Crackling noise from Bose 901 equalizer

[Thomas Oder]

Look at the solder connections on all your inputs and outputs too. Not sure if these equalisers have RCA sockets soldered directly into the PCB or not, but if so, this could be a good place to look

The series 3 EQ’s have them mounted to the metal case with wires running to the board. Any Questionable solder was redone.

 

[Thomas Oder]

So for anyone in the future experiencing a a crackling sound from their 901 equalizer, assuming it has been recapped the carbon comp resistors circled below are likely the sources of the sound.



There are:
4 X 560 Kohm,
2 X 220 Kohm
2 X 5.6 Mohm

For me it ended up being one of the 220 kohm resistors that was causing the noise. I replaced all of them with 1/2 watt carbon film resistors. I also went through and replaced any resistors which were out of tolerance with 1/2 watt replacements. For the most part the original carbon film resistors stayed near their original values, and even the carbon comps were close to what they should have been, but after 42 years they must have deteriorated to the point of causing the crackling noise.

 

[dadade]

So for anyone in the future experiencing a a crackling sound from their 901 equalizer, assuming it has been recapped the carbon comp resistors circled below are likely the sources of the sound.

View attachment 1652494

There are:
4 X 560 Kohm,
2 X 220 Kohm
2 X 5.6 Mohm

For me it ended up being one of the 220 kohm resistors that was causing the noise. I replaced all of them with 1/2 watt carbon film resistors. I also went through and replaced any resistors which were out of tolerance with 1/2 watt replacements. For the most part the original carbon film resistors stayed near their original values, and even the carbon comps were close to what they should have been, but after 42 years they must have deteriorated to the point of causing the crackling noise.

Hi, I know this is an old post but I was just trying to figure out the same problem with my series 3 Equalizer. Looking at the Resistors you highlighted, according to the color codes there are: 4x 1 Mohm 5% (the top ones), 2x 2.2 Mohm 5% and 2x 5.6 Mohm 5%. Could you have made a mistake? (I just checked the color codes on mine)

 

[Skywatcher]

Hi, I know this is an old post but I was just trying to figure out the same problem with my series 3 Equalizer. Looking at the Resistors you highlighted, according to the color codes there are: 4x 1 Mohm 5% (the top ones), 2x 2.2 Mohm 5% and 2x 5.6 Mohm 5%. Could you have made a mistake? (I just checked the color codes on mine)

Just replace whatever is in there from the factory, unless someone knows for sure there was a change (service bulletin) with your particular production unit.

 

[eiraved]

Hi, I know this is an old post but I was just trying to figure out the same problem with my series 3 Equalizer. Looking at the Resistors you highlighted, according to the color codes there are: 4x 1 Mohm 5% (the top ones), 2x 2.2 Mohm 5% and 2x 5.6 Mohm 5%. Could you have made a mistake? (I just checked the color codes on mine)

Welcome to AK!
Have you attempted any of the troubleshooting steps listed on this thread? These should be accomplished prior to replacing components.