JVC THS9 Home Cinema System SMPS No outputs or standby power

[CapLeaker]

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

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.

[Percyveer]

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

To clarify the 76vdc was there with the 47uf 50v cap in there.
But the original 39uf 25v is still producing 37vdc, too much for its spec isn't it?
Or will it drop when the IC is replaced?

[Percyveer]

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

O.k. so the voltage did rise when you took it out. Right now I'd be changing that IC901.
I can't see having 76V DC there. Vinceroger is right... something should went poof. What was c914 originally? The schematic doesn't show correctly.

Hi Capleaker, it was 39uf 25v.

[Percyveer]

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

what voltage is the capacitor you replaced? at that voltage running through it supprised it did not explode.

Vince: The cap used for testing purposes was 47uf 50v.
The spec of the original which is now back in is 39uf 25v.

[CapLeaker]

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

O.k. so the voltage did rise when you took it out. Right now I'd be changing that IC901.
I can't see having 76V DC there. Vinceroger is right... something should went poof. What was c914 originally? The schematic doesn't show correctly.

[vinceroger69]

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

what voltage is the capacitor you replaced? at that voltage running through it supprised it did not explode.

[Percyveer]

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

Thank you all for assisting me thus far, it is greatly appreciated.

Well I carried on and removed the STR G6651, and the voltage across the start up cap charged up to 76vdc, thought that a bit high so replaced the existing cap that appeared to be OK and the cap is now charging up to 37vdc.
With the IC removed I have tested across all the pins to each other and there are no shorts. Is it defective?

[Percyveer]

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

O.k. so in this circuit, if we take out IC901, there should be then the 21V startup juice on cap c914 then, if the IC901 is at fault.

Do I take this road now?

[Percyveer]

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

It has to be at least a 25V cap. I'd try the 22 or better a 47uF. 25V, 35v 50V doesn't matter. 50V 47uF are very common.

I found a 47uf/25v and it is now soldered in.
The voltage now across the cap is difficult to measure, as it is oscillating, but is somewhere between 12.5 and 13.8vdc.
No change in any other voltages.

[CapLeaker]

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

It may be the circuit inside the IC on VCC pin 4 is loading down the Voltage, when check the resistance with the Ohm meter on pin 4 and GND it may not be valid due to the meter does not put out high enough Voltage to cause the circuits inside the IC to conduct.
One way to find out is to use isolated external power supply to feed the IC pin 4 VCC.

O.k. so in this circuit, if we take out IC901, there should be then the 21V startup juice on cap c914 then, if the IC901 is at fault.

[CapLeaker]

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

It has to be at least a 25V cap. I'd try the 22 or better a 47uF. 25V, 35v 50V doesn't matter. 50V 47uF are very common.

[Percyveer]

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

i would change c914 unless you have a capacitance/esr tester too test it correctly

Will do.
I have to hand a 22uf/25v or 47/16v will either of those do for testing purposes?

[budm]

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

i would change c914 unless you have a capacitance/esr tester too test it correctly

I agree, that will be an easy thing to do.

[budm]

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

You must be real careful because you are working in the primary side.
You can run the VCC test by running the board by itself, DO NOT CONNECT THE BOARD TO AC, hook up the 18V batteries, negative to GND, the positive lead to 100 Ohms 1/4 W resistor, the other end of the resistor to pin 4, then check the DCV on pin 4 and GND to see what you get.

[vinceroger69]

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

i would change c914 unless you have a capacitance/esr tester too test it correctly

[Percyveer]

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

It may be the circuit inside the IC on VCC pin 4 is loading down the Voltage, when check the resistance with the Ohm meter on pin 4 and GND it may not be valid due to the meter does not put out high enough Voltage to cause the circuits inside the IC to conduct.
One way to find out is to use isolated external power supply to feed the IC pin 4 VCC.

I could series up a couple of 9v batteries, would this do it?

[Percyveer]

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

Something is holding that startup Voltage down from reaching 16V startup pointy, but I wonder if there was any output Voltage for seconds not when first power is apply. he may have to leave the Volt meter on the output to see if it jumps up, or on the startup cap to see if it jumps up to more than 16V or not.
At this point I would just replace the IC if all other parts tested OK.

Have just done this check and it initially starts at around 21vdc, but that is for milliseconds, and I think it is just power surge, as within the next second it is 13.18vdc.

[Percyveer]

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

Those 3 resistors are within spec. So that isn't it. You can solder them back into place.
The short you measure on IC901 between pin 2 and 3 is due to R907 being so low in value. So by rights, if you lift a leg from R907, the short on IC901 should be gone.

Check / replace C914. Check D904 and R903 and that section.

So there are no shorts on any of the secondary output rails to their corresponding GNDs, correct? Also there is absolutely nothing coming out on any of these secondary power rails?

Have now resoldered those resistors.
I can confirm short across IC901 pins 2 and 3 goes when R907 is removed (have resoldered).
C914 reads megohms when tested across its leads, and rises as it charges so would appear OK?
D904 0.4 forward voltage, open when leads reversed.
R903 as spec.
I have again checked, and the only voltage coming out of the secondary side of T901 is 0.2vdc on pins 7 & 8 to secondary Grd point indicated on diagram.
Secondary output terminal pin measurment results in post 21.

[budm]

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

It may be the circuit inside the IC on VCC pin 4 is loading down the Voltage, when check the resistance with the Ohm meter on pin 4 and GND it may not be valid due to the meter does not put out high enough Voltage to cause the circuits inside the IC to conduct.
One way to find out is to use isolated external power supply to feed the IC pin 4 VCC.

[Percyveer]

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

Yes guys thanks, working on your feedback now......