U2 (SC99) Voltage is really high @ bias config step
Posted: Fri Jul 13, 2012 10:35 pmI recently bought two J99's one is assembled and working but the other is not. The first time I thought everything was ok I hooked a mic up to both to see what a stereo pair would sound like (this is when I fried the SC99 at U2). In the module that is not working, each gain step was noisy and some didn't even work. The trim seemed to go from 0db to 20db instead of 0 to 6db. So I ordered another SC99 and started from scratch... still not working.
Current System/Problem:
When setting the bias for U2, with DMM clipped on pin 4 and 6 of U2, I am reading 15 V, it climbs slowly, and it gets extremely hot. I have already fried one SC99 and ordered/received another. Both SC99's are working; I have tested in the other module
J6 and J7 are set to adjust, I have a jumper at across J1and J2 as the assembly instructions show. J3 and J4 are set to CGND. J5 is jumped.
Things I have tried tested:
1) both sc99 are reading correctly when I test them in U1 and I am able to set the bias for U1 with either SC99.
2) I replaced U3 LT1013CP. Why? I installed it at U9 on accident (it was really really late
). I used a heat gun to remove it and thought I damaged it. I am also afraid the board is messed up? I don't know how to tell.
3) I am able to set the correct Voltage of +-24 V using the V+ and V- adjust and checked them at pins 3 (+V), 4 (ground), 5 (-V) of U1 and U2.
4) Just for giggles I tested pins out, in, and ground of U6 and U7 and got the correct readings
out=+12/-12V
ground=0v
in=+24V/-24V
5) I replaced C21 because it, uh, discharged when I shorted it, on accident of course!
6) I thought it might have to do with R47 (bias 2 adjustment) and it is warm when powered up, but nothing scalding or suspicious.
I have built 5 other boards successfully, I guess this board was the one I was going to screw up royally. At this point I am even doubting that the J99 I think is good is working as it should, I have no control module to test it against. Almost tempted to buy an assembled one just to make sure the one I think is working IS working. Any help would be greatly appreciated. I have limited knowledge in electronics...
Thank you in advance!!!
Current System/Problem:
When setting the bias for U2, with DMM clipped on pin 4 and 6 of U2, I am reading 15 V, it climbs slowly, and it gets extremely hot. I have already fried one SC99 and ordered/received another. Both SC99's are working; I have tested in the other module
J6 and J7 are set to adjust, I have a jumper at across J1and J2 as the assembly instructions show. J3 and J4 are set to CGND. J5 is jumped.
Things I have tried tested:
1) both sc99 are reading correctly when I test them in U1 and I am able to set the bias for U1 with either SC99.
2) I replaced U3 LT1013CP. Why? I installed it at U9 on accident (it was really really late
). I used a heat gun to remove it and thought I damaged it. I am also afraid the board is messed up? I don't know how to tell.
3) I am able to set the correct Voltage of +-24 V using the V+ and V- adjust and checked them at pins 3 (+V), 4 (ground), 5 (-V) of U1 and U2.
4) Just for giggles I tested pins out, in, and ground of U6 and U7 and got the correct readings
out=+12/-12V
ground=0v
in=+24V/-24V
5) I replaced C21 because it, uh, discharged when I shorted it, on accident of course!
6) I thought it might have to do with R47 (bias 2 adjustment) and it is warm when powered up, but nothing scalding or suspicious.
I have built 5 other boards successfully, I guess this board was the one I was going to screw up royally. At this point I am even doubting that the J99 I think is good is working as it should, I have no control module to test it against. Almost tempted to buy an assembled one just to make sure the one I think is working IS working. Any help would be greatly appreciated. I have limited knowledge in electronics...
Thank you in advance!!!
