sceptre x9g-komodo vii totally dead

[cadillacman]

just got a pile of lcd pc monitors. With some luck, it turns out most work fine WHOOHOO!!!

However the best one out of the bunch, this sceptre komodo is totally dead.

Getting ready to tear into it now. If you know of any common issues with these lmk!

[cadillacman]

Re: sceptre x9g-komodo vii totally dead

Ok. so i took it apart and found two vented 470uf/25v caps in the power supply. I thought i cant be this lucky..

replaced those , refolwed some questionable solder, checked every fuse and "0 ohm resistor" i could find on both sides of the power board AND....


still dead as a doornail. Im not reading any dc voltage from case ground to any of the wires that go between the power board and the tcon board. the control panel plugs into the tcon board, so im assuming i shouls be at least seeing a 5 volt power somewhere.

I have checkes ac power in fromt he cord, and into the rectifier bridge. I have good dc power out of the bridge and thats as far as i have gone.

[Scenic]

Re: sceptre x9g-komodo vii totally dead

pics would help.

did you also replace the tiny caps in the PSU area? especially the small startup cap (usually around 35-50V 47uF)
if that one is dead, the PSU just won't start up..

[cadillacman]

Re: sceptre x9g-komodo vii totally dead

HMM.... will hunt for that and load it up in the diagnostic shotgun...


EDIT:

ok all caps ou see that are blue are new/just been replaced. Still no dice. I did not find a 47uf cap anywhere, but i found a 22uf cap there next to the big fat one, i assume thats the startup cap and no difference.

I have already checked the inverter transistors as i guess those are known to short. Mine seem to check not shorted unless im missing something.

I did find some more cold solder at the big diodes right under the big transformer there but no diff still totally dead.

[PlainBill]

Re: sceptre x9g-komodo vii totally dead

Check the inverter transistors on the bottom of the board. They are prone to shorting. Also, decent pictures of the bottom of the board will help. And what is the SMPS controller?

PlainBill

[cadillacman]

Re: sceptre x9g-komodo vii totally dead

i will check the transistors again..

and sorry forgive me, im a newb.. whats a smps controller?( dont shoot me)

heres pics. did the best i can, wife has the good camera this weekend.

Transuistors still checking ok( like 5k ohms none shorted)

this thing is just dead no power led, no blinking, nothing stone dead to the world.

[jetadm123]

Re: sceptre x9g-komodo vii totally dead

i will check the transistors again..

and sorry forgive me, im a newb.. whats a smps controller?( dont shoot me)

I believe what PlainBill is referring to is usually a 8-pin surface mount controller chip that controls the function of the heatsinked mosfet that is closest to the large 450V cap. If you turn your board over and look near the 450V cap solder pads, you should see it.

[cadillacman]

Re: sceptre x9g-komodo vii totally dead

i see! ok lets have a look...
im gonna have to dig out my mag glass to read that man..

ok the only small 8 pin smd ic in that area is this thing..

the numbers on it are:

sg3842gs ( or might be a 5)

ada09268043 ( i think lol)

even with a mag glass, thats damn near impossible to read heh..

[PlainBill]

Re: sceptre x9g-komodo vii totally dead

i see! ok lets have a look...
im gonna have to dig out my mag glass to read that man..

ok the only small 8 pin smd ic in that area is this thing..

the numbers on it are:

sg3842gs ( or might be a 5)

ada09268043 ( i think lol)

even with a mag glass, thats damn near impossible to read heh..

SG3842G is a good number. Pin 5 is Gnd, pin 7 is Vcc. Carefully check the voltage between pins 5 and 7. It should be above 16 volts.

PlainBill

[cadillacman]

Re: sceptre x9g-komodo vii totally dead

does everything need to be plugged in or just the ac input?

and i assume the pins are arranged like this?

8 7 6 5
(part numbers)
1 2 3 4

aha found a generic nte cross reference, heres the data sheet. Not sure if its correct or not (pretty sure the nte version is dip package) but mabye the pins line up at least..
https://cdn.badcaps-static.com/pdfs/...83b2cf193c.pdf

[cadillacman]

Re: sceptre x9g-komodo vii totally dead

Ok with jsut the ac input and the ccfls plugged in, im able to flip the board around and stick a piece of runner down so it doesent arc out to the chassis.

Im reading 16.3vdc across those terminals.

[cadillacman]

Re: sceptre x9g-komodo vii totally dead

edit: it sat plugged in for about 5 mins, rechecked now im only getting 10.2vdc across those terminals.

[PlainBill]

Re: sceptre x9g-komodo vii totally dead

What is the voltage between pin 5 and pin 6? If you haven't done this, measure the voltages with the signal board disconnected.

PlainBill

[cadillacman]

Re: sceptre x9g-komodo vii totally dead

ive got a big fat 0vdc across pins 5 and 6.

rechecking today i have 1.63vdc across pins 5+7 again. Not sure why this checked low at one point yesterday.

im going to check all pins now and report back in a few mins..

ok here we go. with the black lead on pin 5 i get:

pin 1: 0vdc

pin 2: 0 vdc

pin 3: 10mv (dc)

pin 4: 0

pin 5 GND

pin 6: 0vdc

pin 7: 16.3 vdc

pin 8: 0 vdc

should i have like a 10vdc square wave on the output? ( pin 6) If so i should see roughly 5vdc on my meter.. THe only reason i ask is because back int he day when i fixed car amps the power supplies were always cooked. THey ran a tl494/594 and those power supply ics outputted 10 volt square wave on the output pins and i could see that on a scope or read 5vdc with a meter.

If this chip is bad, is it a common chip? I found these and mabye theyre a good replacement?

http://search.digikey.com/scripts/Dk...me=SG3842DM-ND

[PlainBill]

Re: sceptre x9g-komodo vii totally dead

ive got a big fat 0vdc across pins 5 and 6.

rechecking today i have 1.63vdc across pins 5+7 again. Not sure why this checked low at one point yesterday.

im going to check all pins now and report back in a few mins..

ok here we go. with the black lead on pin 5 i get:

pin 1: 0vdc

pin 2: 0 vdc

pin 3: 10mv (dc)

pin 4: 0

pin 5 GND

pin 6: 0vdc

pin 7: 16.3 vdc

pin 8: 0 vdc

should i have like a 10vdc square wave on the output? ( pin 6) If so i should see roughly 5vdc on my meter.. THe only reason i ask is because back int he day when i fixed car amps the power supplies were always cooked. THey ran a tl494/594 and those power supply ics outputted 10 volt square wave on the output pins and i could see that on a scope or read 5vdc with a meter.

If this chip is bad, is it a common chip? I found these and mabye theyre a good replacement?

http://search.digikey.com/scripts/Dk...me=SG3842DM-ND

That chip should work.

PlainBill

[cadillacman]

Re: sceptre x9g-komodo vii totally dead

should i have some sort of output on pin 6 with a good ground and good voltage to the ic?

[PlainBill]

Re: sceptre x9g-komodo vii totally dead

should i have some sort of output on pin 6 with a good ground and good voltage to the ic?

Yes, BUT there are a lot of IFs. The IC does not start driving the output until Vcc reaches 16 Volts, give or take 1 volt. Note you are in the 1 volt tolerance. The output is a square wave at about 50 Khz. It's anybody's guess how your DMM will react to that high a frequency. The pulses will be very narrow if the load on the power supply is low.

I haven't developed a decent troubleshooting approach for the SMPS controllers that can be done using only a DMM. The best approach is to compare the voltage on Vcc to the 'Start voltage' spec in the data sheet and act accordingly. This is one of those cases where a scope and an isolation transformer come in very handy. As an alternative, a $2.80 replacement IC is a pretty good substitute.

PlainBill

[cadillacman]

Re: sceptre x9g-komodo vii totally dead

very true cheapie parts always help.

i do have a bk470 scope, havent used it in a few yeas but ill fire it up and see what i can see with that on pin 6...( what should i set it at?)


got a line on a working but lines-through-display komodo monitor for cheap, so going to try to pick that up to rob the power supply out of

. I would still like to fix this however, i plan to keep this monitor forever and having a good spare power supply sounds like a good idea with these damn things.. Plus i need the learning experience besides.

[PlainBill]

Re: sceptre x9g-komodo vii totally dead

very true cheapie parts always help.

i do have a bk470 scope, havent used it in a few yeas but ill fire it up and see what i can see with that on pin 6...( what should i set it at?)


got a line on a working but lines-through-display komodo monitor for cheap, so going to try to pick that up to rob the power supply out of

. I would still like to fix this however, i plan to keep this monitor forever and having a good spare power supply sounds like a good idea with these damn things.. Plus i need the learning experience besides.

Don't do it unless you have an isolation transformer!!! You'll fry something!!! This is a hot ground circuit.

PlainBill

[cadillacman]

Re: sceptre x9g-komodo vii totally dead

ok. Good thing i have an arcade isolation transformer handy heh. Does the monitor or the scope need to be hooked up to the iso?