Transformer on Emerson LC320EM2 PSU

[MagicSmoke]

Working on the PSU for this tv. Has no proper volts anywhere.

When plugged in to AC on the bench, the primary transformer would instantly start sqealing. No blown fuse at f601. Highest volts readable was 9.9v on the 24v line. 4.2v on STBY.

Pulled transformer out and checked output side and all pins ( 9,10, 13, 14, 15)read .000 on any ohms setting to the ground pins ( 11, 12).

Cannot find any info on the transformer Meikai BCK-35BM LTT3PCMEK015. Service manual for tv lists it as a Trans Power 11714
P/N LTT3PC0KT069. Searched all combinations of those numbers no luck.


Sears has in parts list for tv, but is no longer made or available. Anyone know anything about it? Thanks.

[pocketwatch62]

Re: Transformer on Emerson LC320EM2 PSU

Check i think Q600 or Q601!

[pocketwatch62]

Re: Transformer on Emerson LC320EM2 PSU

also check D604, D610,D607,D640, may need to remove from circuit!

[MagicSmoke]

Re: Transformer on Emerson LC320EM2 PSU

Already de soldered and checked. Only thing that did not give a good reading was the R608 resistor. Supposed to be 0.18 ohms, mine reads .003. NOT blowing F601 fuse like I have read about in the other posts when plugged in to AC.

Now back to the original question about how to test the transformer as I have de soldered it and all DC output pins read shorted to the ground pins, .001 on my meter. Plus when I took it out the short I had on 24v rail went away.

The DC pins give an open reading to the AC which is correct

Meter readings good when testing from power connection CN632 backwards to transformer DC solder points.

Here is a couple of pics of the transformer, have not been able to find any info on it.

[budm]

Re: Transformer on Emerson LC320EM2 PSU

DC resistance of the power transformer will show <1 Ohm, you need a RINGER and Inductance meter for testing inductor/transformer.
The transformer is driven by very high frequency, not by DC, so the impedance will be high.
You can check the transformer to see if it has open winding or not only, not impedance, inductance.

[MagicSmoke]

Re: Transformer on Emerson LC320EM2 PSU

I guess the resistor is part of the problem. Resoldered transformer back in without the resistor in circuit and no more squealing.

Will have to wait on replacement as Digikey was out of them. Thanks.

[Caleb]

Re: Transformer on Emerson LC320EM2 PSU

Check the 1 watt zener diodes on top of the board over where d640 resides under the board. I listed them all out on one of the other Emerson threads. Also a leaky q601 will cause the transformer to squeal. I had one that tested good for gain and looked OK on the multimeter but was the cause of my squeal. Your resistor is probably just fine never seen one yet that went down in value, they always go up. Check out this thread
https://www.badcaps.net/forum/showthread.php?t=36180

[MagicSmoke]

Re: Transformer on Emerson LC320EM2 PSU

Check the 1 watt zener diodes on top of the board over where d640 resides under the board. I listed them all out on one of the other Emerson threads. Also a leaky q601 will cause the transformer to squeal. I had one that tested good for gain and looked OK on the multimeter but was the cause of my squeal. Your resistor is probably just fine never seen one yet that went down in value, they always go up. Check out this thread.

It may be a bad Q601, the one in my PSU is a c5344 not a 2sc2120 like in the other posts. Data sheet here

De-soldered it tests ok on ohm meter, I don't have a cricket tester. The only thing that tests bad is the R608 resistor.

The other thing I have not done is to recap the board, mine is full of Jamicon and Su'scon crap. None appear to be swollen or leaking. I think I'll recap it while I wait on the resistor to show up.

[Caleb]

Re: Transformer on Emerson LC320EM2 PSU

The 5344 can be subbed with the 2120 same basic specs I was also able to sub a bc337 after fixing the pin out. Depends on what transistors you have handy

[MagicSmoke]

Re: Transformer on Emerson LC320EM2 PSU

[QUOTE=Caleb;486410] On the Emerson I replaced
Q600- TK10A50D mosfet
Q601- 2sc2120y transistor
D604- 27v zener
D610- 36v 1w zener
D609- 4148
D640- rectifier diode
D648- 36v 1w zener
R602- 2.2 ohm 5w
R611- 2.2 ohm 5w
R608- .18 ohm 2w
Fuse
[QUOTE]

Replaced all of these on my board, comes on w/o blowing fuse, but 5v is only 4.4v, amp 24v rail is 10v, 36v is 14.2v p-on 24v is 9.9v and +16v is 6.5v.
What do I look at next?

[Caleb]

Re: Transformer on Emerson LC320EM2 PSU

Try the optoisolator, and check the rest of the components in the feedback section

[mu2]

Re: Transformer on Emerson LC320EM2 PSU

I believe there is also a surface mount schottky diode on the underside of the board. I don't have the part number handy.
Usually they short when the other stuff goes. I don't know if it would cause the low voltage issue.

Mike

[joshbsg]

Re: Transformer on Emerson LC320EM2 PSU

That schottky is D640

[CapLeaker]

Re: Transformer on Emerson LC320EM2 PSU

here is another thread with good info about emerson power supply:
https://www.badcaps.net/forum/showth...hlight=emerson