troubleshooting TV SMPS sequence

[CapLeaker]

Re: troubleshooting TV SMPS sequence

At this point I don't think there is a problem with the optocoupler. 360VDC on the primary capacitor should be fine. Neither there is a problem with the PWM, it either works or it doesn't. The booster circuit works too, so now you are stuck in between:
A: The is no load on the circuit, some PSU's will do that when there is no load.
B: a problem in the feedback circuit. It does happen that optocouplers go bad, but most of the time it is something else.
Right now I would put a 1A load on the 12V and see what happens.
I also would like to be able to get the PSU running without that scalar board attached. So try to unhook that and also jump pin 7 on connector 3 with your PSon together.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

Yes, 5VSB is normal and working properly. how do I check an opto coupler and how would I know what the Vcc is on LD7550? That's IC on the hot side of the supply. data sheet says max 36V on vcc. not familiar with the circuit, and I have no idea what voltage I should be expecting on the Vcc pin #2.

Thanks
ilikesteel

[MLOO55]

Re: troubleshooting TV SMPS sequence

Have you checked the optocoupler IC4 and the IC LD7550, is this ic getting the
rigth voltage on the vcc pin. If you get at the main capacitor less than 380v
the output voltage will be not the rigth. By the way, the 5vsb value is normal?
Check and advise
rgds
mloo55

[ilikesteel]

Re: troubleshooting TV SMPS sequence

UPDATE:

CapLeaker and everyone,

I soldered the DS3 and DS5 diodes back in the PS. I removed the cable/pin from the wiring harness that connects to the PS at Conn3, red wire. reconnected the cable to the PS. +12 is not connected to the scaler board.

here is the result:

the +12 pin on the PS reads between 10.3-11.1 volts. it oscillates between those two voltages. you can watch the meter and it jumps by tenths of volts as it goes between 10.3 and 11.1.

The +24 pin on the PS reads between 20.9v and 22.6 volts. It also oscillates up and down between those voltages on the meter. you can watch it count up and down as the +12 V.

just remembered what Budm said earlier in the post. Check the Main cap and I should get between 360V and 400V. I got 360V on the nose. is it possible the 360V is a bit low?

Thanks a bunch!!!
ilikesteel

[CapLeaker]

Re: troubleshooting TV SMPS sequence

take the 12 v pin out of the connector of the scalar board and turn the PSU on. Check the 12V on the PSU.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

CapLeaker and R J,

I rechecked the +12-GND on the scaler board.

however, before that, I checked two resistors that I had on hand. I wanted to check something of a known value on the meter.

1. 1000K ( brown, black, red) resistor. on the diode 2K scale it read 1.05 ohms. just a smidge over 1K.

2. 4.7K resistor (Yellow, violet, red). on the 20K scale it read 4.86 ohms, again very close to 4.7K.

getting back to +12 to GND it read 1.97 on the 2K scale. Isn't that almost 2K ohm resistance? that wouldn't be considered a short, right?

This is really getting deep. perhaps I should reinstall the DS3 and DS5 diodes,
hook everything up and make the voltage measurements from scratch again.
I can make the voltage measurements again with conn3 connected, then remove the cable (hot) while power is still on and then check the PS voltages at the PS connection for Conn3 for the +12 and +24 to see if there is a difference.

I'm open to anything right now.

thanks everyone,
ilikesteel

ilikesteel

[R_J]

Re: troubleshooting TV SMPS sequence

thanks Capleaker. I did remove the cables from conn3, no load from TV set. still had lower voltages at the pin outs on conn3 of the PS for +12 and +24. I just can't get to the next logical step in the flow of troubleshooting it further.

ilikesteel

When I read this, I thought you had disconnected conn3 and still had a problem with the +12 being low. Thats why I thought the fault had to be in the power supply +12 volt circuit.

If this was not the case then you do have a short somewhere on the scaler board +12 and not in the power supply.
You may not measure a direct short on the scaler +12 input as the shorted part could be after some other components (ie another regulator) for example the +12 supplies a +5 volt regulator ic, If the +5 in this case was shorted, that short would not show up on the input (+12v) side of the regulator. but when power is supplied the +12 would be loaded down maybe even to +2 volts as you indicated.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

CapLeaker,

The +12V to GND on scaler board reads almost 2K, 1.97, or am I reading it incorrectly? I can recheck it? what do you think the reading should be approximately? If it's reading 1.97, I should move the range to 200 ohms and it should still be 1.97, right?

I thought I was reading almost 2K, 1.97 on the diode scale.

thanks,

ilikesteel

[CapLeaker]

Re: troubleshooting TV SMPS sequence

aaah! There is a short on the scalar board, dragging the 12V on the PSU down!

[ilikesteel]

Re: troubleshooting TV SMPS sequence

CaplLeaker and friends,

checked at the connector Conn3 cable end and also checked right on the scaler board connector BP103.

+12 to GND = 1.97 on the 2K diode scale both ways (solid).
I thought I'd be smart and check the +24V to GND too.

wow, a crazy reading.

+24 to GND read open on 2k scale, 20K, 200K, 2000K and the 20Meg scale. while on the 20Meg scale for a few seconds, it gave a reading of about 14M, then it gradually cycled down to about .2 on the Meg scale and was still very very slowly going down.

I did the measurements several times on both rails on connector BP103 on the scaler board. same results each time.


thanks,
ilikesteel

[CapLeaker]

Re: troubleshooting TV SMPS sequence

Hmm, something does not make sense right now, you are getting the 24V which is from the same transformer for the 12V, and you do not have any open inductors, the Diodes are tested fine, the winding for the 12V does not show open circuit, the caps are fine. The circuit is just a simple half-bridge rectifier setup, it just does not make sense right now to have very very low output from the 12v section.

Unless the Scalar board is dragging it down? It has on/off, 24v and 12V and it needs to be plugged into connector 3 to power up the PSU? Did I understood that correctly?


ilikesteel:
unplug connector 3 from the PSU and check if the 12V line is shorted on it?

[ilikesteel]

Re: troubleshooting TV SMPS sequence

Alastir E, Budm,

where do I go from here? is it strange for the +24v to have jumped to +26.5 with the two diodes out of the +12V circuit? when I first checked output voltages with the PS intact, I was getting about +20V on the +24 rail, and +2V on the +12 rail.

What do I check for in and around the opto circuits? there are several.

Thanks a bunch,

ilikesteel

[Alastair E]

Re: troubleshooting TV SMPS sequence

Maybe its operating in burst-mode because there's no feedback--perhaps the opto or its associated circuit is messing round....

[budm]

Re: troubleshooting TV SMPS sequence

Hmm, something does not make sense right now, you are getting the 24V which is from the same transformer for the 12V, and you do not have any open inductors, the Diodes are tested fine, the winding for the 12V does not show open circuit, the caps are fine. The circuit is just a simple half-bridge rectifier setup, it just does not make sense right now to have very very low output from the 12v section.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

Budm,

I get .2 of an ohm on each,LS1B, LS4A and LS6.

I also get .2 of an ohm on all three sets of the secondary windings on T1.

DS5 and DS5 are still out of circuit. as well as when I made the voltage measurements in the last post.

Thanks,
ilikesteel

[budm]

Re: troubleshooting TV SMPS sequence

What resistance do you get between Pin 10 and Pin 11 of Transformer T1?
What resistance do you get between the two legs of inductors LS4A, LS1B , LS6?

[budm]

Re: troubleshooting TV SMPS sequence

Your meter probably does not have enough frequency bandwidth to measure AC frequency at 50KHz or higher.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

CapLeaker and friends,

I removed the two diodes DS3 and DS5. had some strange events that followed.

Tried to power up set without the Conn3 cable connected. couldn't get any readings. Main Cap was 160V, and the 5V stndby board did supply AC to the SMPS. no output of any kind.

reconnected the Conn3 cable. PS came up, had 360V on the main cap. However, with DS3 and DS5 out of the circuit, the +12 was .5V. the +24 was 26.5V. That said, I then tried making the AC transformer measurements.

couldn't find data sheet on the J-S BCK-50-298s, 6061903 transformer. on the bottom of the board you can clearly see 4-input pins on the HOT side and 6 pins on the COLD side. enclosed is a picture.
I believe the far right two of the 6 pins are the +12.

I measured all of them across each pair. I got 0 voltages on the first two and 1-3 volts on the +12 pair. I'm really confused. how did I get +26v on the +24v rail?

along with that, several times while trying to power on and removing power from ac outlet I heard a loud POP, like popping a brown bag. I could NOT find anything on the PS popped or burnt. STNDBY 5V was OK.

I'm afraid I'm headed down a dead end road with this one.

Thanks a bunch, you guys are patient and understanding.

ilikesteel

[ilikesteel]

Re: troubleshooting TV SMPS sequence

capleaker,

OK, I will do that tomorrow and report back.

Thanks you
ilikesteel

[CapLeaker]

Re: troubleshooting TV SMPS sequence

O.k. I want you to take the 12V diodes out again, set your meter to AC and measure transformer output pin 10 and 11. One lead to pin 10 the other on pin 11. See what you get when you turn on the PSU.