JVC THS9 Home Cinema System SMPS No outputs or standby power

[Percyveer]

Greetings to all you knowledgeable people,

I am looking for some help and guidance with the above issue, luckily I have managed to find a circuit diagram, but do not have the experience to use it properly!
but I do have a DMM and lots of enthusiasm to find the guilty component.
I have attached the said diagram, there is no visual sign of any damage and fuse is unblown, I have 345 vdc to Grd across the primary winding, and 13.2 vdc to Grd after R905. 160 vdc after R911 but 0.225 vdc after R910

I will upload pictures of the board if needed.

I do hope there is someone familiar with this circuit, or the experience to diagnose the culprit.

Percy

[CapLeaker]

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

Lift a leg of R911, R910 and R905. Then measure each resistor in Ohms mode and verify on the schematic the values for each resistor. If a resistor goes bad, it goes either open or high in value.
Then check IC901 that is is getting Vcc on pin 4. IF those resistors named above went high in value, the IC thinks there is a under voltage condition and wont do anything. Pull up the data sheet for STR-G6651 for voltages you should expect.

[budm]

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

Can we see the pictures of what we are dealing with?
History of the unit?

[redwire]

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

Wait a sec... Make sure there is no charge on C907, measure it with a multimeter before messing with R910, r911. I think these two resistors are also bleeder resistors for C907. In any event, it is always good practice to make sure the primary filter cap is discharged before soldering etc. near it.

[Percyveer]

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

Thank you all for your help so far....

Capleaker: Measurements as follows R910= 465k, R911= 466k, R905= 67.5k.
Shall I resoldered them back in as within spec?
The IC901 has 13.18vdc to pin 1, data sheet states on state voltage between 14.4-17.6vdc.
So appears that voltage is too low, but why?
STR-G6651 data sheet uploaded.

budm:
Pictures of PCB top/bottom uploaded.
Owned from new, not used much, but just started using more now that 5.1 surround is being broadcast here on some programmes, we power it off/on as we use it, never use standby mode in the interest of energy saving.

Redwire: Thanks for the headsup..

Percy

[budm]

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

https://www.badcaps.net/forum/attach...4&d=1485790567
Can you please provide focused picture?

[CapLeaker]

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

Wrong pin. Vcc is on pin 4.
The spec sheet sez:
On-State Voltage: min 14.4V, typ 16V, max 17.6V
So lets say if pin 4 had only 13.18V, it would probably not turn on. as turn off would be max 11V and the IC has under voltage lockout.
See if pin 1, 2 and 3 are shorted?

[Percyveer]

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

Capleaker: Mistake yes Pin 4 Vin, pins 1-2 open 1-3 open 2 to 3 shorted.

[jiroy]

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

I really dont get it how R910 and R911 are in series and there is only 0.225 vdc . on R911 while R910 gets 160 vdc . both are mentioned for 750k. One could assume R911 open . Are those tests accurate ? .

[Percyveer]

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

Jiroy: Yes, and have also taken test of resistor values as Capleaker suggested with one leg removed from board, it certainly does not make sense to me!

[Percyveer]

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

budm: Sorry about the photo, I did another I hope it is OK.

[Andrew F. Ali]

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

I would directly replace IC 901 if all the surrounding cap, diodes and resistors are checked OK. Look at Q991, Opto-Isolators PC-901 and 2. And yes Zener diode ZD 991, too.

[budm]

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

IC901 STR-G6651 Pin 5 (OCP/FB) is terminated to the primary circuit GND through R906 (680 Ohms) in series with the SOURCE current sensing resistor R907 (0.47 Ohms). Very low resistance compared to the 940K (TWO 470K resistors in series), so you are going to get much Voltage on pin 5.
You will get more Voltage at FB when Opto PC901/902 are active.

Feedback Threshold Voltage VFDBK Drain waveform low to high1 0.68V(min) 0.73 (typ.) 0.78 V (max)

[jiroy]

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

Jiroy: Yes taken as Capleaker suggested with one leg removed from board, it certainly does not make sense to me!

Capleaker wanted to remove one leg to check continuity and/or resistance value , not voltage .

[budm]

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

BTW, you are sure that there is not bad diodes in the secondary side, or low resistance on any of the output pins?
I suspect bad SMPS IC if other component tested OK.
BTW, what are the resistance between GND pin against all other pins?

[Percyveer]

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

jiroy: Yes correct, voltage readings taken in circuit.

[Percyveer]

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

I would directly replace IC 901 if all the surrounding cap, diodes and resistors are checked OK. Look at Q991, Opto-Isolators PC-901 and 2. And yes Zener diode ZD 991, too.

Why would I look at those components when there is no voltage presented at T901 terminal 12?

Just curious and trying to understand.

[Andrew F. Ali]

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

Terminal 12 is on the Secondary side of SMPS Transformer. So it would appear to me the Start-up voltage is there and because SMPS IC is not oscillating you may have voltage on Primary winding. Therefore, Run voltage is not being produced to sustain the SMPS. Hence I offered IC 901 as the culprit for your failure. Apart from that I would test PC901/2, Q991 and ZD991, as well.

[Percyveer]

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

Andrew: Maybe I should expand on the detail to my original post, the voltages I have mentioned in that post are the only voltages present on the primary and secondary sides.
It does appear that IC901 is not functioning, but it may be because the voltage present at Vin is only 13.18vdc not enough to start see post 7 by Capleaker.

[budm]

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

Start up DCV, UV/OV DCV.
VCC It has to reach 16VDC for IC to start up.