Funai Model LC220EM2 PS Issues

[walldog1]

This unit came with my new place, left by last owner. I Plugged it in and it WORKED! Tested all inputs, outputs, ran a channel scan and had an excellent picture for it's age.

So as with all electronics, I let them run a long time as heat will eventually show any problems. 2 hours later, fuse blew. Reading other forums on similar PS's, I upgraded the rectifier diodes to the 3W as suggested. Plugged in, measured voltages, and they stopped at R602 which was open. NOW 2 QUESTIONS!

This 1.2 Ohm 3W is not available anymore in any design. If you look at schematic attached, It would only drop around 2 volts but would dissipate 360W before heading to transformer and other PS circuits (HOT). D611 does not exist on the board, so no problems there. Could I just build a solder bridge based on schematic to eliminate R602?

Further testing revealed Zener D607 (36V) as the shorting culprit. Before I buy that one and all other diodes that go to ground in hot section, Could anything else in your opinion have taking an hit from high amp rush? By looking at all components under magnifier, there are no visual signs of any problems except the hole to the shorted Zener D607.

I don't want to keep spending $8 over and over with DigiKey if I am chasing my tail. ALL SUGGESTIONS APPRECIATED!

[budm]

Re: Funai Model LC220EM2 PS Issues

That resistor is used as protector in case you have shorted circuit such as the power MOSFET Q601, that resistor is safety device that is why it marked with caution symbol in the schematic, it should be at flame proof type. What does the BOM of the board show that resistor as? Fusible resistor? That is what it should be. They put that resistor in there for reason so do not bypass it.
Did you test D607 off the board? That D607 is connected in parallel with 0.39 Ohm resistor.
Did you check all the diodes in the cold side?
Did you check Q602?
Did you check R610?

[walldog1]

Re: Funai Model LC220EM2 PS Issues

That resistor is used as protector in case you have shorted circuit such as the power MOSFET Q601, that resistor is safety device that is why it marked with caution symbol in the schematic, it should be at flame proof type. What does the BOM of the board show that resistor as? Fusible resistor? That is what it should be. They put that resistor in there for reason so do not bypass it.
Did you test D607 off the board? That D607 is connected in parallel with 0.39 Ohm resistor.
Did you check all the diodes in the cold side?
Did you check Q602?
Did you check R610?

To budm: Yes, I tested shorted Zener D607 off the board. I will check R610 off the board also just in case.

Regarding 3A flame proof R602, since there appears to be nothing in the aftermarket to replace it, any suggestions? Could I just put another fuse (maybe 3A?) in place of it. The 4amp fuse F601 blew and did it's job, but the short also took out R602. Seems redundant to place 2 fuses in a series circuit, 1 before rectifier, and 1 after. But I don't claim to know it all. I already ordered all the diodes, so I'll know by Saturday hopefully. Maybe you can explain engineer design thoughts behind this

[walldog1]

Re: Funai Model LC220EM2 PS Issues

Being new to this Forum, I did not get an e-mail letting me know someone had responded to my Post. How can I get notified, or is there something different I should be doing? I left the Forum open for several hours after the post and budm responded within 35 minutes, yet I never knew. I do get an email every time a new member posts. Thanks. I want to know how to help and be helped.

[Per Hansson]

Re: Funai Model LC220EM2 PS Issues

There is a subscribe button at the top...

[walldog1]

Re: Funai Model LC220EM2 PS Issues

That resistor is used as protector in case you have shorted circuit such as the power MOSFET Q601, that resistor is safety device that is why it marked with caution symbol in the schematic, it should be at flame proof type. What does the BOM of the board show that resistor as? Fusible resistor? That is what it should be. They put that resistor in there for reason so do not bypass it.
Did you test D607 off the board? That D607 is connected in parallel with 0.39 Ohm resistor.
Did you check all the diodes in the cold side?
Did you check Q602?
Did you check R610?

I did not check Q601, as I was not sure how. I replaced D606, D607, D608 as all tested bad off of board. D605 & D610 tested good. The BOM of the board doe NOT show resistor R602 as Fusible resistor, nor does parts sheet. So I just bypassed it to experiment. Fuse blew instantly and so did D607 again. Looking at schematic, it has to be Q601 as shorting culprit which leads straight thru D607 to ground.

I'll check price of Q601, but I think I have spent enough money already. I am not going to check every diode on cold side as there are 50 or more of them. Besides, problem seems to be Hot side related.

[walldog1]

Re: Funai Model LC220EM2 PS Issues

I found how to test Q602 and it is bad. On Diode setting testing off board, connect + lead to D and - lead to S. It is supposed to read open (1). I get 0.001 Ohms or shorted. Found part on Mouser for $1.45 but cheapest shipping is $9.00. I want to see this work but am tired of wasting money. Plus, I still do not have R602 installed as they are discontinued.

I'll wait to hear from someone before I recycle this. It worked so GOOD until this short.

[walldog1]

Re: Funai Model LC220EM2 PS Issues

[CapLeaker]

Re: Funai Model LC220EM2 PS Issues

Try reading this thread: https://www.badcaps.net/forum/showth...hlight=emerson
It isn't for your exact model, but close enough to give you an idea. The parts location is surely different. Usually with these TV's if they fail, they take the mosfet, switching transistor, diodes, resistors, at least one zener diode out. The one I've repaired in that thread is still running to date.

Next mistake: you plugged the PSU back in without trying to limit the current. I guess you missed that bad transistor and or mosfet and up the parts went again. To rectify this, wire a 100W incandescent light bulb in series (light bulb in series trick). So if there is still a short, the light bulb will shine bright.

This thread has a schematic for your TV: https://www.badcaps.net/forum/showth...light=lc220em2

[walldog1]

Re: Funai Model LC220EM2 PS Issues

Thanks CapLeaker for the light bulb in series trick. I have done that trick with automotive circuits in the past to look for circuit voltage thieves (12v bulb), but that idea never occurred to me with this project. The 2 W resistor has survived, but i'll replace all the small resistors along the path to the MOFSET and Zener D606 & D607. All other diodes test fine, but will change them as well just for age. Then everything including rectifier bridge with new 3W diodes and most of parts in HOT section will be new.

I like learning, sometimes the hard way, but with your encouragement, I might order the Mosfet and replace other parts.

2 hours later, I said what the heck and with Q601, D606, & D607 removed, I put in a lower rated fuse and plugged it in. If it blew, why order more part? But it did not short and did some voltage testing which was good though fuse. SO NO OTHER SHORTS APPARENTLY! I HAVE NOW ORDERED Q601 and Zener's and I think it will be fine. Other parts in HOT section tested correct resistance or passed capacitors. I did not check Q602, but since it is not shorting, should be good. Mouser & Digikey don't stock Q602, but there are some new on eBay, if needed.

[budm]

Re: Funai Model LC220EM2 PS Issues

"That D607 is connected in parallel with 0.39 Ohm resistor." That resistor is probably went open circuit by now too.

[walldog1]

Re: Funai Model LC220EM2 PS Issues

Thanks for mentioning, but I double checked again just now and R610 is fine! Maybe because it measures 0.8 Ohms. Also rechecked R611 which is spot on 2.2K ohms. Somehow, all resistors survived, including the micro sized ones on other side of the board. I don't know if I could R&R R603-606 without damage to circuits as they are so small and each circuit is so close to others. But they measure right at their specified value.

[CapLeaker]

Re: Funai Model LC220EM2 PS Issues

what are the part numbers printed on Q601 and Q602? There should be subs to be found on Digi or Mouser...

So... the 2SC2120 some folks replaced it with a BC337. These have different Hfe ratings, so choose one that has the highest.
The 2SK3561 is probably something similar to some 8 N 50 variant of different manufacturers. FDP8N50NZ-ND

[walldog1]

Re: Funai Model LC220EM2 PS Issues

Mouser has Q601 and I already ordered. Q602 is obsolete on Mouser, Digikey can get if I buy 50 of them. Q602 Manufacturer # is 2SC2120-Y As mentioned previously, eBay has listings for this part. It is a bipolar NPN transistor and neither C or B are shorted to E or else fuse would have blown. Am I correct? It had power to both C & B according to schematic even with Q601 out of the circuit.

[walldog1]

Re: Funai Model LC220EM2 PS Issues

Should I remove Q602 from to test? Do you think it is necessary to test this part?

[CapLeaker]

Re: Funai Model LC220EM2 PS Issues

you have to check the whole gate drive circuit. You have to remember that if the mosfet shorted to the gate, the full power is getting to the gate drive. That means the gate drive transistor is shot too.

So if you just replaced the Mosfet, but not the little gate drive transistor, well... it goes bang again.

Also check these 4 resistors in series (R603 to 605). Better yet check all the resistors if they went out of spec. Usually they go higher in Ohms if they are damaged. Recheck all the diodes and zeners too.

[walldog1]

Re: Funai Model LC220EM2 PS Issues

BC337 would not work physically, and 2SK3561 is MOSFET and would need me to install a heatsink.

[CapLeaker]

Re: Funai Model LC220EM2 PS Issues

Should I remove Q602 from to test? Do you think it is necessary to test this part?

Yes, remove it and test it out of circuit. Some things you have to test out of circuit, because on how the circuit is made. The part could be in parallel with something else and give you a wrong reading.

[CapLeaker]

Re: Funai Model LC220EM2 PS Issues

why will the BC337 not work physically?

[walldog1]

Re: Funai Model LC220EM2 PS Issues

I guess i'll buy that transistor as well. I left a reply to your previous post on suggested subs. They would require board modification. I'll get direct part # from eBay supplier. I do not want to ruin new MOSFET. And all resistors check within 5% except R602 which showed 0.8 ohms but my meter is not a fluke or any $300 or higher meter.