Logik L40DIGB20 bad psu

[llonen]

Does anybody have a schematic for the psu fitted to this set MLT668TL, I need to identify several component values. See pics below R6 and C8

Q1 and D1 appears ok, the controller chip does not show any obvious shorts, bridge rectifyer tests good. I find no other shorted devices,

[stj]

Re: Logik L40DIGB20 bad psu

i bet it has electrolytic caps under the "U" heatsinks!

[llonen]

Re: Logik L40DIGB20 bad psu

There is a 50 volt 10uf under the heat sink and two 450 volt non electrolytic caps, 05k450. not finding anything wrong with these components. the electrolytic shows within its printed value and the two non electrolytic's do not show shorted.

[stj]

Re: Logik L40DIGB20 bad psu

the other heatsink - with no holes in it.

[llonen]

Re: Logik L40DIGB20 bad psu

I did take a look at those, they seem to test as per their stated values and there are no shorts on the diodes D6, D5 and D4. I should really invest in an Esr meter at some point. I am thinking that C8 went short before it blew itself apart and R6 the bands are discoloured to a point I cant read them and is open cct.

[budm]

Re: Logik L40DIGB20 bad psu

C8 is the snubber cap, it should connected in parallel with the MOSFET Q1 Source and Drain pin, please verify.
R6 looks to be the resistor for the Source pin and GND, please verify.

[llonen]

Re: Logik L40DIGB20 bad psu

C8 and R6 are connected together and go between source and drain. this is the hot side of the supply and it does not go directly to ground that I can see. it goes back to L6.

[R_J]

Re: Logik L40DIGB20 bad psu

Have you removed c8 and R6 from the board? C8 should have numbers on one side, (IE 102) check all around the resistor, the colors might still be readable on a side you can't see in circuit.

[llonen]

Re: Logik L40DIGB20 bad psu

C8 might be readable, I have yet to remove it, but the bands on the resistor could be



green, grey, black,
green grey brown,

I would not like to guess

[budm]

Re: Logik L40DIGB20 bad psu

When I mean GND, I mean the circuit GND of the hot side which will be the negative leg of the main filter cap.

"C8 and R6 are connected together and go between source and drain" I do not believe that the resistor will be connected to the Source and Drain pin of the MOSFET. I expect one end of the resistor to be connected to the Source pin of the MOSFET, and another end to be connected to the negative leg of the main filter cap.
I need to see the bottom side of the board so I can see how the resistor is connected.

[budm]

Re: Logik L40DIGB20 bad psu

BTW: Q1, D1 are part of the PFC Voltage booster circuit.

[budm]

Re: Logik L40DIGB20 bad psu

OK, I found the pictures at shopjimmy, that R6 is connected in series with the cap to form R/C snubber network, the network is then connected in parallel with the Source and Drain pin of Q1.
The Source pi is also connected to resistor (RED/RED/SILVER) under the heat sing to the hot side circuit GDN that you also need to check to make sure it did not go open circuit when the blue cap shorted out.
Pictures provided by shojimmy.

[budm]

Re: Logik L40DIGB20 bad psu

This SCH looks to be matched to your board.

[llonen]

Re: Logik L40DIGB20 bad psu

Well looking at the sch R6 appears to be 100 ohms and C8 150pf pn a 400 uhndred volt rail

[budm]

Re: Logik L40DIGB20 bad psu

That C8 should be rated at 1KV.

[llonen]

Re: Logik L40DIGB20 bad psu

The fet on that sch is different to the one on the pcb I have here, which is a K3568, also the stated value for R6 does not appear consistent with what I can read from the remains of on the board which begins with a green band (5)

These are about the best pics I can get of R6

[dick_barton]

Re: Logik L40DIGB20 bad psu

Looks like 56 ohms. Green, Blue, Black.

[budm]

Re: Logik L40DIGB20 bad psu

The third band looks like brown to me. The SCH is REV 1.5 so along the way, the values of the parts are changed.

[llonen]

Re: Logik L40DIGB20 bad psu

So the choices are

56 ohms
58 ohms

or

560 ohms
580 ohms

[stj]

Re: Logik L40DIGB20 bad psu

looks like 58 to me.