LG UBK90 4K Blu-Ray no power

[momaka]

Re: LG UBK90 4K Blu-Ray no power

I’m going to dive back into this over the weekend. Any suggestions?

OK, sorry for the delay. I had to track back a little to see what's going on... and maybe a good thing. Since D102 seems to still test consistently at 50-something Ohms even with the second multimeter, I'll just say to change it. Doesn't have to be an exact replacement diode. Probably any diode will do, even something like a general purpose 1N4148. To avoid having to purchase parts, you can look for one on another scrap PCB or electronic device if you have any. Or maybe borrow the same diode from the working PSU?

If not, we could try the aux. voltage injection method next. But before you jump to that, it might be a good idea to build yourself one of these:
https://www.badcaps.net/forum/showpo...4&postcount=70
^ i.e. a dim bulb tester

Since the power supply in this DVD player also appears to have parts going to the main circuit board, I would say increase the incandescent bulb size to 60-100 Watts... which at this time might be hard to find, due to incandescent bulbs not being sold anymore (not in common hardware stores anyways.) But 40W appliance or specialty incandescent bulbs should still be available, along with 35W and 50W halogens. 2x 35W halogen bulbs or 2x 40W regular incandescent bulbs or 1x 50W halogen might be just enough for the power supply to try to turn on with the rest of the DVD player electronics connected... but if not, you can just try to power the power supply without connector CN103 being connected to anything. At that point, we will just be looking for a voltage on its output - i.e. between secondary side ground and 12VA pins on CN103.

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

I'm going to dive back into this over the weekend. Any suggestions?

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

But for the last few years, I've only been able to do so mostly just some evenings, and that is if I didn't get tired and fall asleep in front of the computer (happens more and more now.) Also on the random odd day where I have time and feel like troubleshooting electronics, but didn't actually have enough will to work on any of my own stuff... hence answer questions / post on here.

Fingers crossed you have a random odd day in the coming week or so.

I'm still trying to figure out what's wrong.

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

Nevertheless, if you can, try unsoldering one side of jumper W103 and check diode D102 again, just to see what readings we get this time. This would also isolate the PWM IC on the Vcc line, so next we can use this to try and measure the resistance of the Vcc line to primary-side ground. For that step, switch multimeter to resistance test (first 200 Ohms scale, then 2k if it goes 0L on 200 when measuring... then 20k if it goes 0L on 2k and so on) and see what resistance you get when you put the red MM probe on the solder pad of W103 that connects to IC101 and the black MM probe on the negative side of the big capacitor CE101 (labeled "P.GND" on the PCB.) Just make sure the primary cap CE101 is discharged again, of course. Post what results you get and on which scale.

Unsoldered the right side of jumper W103 (blue circle).

Checked diode D102 with a result of 057.0 Ohms & 0.087 V in selected diode test. Same reading.

Checking resistance between the solder pad of W103 that connects to IC101 (red circle) and the big capacitor CE101 (black circle) I get 0L with no change regardless of the resistance setting - new mm has an auto mode, old mm I tried 200, 2k, 20k, ...

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

Must be an oddity with the multimeter then that I cannot seem to explain. It's almost as if it sees only the resistance of R121/R123 across the diode and nothing else. If you didn't have that 2nd board to confirm, I would have also suspected bad (shorted) PWM IC... but that's probably not the case if the working board also shows this reading.

I bought another multimeter (AstroAI DM6000AR) and it came in this afternoon. It's yielding similar results, 057.0 Ohms in auto, and 0.087 V in selected diode test. Same readings with both boards.

Nevertheless, if you can, try unsoldering one side of jumper W103 and check diode D102 again, just to see what readings we get this time. This would also isolate the PWM IC on the Vcc line, so next we can use this to try and measure the resistance of the Vcc line to primary-side ground. For that step, switch multimeter to resistance test (first 200 Ohms scale, then 2k if it goes 0L on 200 when measuring... then 20k if it goes 0L on 2k and so on) and see what resistance you get when you put the red MM probe on the solder pad of W103 that connects to IC101 and the black MM probe on the negative side of the big capacitor CE101 (labeled "P.GND" on the PCB.) Just make sure the primary cap CE101 is discharged again, of course. Post what results you get and on which scale.

I'll try this later tonight or tomorrow.

Next, check the resistance of each SMD resistor R105 through R112. I can't see the numbers too well on them, but it looks like "473" written on each (they should all have the same resistance number.) If 473, they should be about 47 kOhms each (use 200k resistor scale to check.) If any are 0L or much higher than their marked number, report which resistor it is. One of these opened or abnormally high in resistance could be the reason the PWM IC is not starting.

All are reading 47.1-3 values. You're correct they're all 473.

Well, Gate to Drain and Gate to Source should always show 0L reading. What you should be getting is a low value reading between Drain to Source once the Gate is charged up (charging the Gate = black MM probe on Source, and red MM probe on Gate.) If it doesn't work with diode mode, you can also try it with 200 Ohm scale or 2k Ohm scale. I do find it strange that your MM can't turn On the MOSFET, as I've dealt and still use a lot of cheap MMs, and all have been fine with testing MOSFETs. But I guess we will see. Maybe this Walmart special really is something... new? (to beware of)

Testing with the old mosfet and the new multimeter in selected diode test. Charging the gate (source=black, gate=red) I get a brief (1 second or so) reading of 2.xxx V between drain(r) to source(b). Testing drain(b) to source(r) yields 0.531 V.

I'm tempted to just go ahead and get a Fluke multimeter, but I wouldn't think the multimeter is to blame here.

[momaka]

Re: LG UBK90 4K Blu-Ray no power

Yes, confirmed, it's 054 in diode mode.
...
I agree that it's strange, but this is the exact same reading that I get on the working board (you'll recall I mentioned I have to of these units - I inherited a working and non-working model).

Must be an oddity with the multimeter then that I cannot seem to explain. It's almost as if it sees only the resistance of R121/R123 across the diode and nothing else. If you didn't have that 2nd board to confirm, I would have also suspected bad (shorted) PWM IC... but that's probably not the case if the working board also shows this reading.

Nevertheless, if you can, try unsoldering one side of jumper W103 and check diode D102 again, just to see what readings we get this time. This would also isolate the PWM IC on the Vcc line, so next we can use this to try and measure the resistance of the Vcc line to primary-side ground. For that step, switch multimeter to resistance test (first 200 Ohms scale, then 2k if it goes 0L on 200 when measuring... then 20k if it goes 0L on 2k and so on) and see what resistance you get when you put the red MM probe on the solder pad of W103 that connects to IC101 and the black MM probe on the negative side of the big capacitor CE101 (labeled "P.GND" on the PCB.) Just make sure the primary cap CE101 is discharged again, of course. Post what results you get and on which scale.

Next, check the resistance of each SMD resistor R105 through R112. I can't see the numbers too well on them, but it looks like "473" written on each (they should all have the same resistance number.) If 473, they should be about 47 kOhms each (use 200k resistor scale to check.) If any are 0L or much higher than their marked number, report which resistor it is. One of these opened or abnormally high in resistance could be the reason the PWM IC is not starting.

I agree, but I replaced the MOSFET (when placing an order that includes $10 shipping, I figured I'd play the odds and just order a replacement mosfet and optocoupler).

Yeah, I know, makes sense to order more parts for a small order like this, since the shipping is really the bigger cost anyways and the parts don't really add up that much to the price. That's a good practice.

Also, I do blame my multimeter (not having enough test voltage) as both the replacement and original mosfet (out of circuit) wouldn't provide a reading going from gate to drain.

Well, Gate to Drain and Gate to Source should always show 0L reading. What you should be getting is a low value reading between Drain to Source once the Gate is charged up (charging the Gate = black MM probe on Source, and red MM probe on Gate.) If it doesn't work with diode mode, you can also try it with 200 Ohm scale or 2k Ohm scale. I do find it strange that your MM can't turn On the MOSFET, as I've dealt and still use a lot of cheap MMs, and all have been fine with testing MOSFETs. But I guess we will see. Maybe this Walmart special really is something... new? (to beware of)

I saw another post on testing resistance of IC101 (3S111) in another thread, I'm going to see if I can figure that out next.

I usually skip such tests, as resistance readings can't tell enough or anything at all of what's going on. At most, I only test if the Vcc pin is shorted to (primary) ground and/or if the Output pin (the one that goes to the MOSFET's Gate pin) is shorted to (primary) ground or Vcc. That's about it, though. Since your original MOSFET nor its Source resistor weren't blown, I suspect the IC should be OK.

There is another test we can perform after this, but it's a bit more risky (involves injecting voltage into the Vcc pin of the IC with the adapter plugged it... though through a series incandescent bulb to limit current if something goes wrong.) So instead, let's see what readings you come up for the items above, and then we can think how to proceed next.

I've been familiarizing myself with this site and the forums, you post a lot. I greatly appreciate any slice of time you provide this thread.

You're welcome.

Well, I used to post a lot more in the past. Not sure if that can be considered good or not. But for the last few years, I've only been able to do so mostly just some evenings, and that is if I didn't get tired and fall asleep in front of the computer (happens more and more now.) Also on the random odd day where I have time and feel like troubleshooting electronics, but didn't actually have enough will to work on any of my own stuff... hence answer questions / post on here.

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

K, sorry for the late reply.

I've been familiarizing myself with this site and the forums, you post a lot. I greatly appreciate any slice of time you provide this thread.

I find this reading worrisome.
In diode check mode, do you really get [0]54 (mV) and not 540 mV?
If yes, that diode might be bad. Remove out of circuit and re-check using diode mode.
With red probe on anode and black probe on cathode (side with white/gray stripe) --> around 500 to 700 mV Vdrop.
Now reverse the probes (black on anode and red on cathode/strip side) --> 0L
This last one is very important - if you don't get anything else but 0L, the diode could be bad... and most certainly is if this test is performed with the diode out of circuit.

Yes, confirmed, it's 054 in diode mode.

That is strange.
You should see a normal diode drop one way and 0L (open-circuit) or very high mV reading the other way - that is stable reading within a second or so. Electrolytic cap CE105 is sort of in parallel to this circuit, since the aux. winding on the transformer is pretty much a short-circuit at DC... thus, it would appear as if CE105 is in parallel with series network of D102 and R121/R123. So the changing values could be due to charging up and then discharging this capacitor through your multimeter.

Thus, it might be a good idea to remove D102 as mentioned above and test it out of circuit. Now, if you're getting a hard time trying to remove D102 due to it being an SMD component, you can remove jumper W103 (labeled "Vcc") and CE105. This will isolate D102 as if it was out of circuit. Then test and report back if you get proper diode drop in forward direction and 0L only in reverse direction.

I agree that it's strange, but this is the exact same reading that I get on the working board (you'll recall I mentioned I have to of these units - I inherited a working and non-working model).

Hmm...
Should be 3 readings here... well, 2 really, but let's break it down into 3 steps to confirm your MM can measure MOSFETs.

1) black MM probe on Source and red MM probe on Gate --> 0L
2) after step 1) above, don't touch any of the pins and move red probe to Drain (black probe still on Source) ---> 001 mV diode reading or thereabouts. NOT 0L. If 0L, your multimeter might not have high enough test voltage to test HV MOSFETs.
3) touch all 3 pins with finger while keeping probes the same way as last part in step 2 above --> 0L

Also note that the above test can only be done on MOSFETs outside of a circuit. In-circuit readings won't work, typically due to Gate pull-down resistors in the circuit. The above tests also won't work on any conductive or even slightly conductive surface (such as the skin of your hand/body.)

In any case, since the MOSFET's Source resistor (R122) is good, Q101 MOSFET should also be good. So no need to test it any further (unless you want to do this for practice.)

I agree, but I replaced the MOSFET (when placing an order that includes $10 shipping, I figured I'd play the odds and just order a replacement mosfet and optocoupler). Also, I do blame my multimeter (not having enough test voltage) as both the replacement and original mosfet (out of circuit) wouldn't provide a reading going from gate to drain.

[momaka]

Re: LG UBK90 4K Blu-Ray no power

K, sorry for the late reply.

Voltage 00.2 ... 00.1 ... 00.0
Diode settles on 54.

I find this reading worrisome.
In diode check mode, do you really get [0]54 (mV) and not 540 mV?
If yes, that diode might be bad. Remove out of circuit and re-check using diode mode.
With red probe on anode and black probe on cathode (side with white/gray stripe) --> around 500 to 700 mV Vdrop.
Now reverse the probes (black on anode and red on cathode/strip side) --> 0L
This last one is very important - if you don't get anything else but 0L, the diode could be bad... and most certainly is if this test is performed with the diode out of circuit.

It's been a little over a week, so I've been going over this again.
...
I can't seem to get a voltage reading across D102.

In diode mode, it starts high 1700+ and drops to 54. In reverse, I get the same behavior (1700+ and settles on 54).

That is strange.
You should see a normal diode drop one way and 0L (open-circuit) or very high mV reading the other way - that is stable reading within a second or so. Electrolytic cap CE105 is sort of in parallel to this circuit, since the aux. winding on the transformer is pretty much a short-circuit at DC... thus, it would appear as if CE105 is in parallel with series network of D102 and R121/R123. So the changing values could be due to charging up and then discharging this capacitor through your multimeter.

Thus, it might be a good idea to remove D102 as mentioned above and test it out of circuit. Now, if you're getting a hard time trying to remove D102 due to it being an SMD component, you can remove jumper W103 (labeled "Vcc") and CE105. This will isolate D102 as if it was out of circuit. Then test and report back if you get proper diode drop in forward direction and 0L only in reverse direction.

3) black MM probe on Source and red MM probe on Gate (leftmost pin), then move red probe to Drain ---> 0.x V diode reading or just a few Ohms on continuity check / lowest resistance scale. Then touch all 3 pins with finger ---> low diode / resistance reading between Drain and Source disappears.

EverStart 10711WDI, switched to diode mode
...
0L (old, out of circuit) / 0L (new, in circuit)

Hmm...
Should be 3 readings here... well, 2 really, but let's break it down into 3 steps to confirm your MM can measure MOSFETs.

1) black MM probe on Source and red MM probe on Gate --> 0L
2) after step 1) above, don't touch any of the pins and move red probe to Drain (black probe still on Source) ---> 001 mV diode reading or thereabouts. NOT 0L. If 0L, your multimeter might not have high enough test voltage to test HV MOSFETs.
3) touch all 3 pins with finger while keeping probes the same way as last part in step 2 above --> 0L

Also note that the above test can only be done on MOSFETs outside of a circuit. In-circuit readings won't work, typically due to Gate pull-down resistors in the circuit. The above tests also won't work on any conductive or even slightly conductive surface (such as the skin of your hand/body.)

In any case, since the MOSFET's Source resistor (R122) is good, Q101 MOSFET should also be good. So no need to test it any further (unless you want to do this for practice.)

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

3S111 - SSC3S111 (SanKen)

Thanks lotas. I'm assuming this is simply an identification and not a ... "this is probably the issue". Though, I'm considering replacing it as I'm at a loss at this point.

[lotas]

Re: LG UBK90 4K Blu-Ray no power

3S111 - SSC3S111 (SanKen)

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

It's been a little over a week, so I've been going over this again.

D102: rectifier for the aux. supply rail. Should get about 0.5-0.6V or 500-600 mV in the forward direction (red MM probe on anode, black MM probe on cathode), depending on how your multimeter shows diode readings when using the diode check function. Reverse should (likely) show open-circuit / very high reading on diode check.

I can't seem to get a voltage reading across D102.

In diode mode, it starts high 1700+ and drops to 54. In reverse, I get the same behavior (1700+ and settles on 54).

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

Cleaned with IPA, found my magnifying glass, and used my lamp - at just the correct angle, I was able to read the following:

35111
SK021
226L

Testing the following diodes using the diode setting on my multimeter:

D102 54/54
D104 554/0L
ZD101 571/0L & 571/0L
ZD102 706/0L

Upon further review, it looks like it's actually:

3S111
SK021
226L

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

You will likely need to clean the top of the ic with alcohol to read the number, Check that ZD101 is not shorted, I suspect the ic will have an internal startup cell to supply the initial vcc for the ic, but without the number it is just a guess. This vcc should be around +20v

Cleaned with IPA, found my magnifying glass, and used my lamp - at just the correct angle, I was able to read the following:

35111
SK021
226L

Testing the following diodes using the diode setting on my multimeter:

D102 54/54
D104 554/0L
ZD101 571/0L & 571/0L
ZD102 706/0L

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

Well, at least now you won't be chasing after ghost problems from bad caps, so let's not give up quite yet.

I'm committed, or is that I should be committed?

First try measuring the voltage on the main output connector between pins 1 and 2/3. Pin 1 is GND and pin 2/3 are the 12V rail. What DC voltage do you see? If you have 12V (or thereabouts), the PSU is working and the fault might be on the logic board then. If no 12V, note what voltage you get (to report back here) and continue below.

0V ... I have a cheat - I have another UBK90 and swapping power supplies works, so I know it's the power supply.

2nd (if continuing from above), check DC voltage directly on the pins of the (new) 400V cap on the primary side. BE CAREFUL! This is the primary side and you'd be dealing with potentially dangerous/lethal DC voltage here. You should see about 170V DC (since you have 120V AC mains). Side note: for people troubleshooting this with 230/240V AC mains, expect around 320-340V DC. If no high voltage DC is present on the main cap, check the input fuse (F101/F102/F103) and NTC thermistor TH101 for resistance/continuity - should see nice low resistance/continuity for both.

169.5V

If you do have high voltage DC on the primary side mentioned above, then check the output rectifier on the secondary side for short-circuit next. But BEFORE doing this, first disconnect AC power from the PSU and see if the big cap on the primary side needs discharging, as often times it will remain charged when the PSU has a fault. Not doing this could give you a surprise shock if you happen to touch the "right" components or damage your multimeter when trying to measure components on the primary side. To discharge big cap, use something like a hot glue gun or hair dryer and connect its plug right across the main cap's pins. In the case of using a high-power device like a hair drier, you might see/hear a spark (sometimes loud-ish)... just telling you in case.

Discharged - thanks for the helpful writeup.

With that out of the way, here is the simplest way to check the output rectifier: disconnect PSU from logic board and use your multimeter to measure resistance between pins 1 and 2/3. You should get very high (KOhms-range or higher) resistance, after a few seconds of keeping the probes on there (to charge the output caps.) Just to verify, report back what resistance you get here.

0.75 with the setting at 2KOhms.

If all is good with the output rectifier, let's jump back to the primary side and test the aux. supply components. That would be L101, R121 & R123, and D102 --> all SMD parts.

L101: it's a ferrite bead / tiny inductor and should read very low resistance on your multimeter (less than 3 Ohms).

2.1 ... then works it's way down to 0 and often reading 0.2 to start.

R121 & R123: 100-Ohm resistors in parallel... so should get about 50 Ohms for the pair when testing in-circuit.

49.3

D102: rectifier for the aux. supply rail. Should get about 0.5-0.6V or 500-600 mV in the forward direction (red MM probe on anode, black MM probe on cathode), depending on how your multimeter shows diode readings when using the diode check function. Reverse should (likely) show open-circuit / very high reading on diode check.

Voltage 00.2 ... 00.1 ... 00.0
Diode settles on 54.

Lastly, check resistor R117. It's the Source resistor for the MOSFET on the primary side. Usually, you won't find it bad unless the MOSFET was also bad itself... but worth a check anyways. It should read very low resistance (typical resistance value for these types of resistors are in the single-digits Ohms or under 1 Ohm values.)

0.3

Let us know what you find with these tests.

Try using diode test on your MM (though on cheaper meters, that's often the same as continuity test... but not always.)

EverStart 10711WDI, switched to diode mode

Tests to do:
1) black MM probe on Source (rightmost pin) and red MM probe on Drain (tab or middle pin) ---> open-circuit

0L (old, out of circuit) / 0L (new, in circuit)

2) red MM probe on Source and black MM probe on Drain ---> 0.5-0.7V diode reading

572 (old, out of circuit) / 575 (new, in circuit)

3) black MM probe on Source and red MM probe on Gate (leftmost pin), then move red probe to Drain ---> 0.x V diode reading or just a few Ohms on continuity check / lowest resistance scale. Then touch all 3 pins with finger ---> low diode / resistance reading between Drain and Source disappears.

0L (old, out of circuit) / 0L (new, in circuit)

This is for N-ch MOSFETs, BTW.

Indeed.

Though sometimes, a cold solder joint could also be temporarily mended (or worsened) by this trick, so it can still be done as a test on a device, just to see what happens / if anything changes. More applicable to intermittent faults, though.

[nomoresonys]

Re: LG UBK90 4K Blu-Ray no power

I have not, my understanding is that using the hairdryer would simply determine if the caps were bad - I replaced them all.

It can also works on optocouplers.

[R_J]

Re: LG UBK90 4K Blu-Ray no power

Even with a high quality zoom, I can't seem to make out any numbers. I did find a service manual for the UBK80 which has a similar board layout when it comes to IC101, even though it doesn't show a clear picture to make out any model info:

https://www.manualslib.com/manual/24...ected=1#manual

With the multimeter on 20, the voltage across CE102 is 0.59. I think I did that right.

You will likely need to clean the top of the ic with alcohol to read the number, Check that ZD101 is not shorted, I suspect the ic will have an internal startup cell to supply the initial vcc for the ic, but without the number it is just a guess. This vcc should be around +20v

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

What is the number on IC101 and what is the dc voltage across CE102?

Even with a high quality zoom, I can't seem to make out any numbers. I did find a service manual for the UBK80 which has a similar board layout when it comes to IC101, even though it doesn't show a clear picture to make out any model info:

https://www.manualslib.com/manual/24...ected=1#manual

With the multimeter on 20, the voltage across CE102 is 0.59. I think I did that right.

[momaka]

Re: LG UBK90 4K Blu-Ray no power

So, at the end of the day, the board is still not working. Though, I did get more experience soldering, so that's nice.

Well, at least now you won't be chasing after ghost problems from bad caps, so let's not give up quite yet.

First try measuring the voltage on the main output connector between pins 1 and 2/3. Pin 1 is GND and pin 2/3 are the 12V rail. What DC voltage do you see? If you have 12V (or thereabouts), the PSU is working and the fault might be on the logic board then. If no 12V, note what voltage you get (to report back here) and continue below.

2nd (if continuing from above), check DC voltage directly on the pins of the (new) 400V cap on the primary side. BE CAREFUL! This is the primary side and you'd be dealing with potentially dangerous/lethal DC voltage here. You should see about 170V DC (since you have 120V AC mains). Side note: for people troubleshooting this with 230/240V AC mains, expect around 320-340V DC. If no high voltage DC is present on the main cap, check the input fuse (F101/F102/F103) and NTC thermistor TH101 for resistance/continuity - should see nice low resistance/continuity for both.

If you do have high voltage DC on the primary side mentioned above, then check the output rectifier on the secondary side for short-circuit next. But BEFORE doing this, first disconnect AC power from the PSU and see if the big cap on the primary side needs discharging, as often times it will remain charged when the PSU has a fault. Not doing this could give you a surprise shock if you happen to touch the "right" components or damage your multimeter when trying to measure components on the primary side. To discharge big cap, use something like a hot glue gun or hair dryer and connect its plug right across the main cap's pins. In the case of using a high-power device like a hair drier, you might see/hear a spark (sometimes loud-ish)... just telling you in case.
With that out of the way, here is the simplest way to check the output rectifier: disconnect PSU from logic board and use your multimeter to measure resistance between pins 1 and 2/3. You should get very high (KOhms-range or higher) resistance, after a few seconds of keeping the probes on there (to charge the output caps.) Just to verify, report back what resistance you get here.

If all is good with the output rectifier, let's jump back to the primary side and test the aux. supply components. That would be L101, R121 & R123, and D102 --> all SMD parts.

L101: it's a ferrite bead / tiny inductor and should read very low resistance on your multimeter (less than 3 Ohms).

R121 & R123: 100-Ohm resistors in parallel... so should get about 50 Ohms for the pair when testing in-circuit.

D102: rectifier for the aux. supply rail. Should get about 0.5-0.6V or 500-600 mV in the forward direction (red MM probe on anode, black MM probe on cathode), depending on how your multimeter shows diode readings when using the diode check function. Reverse should (likely) show open-circuit / very high reading on diode check.

Lastly, check resistor R117. It's the Source resistor for the MOSFET on the primary side. Usually, you won't find it bad unless the MOSFET was also bad itself... but worth a check anyways. It should read very low resistance (typical resistance value for these types of resistors are in the single-digits Ohms or under 1 Ohm values.)

Let us know what you find with these tests.

Though, the mosfet wouldn't show continuity after switching gate to drain - but, neither did the new replacement, perhaps it's my cheap multimeter.

Try using diode test on your MM (though on cheaper meters, that's often the same as continuity test... but not always.)
Tests to do:
1) black MM probe on Source (rightmost pin) and red MM probe on Drain (tab or middle pin) ---> open-circuit
2) red MM probe on Source and black MM probe on Drain ---> 0.5-0.7V diode reading
3) black MM probe on Source and red MM probe on Gate (leftmost pin), then move red probe to Drain ---> 0.x V diode reading or just a few Ohms on continuity check / lowest resistance scale. Then touch all 3 pins with finger ---> low diode / resistance reading between Drain and Source disappears.

This is for N-ch MOSFETs, BTW.

I have not, my understanding is that using the hairdryer would simply determine if the caps were bad - I replaced them all.

Indeed.

Though sometimes, a cold solder joint could also be temporarily mended (or worsened) by this trick, so it can still be done as a test on a device, just to see what happens / if anything changes. More applicable to intermittent faults, though.

[thewolfe]

Re: LG UBK90 4K Blu-Ray no power

@thewolfe, did you try heating with hairdryer per Momaka's suggestion.

I have not, my understanding is that using the hairdryer would simply determine if the caps were bad - I replaced them all.

[R_J]

Re: LG UBK90 4K Blu-Ray no power

What is the number on IC101 and what is the dc voltage across CE102?