 7915 regulator failed for no reason, they are usually quite reliable. It's worth replacing it, or testing it out of circuit if you have the means
Yes, i was wondering what caused it to fail. I'm going to replace it anyway so will let you know how i go.
sazgaz replace both regulators the brand used in the Marantz PM6000 series is the same as the Pioneer A10,A20 & A40 and are known to fail.
replaced both regulators and working fine now. Hopefully it will stay fine and not fail again!!!
As I assumed 78xx/79xx have the reliability of an M3 bolt I am curious which exact brand and type these are. Can you tell?
Interesting.. i have some 7805's made by them in my stock of reclaimed parts.. i will keep an eye out in future!