max1761 substitute ?

[petehall347]

Re: max1761 substitute ?

now i think its using like this circuit as V+ and ON1 are on the same track . which means there might not be a short ..suppose i could lift the inductor to find out .
ok out2 and cs2 appear shorted so it's more like this circuit ..i haven't noticed any zeners on the board though . there are resistors tied together which i presumed were voltage dividers .
if anyone can help here it would be much appreciated ..i can post pics no problem .

[petehall347]

Re: max1761 substitute ?

ok have been doing some measurements ..output is now at 3.44v so better than yesterday somehow .
i need to get it down to 3.3v but i am crap at working out voltage dividers . i have however got the voltages .
voltage drops on the divider are ....
r47 1.03v
r48 2.42v .
r48 is same as r1 on above diagram .
r47 same as r2 .
r47 marked 10k
r48 marked 23.7k .
which one is bad ?

[petehall347]

Re: max1761 substitute ?

ok i now have out of circuit readings for r48 r47
r48 23.6k
r47 10k .
so fairly close to spec i guess .

[petehall347]

Re: max1761 substitute ?

ok from this it appears that if i increase r1 it should drop the output voltage .. thing is fb is already at 1.0v .r2 10k if i was to try a higher value then what should i use to try ? or would it not work as i would expect ?
that equation is something i do not understand

[petehall347]

Re: max1761 substitute ?

ok found i can use my calculator .
1x(1+23.7÷10)=3.37v . so maybe its fine after all .
now i suspect the backlight inverter as lights aren't working .i can light the tubes with an external inverter so they are ok . if i jumper the fet that feeds the inverter still no lights .