I retrieved a LC32EM1F from the dump and found that it draws current as I slowly bring up the AC using an isolated xformer. At about 40 VAC, the current rises to 2A. Power transformer has an audible buzz so started looking there after disconnecting the inverter board and the main board. Made sure that the FET attached to the primary transformer was good and then looked at each winding on the primary transformer. The primary side is good (~2 Ohms), but the secondary side looks like they are all shorted together. Other thing I noticed is that when I disconnect the main board, the current drops. The transformer part number is ltt2pc0xb043, but I could not find specifications for it. Anyone help with this one?
Announcement
Collapse
No announcement yet.
Funai LC32EM1F - blowing fuses
Collapse
X
-
Re: Funai LC32EM1F - blowing fuses
This type of power supply is a self-resonating design so its current limiting is done via the main fuse! Very bad design in my opinion, hard to get cheaper than this. I would remove the fuse and briefly put a 100W bulb across it, then see if it stays lit. Check for shorted surge protection too. The secondary of a switching transformer will always read shorted.Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
For service manual, schematic, boardview (board view), datasheet, cad - use our search.
-
Re: Funai LC32EM1F - blowing fuses
Dis connect the Red/Black wires to the inverter board. Discharge that big cap first and then check the resistance reading between the +/- cap terminal to see if it shows really low resistance, the resistance should be rising as the cap is charging up by the meter. All those diodes in the secondary side are good? This looks the saem as SANYO TV (same company owns SANYO, EMERSON) I have seen in the forum before.
What resistance do you get measure between black and white power cable attached to the board?Last edited by budm; 08-16-2012, 03:27 PM.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
-
Re: Funai LC32EM1F - blowing fuses
Tha20 Ohms indicated you have short circuits. Are you sure that the MOSFET and the rectifiers are good? try removing the MOSFET, lift one leg of each rectifer one at a time, etc. Closed up pictures of the primary side of both sides of the board?Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
-
Re: Funai LC32EM1F - blowing fuses
Replaced the FET with (K3563) with 65E6600 just to make sure. Still high current. I have not soldered the secondar side of the transformer back down yet either. Unsoldered each of the diodes on the primary side as well the the 10 or so closest to the transformer. All appear to be good. I also checked the glass/switching diodes nearest the FET. One (D612) looks shorted when soldered in, but turned out good when desoldered. Pictures below.
Comment
-
Re: Funai LC32EM1F - blowing fuses
Back at it again. I disconnected the peripheral boards and then desoldered the secondary pins on the primary xformer. Current immediately rises as I turn up the AC on isolated xformer. The transformer buzzes pretty loudly and the heatsink for the FET gets hot instantly. Measured across all the zener diodes and though I had found a shorted one (D612), but was not the case. Unsoldered one side and still high current. Suggestions on what to check next?
Comment
-
Re: Funai LC32EM1F - blowing fuses
That means the MOSFET is not swithcung on/off at high frequency like it should, so it can be that the Gate is getting steady voltage to turn it on instead of the pulses. I would suspect the IC next. When MOSEFT goes out, it will usually damaged the IC Gate drive circuit inside the IC also.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
-
Re: Funai LC32EM1F - blowing fuses
There is no IC in this design bud -- it's a self-oscillating converter using one NPN transistor and the MOSFET. It oscillates around the properties of the transformer. A rather ingenious design, I must admit, but a very bad one for several reasons. It tends to be unstable; it can go out of control and make the output voltage shoot too high. It's a pain in the *@#! to debug.
In general, I'd say the only way the MOSFET could fail by getting hot would be:
1.) it's shorted but high ohms short (a couple kohm would do it)
2.) it's got a drain-gate short
But the circuit has many other ways it can fail:
1.) if R5 goes too high in value (it dissipates about 1/4W) the MOSFET will not be efficiently switched and voltage will not rise high enough
2.) if Q1 goes open, the circuit will not oscillate (gate will remain at 18V, which wouldn't be good!)
3.) if R7 goes open or high in value (it dissipates about 1/2W) the circuit will not regulate the output voltage (it will go high)
4.) if R3 fails by reducing resistance (rare), current limit characteristics will change
5.) if C3 fails, output will go out of control (2-3x rated voltage)
6.) any bad caps on output will cause the circuit to be unstable
7.) snubber failure (as with any flyback)
8.) ... probably other ways it can fail too, just some I can think of
On these Funai TVs and similar TVs, they also use the self-oscillating circuit for generating the ~135W backlight supply, only slightly modified. I wish I was kidding.
Short circuiting the output of a self-oscillating converter will normally kill it, the MOSFET fails short.Last edited by tom66; 10-25-2012, 01:12 PM.Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
For service manual, schematic, boardview (board view), datasheet, cad - use our search.
Comment
-
Re: Funai LC32EM1F - blowing fuses
Thanks TOM, I just look at the bottom side of the board and see two transistors and an Opto connections.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
Comment
Comment