Hi,
I’ve got a lovely old u67 that I hadn’t used for a while.
A few hours into a vocal tracking session, on the last of the punch ins, I started getting a low noise problem. A bit hard to describe, but it felt like it could have been a loose connection or something.
So I checked all the cables, opened the psu, poked around carefully with a long wooden skewer and still managed to give myself a couple of pretty nasty shocks.. the noise was present even when the microphone was not connected. The noise also came and went over longer periods of time.
I’ve found:
-that the psu looks to have been worked on at some point. I can’t say it’s the cleanest work I’ve ever seen. I suspect that there were possibly issues with lifting traces on the pcb.
-That the one different looking capacitor(older?) appears to have failed(white crust out of one side). It is marked C4 on the pcb
-That there are only two prongs of the kettle lead connectors wired up. The psu is not grounded. There is a banana plug socket for grounding on the unit that is still wired up from original, but I’ve never even thought about it, and just took it for granted that the kettle plug was grounding the unit.
I live on an island with very limited tech support, and have done a fair amount of work myself so I’ve got a view to replacing the capacitor myself. I’ll try snip the wires close to the failed cap and soldering the new cap to the old wire, to avoid messing with that pcb.
I’ve come across a few different schematics for nu67 psu’s, so I’m not 100% sure of the value of the capacitor. Until I get it off the board I can’t be certain that I will be able to read the value directly off the cap.
My questions are:
-Should I replace the capacitor with a generic electrolytic cap with suitable values that I can source locally, or should I look for a fancier capacitor for this role?
- the other big psu capacitors don’t look particularly fancy, one of them seems to have the plastic end degrading and cracking. Should I be looking to totally recap the psu at this stage or just replace the visually failed “odd-one-out” cap for now, and see if I solve the issue?
- should I be grounding the psu? Is it simply a matter of hard wiring the “earth” banana plug connector to the ground pin on the kettle lead? Should I be thinking about adding a ground lift switch if so?
Any guidance would be much appreciated.
Thanks!
Rob
I’ve got a lovely old u67 that I hadn’t used for a while.
A few hours into a vocal tracking session, on the last of the punch ins, I started getting a low noise problem. A bit hard to describe, but it felt like it could have been a loose connection or something.
So I checked all the cables, opened the psu, poked around carefully with a long wooden skewer and still managed to give myself a couple of pretty nasty shocks.. the noise was present even when the microphone was not connected. The noise also came and went over longer periods of time.
I’ve found:
-that the psu looks to have been worked on at some point. I can’t say it’s the cleanest work I’ve ever seen. I suspect that there were possibly issues with lifting traces on the pcb.
-That the one different looking capacitor(older?) appears to have failed(white crust out of one side). It is marked C4 on the pcb
-That there are only two prongs of the kettle lead connectors wired up. The psu is not grounded. There is a banana plug socket for grounding on the unit that is still wired up from original, but I’ve never even thought about it, and just took it for granted that the kettle plug was grounding the unit.
I live on an island with very limited tech support, and have done a fair amount of work myself so I’ve got a view to replacing the capacitor myself. I’ll try snip the wires close to the failed cap and soldering the new cap to the old wire, to avoid messing with that pcb.
I’ve come across a few different schematics for nu67 psu’s, so I’m not 100% sure of the value of the capacitor. Until I get it off the board I can’t be certain that I will be able to read the value directly off the cap.
My questions are:
-Should I replace the capacitor with a generic electrolytic cap with suitable values that I can source locally, or should I look for a fancier capacitor for this role?
- the other big psu capacitors don’t look particularly fancy, one of them seems to have the plastic end degrading and cracking. Should I be looking to totally recap the psu at this stage or just replace the visually failed “odd-one-out” cap for now, and see if I solve the issue?
- should I be grounding the psu? Is it simply a matter of hard wiring the “earth” banana plug connector to the ground pin on the kettle lead? Should I be thinking about adding a ground lift switch if so?
Any guidance would be much appreciated.
Thanks!
Rob
