[dankoby]

I've been using the module for several months and am very satisfied -- it sounds great!  However today it appears to be malfunctioning.  I'm getting output but it's VERY low, even at max gain.  The preamp gain pot seems to only produce audible output when it's between 3/4 and fully maxed.  

I removed all the other modules from my rack, and tried this module in several different slots confirmed to be working with other modules.  I checked the setup guide and confirmed all the voltages at the test points.  Where else should I look?  This was working perfectly as of yesterday, so I think something has broken.

[JPK]

Does the gain drop occur in all 3 modes?
Is there a difference in level when you turn on the preamp?

[dankoby]

Yes, all 3 modes exhibit the same behavior -- there's no audible output until the preamp gain pot is 3/4 of the way up.

With the preamp switched off there's no audible output at any level of the preamp gain pot.

Until yesterday I had output over the full range of the preamp gain pot, though, so I suspect something has failed.

[JPK]

So the preamp is working, right?
Maybe a bad solder joint :
Check the resistor R1, transformer T1, switch SW5, relay RLY4.

[dankoby]

Unfortunately that didn't seem to fix it.  I reflowed all of those joints.  I also shot some contact cleaner in both pots, just in case.  It's still exhibiting the same behavior.  Could a problem in the output section cause something like this?  The preamp does seem to be working correctly.

[JPK]

You can try to send a strong test signal (sine 1VAC) at the instrument input and check you can measure it

- on TP1 (against 0V) at the same value,
- between pins 2 & 3 of U3, attenuated to 80mVAC,
- on TP3 (against 0V) after preamp, level depending on preamp gain.

[dankoby]

Ok thanks for your help.  I'll troubleshoot and let you know what the problem was when I figure it out.

[dankoby]

The 503J was, in fact, working perfectly the whole time.  There were a series of other issues elsewhere in my setup.  

I wouldn't have been able to track them down without your help though, so I sincerely appreciate your assistance.  My apologies for the trouble.

[JPK]