bridge pickup no sound. lots of crackling sounds

[FC Bass]

It's cut in my new Series II, so I guess it's supposed to :-)

[FC Bass]

This is from the '79 Series I I sold a couple of years ago, stripped but not connected.

[dslapster64]

Wow oK Thank you all.  My tech  said he has isolated it to the board somewhere. It's either the plug on the board or the ribbon cable possibly. The pick-up itself is perfectly fine. So I'm really not sure what the problem is. I'm hoping it's not the circuit board itself. Any other suggestions?

[dslapster64]

Hello everyone, so there are still problems somewhere. We cannot seem to figure out what the issue is. All the wires have been traced and we cannot figure out what the problem is with the connection. I am so hoping that we don't need a brand new circuit. Any suggestions anywhere out there.

[JimmyJ]

David,

Again, this is not rocket science (although compared to a passive instrument it's getting close).  I have an idea....

Since Mica says the grey "can" capacitors are definitely not from the factory (and who knows why they would have been replaced?), I suggest you take the board off the brass plate and examine the solder work related to those two components.  It's possible somebody got a little carried away there and MAYBE you have a weak solder joint at or near the pickup connector which is causing your trouble.

And let me post this again: please import those HEIC pics into the MacOS Photos app or Windows equivalent and then export them as medium sized jpegs.  Then as you write a reply, click "Preview".  On that page scroll down below your note and click "Attachments and other options". Then "Choose File", navigate to a nice jpeg (smaller than 1MB), and click "upload".  Your attachments will NOT appear in Preview mode but should appear once you hit "Post".  Give it a try and send us a pic of the back side of the board if you can.

Cheers!
Jimmy J

[dslapster64]

Here we go, hopefully this works thanks
 let me know what you think

[JimmyJ]

OK, nice going on the pics.  Next time try them a little bigger.

So I believe that capacitor in parallel to that diode is related to power regulation on the board.  That's as far as my knowledge goes (actually farther since i had to ask uncle google for some ideas about circuitry...)  Anyway, again there's no explaining why those two components on your board are unusual to all of us but we would hope they are the same value as the originals.  The markings on those components on my PF-6B board pictured below are "155 k 35V" followed by the "+" sign which marks its direction. I think that means 155 microfarads +/-10% tolerance with a voltage rating of 35V.  (Thanks again uncle g).

Anyway ... You will see the solder points marked on my and your boards below.  Worth a close (VERY close) inspection of those points to make sure they are solid and not physically moving.

Now a bit more about the overall circuit.  What we have here is essentially 3-channels of amp which are then "mixed" through the hum balance controls into 2-channels of output.  That's why you see 5-chips, 3 + 2.  What that means is, either your bridge pickup or your neck pickup should send audio through ANY of the 3 inputs (I believe that's true even of the center "H" input but don't hold me to it).  Plugging one pickup into any input should produce clean audio at one of the stereo outputs.

So again I have to ask, if you plug your neck pickup all by itself into each input, power up and listen, is the output clean?  Repeat that with the bridge pickup all by itself into either input, is it clean?  You can also gently tap on the board while testing to see if you can cause any unwanted noise.

We're getting closer to figuring it out.

Jimmy J

[rv_bass]

I think those two capacitors act like circuit breakers in a way preventing a power surge from frying the board (you fry the capacitors instead). I could be wrong though. Thanks for the capacitor values, Jimmy.

[Songdog]

Close - I think the mystery capacitors are power supply filters that take out the last trace of noise on the incoming power, and the diodes protect against reverse polarity (miswired cable), which would most certainly fry the preamp.

[rv_bass]

Close - I think the mystery capacitors are power supply filters that take out the last trace of noise on the incoming power, and the diodes protect against reverse polarity (miswired cable), which would most certainly fry the preamp.

Ah yes, thanks 😊

[dslapster64]

My word! , You all know your stuff. My tech is still working on it. I am frustrated that this is happening to my favorite of all my basses.Thanks , and I will keep you posted.
David

[Stefano]

You may also try to clean the preamp card softly with an old toothbrush and alcohol (or rosin remover) to remove the solder paste from the joints. This worked well on my S2 that was producing distorted and crackling sounds when hitting or strumming the strings harder.

[dslapster64]

@ stefano
Thank you. I will give that a try.

[dslapster64]

Hello everyone so I had my tech clean out the whole board and it looks spotless. He touched up the solder joints,  reassembled and all the connections seem to be intact. However, we are still not getting any signal through the rear signal plug. The other suggestion now is to take the board and have Alembic look at it test it may be or it could be replacing the ribbon cable itself. Please let me know what you all think. Mica, if you're able to chip in here, I would certainly appreciate your expertise and suggestions.
Thanks
David

[JimmyJ]

Hey David,

Sorry you are still chasing this.  Let me once again describe what you are experiencing because it's always tricky to put it in words. 

Looking at the attached picture of our preamp board - you are saying that the circled "input", for the bridge pickup, is not able to pass audio to any output.  Neither pickup plugged into that "input" passes audio to the output?  But either pickup plugged into the other "input" DOES pass audio through to the outputs?  [[Note that on these boards "T" means "Treble" or bridge p/u and "B" means "Bass" or neck p/u.  That can add to the confusing when describing what's happening  .]] 

Have I got it right?

Now I need to ask - the first thing you told us in your other thread was that you relocated your pickup selector switch.  Did the bass work as designed before you made that mod?  The pickup selector switch is the final component before the output of the bass.  In "Standby" mode that switch shorts the outputs of both channels.

If your tech has a good volt-ohm meter they could test it.  With the selector switch in "standby" mode (counter-clockwise position 1) the XLR should have near 0 resistance between pin-1 and pin-2 and between pin-1 and pin-3. 

Moving the switch one click to position 2 should give you about 2.6k ohms between pin-1 and pin-3.  Pin-1 to pin-2 should still show near 0. 

Moving the switch one more click to position 3 should give you about 2.6k ohms between pin-1 and either pin-2 or pin-3. 

Switch position 4 should give you about 2.6k ohms between pin-1 and pin-2, while pin-1 to pin-3 should be back to 0.

Of course a close examination of that relocated switch in its new position would be good to be sure none of the connected wires has been broken or come away from the solder terminals.  Any chance you can post a pic of that part of your control cavity so we can see where it's mounted - from the inside?

I'm almost out of ideas.  Sending the board to HQ is always a good idea.  You might consider pulling and sending in the entire wiring harness.  Or maybe even the bass itself if that's a possibility.  Gotta be patient though, it's a small shop with a heavy work load.

Jimmy J