Wanted: Behringer BSY600 Bass Synthesizer schematic

[beerbunny]

I'm new to this forum, so hi to all.

A friend recently asked me to have a look at his son's BSY600. What I found is that what appears to be the main regulator for the board has 600mV on its output. I think it should be at least 5V. Also, what appears to be a protection diode which is connected across the supply so that it's normally reverse-biased is open-circuit. I suspect that the pedal has been connected to a supply of the wrong polarity.

So far, so good. This is where it all goes pear-shaped; I can't find any info atall for this device, and so far I haven't found a schematic for the pedal.

Can anybody point me in the right direction for a schematic, please? I'd be prepared to pay a reasonable amount for one (or rather, my friend would be).

In case anybody can help with the regulator, the markings on it are, from left to right;- a small triangle with an 'S' above it, next to that, '2G', then lastly, turned through 90deg relative to the rest of the characters, ':4'. The device outline is SOT23.

Thanks,

John

PS Please don't ask me for photos, I've tried several times and I can't get anything that would be of use to anybody.

[Enzo]

Good luck on the schematic. Behringer does not send them out, and service centers have to sign a non-disclosure agreement. And as a service center, I even checked the support web site, and they don;t have schematics for that pedal on there. As a warranty repair, it would certainly be an exchange item rather than a repair.

If there is DSP going on, it might run on 3.3v instead of 5v. but 5v is a reasonable guess.

I know it is not the photo you meant, but here is a picture

[jrfrond]

The NDA we signed with Behringer has nothing to do with this product. You simply CANNOT get a schematic. This is a replace-only, inexpensive product.

[Mark Black]

One other thought/option - see if you can figure out which other maker's pedal Behringer cloned and try to get a schematic for that.

Part designators might be different (or not), but the circuit is likely the same as something out there.

I guess I could be wrong - this might be an actual original design, but previous experience with some other Behringer products leads me to at least make the suggestion...

Good luck!

[Enzo]

Other than the philosophical point about whether it might apply to that which doesn;t exist, my NDA doesn;t specify any exception. As far as I know, and as it was explained to me, it applies to all technical documents from the company. Any documents that exist are not to be distributed.

[beerbunny]

Thank you for responding, gentlemen.

Enzo, you're right, there is DSP going on, but the 3V3 is taken care of by a stepdown regulator which takes its input from the output of the faulty device that I'm looking to replace. Looking at the spec for the stepdown reg, it needs a minimum i/p voltage of 6V5, so that tells me what the o/p of the faulty reg should be, I guess.

And thanks to all of you for confirming what I'd already begun to suspect; the schematic for the BSY600 is simply not to be had. Basically, unless I can identify the faulty reg (I must admit that I don't know for certain that it is a reg and not a transistor, although the circuitry around it doesn't make sense for a transistor.), and find a source for a replacement, my friend's son is out of luck.

Mark, I'll try your suggestion, though I'm not hopeful.

Cheers,

John

[jrfrond]

Other than the philosophical point about whether it might apply to that which doesn;t exist, my NDA doesn;t specify any exception. As far as I know, and as it was explained to me, it applies to all technical documents from the company. Any documents that exist are not to be distributed.

Yep. It's ALL top-secret.

[Enzo]

SO it is now at the what is there to lose stage, right? FInd a SOT23 regluator of a voltage you think appropriate and solder it in.

[Steve Conner]

Check the voltage rating of any capacitors on the regulator's output for clues. 5V, 6.3 or 10?

Is the regulator fixed or adjustable? If the latter, you'd see two setting resistors, and you can assume the reference voltage is 1.25V and estimate the output voltage that way.

How many pins, 3, 5, 6?

Also try connecting a bench power supply to the regulator output and bringing the rest of the circuit up that way.

But somehow the "2G" marking makes me think it's a transistor. I work on SMT boards at work, and I'm sure I've seen similar markings on the transistors. Maybe for reverse polarity protection.

[beerbunny]

Hi Steve, I live in the Scottish Borders and worked in electronics until I was made redundant 9 months ago.

Anyhoo, back to the subject in hand;

The electrolytic voltages around the device in question are all 25V or 63V. I don't know which if any are connected to the device.

I've attached a JPEG of the circuit around the device, including my attempt at drawing the device itself, complete with markings. All the SOT23 devices marked 2G that I found were NPN with pin 2 as the emitter. This would put +9V on the emitter, which I've never come across in 20 years as a technician (or if I have, I've forgotten ). This was why I came to the tentative conclusion that it's a regulator, although I haven't found any that use that circuit. Incidentally, I breadboarded the circuit with a 78L05, an NPN and a PNP transistor. None of them did anything I would regard as useful.

I must admit I hadn't considered that that part of the circuit might be reverse polarity protection, although my breadboard experiments didn't support that possibilty.

Enzo, I emailed my friend with the very same suggestion (that with nothing to lose, we should try a regulator with what we think is the right voltage) yesterday. However, Steve's idea that this circuitry might be to do with reverse-polarity protection makes sense to me, and I may just try replacing the SOT23 device with a 1N4148 and see how that goes. I'm waiting to hear from my friend as to whether he wants me to go ahead with that.

Thanks to you both for coming back.

Cheers,

John

[Steve Conner]

Thanks for posting the schematic. If the device were a PNP transistor with pin 1 base, pin 2 collector, and pin 3 emitter (according to the pin numbers in your schematic: they're not standard) we'd have a reverse polarity protection circuit. The transistor turns on for the proper polarity of input, and off for the wrong polarity.

The reason for not using a diode is that the diode wastes 0.7 to 1V, whereas the transistor can have a drop as low as 0.1V.

I've worked as a designer for several small companies, and we've always had all of our stuff manufactured in Scotland.

[beerbunny]

Hi Steve,

I just simulated your suggestion in LTSpice IV, and it doesn't appear to act as reverse polarity protection. With the supply reversed, there's -7.96V across the load. NB, The transistor and the diode were chosen as typical small signal devices, and the 5K load seemed to me to be a reasonable representation of the real load. I've attached a screenshot of the circuit.

I take your point that a transistor would have a smaller drop across it than a diode in this situation; I could minimise the drop by using a Schottky diode.

Incidentally, there's 8R between pins 2 & 3 on this device; I seem to remember from my time as a tech that you could get low readings like this on FETs (between source and drain, if memory serves). Any mileage in that, do you think?

Cheers,

John

[Steve Conner]

Try swapping the collector and emitter in your simulation. Emitter should be to the supply and collector to the load.

Power FETs have a parasitic diode between drain and source, so depending on your meter, it can forward bias this diode and read a low resistance. All other readings should be infinite, unless the gate happens to be holding charge when you measure between drain and source.

[beerbunny]

Oops.

I repositioned the transistor, and got 2V9 across the load which equates to a current of 578uA. Does that sound reasonable?

Cheers,

John

[beerbunny]

Hi Steve, I bit the bullet and removed the faulty transistor and tacked a leaded device (again, I can't remember the correct term; an old-fashioned 3 legged transistor) in place, and Lo and Behold! we have sounds and red and blue LEDs and stuff. The replacement transistor will have to be fitted properly (my eyesight's pretty much shot), but fortunately, the friend I've mentioned still works at the place from which I was made redundant, so he can get one of the repair people to tidy it up a bit.

It turns out that I had grossly under-estimated the current drawn by this thing; with the battery I was using to power it down to 5.7 volts, it drew 90+mA.

I haven't had the nerve to try reverse-connecting the battery yet, it'll probably happen in use at some point and then we'll know if it works.

Thanks very much for pointing me in the right direction. Good on ya!

John