rocknroller
Active Member
Have a Crown IC 150 preamp, 14,000 series serial number so last revision made, that has a odd popping sound under very specific circumstances. Initally thought it was just dirty controls but after cleaning convinced it's a part failure, likely a cap but not sure which one.
The problem occurs on the RIGHT channel only (no source audio connected to rule out source issues), and only when one of the two phono preamps are selected (either) and only under these 3 conditions:
1) Engaging or disengaging the loudness control and the volume is set to approx 75% or less (if volume is higher, the engage/disengage doe snot cause a problem)
2) If the volume control is moved in the 80-90% range approximately, no other controls touched (but one of the phono inputs has been selected previously)
3) If the volume is approx 75% or higher and the phono input is DE-selected over to another source input type. There is about a 1/2 sec delay for the pop in that instance, like a cap that is releasing
None of these seems to occur with any other input type selected, only the phonos. That doesn't necessarily mean the issue lies on the phono board, since a part/cap could be stressed on the main baord when the phono circuit is engaged.
Visually, C8 on the main board (100pf brown mica) appears darkened, almost like it has been burnt.Given it's place in the circuit (see pic - between the loudness and the volume control) does it make sense that this might be the culprit? Or should I be looking at a different spot for the problem? Thanks is advance for helpful suggestions to DIAGNOSE the problem (not just blindly replace every cap on the board)
Main board excerpt
Phono board
The problem occurs on the RIGHT channel only (no source audio connected to rule out source issues), and only when one of the two phono preamps are selected (either) and only under these 3 conditions:
1) Engaging or disengaging the loudness control and the volume is set to approx 75% or less (if volume is higher, the engage/disengage doe snot cause a problem)
2) If the volume control is moved in the 80-90% range approximately, no other controls touched (but one of the phono inputs has been selected previously)
3) If the volume is approx 75% or higher and the phono input is DE-selected over to another source input type. There is about a 1/2 sec delay for the pop in that instance, like a cap that is releasing
None of these seems to occur with any other input type selected, only the phonos. That doesn't necessarily mean the issue lies on the phono board, since a part/cap could be stressed on the main baord when the phono circuit is engaged.
Visually, C8 on the main board (100pf brown mica) appears darkened, almost like it has been burnt.Given it's place in the circuit (see pic - between the loudness and the volume control) does it make sense that this might be the culprit? Or should I be looking at a different spot for the problem? Thanks is advance for helpful suggestions to DIAGNOSE the problem (not just blindly replace every cap on the board)
Main board excerpt
Phono board