KDS LCD monitor, Sampo Inverter..

[Jamie]

It appears I have a failing inverter with a KDS 17" monitor.
this is a dual unit Sampo QPWBGL9151DG
http://www.lcdpart.com/Products/qpwbgl9151dg.html


I found a pin out on the net and states that pin's
1,2 = 12V, it has that, pin's 3 is a On/Off, it's at
~ 4.1 volts via a resistor from the processor board coming from
a 5 volt source. Pin 4 is a dimmer control, it's at 3.35 volts,
5 is ground/common..

With that, I assume the inverter board should be operating and
generating some voltage to the CCL lamps?

Is my assumption correct? If So, I guess I need to repair the
inverter ?

So, I guess my other question would be, have any of you ever come
across this inverter and repaired it? It seems to be in the master
turn on because there are 2 output sections. neither work.

P.S.
The monitor it self seems to function with its yellow/green
pilot when I apply a signal, so that tells me the major part
of the unit is ok..


http://webpages.charter.net/jamie_5"

 

[Franc Zabkar]

It appears I have a failing inverter with a KDS 17" monitor.
this is a dual unit Sampo QPWBGL9151DG
http://www.lcdpart.com/Products/qpwbgl9151dg.html


I found a pin out on the net and states that pin's
1,2 = 12V, it has that, pin's 3 is a On/Off, it's at
~ 4.1 volts via a resistor from the processor board coming from
a 5 volt source. Pin 4 is a dimmer control, it's at 3.35 volts,
5 is ground/common..

With that, I assume the inverter board should be operating and
generating some voltage to the CCL lamps?

Is my assumption correct? If So, I guess I need to repair the
inverter ?

It could be that the ON signal is active low, in which case shorting
it to ground should turn on the inverter. To find out for certain, you
may find an application circuit in the datasheet for the main IC (top
centre in your photo). It may also be helpful to view the data for the
8-pin ICs below each of the coils.

The usual culprits in inverters appear to be electrolytic capacitors,
so I'd change those first. I'd also reflow the solder joints at the
transformers and coils.

- Franc Zabkar

 

[Jamie]

It could be that the ON signal is active low, in which case shorting
it to ground should turn on the inverter. To find out for certain, you
may find an application circuit in the datasheet for the main IC (top
centre in your photo). It may also be helpful to view the data for the
8-pin ICs below each of the coils.

The usual culprits in inverters appear to be electrolytic capacitors,
so I'd change those first. I'd also reflow the solder joints at the
transformers and coils.

- Franc Zabkar

Ok, i've already tried pulling that On/off signal to ground.
It does nothing, Normally standard markings of on/off is the same
order as +/-, since I'm getting + to that pin from the processor board
via a resistor from a 5 volt supply, I guess that thought is out the
door, but like I said, I did pull it low with out success.

There is 1 electrolytic on that board that seems to be related to both
inverters . I will lift the board from the chassis and inspect closer..

thanks.

http://webpages.charter.net/jamie_5"

 

[Arfa Daily]

Ok, i've already tried pulling that On/off signal to ground.
It does nothing, Normally standard markings of on/off is the same
order as +/-, since I'm getting + to that pin from the processor board
via a resistor from a 5 volt supply, I guess that thought is out the
door, but like I said, I did pull it low with out success.

There is 1 electrolytic on that board that seems to be related to both
inverters . I will lift the board from the chassis and inspect closer..

thanks.

I'm pretty sure that I can see two electros on there - one conventional
through-hole, and one s.m. Have you looked carefully for a s.m. fuse ? They
usually have one soon after the incoming supply, and it is not at all
uncommon for them to fail for no good reason. Have you followed print from
the on / off control input to see if you can find a transistor that does the
actual switching ?

Arfa

 

[Jamie]

I'm pretty sure that I can see two electros on there - one conventional
through-hole, and one s.m. Have you looked carefully for a s.m. fuse ? They
usually have one soon after the incoming supply, and it is not at all
uncommon for them to fail for no good reason. Have you followed print from
the on / off control input to see if you can find a transistor that does the
actual switching ?

Arfa

Actually, I made a mistake on the vender of the monitor, it's AOC, not a
KDS, I don't know where my head was at on that one.

Any ways, last night I got back into it, yes, the large cap in the
view was defective. Spec'ed out to be a 50uf 30v, tested as 1.2 uf.

So, I replaced it with what I had close to it at the time, 47uf, 35V

Still does not fire up how ever, I'm not sure as to what the
"On" signal voltage is suppose to be? Currently I have 4.18 volts when
unit is switched on at the control pin. Since this unit operates from
a 12 volt level, I'm making assumptions that I'll need to insert a
video signal and see if this level turns into like 12 volts of so..

At this point, I just assumed the inverter should kick in with no
video signal and at least show something for a short time like a
"No signal" or Menus before it goes to sleep.

Tonight, I am charging up one of my older laptops to be used as a
video signal to give this a try...

I may have it fixed, Just may not have one of those monitors that
shows anything at all unless I active it out of sleep mode with a
video signal (yellow light)..

P.S.
I didn't want to override the on signal with something higher than
that in fear of unneeded additional damaged.

It sure would be nice if I had a service manual for this to so me the
prints.. To me, this is just a shot in the dark project to see if I can
save this monitor and use it for a spare.. It's not worth it to me to
sink lots of money into when you can buy them so cheap these days.


http://webpages.charter.net/jamie_5"

 

[me]

Actually, I made a mistake on the vender of the monitor, it's AOC, not
a KDS, I don't know where my head was at on that one.

Any ways, last night I got back into it, yes, the large cap in the
view was defective. Spec'ed out to be a 50uf 30v, tested as 1.2 uf.

So, I replaced it with what I had close to it at the time, 47uf, 35V

Still does not fire up how ever, I'm not sure as to what the
"On" signal voltage is suppose to be? Currently I have 4.18 volts
when
unit is switched on at the control pin. Since this unit operates
from
a 12 volt level, I'm making assumptions that I'll need to insert a
video signal and see if this level turns into like 12 volts of so..

At this point, I just assumed the inverter should kick in with no
video signal and at least show something for a short time like a
"No signal" or Menus before it goes to sleep.

Tonight, I am charging up one of my older laptops to be used as a
video signal to give this a try...

I may have it fixed, Just may not have one of those monitors that
shows anything at all unless I active it out of sleep mode with a
video signal (yellow light)..

P.S.
I didn't want to override the on signal with something higher than
that in fear of unneeded additional damaged.

It sure would be nice if I had a service manual for this to so me
the
prints.. To me, this is just a shot in the dark project to see if I
can save this monitor and use it for a spare.. It's not worth it to
me to
sink lots of money into when you can buy them so cheap these days.


http://webpages.charter.net/jamie_5"

I have often found that the small value ceramic capacitor across the
inverter coil causes backlight failure, so you might try replacing it.

 

[Franc Zabkar]

P.S.
I didn't want to override the on signal with something higher than
that in fear of unneeded additional damaged.

FWIW, this 12V Sampo inverter requires a signal greater than 3V to
switch on:
http://monitor.espec.ws//files/sampo_lcd_inverter_power_l0048_79al.pdf

According to the circuit diagram, there is a digital transistor
(DTC144) at the on/off input.

The document shows a test fixture where a CCFL can be simulated with a
100K or 110K load resistor. The test current at max brightness is 6mA,
so that equates to a power dissipation of around 4W. The current at
minimum brightness is 2mA. A 10 ohm resistor is used for current
sensing.

- Franc Zabkar

 

[Jamie]

FWIW, this 12V Sampo inverter requires a signal greater than 3V to
switch on:
http://monitor.espec.ws//files/sampo_lcd_inverter_power_l0048_79al.pdf

According to the circuit diagram, there is a digital transistor
(DTC144) at the on/off input.

The document shows a test fixture where a CCFL can be simulated with a
100K or 110K load resistor. The test current at max brightness is 6mA,
so that equates to a power dissipation of around 4W. The current at
minimum brightness is 2mA. A 10 ohm resistor is used for current
sensing.

- Franc Zabkar

Thanks for the reply, I have found the problem with the inverter.

The link you provided seems to be a little different in design.

The digital transistor on this unit is a PNP that drives the PNP that
turns on the PWM (dual) vcc.

This unit employs a TI1451L dual PWM modulator. etc.

after experimenting with video signals to get a out of sleep mode
state, I've deducted this since it pulls the On/Off trigger low in the
attempt to fire it up.

The first digital PNP is bad. (opened)for lack of better terms..

Also, both electrolytic caps were almost dead!. I replaced those first
thinking it would solve the issue but didn't, it must of been running
on weak caps before the digital tranny died.

I pulled the second PNP base to common and it fired up fine.

Thanks for the help.


P.S.
I don't do a lot of repairs like I used to how ever, I remember it
was a golden rule to always check the PNP transistors first if the
suspected area had one

http://webpages.charter.net/jamie_5"

 

[Arfa Daily]

Thanks for the reply, I have found the problem with the inverter.

The link you provided seems to be a little different in design.

The digital transistor on this unit is a PNP that drives the PNP that
turns on the PWM (dual) vcc.

This unit employs a TI1451L dual PWM modulator. etc.

after experimenting with video signals to get a out of sleep mode state,
I've deducted this since it pulls the On/Off trigger low in the
attempt to fire it up.

The first digital PNP is bad. (opened)for lack of better terms..

Also, both electrolytic caps were almost dead!. I replaced those first
thinking it would solve the issue but didn't, it must of been running on
weak caps before the digital tranny died.

I pulled the second PNP base to common and it fired up fine.

Thanks for the help.


P.S.
I don't do a lot of repairs like I used to how ever, I remember it was
a golden rule to always check the PNP transistors first if the
suspected area had one

http://webpages.charter.net/jamie_5"

These days, I would say that silicon NPN/PNP types are equally (un?)
reliable, but I too remember those days of that 'golden rule'...

Arfa