Hello, I am trying to repair a DBX 3BX Series I (revision 2, the one without the daughter boards).
Some things I managed to fix but I still have a problem with the MF circuit. As soon as I raise the expansion, no matter the transition level, the output goes up as you can see in the video (don't mind the LF and HF meters, they are not calibrated and two CA3058 are waiting for the replacement to arrive).
I tried swapping the LCD pcbs and the problem still persists so it's not a metering issue, so I started poking around and tracked the problem to what I guess could be the RMS section. I measured the dc voltages and reported them on the schematics (attached pdf) and as you can see the 146221 pins 5 and 1 in the MF section are at a whopping 9,6 vdc, while in the LF and HF they swing around zero.
I already tried swapping the 146221s but nothing changes so that's not the problem (fortunately as they are DBX's proprietary ICs). I also replaced all the electrolitics.
I think it could be OA24 as its inputs are 4,68 vdc (input 6) and 0 vdc (5) instead of being both at zero so it looks to me like it is overcompensating and outputting a voltage which is too high, but I am not sure really.
Anyone can help me find the issue? Thank you very much!
Some things I managed to fix but I still have a problem with the MF circuit. As soon as I raise the expansion, no matter the transition level, the output goes up as you can see in the video (don't mind the LF and HF meters, they are not calibrated and two CA3058 are waiting for the replacement to arrive).
I tried swapping the LCD pcbs and the problem still persists so it's not a metering issue, so I started poking around and tracked the problem to what I guess could be the RMS section. I measured the dc voltages and reported them on the schematics (attached pdf) and as you can see the 146221 pins 5 and 1 in the MF section are at a whopping 9,6 vdc, while in the LF and HF they swing around zero.
I already tried swapping the 146221s but nothing changes so that's not the problem (fortunately as they are DBX's proprietary ICs). I also replaced all the electrolitics.
I think it could be OA24 as its inputs are 4,68 vdc (input 6) and 0 vdc (5) instead of being both at zero so it looks to me like it is overcompensating and outputting a voltage which is too high, but I am not sure really.
Anyone can help me find the issue? Thank you very much!
