Funai Model LC220EM2 PS Issues

[walldog1]

Re: Funai Model LC220EM2 PS Issues

Thanks budm & Capleaker for your help and advice. I put in all the new parts today, plugged it in and the fuse did not blow. I was happy, but I waited a couple of minutes. Then I decided to get meter and start checking Voltages. That is when I smelled smoke and then the fuse F601 blew. Smoke came from L601, AC Voltage line conditioner. I touched it and it was very hot! It must be shorted on bottom side because the top and sides look new!

So maybe L601 WAS THE ORIGINAL CULPRIT all along and he wiped out everything downstream. All my Zener's were shorted again. I did not bother testing Transistors. This is getting recycled. Too bad, it worked so good those first 2 hours.

I did gain valuable knowledge during this process (and only cost me $23), so again I say "Thanks" I hope this thread helps someone else someday. I now have lots of spare parts that I'll probably never use.

[walldog1]

Re: Funai Model LC220EM2 PS Issues

I could not amend my order with Mouser this morning, but they waived the shipping on the BC33740TA. YEAH! This NPN had the highest Hfe of the 3 to pick from. I assumed it was bad as when I finally figured out C,B,E from PDF's and plugged it into my meter on Hfe setting, it read zero.

I never used this feature before but I guess it must apply some current or voltage and you would get some number on the meter. And yes, I will have to twist the leads on new Q602 as different CBE order. Thanks, and I'll let you know in a few days if it all works.

[budm]

Re: Funai Model LC220EM2 PS Issues

The 0.8 Ohm reading is due to the added probe leads resistance, so you are OK, I am surprised that it survived.

[walldog1]

Re: Funai Model LC220EM2 PS Issues

You are correct. I just explained in different post what my mistake was. Thanks again. I wish I would have held off on my Mouser order until now.

[CapLeaker]

Re: Funai Model LC220EM2 PS Issues

The Mosfet I picked is a direct replacement. Not sure if I can find something better than the BC337 to replace the driver transistor.

[CapLeaker]

Re: Funai Model LC220EM2 PS Issues

R602 is fine. Don't worry about that. The BC337 has a different pin out than the original transistor. You could leave one of the legs longer and bend them to the pin out you need.

[walldog1]

Re: Funai Model LC220EM2 PS Issues

PDF shows it will work, bad link before I guess.

[walldog1]

Re: Funai Model LC220EM2 PS Issues

I just looked at a PDF and it will work. Must of had a bad link before, sorry.

[walldog1]

Re: Funai Model LC220EM2 PS Issues

Picture showed round flat with 2 mounting holes and only 2 leads. Maybe case is 3rd lead? Current Q602 is the common usual small body (3-4mm) with three leads.

[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.

[CapLeaker]

Re: Funai Model LC220EM2 PS Issues

why will the BC337 not work physically?

[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.

[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

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

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

[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.

[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

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.

[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 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.