JVC THS9 Home Cinema System SMPS No outputs or standby power

[Percyveer]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

aliexpress are a good company been having a fair few parts etc from them but delivery time varies im on my 6th week for one part too arrive but saying that other stuffs been just over 3 weeks so cant complain i guess,

So have you bought IC clones, if so, is your experience a good one?

[vinceroger69]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

too be honest everything i have brought has worked so far.

[CapLeaker]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

I have to say I have about a 85% success rate with ali.

[Percyveer]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

Good to know, on that basis I will place an order, and wait for them to arrive.

[sam_sam_sam]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

If I were replacing that 39uf cap I would go to 100 volts if you can get one

[rievax_60]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

Many SMPS ICs have Over Voltage Protection. If the VCC pin even briefly exceeds usually 25V, the IC will totally latch off and wont attempt a restart until totally powered down.

[Percyveer]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

If I were replacing that 39uf cap I would go to 100 volts if you can get one

Maybe.

But surely it is only because the IC is out of circuit that the voltage gets to 37vdc, so with a new IC, the currently rated 25v one should be OK.

Or am I missing something?

[Percyveer]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

Many SMPS ICs have Over Voltage Protection. If the VCC pin even briefly exceeds usually 25V, the IC will totally latch off and wont attempt a restart until totally powered down.

Thanks Rievax.
Yes the STR-G6651 has that feature.
Data sheet has been uploaded.

[rievax_60]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

Does any voltage briefly appear at any output rail when power is first applied after it has had a long rest?

[Percyveer]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

Does any voltage briefly appear at any output rail when power is first applied after it has had a long rest?

No, I also tried cycling the power on/off to unlatch as mentioned in data sheet, but it had no effect.

[Percyveer]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

In the interest of educating myself, and maybe others here, with the IC now removed, and if I put a 16vdc power supply across pins 3 & 4, Grd & VCC, on a functional IC what should happen?
I guess pins 1 and 2 source/drain switch should start oscillating on/off, or is the feedback circuit needed on start up?
In other words how do you test it, and is it possible without an oscilloscope.

Percy

[rievax_60]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

I have done a similar thing with the part still in circuit by connecting a bench supply directly to the HVDC rail. NO MAINS CONNECTION MUST BE MADE, just the bench supply.
An alternate start resistor has to be temporarily added.
It is best to have an oscilloscope.

[CapLeaker]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

Maybe.

But surely it is only because the IC is out of circuit that the voltage gets to 37vdc, so with a new IC, the currently rated 25v one should be OK.

Or am I missing something?

Nope.

[Percyveer]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

Nope.

Can you expand on that.
Is it nope I am missing something, or nope the existing 25v cap will not be OK, if so can you explain why?
Thanks Capleaker.

[Percyveer]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

I have done a similar thing with the part still in circuit by connecting a bench supply directly to the HVDC rail. NO MAINS CONNECTION MUST BE MADE, just the bench supply.
An alternate start resistor has to be temporarily added.
It is best to have an oscilloscope.

The STR-G6615 data sheet has no description of operation.
Are you talking about this IC or generally?
I have read some well written data sheets on similar IC's, and some of them start from the drain pin and then switch over to the Vin pin when running.
Looks to me like that is what happens with this one, because in the data sheet functional block diagram, it shows a zenner across source to drain, this is the start up is'nt it, if so it only passing from source to drain (o/c with probes reversed), in which case that is the element that has failed.

Percy

[CapLeaker]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

Maybe.

But surely it is only because the IC is out of circuit that the voltage gets to 37vdc, so with a new IC, the currently rated 25v one should be OK.

Let me rephrase my last answer then. I agree with that above.

[rievax_60]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

The STR-G6615 data sheet has no description of operation.
Are you talking about this IC or generally?
I have read some well written data sheets on similar IC's, and some of them start from the drain pin and then switch over to the Vin pin when running.
Looks to me like that is what happens with this one, because in the data sheet functional block diagram, it shows a zenner across source to drain, this is the start up is'nt it, if so it only passing from source to drain (o/c with probes reversed), in which case that is the element that has failed.

Percy

Generally, mainly with the early UC3842 SMPS control ICs. The STR-G6615 needs start bias current into pin 4. I would use a 1K resistor. Remember, none of this involves applying mains voltage.
The D to S zener symbol indicates the intrinsic avalanche diode that most MOSFETs have.

[Percyveer]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

The D to S zener symbol indicates the intrinsic avalanche diode that most MOSFETs have.

That was puzzling me, thank you.

[Percyveer]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

Hi there Capleaker,

39uF is a very odd value, but that is what the schematic shows too... I thought that was a misprint. Put the original cap back in its place for now and change that IC. Because we need to know that the IC is working to hopefully fix the situation or troubleshoot it further.
Having too much voltage on the cap isn't good, but I am wondering "what" you actually measured. I expected the voltage to rise on the cap, when the IC is gone, but surely not a value of 76V.
Lets see if budm sees this.

I have now replaced the STR G6651, no change in any voltages on primary side, except the Vin to the IC has gone down to 13v now, and have a few weird fluctuating voltages on the board outputs, which I have marked in megenta on the uploaded drawing.
Is it the Vin voltage too low at 13v, what could be causing this?

[budm]

Re: JVC THS9 Home Cinema System SMPS No outputs or standby power

"and have a few weird fluctuating voltages on the board outputs," Before the IC was replaced you DID BOT get any Voltages on the secondary side at all, right. It sounds like the new IC is startup/shutdown mode.
BTW, your meter is not capable of measuring high frequency AC of the output of the transformer winding. your meter does not have enough bandwidth to measure High frequency AC Voltage, it is in 50~100KHz range.