Sterling SUB bass- active electronics stopped working

[bassman]

I have a MM Sterling SUB bass and the active electronics stopped working suddenly . I was checking over the bass and I think that I may have inserted the 9V battery in reverse polarity.

Would that fry the electronics?

The symptoms are that the bass works but only as a passive, volume only instrument.
The bass/mid/treble contols now do nothing.

I have tried to check the connections inside the bass and everything looks OK.
The IC chip is directly soldered to the circuit board. It has no socket like on a G&L.

Anybody have any ideas?
Thanks in advance.

bassman

[Ken Baker]

I have a MM Sterling SUB bass and the active electronics stopped working suddenly . I was checking over the bass and I think that I may have inserted the 9V battery in reverse polarity.

Would that fry the electronics?

I can't say for sure, but I'd guess not. Most circuits have some sort of protection for that possibility, such as a diode.

I have tried to check the connections inside the bass and everything looks OK.
The IC chip is directly soldered to the circuit board. It has no socket like on a G&L.

Anybody have any ideas?

A couple of common places to look:

1. Make sure that the metal contacts in the battery box are actually making contact with the battery. You can usually bend them out, toward the battery.

2. Check that the battery lead wires are connected in the battery box. They're pretty fine gauge and are known to break. You might also check their connections to the preamp board.

3. If the chip itself is actually toast, you can proceed a couple-three ways: Contact EBMM customer service and arrange to ship the bass to them for repair, repair it yourself, or have a local tech do it.

If you're handy with a soldering iron, you can de-solder the chip and solder a socket in its place. Then just drop in a replacement chip. They're a common part and the same as G&L uses.

Ken...

[bassman]

Thanks for the tips, Ken.

I will check the battery connections more carefully. Obviously, you are familiar with an active MM Sub bass, since you had your project SUB five string that you did extensive mods to.

This is just wierd. I have bent those battery connection tabs and I even took the battery box out of the bass to check the connections.

The bass does put out some sound but the volume control is the only pot that works and its the same with a good or a dead battery.

I'll check it again.

Thanks,
Bill

[Ken Baker]

This is just wierd. I have bent those battery connection tabs and I even took the battery box out of the bass to check the connections.

There is a LOT of anecdotal evidence for the wires falling off either/both the battery box and/or the preamp board. They're also really thin and could develop a break anywhere along their length, though that would be hellishly unusual.

The bass does put out some sound but the volume control is the only pot that works and its the same with a good or a dead battery.

That's the indication of a dead battery or dead preamp. You could take the thing completely passive using the L-2000 tone circuit. It'd work just fine. But being a StingRay at heart, it really does like that preamp to be there.

Ken...

[fender3x]

Hmmm.... if not the battery, perhaps a loose ground? I know someone <ahem> that had a problem with that once. Sound was suspiciously similar....

[Ken Baker]

Hmmm.... if not the battery, perhaps a loose ground? I know someone <ahem> that had a problem with that once. Sound was suspiciously similar....

Possible, but less likely with the EBMM basses than the G&Ls.

Here's the preamp:


And the 4250


In stock configuration, 5 wires connect to the preamp board: 2 from the battery box, 2 from the parallel connected humbucker, and 1 from the bridge. That's it. There really isn't a lot that can go wrong unless someone mucks around in there with a chainsaw.

Ken...

[deltafred]

Hi

That is the stock preamp used in all EB 2 eq basses from 1979 to date.

There is no protection (idiot diode) for the op-amp. It would be a very simple and feasible mod to add a parallel (shunt) protection diode, but a series protection diode would drop some of the already low voltage for the op-amp.

I suspect if you have had the battery in the wrong way round then you have probably fried the op-amp. If you can wield a soldering iron (or know someone who can) then you could replace the 4250 chip. I would suggest putting an 8 pin socket in so if the same happens again you can plug in a new one with no soldering.

The 4250 is a pretty old chip and if you cannot get hold of one then a TL061 will do the job but you need to remove a resistor so it is starting to get complicated. (I have built a clone of this circuit and used a TL071 as I had one in my spares box but I have seen the TL061 recommended, without looking it up I cannot remember the differences between the TL061, 071 and 081.)

If you fancy a go at this mod it is the resistor at the right hand side of the chip in the photo 'And the 4250' of Ken's post (between the chip and the legend 'C4'), the one with the coloured bands (bottom to top) Brown, Green, Black, Yellow, Brown. It's value is 1M5 (1.5 mega ohms).

If you attempt to change the chip then you do it at your own risk, don't blame me if you completely screw it up.

I understand that Ernie Ball will only supply an exchange unit, but being an electronics engineer have never had to put this to the test.

Hope this is some use.

[Ken Baker]

There is no protection (idiot diode) for the op-amp. It would be a very simple and feasible mod to add a parallel (shunt) protection diode, but a series protection diode would drop some of the already low voltage for the op-amp.

Do you mean a protection diode on the power side? I agree that a series diode could be problematic due to voltage drop. OTOH don't you think it's possible that a parallel connected shunt diode might cause the battery to overheat if the battery is installed backwards, assuming that the diode is rated for the current of a shorted battery?

The 4250 is a pretty old chip and if you cannot get hold of one then a TL061 will do the job but you need to remove a resistor so it is starting to get complicated. (I have built a clone of this circuit and used a TL071 as I had one in my spares box but I have seen the TL061 recommended, without looking it up I cannot remember the differences between the TL061, 071 and 081.)

Here in the US, the LM4250 is a common part and is widely available on the cheap.

Hope this is some use.

Thanks!

Ken...

[deltafred]

Hi

Ken what I meant is that there is no protection whatsoever against reversing the battery on the power side, either series or parallel so putting the battery in the wrong way round will almost certainly fry the 4250.

A parallel (shunt) diode would kill an incorrectly fitted battery in no time but protect the 4250. It would have no effect on a correctly fitted battery.

I doubt if a PP3 would overheat even with a dead short as there is so little energy stored in it.

Almost any silicon diode could be used but I would tend to go for a 1N4001 as they are rated at 1A and are dirt cheap.

The LM4250 is available here but for silly money whereas the TL061 etc are for pence (or cents).

[bassman]

I know its been months since anyone posted to this thread but I want to thank both of you for the very informative discussion of my predicament. I have not yet done anything to the bass, but finding and reading these posts gives me some information to go on and an approach to fixing my bass that I didn't have before.

I will let you know what happens when I finally delve into it.

Thanks,
bassman Bill