Alembic Guitars Club
Alembic products => Owning an Alembic => Troubleshooting => Topic started by: dslapster64 on June 26, 2025, 02:33:22 PM
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Hi everyone, it's me with the old 1979 series one. All of a sudden the bridge pick up is not working. Coupled with lots of crackling as well. So I took the back cover off and found that one of the plugs was disconnected, so I did connect, but for some reason it is still not working. On looking at it and the circuit, etc. obviously it's very old and I'm not sure if it's just simply worn out. Let me know what you all think, and I'm open to any suggestions. My guess is that the whole circuit is probably the original one from 1979.
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These circuits typically don't "wear out". Although components can fail it's pretty rare. More typical is that the pots and switches all need to be exercised about 50 times. If they haven't been moved for years they can stop performing correctly. But sweeping the pots and switching the switches can often "wake them up" and return them to proper service. Give that a try before anything else.
Jimmy J
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I've definitely tried that a few times. However, it was working fine earlier on in the day. I am wondering if some soldering may have slipped off. I'm gonna take a look again inside to see what's going on.
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David, since your pickup selector switch has been moved, you might verify that nothing is loose on the switch itself that's preventing continuity. I want to include the clear disclaimer that my Wire Dunce Credentials are clearly established here. ::)
Just seems like something I'd do...
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lol . I am looking into all that as we speak. Love you guys.
David
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@Jimmyj
So I swapped around the bridge and neck pick up plugs and definitely. And the neck pick up work just fine. So it appears to be the plug itself or the wires that attached to the plug. Does Alembic sell those plug connectors? Or are they automatically connected to the pick ups? Any other ideas would be appreciated. What say you.?
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I don’t recall seeing those two big gray resisters on any of my Series basses, but I could be wrong. I’m wondering what it says on the tape on the cavity lid?
Make sure that the 14 pin connector is secure. Maybe also check where the wire inserts into the molex connector to make sure that is still a solid connection.
Are you using the 5-pin or 1/4 jack? Does the problem happen with both?
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@rv_bass
I don't see anything loose except the plugs and connectors themselves. The result is the same either using a quarter inch or the five pin. I'm going to have a tech guy look at it tomorrow, and hopefully it's not a big deal. Just hoping to get something very simple that I'm not able to see myself.
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The larger gray caps are an unusual sight but I believe that to be factory work possibly due to an interruption in standard component supplies... Just a guess.
So by swapping the pickup plugs you've determined that the bridge pickup is the problem, right? The neck pickup sounds fine in either input? That calls for a close inspection of the bridge pickup connector to be sure there isn't a loose shield wire somehow shorting the two conductors. Then follow the wire to be sure it hasn't been pinched somewhere on the way to the pickup. Last place to look is the underside of the pickup to be sure it hasn't been yanked away.
But really, as e-of-h mentioned above, if all worked fine before you moved your pickup selector then you need to be sure nothing is touching those exposed switch terminals.
And a special request: if you're on a Mac and an iPhone, please import those HEIC pics into the Photos app and then export them as medium sized jpegs. Then your attachments should appear in the thread as opposed to "downloadable" only.
Keep us posted.
Jimmy J
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Hey JimmyJ
Thank you so much for that advice much appreciated. I will definitely keep you posted
David
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I showed those big capacitors to my dad and he told me they weren't one we used so they are replacements.
If you have a problem with the crimped end of one of the pickups, we can get you a short length of wire pre-crimped that you can splice on and seal up the splice with shrink tubing.
Looking forward to the pickup selector report - include pics if possible.
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Thank you Mica
I would that if possible. My tech is working on the bass now. Once o get the pickup selector done I will be sending pics.
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Mica, do you think the capacitor changed makes any significant difference with the sound or quality of the bass?
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OK so my tech is working on my series one, and he asked this question:
"I notice this brown wire that is cut or broke on the ribbon cable. I don’t see the broke off piece anywhere. Can you reach out to Alembic and see if this is supposed to be cut? "
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Sorry, let me try and send that picture again.. stay tuned
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It's cut in my new Series II, so I guess it's supposed to :-)
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This is from the '79 Series I I sold a couple of years ago, stripped but not connected.
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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?
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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.
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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
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Here we go, hopefully this works thanks
let me know what you think
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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
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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.
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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.
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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 😊
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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
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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.
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@ stefano
Thank you. I will give that a try.
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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
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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 :D .]]
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
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Hi JimmyJ
You are exactly correct. I do believe that the pick up selector was working after it was prepositioned. But then very soon after that something changed. I've sent this information to my tech and he's gonna check it out, especially concerning the meter information. I'm gonna have him send me a picture of the control cavity so we can see where the mounting is. Thanks so much for responding. I definitely don't want to send the whole Bass in. That will be just too expensive. Sending the board to HQ may be an idea, but I'm going to exhaust as many other avenues as possible. Thanks again for your assistance, my friend. stay tuned
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OK so I just spoke with my tech and he has done all of that that was suggested that's fine. He even sent me a video and showed me some examples of what has been attempted and what is going wrong.I think the video won't fit in the attachment area.
We both believe it appears to be a problem with the board itself. How do I go about either getting a new circuit board for my Series 1 or getting this one fixed? Do I just send the board to Alembic?
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Sorry it hasn’t worked out yet with your tech. I would suggest calling and speaking to Mica if you choose to go the new/repaired board route with Alembic.
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As I initially said, it is very rare for these boards to fail but the individual components mounted on them can and occasionally do.
There's one last thing your tech can try - if he hasn't already thought of it. As you can see, all the square black opamp chips are the same. They are also in sockets which means they are interchangeable. Your tech could try swapping them around to see if they can identify a failed chip. If it turned out that you simply lost one of those opamps it would be a cheap fix!
Next best alternative is to send the board to Alembic HQ and let them diagnose it. We're still confused about the grey "can" capacitors and how they came to be there so sending it in may be the most reliable way to go.
The biggest drag about all this is that you've been unable to enjoy the bass during this problem. Sad!! If you send the card in, just play the bass acoustically until you get it back.
Jimmy J
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Thank you Jimmy, I will look into that. Man this is really been extremely frustrating. I tried calling HQ but got no response.
David
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I know that you may have heard this before, but Alembic is a small, family run operation. The best way to connect is to call when they are in the office 10:00-4:00 PDST. With California being 3 hours behind Florida that would mean 1:00-6:30 or so for you on the East coast. You will probably need to call a number of times to reach them but when you do they will spend the necessary time with you to ensure that you get the help you need. My experience is that a phone call with Alembic staff can last 30 minutes or more because they want to ensure you are getting what you need. With limited numbers of staff, when they don't answer it almost always means that they are helping someone else.
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@Hammer
I certainly understand that Alembic is small and I will just need to be patient. I was just notifying that I have not yet been able to reach them as yet. That's really it.
I did call between the hours of 10 and 4 PDST. I'm just hoping that I will probably be able to either have them test and repair the old one, or simply just buy a brand new circuit board. I really would rather not ship the whole Bass over there, as it would probably be too costly. My tech has worked with many Alembics before, and this one seems to have him stumped. Just looking for alternatives that's all.
Thanks.
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David, maybe there is someone near you with a Series bass that would be willing to let you use the board in their bass to test and see if it is actually the board in your bass that is causing the problem.
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Hello rv_bass
I personally don’t know anyone with an Alembic let alone a Series 1 . Thanks for the suggestion though. That’s also a tall order . I will wait until I can reach someone at Alembic for alternatives. I do not want to get rid of the bass at all.