Just acquired a bass - wiring issues. Any help appreciated

PeteB100

I have recently acquired an Aria Pro Magna Series II Bass (MAB50).

The previous owner did say that he had had a problem with the electrics and that he had it repaired but didn’t tell me what the problem was.

I believe the that the blending control is not working as it should. Turning the control to one extreme has one pickup working only, middle has both pickups working and the other extreme also has both pickups working.

I took the back panel off and it was obvious that someone has had a go at the wiring to the blending pot.

Both pickups have been wired to the top blending pot terminals.

Next to the blend pot are three electrical poles/posts. These may connect to the bottom three lugs but I can’t tell without removing the circuit board.

I ran a multi-meter across the top three pot lugs while turning the control. I also measured the resistances across the three posts, again turning the control.

The results can be found in the attached sketch. (The pickups are active and there is also a red wire running between each pickup wire and the circuit board but I left these off the sketch for clarity. Also, with the pot lug values for L1 to L2, there was a gradual rise in resistance from 0 to 2.5k to midway then the value stayed at 2.5k for the rest of the control travel. I did not repeat this procedure for every measurement - just recording the readings at the three points on the pot travel A, B & C. Actually, I think I may have the decimal point in the wrong place throughout as the values should be more like 250k?).

I have also attached a photo of the circuit board.

I did manage to find a photo of inside another MAB50. The circuit board appears to be identical to mine but the white pickup wires are running to the posts adjacent to the blending pot instead of being directly soldered onto the pot lugs so something may well be wrong with my wiring.

I would greatly appreciate any advice as I am struggling to work out what I need to do, if anything, to get the blend pot working as it should.

Thanks for any help.

 

ICBM

That's definitely not wired right - with a standard balance pot, one pot section is for one pickup and one for the other. From what I can see in the pic, the three copper-coloured posts at the edge of the PCB should be the connections for the lower pot - what's odd is that they don't appear to have ever been soldered to.

What I would do if I was working on it myself is to first remove the pickup wiring and clean up the terminals, and then see what you get from the pot readings, since it's possible it's been deliberately bodged in order to get around a faulty pot issue. The reading aren't likely to make much sense with the pickups still connected anyway.

Funkfingers

It might help to see the entire controls PCB.

My thought is that the pickups should be soldered to the PCB somewhere out of shot. The soldering illustrated in the OP photograph is a bodge up.

prowla

I would assume that the output should be from the centre tab and the pickups should be at the opposing end tabs.
The blend pot itself should have tapers upward from the opposing end of travel to the mid-point and full from there. 

Funkfingers

A blend/balance control is normally dual-ganged, with one resistance track in the opposite direction to the other.

Looking at the OP photograph, the pot we can see is in the position where you would expect to find the master volume control. 

ICBM

Funkfingers said:

Looking at the OP photograph, the pot we can see is in the position where you would expect to find the master volume control. 

It's likely that it has a weird layout with the pickup balance closest to the playing position - my old Ibanez 5-string was like that until I swapped them.

If the PCB is well-designed, you only need three external connections, so the three copper posts should be all you need to connect to. The one furthest from the camera looks like the ground (large wide PCB trace) and the other two should be the pickup connections.

Regardless, the first thing I would still do is remove that mess of wiring and solder and see what you get from the pots.

Dave_Mc

ICBM said:

What I would do if I was working on it myself is to first remove the pickup wiring and clean up the terminals, and then see what you get from the pot readings, since it's possible it's been deliberately bodged in order to get around a faulty pot issue. 

Some of my guitars have been deliberately bodged to get around a faulty solderer issue...   

EDIT: Seriously, though, any bass balance pot wiring I've seen (which is not many!) have been as @ICBM and @Funkfingers said, with a dual-gang pot and each pickup going to each part of the dual-gang pot separately.

ICBM

Aha... well I was right about that. This is a different bass (Integra series) but appears to have the same or a very similar preamp board.

http://ariabasses.blogspot.com/2010/



It appears that the pickup hots (white and black) are connected to the two copper posts nearest the camera; the grounds (red wires at the top of the pic) are currently disconnected.

Interestingly, when the repairman reassembled it he connected the black and white to the third terminal and the reds to the two pickup posts. (Not sure why, but he sounds knowledgeable so it may be for better shielding.)



Hopefully that's useful, assuming your balance pot is OK.

PeteB100

Hey guys, really sorry I haven't responded before now. I am not getting email notifications for some reason and only just seen the replies.

Anyway,  thanks for all the input, and the photos. Greatly appreciated.

Upon (a much) closer inspection the blending pot does have 6 lugs. The bottom 3 were obscured at first glance.

I then thought the 3 posts were the the connections for the bottom pot but running a multimeter across the lugs and posts concluded that the pot lugs were interconnected as you would expect for a blending pot and also the post connectivity to the pot was confirmed.

ICBM said:

If the PCB is well-designed, you only need three external connections, so the three copper posts should be all you need to connect to. The one furthest from the camera looks like the ground (large wide PCB trace) and the other two should be the pickup connections.

Good one @ICBM. It turns out that this was exactly the case.

I moved the two pickup connections onto posts 2 and 3 respectively and I was going to move the shield onto post 1 but left it where it was. The blending pot now works perfectly. I am able to pan/fade between the two pickups.

Thanks once again everyone.

ICBM

PeteB100 said:

Good one @ICBM. It turns out that this was exactly the case.

I moved the two pickup connections onto posts 2 and 3 respectively and I was going to move the shield onto post 1 but left it where it was. The blending pot now works perfectly. I am able to pan/fade between the two pickups.

Fantastic! I thought I was probably on the right track but it was a bit of an educated guess with limited information...

You're right to leave the ground where it is, it makes no difference electrically and there is (admittedly small, but not zero) a risk of disturbing something you don't want to.

Dave_Mc

Excellent news @PeteB100