Need help Bose Soundtouch 30 smps switches off when tweeter speaker connected.

[spdy]

I am trying to repair a Bose Soundtouch whose smps shuts down. Unfortunately I do not have a circuit diagram and Bose do not provide one.



This set has two ic's, TDA3100d2 to power the tweeters and TDF8599B to power the woofer, both of which are getting power (24 volts) from the same smps.



The smps works if I connect the woofer but disconnect the speakers from the other ic, TDA3100d2. If I connect the speakers, it works for about 2 seconds as the smps shuts down.



I am wondering if there is a current overload problem in the smps? Note this happens only if I connect the speakers (tweeters) to TDA3100d2, which remains connected to the smps.



Also a peculiar thing I noticed is that the smps output REC, FAST SWTG, 4A, 400V double diode UH840 on the secondary side shows voltage of about 130 but the output electrolytic capacitor shows about 24 volts.



I ran the unit on the woofer, with tweeters disconnected for about 45 minutes and then put it off and checked, this diode is not getting hot and I could touch it with my finger.



Any suggestions or assistance would be greatly appreciated.

 

[alec_t]

Welcome to ETO!
Have you checked the tweeters to see if they still have their rated impedance and aren't shorted?

 

[spdy]

Thanks, the tweeters are OK and tried them from a different sound source and they work. Also tried another small tweeter in place of these tweeters and then also smps went to zero output.
Incidentally without the speakers the alternate pins at the output (for tweeters) show about 9.3 volts.

 

[crutschow]

What's the DC voltage across the tweeters when connected?
It should be 0V.
If not, then there's a problem with the tweeter output stage.
If there's an electrolytic DC block capacitor in the output, it may be bad.

 

[spdy]

Thanks, but unfortunately when I connect the tweeter the smps output goes to zero and I cannot check. Incidentally the woofer output voltage is about 11.9 on both of its terminals(there are two tweeters but a single woofer), when it is connected and working.
On the tweeters for the two speakers not connected the voltage is about 9.3 and .03 volts each.

 

[Nigel Goodwin]

On the tweeters for the two speakers not connected the voltage is about 9.3 and .03 volts each.

That's the obvious answer - you're putting 9V DC directly across the tweeter, luckily the unit is detecting the overload and shutting it down, or you'd have killed the tweeters.

Fairly obviously the amplifier IC's will be duff, probably because there's been a short on the output?.

 

[spdy]

But then why is the woofer showing 11.9 volts while functioning?

 

[audioguru]

The woofer amplifier and both tweeter amplifiers are bridged. You said "the woofer output voltage is about 11.9 on both of its terminals" so it has no DC across the woofer and no DC current in it. But you said the tweeter output terminals do not have the same voltage. Then there is DC across the tweeters which draws a very high current in them that shuts down the tweeter amplifiers.

 

[crutschow]

So it would seem there is a problem with the tweeter amplifiers, as the DC voltage for both tweeter terminals should be the same, just as it is for the woofer terminals.

 

[unclejed613]

there should be DC blocking caps for the tweeters, either on the PCB or on the tweeter frame. if they are on the tweeters, you may have one that has a shorted cap. they might also be near the tweeters in the unit's frame. i'm trying to remember where those caps are... if there aren't any capacitors mounted on the tweeter, they have to be in the frame assembly between the board and the tweeters.

Bose only allows access to service manuals to factory authorized service centers, for two reasons, first there are many safety upgrades and engineering changes in their products, and BOSE wants to make sure those get done when a piece of equipment comes in for repair, and second, BOSE regularly gives training classes to authorized service centers. there are a lot of BOSE products with various tricky assembly methods, which if not done correctly can damage the equipment (with the price of BOSE equipment, mistakes can get expensive), and there are often firmware upgrades and installs that need to be done. basically they want to make sure everything gets done right by someone who has been trained properly.

 

[spdy]

Thanks, as far as I can see both the tweeters are connected directly as there is almost zero resistance between the pins and the pinouts on the ic. There may be a ferrite bead in between I cannot seem to locate it.
Also the tweeters also do not show much resistance and do not have a capacitor on them. The tweeters are intact and have been checked with an alternate sound source.
The woofer also seems to be connected directly to the pinouts of the woofer ic, perhaps there may be a ferrite bead in between.
You are right Bose refuses to give a circuit diagram. I think it is a short sighted policy and I hope one day, somebody complains to F.T.C. Practically every other manufacturer gives a schematic.

 

[audioguru]

there should be DC blocking caps for the tweeters

No, the amplifier is bridged so there is no DC across the speaker, each speaker wire will have the same DC voltage. The TDA3100d2 datasheet from Texas Instruments spec's a DC difference of typically only 5mV (50mV max). But the OP measured a difference of 9.3V so one of the bridged amplifiers is fried.

Since the amplifier for each tweeter is from Texas Instruments and they publish a detailed datasheet for it then why bother with Bose??

 

[Nigel Goodwin]

You are right Bose refuses to give a circuit diagram. I think it is a short sighted policy and I hope one day, somebody complains to F.T.C. Practically every other manufacturer gives a schematic.

Actually they don't, very few supply schematics these days - but Bose have always been useless, basically 'designer' audio, vastly overpriced and not terribly good quality.

But I've already told you what's wrong, the amplifier chips are blown.

 

[spdy]

I have another small amplifier which I use as a signal tracer, if I connect this to the audio in.
of the tweeter ic it gives good quality sound.
But if I connect this to the woofer ic audio in, the smps immediately shuts down.
This puts a small doubt in my mind about my thinking the tweeter ic is bad.

 

[Nigel Goodwin]

This puts a small doubt in my mind about my thinking the tweeter ic is bad.

There's no doubt whatsoever, if one of the bridged outputs reads 0V then the chip is DEAD!!!.

You're probably upsetting the DC conditions of the woofer IC when you connect it to that, and likely going to kill that chip as well.

 

[unclejed613]

Actually they don't, very few supply schematics these days - but Bose have always been useless, basically 'designer' audio, vastly overpriced and not terribly good quality.

But I've already told you what's wrong, the amplifier chips are blown.

true, most manufacturers these days, except for companies like Yamaha, Denon, etc... don't supply schematics anymore, the repair tech often gets a troubleshooting flow chart that tells what board to order. there aren't component parts available for most home theater stuff anymore, just part lists containing the part numbers for the boards. companies like Yamaha, Denon, etc still supply schematics, but the only component parts available for those are in the amplifier and power supply sections. DSP boards, and HDMI boards are board swap repairs, because even the entry level soldering equipment for BGA chips are expensive.

Nigel, i have to agree with you, Bose consumer gear is expensive junk. their pro-audio gear is pretty good, like their PA amplifiers, etc... but i don't like their consumer stuff, especially when they rely on a "sonic illusion" to fill in low frequency sound that's really not reproduced by the speaker. the old joke "no highs, no lows, must be a Bose" is just as true today as it ever was.

 

[spdy]

Thanks, I have today replaced this ic , but i am still not getting any sound in the speakers (tweeters) though now both sets of output pins show 7.6 volts with speakers connected.

As I had mentioned earlier previously the smps used to go to zero volts when speakers were connected, this is not happening now, with the new ic.

I am able to trace the audio into the input of the ic.

With best wishes.

 

[spdy]

Sorry I have delayed replying, I finally decided to substitute this with a small amplifier board using the same ic tpa3100d2, which costs only a few dollars, but ordered two from separate sellers, as one got lost.
Now this unit is working well. I removed the old ic completely.