Forgot to mention that I also swapped TL431 with a good channel in my previous post. Prior to that I have used external supply and tested TL431 in circuit and it was OK.
Perry, any idea what would be suitable zener diode replacement for Xtant X604. I guess it is small enough and I should use 500mW version. Should I swap both Zeners at the same time (rail+ and rail-)?
Unless they run hot or are out of tolerance, I'd only replace the one that failed. Any 1N5239 should work. In photos, it appears to be 1/2w (as you stated) but confirm by measuring with dial caliper.
I haven't ordered the 9.1V zener yet, but was able to get the part from another project I am currently working on. No changes were noted. The amp still had negative offset in -4.8V to 7.4V range. Power supply was making the most amount of noise when I was near -4.8V. Wondering if output transistors could be culprit in here.
Also I don't know what Q1 transistor is. Need to figure out what Q1 transistor is and whether I could source it on digikey/mouser.
Also I don't know what Q1 transistor is. Need to figure out what Q1 transistor is and whether I could source it on digikey/mouser.
I don't believe it is defective not do I believe the output transistors are defective but I have figured if I am going to place the order might as well get more parts just in case. I have hit the wall with this failure. I need to inspect it once again under the microscope, but there is not much there to inspect.
Q1 D428 seems like 2sd438 and comes in TO-92 package.
Q1 D428 seems like 2sd438 and comes in TO-92 package.
Latest update. Removed output transistors to continue debugging without risking transistor damage. Ran into a problem possibly caused by me. One of the gate to source zener diodes have died and R815 (R155) was burned. I had some flux leftover from removing the output transistors and/or possibly wet spot on the shelf the amp was placed in the trunk. Need to source 12 v zener to get it replaced. Cleaned up the circuit board ad it became conductive. Though still measuring lower resistance than on the good channel with Moffett removed. Updated schematic while fixing this issue. Attached is the picture of latest measurements without output resistors. At one point in time I was able to adjust the offset in positive and negative range but then amp started to misbehaved.
