Troubleshooting TL072

[scottosan]

I know I reaching here, I know you guys know your stuff.  I have a bogner shiva.  An older oen that has a line level boost using a (TL072) to compensate for a horrible loop design. I am not and IC guy, but I have alot of experience with passive electronics utilizing turrets and/or point to point.  I have limited experience with PCBs and IC's.  The problem is that the line level boost intermitently start malfunctioning with a very week distorted sound. Pins 4 and 8 look good with -18V/18 volts.  The problem can be localized to pins 1 and 2 by looking at the scope. Legs have been resoldered to insure good joints.  I have done this twice. It's seem to work for a while, then act up again. I try moving the amp around to recreate the problem.  SOmetimes I can recreate it, and sometimes it happens without any apparent reason.  What are the chances of the tl072 being bad vs the chance of the solder joints?  To replace the chip would be difficult without removing the entire board unless I snip it out and solder the new chip to the old legs, but if there is a bolder joint, then I snipped it out for nothing.  Please advise.

Thanks,
Scott

[R.G.]

I advise you to clean the contacts of your loop jacks. These things usually rely on the tip shunt contact to carry the main signal all the time. If one or both of these contacts gets dirty, you weak or no signal and it's intermittent. Do that before messing with the opamps.

[scottosan]

I cleaned and retensioned the jacks and have toned out the ring to ground and tip has a good signal all the way to the board.

[scottosan]

Also,  I had it to a full time tech last weekm who showed me the scope and said something along the lines of the signal off pin onewas low/week or something because it wasn't getting a negative feedback signal from pin 2 I believe.  He was the first to resolder the joints base that was a temporary fix.  The thing is moody,

[Derringer]

Not the same ... but similar.

I had a Crate tube amp (VFX5112) crap out on me and I traced it down to a TL072 in the preamp section. I replaced the chip and all was well.

You may just have to replace it.

[scottosan]

Thanks,

It's hard to troubleshoot because it's not consistant.  I just wish it woulbe break completely so I can fix it an move on.

[scottosan]

New update.  This only happens if I am running my rack unit through the boost (as desgned).  If I run a patch cable in the boost simulating going through a rack, I have no issues. I can recreate if very easie using the rack unit.  The rack unit appears to work fine in any of my other 5 amps, all of which have tube buffered loops.  The interesting thing, is that once I recreate this in the shiva,  I can remove the rack gear and the boost will continue to act up for a random amount of time, even though I would just have a patch cable int the boost. So, my tack unit seems to be fine, but it appears to be trigginering something with the boost circuit.  Any thoughts?