jdlahmann
New member
Hello all - new here, I didn't know there was a forum for quad stereos! Super stoked to find it!
For the past several weeks I have been working on a QX-949 that had multiple issues. I have worked through all of the PC boards successfully (power supply, protection, preamp, tone control, matrix, decoder, CD-4, tuner, and both power amps). Everything was working well and there was a lot of testing in between each board. After the power amps were went through I set the bias and DC offset and everything was working *far* better than it was before.
After that I played it in for about an hour or so and everything was still where it should be and things sounded great. I moved on to replacing the four large 10,000 MFD electrolytic capacitors and things went sideways. Yesterday I replaced the first two with no problem everything still worked 100%. This morning I replaced the other two and the receiver would not come out of protection. I took some quick measurements and have approximately 15.5V (not mv) of DC offset on pin 5 of both amplifiers. This value should read 0v or somewhere is the very low millivolts. Bias still reads right where it should on all four channels, and DC offset is correct on the other two channels.
I have checked every wire for conductivity, re-soldered every connection, tested voltages all over and everything is right where it should be aside from the sky high offset voltage. I have also verified that everything is wired in correctly multiple times with the service manual schematic. I am stumped and can't figure out what is going wrong here. Out of everything that I have worked on throughout this receiver this *should* be one of the most simple part swaps that shouldn't take more than an hour.
If anyone could help with some advice on how best to proceed I would appreciate it so much! I am out of ideas and feeling pretty defeated after coming so far and making so much progress to be back on square one when this was literally the last thing to do. Thanks in advance!
For the past several weeks I have been working on a QX-949 that had multiple issues. I have worked through all of the PC boards successfully (power supply, protection, preamp, tone control, matrix, decoder, CD-4, tuner, and both power amps). Everything was working well and there was a lot of testing in between each board. After the power amps were went through I set the bias and DC offset and everything was working *far* better than it was before.
After that I played it in for about an hour or so and everything was still where it should be and things sounded great. I moved on to replacing the four large 10,000 MFD electrolytic capacitors and things went sideways. Yesterday I replaced the first two with no problem everything still worked 100%. This morning I replaced the other two and the receiver would not come out of protection. I took some quick measurements and have approximately 15.5V (not mv) of DC offset on pin 5 of both amplifiers. This value should read 0v or somewhere is the very low millivolts. Bias still reads right where it should on all four channels, and DC offset is correct on the other two channels.
I have checked every wire for conductivity, re-soldered every connection, tested voltages all over and everything is right where it should be aside from the sky high offset voltage. I have also verified that everything is wired in correctly multiple times with the service manual schematic. I am stumped and can't figure out what is going wrong here. Out of everything that I have worked on throughout this receiver this *should* be one of the most simple part swaps that shouldn't take more than an hour.
If anyone could help with some advice on how best to proceed I would appreciate it so much! I am out of ideas and feeling pretty defeated after coming so far and making so much progress to be back on square one when this was literally the last thing to do. Thanks in advance!
