Low output from active bass

[badgermark]

Hi gents,

I have my friends Musicman Stingray bass to look at, symptoms are very little output resulting in a quiet and pussy weak signal. Hasn't always been like this, output has dropped recently. Basically where do i start to troubleshoot this bad boy? It's got a 3 band active eq, and volume control. Any pointers?

Oh and its not the battery, it's brand new and when put into another bass it sounded huge.

[Philly Q]

Oh and its not the battery, it's brand new and when put into another bass it sounded huge.

Loose connection to the battery, perhaps?  Or maybe something's shorting out against some shielding paint somewhere?  I had that happen on a Strat with EMGs once.

[38thBeatle]

Or maybe the jack socket-I say that because I had the same symptons when I had emgs in my strat. Changed the socket and it was fine( though I went to BKPs obviously at some later point).

[WezV]

you wouldnt believe the number of times i have had people turn up with an active instrument that wasnt working properly.  it generally goes,
'have you changed the battery'
'what battery'!!
:)

do you have a multimeter?  Start checking components

[Kilby]

Does it sound the same if you remove the battery entirely, quite often the battery connector

If the circuit isn't potted in epoxy make sure you have no issues with the battery connection.

Also a quick visual for cracked tracks or unhappy solder joints would be an idea

[badgermark]

Thanks for that folks. I was thinking maybe the battery section might be to blame, there seems to be no difference when it's in or out. That's the first check to do.

I've had a look at the circuit board for the preamp, and the solder connections look fine, as does the jack. Everything is solid visually and nothing wobbles. Shall pop the scratchplate off and check connections today then.

[badgermark]

Ok an update, and a cry for help.

Found a loose wire going to the battery, so made a cut and added two new lengths of fresh wire to connect up the battery. That done, and now there is no signal. Poking the battery compartment yields crackles and pops, no bass signal though. To eliminate the battery compartment i whipped it out and tried attaching the battery directly to the jack via a spare battery snap for an effects pedal, still same results, no signal and pops and crackles.

I unhooked the pickup from the preamp and attached it to a jack, everything works there. Oh and the jack itself, looks solid and no loose wires or dry solder joints.

Is there anything I've missed? My friend loves his bass and will likely murder me if it's not fixed. I can't really see that i've bodged anything, and not been soldering near any sensitive components. c--ks!

[the guitar repair workshop]

dont worry - its going to be a simple fix once youve found it!

So this is what i'd do:
download a cct diagram if possible and check it slowly and carefully. the wire you re-connected, are you 100% certain its in the right place?
check battery leads for continuity, the jack going into the socket acts as a switch on the black wire usually, test with a dvm.
check again they are joined to the board properly. you may have stretched and broken them.

connect battery and using a dvm i'd look to see if the voltage is getting to the preamp only when the jack is inserted. ie there's no voltage when its not plugged in.

if there is a good 9+volts when jack is in then you can forget about that part (it really did sound like it was the initial problem)

it sounds stupid but check all the obvious stuff:
are all pots wound to max not min, all other leads, amp etc is on and working properly etc.

if the signal is still not there but comes on momentarily when prodded then try to make it come on for longer by pressing different parts. A dodgy connection might suddenly work this way obviously - so re-solder anything suspicious.

or just take it to a tech and get them to get it find it - you may find its a very quick cheap easy fix (most likely is)

you can tell your friend you're getting it set up for him, mums the word!
cheers
steve

[badgermark]

Thanks repair shop guy! I know it will be something obvious, but i cant for the life of me see it. Once i find my dvm i'll poke and prod my way around the circuit.

And i explained my troubles to the friend in question, he trusts me and i'm blame free. Phew...

[the guitar repair workshop]

anytime Badgermark,
trust me, everyone whose worked in electronics (i used to work for Amek who made all the Rupert Neve stuff) has had times where they just can't see the problem, a fresh pair of eyes is all it takes sometimes.

When i made a valve amp a few years ago i ran into problems, I just put away the cct diag, drew the cct i'd made in full then grabbed the original diag again and compared. Found all manner of problems, sorted them all and now have a lovely little amp.

Tracing back your steps to the point where the problem occurred, then going forwards again can often show a little mistake early on (its easy to assume something and get it slightly wrong) that is catastrophic in th end.

anyway, like i say, if it gets too stressful take it to a repair guy and be honest about whats happened - you may even find that if its something minor it costs less that a new set of bass strings!
cheers,
steve

[badgermark]

Right an update. No idea what any of this means but here we go.

Got out my dvm, new battery in and my reading at the junction of my new wires is a healthy 8.99V. going further back the jack also reads around 9V from the ground prong to the -ve in prong. ALSO! strangely the voltage from the red into the jack from the battery to the red out of jack to pcb is reading ~9V. That's with the jack out.


When the jack is in everything goes a bit weird. Reading at the battery wire junction floats around 7V, same around the jack. Most bizarrely- not got a voltage between the jack and pcb. BUT the IC in the circuit is getting warm, i'm assuming it's getting power somehow.

I'm using this schematic, , and everything seems ok to me so far. This gave anyone a clue to what might be up?

[the guitar repair workshop]

hi,
try putting the black lead from your dvm onto ground, you can leave it there, the 9v from one end of the red lead to the other (if i'm reading it right) is def wrong!

i keep getting the idea that the wiring to/ from the battery has a minor mistake there somewhere, like i say - could be me reading what youre saying wrong tho.

with the black lead grounded:
look at voltage from red lead, should obv be 9v at jack.
the power cct is switched on when the shaft and tip are connected, so see if you can observe that.

[badgermark]

Ok, got a mono jack in, got the dvm out and started checking the preamp.

What i get when i have the black probe at ground at the jack and the red lead poking around is-

I get readings of a few volts all around the preamp, except a few points around the volume pot. no reading at all on the dvm. The pot itself is giving me the correct resistance when poked with a dvm. the pickup is fine, checked that during the week.

Also nothing on the dvm at the white wire leading to the output jack.

Basically is the preamp knackered? The dvm reading stops across a capacitor, one leg is fine, the other absolutely nothing. I know very little about electronics mind, this might be totally normal!

[the guitar repair workshop]

hiya,
yes, that mostly sounds correct around caps etc, its the voltage at the jack that seems odd.
(by the way I should have mentioned that you shouldn't really poke around too much, you can short a chip out pretty easily!)

What we need to establish is if the jack is soldered/ wired correctly. Sorry to keep repeating myself (i wish you could just bring it to my workshop - i'd do it for free!) but are you 100% certain the jack is wired exactly as shown on the wiring diag? - the missing corner orientated the same as the diag is important.
When you plug the lead in, the cct is should be completed and start draining the battery. If you aren't getting that then  thats where we need to concentrate.
The black leads are all ground by the look of it. Which one connects to the tip, red or white? the other is the one that switches on the cct. we need to be cast iron certain that these are in the right place.
If they are right, and still no joy then its possibly more tricky.
wish i could be of more help...

[badgermark]

Right now there is NO stereo jack. I thought it was the culprit and whipped it out and replaced with a brand new mono jack. It's wired like the old stingrays, and voltages are fine around the jack. I'm keeping it a few days longer, then it's off to a local tech to see if he spots anything I've missed.