Harman/Kardon Onyx Bluetooth Speaker - No Power

[caphair]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Add a resistor to r304 or r306? R306 is the one going to the reset pin

[caphair]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Ok so I didn't have a 1k resistor but I had a 2k, soldered it in across R304... And it worked!! This thing is alive and working. Wow thanks so much guys I honestly appreciate it a lot.

I'm curious, how did the addition of that resistor work if the resistor is a B-E resistor? I thought those were just used for internal current of the transistor. Confused how it brought it to life

Also it brought the voltage to 2.53 to that reset pin and 3.25 is on the opposite side of that same resistor. So was r304 just simply open? Because before I measured 3.25 on one end and only 1v on the other where now it's 2.53 with added 2k resistor.

[caphair]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Wait! I'm thinking of R308 connected between B and E oops. What was R304 connected to?

And can I keep the 2k resistor soldered in and use the unit or will it cause damage somehow?

[fzabkar]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

The "fix" is really only a temporary kludge. Leakage usually gets worse over time, so eventually the 2K resistor will no longer be able to compensate for the increased leakage.

That said, smt rework is fiddly. I would try to narrow down the fault by heating the collector of Q301 with your iron, and measuring the reset voltage before and after. Do the same for C306, after allowing Q301 to cool. Hopefully the leakage will be thermally sensitive.

Before you try this, I would wait for Agent24 to come online. Perhaps there is a better approach.

[fzabkar]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

I would also perform a B-E and B-C diode test on Q301, in both directions.

Something else which occurred to me is that R304 and C306 determine the RC time constant for the reset power-on delay. The miminum delay is specified as 5ms so we would need to ensure that lowering the value of R304 does not violate this spec.

The other thing that bothers me is the measured value of 781 ohms for C306. My calculations suggest that the leakage resistance required to produce a reset voltage of 2.53V is around 6Kohm. I'm wondering if this discrepancy could be the result of deforming the capacitor during the measurement process.

[Agent24]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Ok so I didn't have a 1k resistor but I had a 2k, soldered it in across R304... And it worked!!

That's good, it seems we're getting somewhere

Also it brought the voltage to 2.53 to that reset pin and 3.25 is on the opposite side of that same resistor. So was r304 just simply open? Because before I measured 3.25 on one end and only 1v on the other where now it's 2.53 with added 2k resistor.

Wait! I'm thinking of R308 connected between B and E oops. What was R304 connected to?

R304 provides pull-up for the Reset line, but at 14k, it's rather weak, so any significant current draw on the reset line will lower the voltage (and it did, to 1v)
Both sides would be very close to 3.25v during normal operation, since the BT module's CMOS input will draw very little (effectively no) current.
But in this case, something is drawing more current than it should, as evidenced by the fact that you still only get 2.53v with the much stronger 2k pull-up resistor.

Can I keep the 2k resistor soldered in and use the unit or will it cause damage somehow?

The "fix" is really only a temporary kludge. Leakage usually gets worse over time, so eventually the 2K resistor will no longer be able to compensate for the increased leakage.

Exactly. It might work for now but something is still wrong with the circuit. What you have proved though is that the BT Module is probably OK (Since it's now functioning), so it's likely just down to C306 or Q301 being faulty.

That said, smt rework is fiddly. I would try to narrow down the fault by heating the collector of Q301 with your iron, and measuring the reset voltage before and after. Do the same for C306, after allowing Q301 to cool. Hopefully the leakage will be thermally sensitive.

Before you try this, I would wait for Agent24 to come online. Perhaps there is a better approach.

Heating (or using freezer spray, or both) on Q301 could prove the theory if it's the fault, aside from poking it I can't think of anything else at the moment. I would be leery of heating C306 though as they can be easy to damage with thermal shock. You're *supposed* to use hot air on MLCCs.

The other thing that bothers me is the measured value of 781 ohms for C306. My calculations suggest that the leakage resistance required to produce a reset voltage of 2.53V is around 6Kohm. I'm wondering if this discrepancy could be the result of deforming the capacitor during the measurement process.

And the calculations for a 781 ohm and 14k don't make sense either, the resulting voltage should be around 0.2v, not 1v.
C306 could be pressure sensitive (would make sense for a cracked MLCC I guess), or perhaps the voltage\current supplied by the meter is different enough to show a different result compared to the in-circuit operation.

[caphair]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Thanks guys. I'm curious, what's the purpose of the reset line? Is it important for operation? In other words if I removed c304 or r304 to disable it, would the unit work fine?

Also suppose c304 is leaky, how do I determine the value to replace it?

And btw I measured the same 781 ohms from C to E of Q301 in one direction and open in the other using the diode function, if that helps.

Which calculations are you using to determine something is a miss with the provided info?

And one other thing, I had the unit plugged in over night to charge the battery, on this unit the power button flashes while it's charging and should go solid when charged but it didn't it continues to flash. Being plugged in overnight I'd imagine it should be charged. Could the resistor added be part of this behavior?

[caphair]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Ok I removed the resistor I added and desoldered c304 and the unit powered up.

I measured C to E on Q301 and got .793 in one direction and infinity ohms in other under diode setting.

I replaced c304 with another smd capacitor off a junk board (it's a little bigger in size than original on there) can't tell what capacitance original was, and unit works I just noticed that it takes maybe fraction of a second longer to turn on now.

I'm going to try running it like this for a while and see what happens.

The flashing power button indicating low battery/charging is still going on and the battery reads 3.78v so it didn't charge at all over night.

I'm wondering if the excessive current draw from adding the 2k resistor kept it from charging?

[fzabkar]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

What is the reset voltage now? Is it sitting at 3.25V? Does the original capacitor test resistive out of circuit?

I'm wondering whether the charging problem is related to your earlier troubleshooting work (4V voltage source, thermistor, etc).

[caphair]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Reset voltage is now sitting at 3.25v

The capacitor I removed reads open/high ohms

Think I damaged something with my earlier troubleshooting?

[Agent24]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Thanks guys. I'm curious, what's the purpose of the reset line? Is it important for operation? In other words if I removed c304 or r304 to disable it, would the unit work fine?

The reset line is to reset the BT module into a known state on power up. Pretty much every digital circuit aside from very basic ones need a reset signal, because logic gates, flip-flops, RAM etc don't automatically power up in a known state, and each chip will have slightly different behavior due to manufacturing differences. An external reset signal (and the corresponding internal reset circuitry of the module) deals with all these unknowns.
So no, disabling the reset line completely would not be a good idea.

Also suppose c304 is leaky, how do I determine the value to replace it?

Unfortunately it would be impossible without a schematic if the original capacitor was faulty and unmeasurable.. But given the pull-up resistor value and the capacitor charge formula, it would be easy to calculate which value would keep reset line low for at least 5ms as per the BT module spec.

And btw I measured the same 781 ohms from C to E of Q301 in one direction and open in the other using the diode function, if that helps.

Interesting, I wonder if Q301 has gone leaky C-E in one direction only.
EDIT: this one still puzzles me, since it now looks like C306 was the culprit for the low reset line voltage.
Which way around were the leads when you measure that 781 Ohms?

Which calculations are you using to determine something is a miss with the provided info?

Simple voltage divider formula, that's what I was using at least. But that is a static analysis from your static measurements. When normal power is applied in the circuit, the conditions of the fault may change, which probably explains the discrepancy.

[Agent24]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Ok I removed the resistor I added and desoldered c304 and the unit powered up.

I measured C to E on Q301 and got .793 in one direction and infinity ohms in other under diode setting.

I replaced c304 with another smd capacitor off a junk board (it's a little bigger in size than original on there) can't tell what capacitance original was, and unit works I just noticed that it takes maybe fraction of a second longer to turn on now.

Reset voltage is now sitting at 3.25v
The capacitor I removed reads open/high ohms

So it all worked with your 2k resistor and C306 removed? With a new capacitor it measures 3.25v on the line? That's good, sounds like C306 was leaky then. If it was faulty before, your desoldering may have finished it off, and made it open circuit. You would have to test with a capacitance meter to be sure.

The flashing power button indicating low battery/charging is still going on and the battery reads 3.78v so it didn't charge at all over night.

I'm wondering if the excessive current draw from adding the 2k resistor kept it from charging?

When I say 'excessive' it's relative. It would be excessive for a reset circuit which would normally draw almost nothing. I doubt it would interfere with the battery, since it would only draw about 2mA even if C306 was dead shorted.

[caphair]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

So now I have a new charging issue? Lol

Also since I soldered in a new unknown value capacitor would that affect anything?

[Agent24]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

I'm wondering whether the charging problem is related to your earlier troubleshooting work (4V voltage source, thermistor, etc).

Think I damaged something with my earlier troubleshooting?

Possible. What exactly did you do when you were playing around with the battery and thermistor input?

[Agent24]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Also since I soldered in a new unknown value capacitor would that affect anything?

No that should not be an issue. That capacitor only determines the time it takes for the reset line to reach a logic high and bring the BT module out of reset. You said it turns on a little slower now? Likely the capacitor you put in is just a little larger than the old, so it takes a little longer to charge. Unless the longer delay bothers you, don't worry about it.

[caphair]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Possible. What exactly did you do when you were playing around with the battery and thermistor input?

I fed it an outside voltage of 4v from my adjustable power supply to rule out a defective battery.

Then I tapped into the thermistor pin on the circuit with my adjustable psu while the battery +/- were connected to the pins on the circuit board so I could adjust the thermistor voltage manually seeing if it would power on (obviously before we knew the issue was at the reset pin)

Also, with the removals of c306 and unit powering up was that enough to know the cap was the issue and not the transistor? (As further troubleshooting reference)

"So it all worked with your 2k resistor and C306 removed? With a new capacitor it measures 3.25v on the line?" it all worked with my 2k resistor and c306 removed and yes with new cap and original resistor I get 3.25v

[fzabkar]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

The output of the BQ24090 chip should be 4.20V when it has reached the final charging stage. That's the maximum voltage. If your chip is exceeding this spec, then I would say that it is faulty. In any case I would test for a short between out and input, with the battery removed.

The TS pin (thermistor) is driven by an internal 50uA current source. Impressing an external supply voltage on this pin would have been a bad move.

[fzabkar]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

You may be able to test the TS pin by measuring its voltage (Vt), then removing the battery and measuring the resistance of the thermistor (Rt).

This should enable us to work out the value of the current source.

Isource = Vt / Rt

AIUI, the datasheet specifies 50uA during charging, and 30uA when charging is disabled.

[fzabkar]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

Resistor R712 appears to be connected between pins 2 and 3 (Ground) of U701. If so, then this is the ISET resistor that determines the maximum charging current. Can you tell us the markings, or can you measure its resistance, with the battery disconnected?

Can you measure the voltage on R712 when the battery is being charged? This will tell us the actual charging current.

According to the datasheet ...

Voltage on pin 2 = Iout x (1.5 / 540) x R712

... so ...

Iout = V2 x 540 / (1.5 x R712)

[Agent24]

Re: Harman/Kardon Onyx Bluetooth Speaker - No Power

The TS pin (thermistor) is driven by an internal 50uA current source. Impressing an external supply voltage on this pin would have been a bad move.

I'm not so sure putting an external supply on Pin 9 would have been a problem. The datasheet says:

Temperature sense pin connected to bq24090/2/5 -10k at 25 ° C NTC thermistor & bq24091/3 -100k at 25 ° C NTC thermistor, in the battery pack. Floating TS Pin or pulling High puts part in TTDM “ Charger ” Mode and disable TS monitoring, Timers and Termination. Pulling pin Low disables the IC. If NTC sensing is not needed, connect this pin to VSS through an external 10 k Ω /100k Ω resistor. A 250k Ω from TS to ground will prevent IC entering TTDM mode when battery with thermistor is removed

And the TS pin, along with the rest of the inputs is spec'd at being able to handle from -0.3v to 7v.

I suppose it depends if those voltage limits were exceeded or not. Were they?

EDIT: Original statement "However, if he did pull the TS pin high, the charger may have tried to charge the output of the bench PSU. Perhaps this is where the damage occurred." seems incorrect. Re-reading post #96 it seems you had the battery connected normally but the bench PSU connected to the TS pin, so it should not have tried to charge the PSU if you enabled the charger by mistake.