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Intermediate Member
Username: karl

Post Number: 196
Registered: 7-2002
Posted on Monday, November 28, 2011 - 10:19 am:   Edit Post

Hi there,

I have an SC signature deluxe from 1993, and have had an ongoing issue with it for the last couple of years. I keep thinking I've fixed it, but then it recurs and leaves me flummoxed again.

Briefly, what happens is that when I first plug in the bass, I often find that it sounds as if the bridge pickup isn't working at all - ie. the sound is bassy and muffled, without the clarity you get from the bridge pickup, and the pickup pan doesn't seem to do anything. Usually, after a few seconds of twanging strings and moving around a bit, the bridge pickup kicks in and everything is fine. Until I unplug for a while and the same thing happens on plugging in again. This only ever seems to happen when I take the bass to gigs, so I'd started leaving it at home in favour of a different bass which I knew woudln't let me down. Which is a shame. I used to think it was a slightly dodgy connection where the bridge pickup wire clips onto the circuit board. However, after last night's performance, I'm beginning to suspect that it might be that something in the control cavity is moving around and shorting something. Here's my reasoning:

It only happens when I play the bass at gigs, very rarely at home. So either the bass is just plain evil or there's something about the gig situation that's different to my home practice situation. And I think I know what that is: at home, the bass lives in its case, laid flat on the floor. On a gig, I carry the bass upright in a gigbag and stand it upright on a stand before I plug in. I think that when the bass is upright, the metal sleeve around the pickup wires in the control cavity is moving in such a way that it touches something else in the cavity and shorts it. This rarely happens at home because I never really hold the bass in the upright position - it goes straight from the case to round my neck! This may also explain why the problem usually fixes itself after a few seconds of twanging and moving - presumably, whatever short circuit is being made in the control cavity is being broken again as I move the bass.

Furthermore, something else that happened last night may also support this theory: when I plugged in last night, no amount of twanging strings and jigging the bass around would get the bridge pickup to kick back in. So I left the cable plugged into the jack socket and opened up the contril cavity to have a look - I thought maybe the jack wasn't connecting properly, or maybe I could see where the problem might be. I saw immediately that the metal sleeve had indeed moved and was touching one of the circuit boards. As I moved it away, I inadvertantly touched it against the (metallic) bottom of the neck pickup Q switch housing. At which point the neck pickup seemed to stop working. The only way I could get that to come back was to disconnect the neck pickup clip from the circuit board and reconnect it. All fine again from that point on.

My question, then, is simply: does this theory sound feasible? Is the metal sleeve around the pickup wires causing a short circuit whenever it touches anything metallic in the control cavity? And if so, is the solution simply to stop it moving? Or to wrap it in gaffa tape so that it's insulated even if it does move and touch anything in there? Or am I barking up the wrong tree entirely? Any advice would be greatly appreciated! It's getting very frustrating!

Thanks in advance,

Senior Member
Username: funkyjazzjunky

Post Number: 711
Registered: 5-2007
Posted on Monday, November 28, 2011 - 2:25 pm:   Edit Post

Have you tried exercising the jack?

Senior Member
Username: terryc

Post Number: 1732
Registered: 11-2004
Posted on Tuesday, November 29, 2011 - 5:18 am:   Edit Post

From the description it does sound like a component is shorting against the silver shielding paint or another component.
Have you swapped the connector leads so the bridge is on the neck side of the pan pot and vice versa to rule out PU failure or problem.
I would check that no circuit boards, control connectors or the socket is touching the silver sheilding paint in the cavity.
Username: mica

Post Number: 7515
Registered: 6-2000
Posted on Tuesday, November 29, 2011 - 1:23 pm:   Edit Post

The sleeve (ferrite bead) the pickups pass through is not conductive, so it can't be shorting anything out. These were originally added to allow use of wireless. If you don't use wireless, you should be able to remove it, but I need to confirm.

I'll ask my dad to review your history and see if he can come up with any advice for your situation.

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