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LCD Power Supply

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karyoker

New Member
This Tv is a Polaroid FLM-323B 32". It's blowing fuses in the power supply. Shown is a partial schematic and a data sheet of components involved.

Q2 and the Zener on the source were shorted. I replaced Q2 with a FVP 11N60 and the zener. I then had 5VSB and led lit. I hit the on/off switch and the led turned blue then in about 5 seconds the fuse blew again. Q2 and the zener are shorted again. The source has 5 resistors to ground all marked 1R5 which I take to be 1.5 ohms.

I did replace the 2 infamous caps in this power supply BTW this is a 200-P00-MLT666A-AH I do have the full schematic and working on a parts list with Mouser stock numbers and digital macros of trace brd to sell later on.

There are no other signs of bad components or ohmed shorts.

schematic http://cabaret-karaoke.com/fix/_1.PDF

data sheet http://cabaret-karaoke.com/fix/Q2.pdf

I did find out later Q2 is a 18N60 which is an 18 amp and not 11 amp which I replaced it with. Do you think that is why it shorted again or do you think its a bad inverter board which is puttting too much of a load on the power supply?
 
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Techyboy

New Member
When you say the Zener was shorted, were you measuring with the component in-circuit or removed? If your drawing is correct you are stating that their are "5" 1.5ohm resistors in parallel so using a regular DMM will not give you an accurate reading. If that zener does have a short reading with the component removed, you have to also check those parallel resistors, if even one of them was open your meter still wouldn't be able to detect it, that is, unless you have a milliohm meter which most hobbyists don't posess.
 

karyoker

New Member
It was removed and using the diode or ohms function it is shorted both ways (no front to back ratio) . The fet is shorted all 3 elements. I did discover a .5 ohm 1/2 watt resistor under the heat sink in parallel with the 1R5,s. After removing it ohms about .5 and the smd's ohm about .5 ohms.

Here is a jpg you can call it up with paint and magnify. Maybe it will give you a better (feel) for the problem.

Q1 does have a front to back ratio in circuit so I do think it's good.

I cant right now but I think I will order the 18 amp from Mouser and replace everything and try with the inverter unplugged and see if it will turn on. Or what are your thoughts?

photo
 

Techyboy

New Member
By the way, what is the fuse rating of the power supply that is blowing?
Those devices that you are replacing can obviously handle alot of current, so they shouldn't be easy to short like they appear to be doing. It has to be something else also, i would check to make sure no other diodes/components are open before that part of the circuit, such as D2. It would be wise to replace the part with OEM rated(current) or it could get expensive.
 

karyoker

New Member
By the way, what is the fuse rating of the power supply that is blowing?
Those devices that you are replacing can obviously handle alot of current, so they shouldn't be easy to short like they appear to be doing. It has to be something else also, i would check to make sure no other diodes/components are open before that part of the circuit, such as D2. It would be wise to replace the part with OEM rated(current) or it could get expensive.
It is a 5Amp/250V.

I dont have a clue what IC5 (it triggers Q1) is. I think when I get the replacement parts I will load the power supply and scope out some signals and measure voltages.

BTW I did get most of the rest of the schematic done and weeding out mistakes etc.

schematic
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Just to perhaps help you out a little, it's common practice to have a power factor correction circuit before the main power supply - IC5 and associated parts may be the PF correction section, and the actual PSU is the part to the right of IC5. The bottom part, as I'm sure you know, is the standby PSU.
 

karyoker

New Member
ust to perhaps help you out a little, it's common practice to have a power factor correction circuit before the main power supply - IC5 and associated parts may be the PF correction section, and the actual PSU is the part to the right

Ok Nigel the 12v &24v are driving opto P4 which triggers IC5. Do you think there ia a fault in this circuit which is not switching Q2 and as a result Q2 is in runaway?

We know the 5VSB works because I had a red led and blue when I turned it on. Thats when the fuse blew again.
 
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chriss123

New Member
Hi,

Can someone tell me the pin number that is activated (and how) when the unit (power supply) is turned on.

Thanks
 

karyoker

New Member
It is STB on pin 10. It turns on Q10 which turns on the fet Q13. It also lowers the voltage to the LED on P2.

I would like to get a part # on !C1 & IC 5.. or generic equivalent..

Actual designation on chips IC1 62674.. IC5 2F473.. (I think its hard to read) Same chip in a 15" power supply 1D7575RS...
 
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chriss123

New Member
It is STB on pin 10. It turns on Q10 which turns on the fet Q13. It also lowers the voltage to the LED on P2.

I would like to get a part # on !C1 & IC 5.. or generic equivalent..

Actual designation on chips IC1 62674.. IC5 2F473.. (I think its hard to read) Same chip in a 15" power supply 1D7575RS...

Hi,

Your schematic does not match my PSU for this TV (Model FLM 323B). You show two 10-pin connectors with the STB being pin 10 of one of them. My PSU board has a 10-pin connector and a 7-pin connector. It looks like the STB pin is pin 7 of the smaller connector. Would you happent to know if this is the case?

Thank you.
 

karyoker

New Member
Chris I se these power supplies on Ebay for the FLM-323b

photo

Mine is different..

photo

In fact there is no wire going to the 5V on the plug. I assume they use a 5V regulator on the control board from the 12V for 5V.

And this which looks like a mod on the cntrl brd. Yellow wire cut. Is yours like this?
mod
 
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chriss123

New Member
Hi,

The TV is completely dead, nothing happens when the power switch is pressed. I am a retired electrical engineer, what I need is a schematic diagram so that I can troubleshoot and fix the unit.

Thanks
 
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