Promethean 5110 humming

[SmartDaddy67]

hello Bass Experts,
I recently got a Promethean 5110 Combo, had 2 Jazz gigs with it and was quite happy .

Now I observe sth strange:
- sometimes I hear strange noise, as if some unshielded hot wire was moving around (not humming)
- unplugging the bass and turning up the preamp there is quite a strong humming sound (that hum is also there when the bass is plugged in). It seems independend from touching a plugged in cable with fingers etc.

I wonder how sth like that could have happened inside the case without the device being exposed to humidity, dust, mechanical stress etc. Just practicing in the living room ..

Did You experience anything similar ? Found a fix ?

thanks in advance

 

[SmartDaddy67]

Hello Experts,
after initial posting I decided to look at it myself .
I found 3 issues and tried some improvements described below.

And guess what: success, no more humming !

I am surprised about certain really bad manufacturing details.
I did three things, and I actualy dont know which one did the fix

(1) resoldering of the preamp potentiometer on the analog front panel PCB:

I guess the potentiometers had been soldered manually, other than those SMD parts on the other side of the PCB. Poor soldering may lose electric conductance over time. Please do this only if You really know about electronic soldering !

(2) grounded shielding of the connection from input plug to the analog input PCP:

Its done by some adhesive aluminium foil (blue arrow) plus a small wire wrapped with the foil and soldered to the input plugs ground pin (blue circle). I really wonder how they could have manufactured this without using soldered cables.

(3) moving of a wire with 230V 50Hz away from the location close to the (sensible) input wire

the 230V wire part (green circle) was only 5mm away from the hot input wire (here already shielded, blue arrow). I fixed the power wires new position by winding it around the mounting cylinder (green arrow)
I actually wonder how they could place the hot input plug and wires so close to the power input filter PCB.

 

[SmartDaddy67]

I really wonder how they could have manufactured this without using soldered cables.

should have written: ...without using shielded cables

 

[Tracso]

Good informational read.