Hi everyone, thanks for reading. I have an anthem MRX 700 receiver which I have used for years. Recently, I noticed the volume for my front right, center, back left, and surround left channels were at a much lower volume (not distorted or entirely silent just ~18db lower than the rest). I'm trying to troubleshoot this and see if it is fixable myself since I dont have the opportunity to replace it or send it in for official service right now. I do have some experience in electrical engineering so hopefully that will be possible. I don't have a service manual unfortunately(let me know if you do please!). I've done the basic troubleshooting (swapping cables/speakers/outputs) and have narrowed down the issue to the receiver itself. The channel outputs look clean at the connection. I took off the outer case and can see some corrosion around the hdmi board but nothing else. I did notice that the channels in question are physically in a line next to each other at least for part of the amp board near the transistors as well as on the preamp board and bus. That can be seen here:
voltage output for each channel with no audio is 0.029V. when doing noise output for level calibration FR goes up to 0.7V SR goes up to 0.15V BSR goes up to 0.15V as well, on the low volume speakers voltage increases to 0.039 on each when noise is output to their channels. connection from the analog board to the amp shows 0.024V on the pre signal for the channel with noise 0v otherwise, same with the connection from analog board to pre-amp.
Any idea what would be some good steps to potentially troubleshoot or fix this? Thank you again!
voltage output for each channel with no audio is 0.029V. when doing noise output for level calibration FR goes up to 0.7V SR goes up to 0.15V BSR goes up to 0.15V as well, on the low volume speakers voltage increases to 0.039 on each when noise is output to their channels. connection from the analog board to the amp shows 0.024V on the pre signal for the channel with noise 0v otherwise, same with the connection from analog board to pre-amp.
Any idea what would be some good steps to potentially troubleshoot or fix this? Thank you again!
Hi kryonas,
I have the exact issue with my MRX 500. It seems to be the pre-amp board and not the power amps as the headphone socket is very quiet on the left channel.
Did you work out a solution? I'm experienced with electronics servicing/repair and I'd like to know what and where the offending op-amp or audio switch is so that I'd hopefully be able to replace that. But the schematics don't seem to be available from what I can find. I doubt I'd be able to get a new pre-amp board from Anthem. I'm in the UK.
I guess I'll need to do some circuit tracing and reverse engineering. I do have an oscilloscope so hopefully I can trace a signal and find out where the signal trail goes cold.
I have the exact issue with my MRX 500. It seems to be the pre-amp board and not the power amps as the headphone socket is very quiet on the left channel.
Did you work out a solution? I'm experienced with electronics servicing/repair and I'd like to know what and where the offending op-amp or audio switch is so that I'd hopefully be able to replace that. But the schematics don't seem to be available from what I can find. I doubt I'd be able to get a new pre-amp board from Anthem. I'm in the UK.
I guess I'll need to do some circuit tracing and reverse engineering. I do have an oscilloscope so hopefully I can trace a signal and find out where the signal trail goes cold.
Anthem MRX 500-700 very low output on one channel
I have the same problem (very weak right channel and the one in the center is not at 100%) My analyzes detected that this was not due to the preamp board because it conducts the signal very well on each of the channels external . I have already replaced the capacitor on the AMP board even if all the voltages were identical on each of the channels. I also take the headphone very low on the right channel as on the output speaker direction. It should not be forgotten here that precisely the headphone socket is attached to the HDMI board. Which makes me believe that the origin of the problem comes rather from the latter. But the most unfortunate thing about this is that Anthem does not want to give us the source of the problem, even if a multitude of tests have been done in the device. They are really unhelpful !! and there the word is weak
I have the same problem (very weak right channel and the one in the center is not at 100%) My analyzes detected that this was not due to the preamp board because it conducts the signal very well on each of the channels external . I have already replaced the capacitor on the AMP board even if all the voltages were identical on each of the channels. I also take the headphone very low on the right channel as on the output speaker direction. It should not be forgotten here that precisely the headphone socket is attached to the HDMI board. Which makes me believe that the origin of the problem comes rather from the latter. But the most unfortunate thing about this is that Anthem does not want to give us the source of the problem, even if a multitude of tests have been done in the device. They are really unhelpful !! and there the word is weak
Regarding the low output on the anthem mrx series amplifier
I see multiple posts over the Internet regarding this repair and this particular problem Anthem do not make the service data available, I had one in workshop.. so decided to address problems. symptom low output on surround sound... The solution was to remove the plugin preamp board and replace the two 10uf 50V capacitors on the offending channels they are actually marked on circuit board.
I replaced all the capacitors with 4000s numbers on each channels since all of them had a very high esr. quick note be careful not to pull out feed throughs. apply enough heat or preheat underside.... also replace the large 3300uf 16V capacitor on hdmi board if any signs of leaking electrolyte.
I see multiple posts over the Internet regarding this repair and this particular problem Anthem do not make the service data available, I had one in workshop.. so decided to address problems. symptom low output on surround sound... The solution was to remove the plugin preamp board and replace the two 10uf 50V capacitors on the offending channels they are actually marked on circuit board.
I replaced all the capacitors with 4000s numbers on each channels since all of them had a very high esr. quick note be careful not to pull out feed throughs. apply enough heat or preheat underside.... also replace the large 3300uf 16V capacitor on hdmi board if any signs of leaking electrolyte.