AOC LM725 screen goes blank

[selldoor]

Re: AOC LM725 screen goes blank

Stumbled across this info - (dont know for certain if it is correct)
TT2140 Transistor. Used as a Horizontal Output Transistor in newer Funai,
Sylvania, Toshiba, etc... sets. Will Sub with any of the following info
below;

TT2140 = AD301779 $1.16 (Tritronics) Original Transistor with TT2140 Written
on it.
TT2140 = BZ510120 $2.31 (Tritronics) Original Transistor with TT2140 Written
on it.
TT2140 = 2SD2627 $2.89 (Tritronics) Subs fine and same part Funai sends
out.
TT2140 = NTE2640 $2.35 (Tritronics) Silicon NPN Horizontal Output
Transistor.

TT2190 = Also will sub with any transistor-cross above for the TT2140.

[benja1475]

Re: AOC LM725 screen goes blank

this is what I'm wondering... why TT2190 is being use as a driver by the other transformer while the c5706 is capable of doing the job...

[budm]

Re: AOC LM725 screen goes blank

I always use 2sc5707 in place of 2sc5706. The 2SC 5706/5707 have very low Vsat compared to the TT2190, BUT TT2190 has much much higher Vce (1500V), unless the design of the ciruits has very high kick back voltage, so they use the high voltage transistor instead. you can try the 2sc5706/5707 ad see what happen, but make sure to check those two blue caps.

[Falipene]

Re: AOC LM725 screen goes blank

I had the same problem, monitor works for 3-4s then screen goes black.

I had laying around this one for long time, and bought the 5706 off ebay while ago.

So without testing, I swapped all 4 5706 for new ones and 2 caps (green ones) and the screen not even turned on, always black (power light works)

Then I put again old caps and same black screen.

So desoldering transistors for checking I saw this:


Soldered again two caps and four 5706 and fixed the transformer same black screen.

This pictures as it is now:
TOP:

bottom:

Should I replace this caps too?


Thanks!

[selldoor]

Re: AOC LM725 screen goes blank

Please update your profile with Country and Mains voltage.
Many members do not like images posted in line or offsite - they should be posted using
manage attachments

[Falipene]

Re: AOC LM725 screen goes blank

Please update your profile with Country and Mains voltage.
Many members do not like images posted in line or offsite - they should be posted using
manage attachments

I'll fix it asap I can edit my last post

Meanwhile I uploaded here the images.

Sorry.

[selldoor]

Re: AOC LM725 screen goes blank

Ok Better check further with a magnifier for cold joints.
Can you also check q212, q209 and q210 again for solder bridge on the legs. Probably just the pic but better check.
You should also resolder (Remove the old solder and replace)
on C213 and C214 and C201.

[Fred_Brook]

Re: AOC LM725 screen goes blank

Can you tell me the function of CN102 connector signals?
Or share the circuit... it would be enough to understand

[jeromy]

Re: AOC LM725 screen goes blank

hi kharr, where did you buy transistor c5706?.. im from manila philippines... thanks...

hello, Hope you already able to buy said transistor in manila, its available in Deeco , the biggest electronic store in Quiapo near Raon, around 25- 30 php each