problems

[Sean S]

Hi,

I just built my first A12 last night, powered up and set the voltage to precisely +/-18v, no problem. Put the SC25 in place, powered up again, measured between U1 pins 4 and 6, read a fluctuating voltage between -.4 and -.9v. I tried to get the voltage to drop to 0, but adjusting R16 seemed to do nothing. I let it sit for a while to get up to temp, came back and measured again, got the same results. I went to see if it would pass signal, but as soon as i plugged the output into my converter, the meter lit up into the red with no signal present. I tested the N72 that i have in the rack with it, and it passed signal, but now had a fast steady pulsing sound.

I came back and tested again this morning, pulled the SC25 and checked the voltages, still reading steady +/-18v. I added the opamp and powered up again, this time I noticed the front panel LED was blinking for about a minute before it came on solid. Tried to set the offset voltage again, still fluctuating, this time between -4 and -9v, and R16 still made no change, even adjusting it to both extremes. I checked the supply voltages again, pin 3 and 4 still read 18v, but pin 4 and 5 was reading a fluctuating voltage that was much lower. I also noticed that U5 became very hot, and that I could actually hear the pulsating sound coming from the circuit board, probably the LED.

Any ideas?

[tpryan]

Probably a failing SC25. Send an e-mail to rma@seventhcircleaudio.com for return instructions.