troubleshooting TV SMPS sequence

[CapLeaker]

Re: troubleshooting TV SMPS sequence

Resolder the transformer T1 and the inductors, diodes, capacitors on the 12V and the 24V. When you get it back together, if still doesn't work, I'd be putting an oscilloscope to it.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

update
CapLeaker, Barton, R J,

ran into a dilemma trying to put a 1K resistor from junction of RS22 and RS23 to GND.

first I re-soldered the DS3 and DS5 diodes back on the board. I re-soldered the transformer, caps, and coil connections on both supplies.

when I went to identify the resistors RS22 and RS23 on the underside of the board, RS22 appears not to be on the board. it looks like a blank space where it should be.

RS23 is a 6800 ohm resistor. the marking on it indicates that (682). it truly measures 6.8K across the resistor.

RS22 should be a 15,000 ohm resistor (153). there are no resistors in that area marked 153. Also, on the schematic, RS24 should be a 15K ohm resistor, but it's not. It's marked 18 followed by a 0 or a C.

there's a blank for RS22 and also for DS23 which the cathode should be connected to RS22 as shown in the schematic.

I haven't tried applying power to the supply. I thought I should check first with you guys to see what the next step should be.

Thanks,
ilikesteel

[ilikesteel]

Re: troubleshooting TV SMPS sequence

My apologies. here's a close up of the underside of the PS for the parts we're talking about. sorry!

ilikesteel

[R_J]

Re: troubleshooting TV SMPS sequence

why put a 1k resistor to ground? I thought you had problems with the +12 volt supply not working and the +24 was working but only +20 volts?
Does the power supply still work?
It can't be any simpler. T1 has 2 secondaries, 12-14 is for the +24volts. 10-11 is for the +12 volts, These supply a/c (20-30 khz) to ds3 and ds5 which rectifies the a/c to dc and goes through ls1b and is filtered by cs32 and cs7. the dc also flows through ls6 and is further filtered by cs8 which gives you +12 volts.
Try and measure the ac coming from the transformer, 12-14 should be close to +20vac
10-11 should be around 10vac depending on the meter etc.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

update
guys,
just a little recap, I should have included this.

separate 5V stndby on a small board. that's working. remote turns on the relay on the stndby 5V supply and that allows the 120vac to be applied to the main SMPS.

main SMPS shows 20V on the +24 rail and 2V on the +12 rail. I removed the PS connection, Conn3 which has all the outputs going back to the scaler board. so there is no load on the main SMPS. I still get the same results.

when I first received the TV and knew the stndby 5V was working, I arbitrarily
swapped out the 6 capacitors in the two output sections, 3=1000uf 16V for the +12 and 3 =1000uf 35V in the +24 rail. they were Panasonic FR series caps.

That's where we are right now. I made the above tests as indicated. so far from the replies and my testing, doesn't seem to anything jumping out as a bad component. I would like to save this from an early grave. I've included a pic of the 1W 5V stndby board and SMPS. my original post was" RCA L37WD12 Won't Power Up". I got so far with that one and the replies stopped coming. then badcaps was out for a week changing to a new server.

I thought I'd re-post a little differently because I wanted to find the logical sequence in troubleshooting a SMPS. If I can learn the sequence I may be able to make more checks before posting a problem. I got as far as checking the main cap for voltage. I did have 360V at the main cap. I was clueless after that, then I posted this post about troubleshooting sequence for a smps.

Thanks for everyone's patience. I won't try and fire this one back up until I've had some more input from any of you. there's no other forum like this one, not one.

Thanks,
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.

[ilikesteel]

Re: troubleshooting TV SMPS sequence

capleaker,

OK, I will do that tomorrow and report back.

Thanks you
ilikesteel

[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

[budm]

Re: troubleshooting TV SMPS sequence

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

[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?

[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

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.

[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....

[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

[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

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

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

[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

[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 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