Testing the c5707 transistors

[playman]

Hi there

Could some one tell me how to test those C5707 transistors correctly with a DMM?
I've tried searching the net and this page for a definitive answer but no luck.

I've seen few way's how to test them, in-circuit, out of circuit, using Ohm on DMM, using diode
testing on DMM, and so on, but none of them really answer my question if they are broken or not, so now
I'm wondering if some one would be so kind to teach me how I can do this correctly.

[mancaveman]

Re: Testing the c5707 transistors

Not sure if it fits your scenario or not but these were used in the PSU/Inverter boards of several BenQ/Dell/HP monitors where they were usually shorted due to bad solder joints on the transformers and ballast caps.
I'd probably move on to checking other components if I couldn't find a short between the transistor's pins. (A beep in continuity check or less than 2 ohm resistance in 200ohm range if your DMM doesn't have continuity check)
There shouldn't be a short between any 2 pins of the transistor. (only exception being between the center pin and the tab)

If there's no short and you really want to check that it's operating within tolerance you could use a DMM with transistor gain measurement function or a component analyzer to check the hFE and compare it to the datasheet value I guess but at that point the issue is probably elsewhere.

[budm]

Re: Testing the c5707 transistors

Check for cold solder joints (you can see ring developed around the pin) around the transformer pins, transistors, capacitors. Also check the tuning caps (the grey or white caps sitting between the two transistors)
http://s807.photobucket.com/user/bud...?sort=3&page=1

http://s807.photobucket.com/user/bud...?sort=3&page=1
http://s807.photobucket.com/user/bud...?sort=3&page=1

[playman]

Re: Testing the c5707 transistors

Thanks for the reply guy's

Still some questions remain.
I have a c5707 I took from a Medion LCD pc display.

The readings I have are.
Using 200Ohm setting
Black probe on first pin red probe on second pin = No reading (shows just 1 on screen, after little googling that tells me it's open circuit)
Black probe on first pin red probe on third pin = No reading (same as above)
Black probe on second pin red probe on third pin = No reading (same as above)

This is the same reading I get from all 4 c5707 transistors.
So I guess that means that the c5707's are okay and there is something else that is causing black screen, right?.
Am I right to assume that if I get any reading on the DMM beside "open circuit" the c5707 (or any other transistor) is broken?

I did replace the 16v 1000uf capacitor (circlet in picture) as it was bulked, but that did nothing for me.
I did not notice any cold solder points, but I'm going to try and resolder them.
I guess I need a Capacitor tester to check out those tuning capacitors right?

I did take a picture of the board.

[budm]

Re: Testing the c5707 transistors

Did you check that black fuse PF701 sitting between the caps? That fuse feed the B+ to the inverter circuit. It should show <1 Ohm on 200 Ohms scale on the meter.

[playman]

Re: Testing the c5707 transistors

Yeah I did test it earlier and it gives me 0.8 Ohm connected to the PCB.

[R_J]

Re: Testing the c5707 transistors

To check the transistor, put meter on diode test, put red probe on base (B) of transistor and black on collector (C or center pin) you should read about .6 or 600 dependson the meter, then put the black probe on the emiter (E) and it should read around .6 or 600, then reverse the leads and do the same check, that should read like an open, then check between emiter and collector, either way the probes are should check open.
You need to be on diode test or a good transistor will read open.
As above check for poor solder connections, you may need a magnifier to see the poor connections.

[playman]

Re: Testing the c5707 transistors

Red probe on (B) Black probe on (C) = 745-750
Red probe on (B) Black probe on (E) = 745-750
I tested all four c5707's and they ranged from 745 to 750
Reverse on that gave me open.

Red/Black (E) Red/Black (C) gave me open on all of them

Is 750 okay number?
What number range is safe?
Does this work with all transistors also?
Is this the best way to check them?

I checked the board with magnifier and saw no poor connections, but I'm going to
resolder just in case.
When I resolder, is it enough to just melt the connection or ad a little more tin to the connection or even remove the old tin and replace it with a fresh one?

[budm]

Re: Testing the c5707 transistors

750 (0.75V) represents the Vf (forward bias voltage which is 0.6v~0.7V range) of the P-N junction, so they are correct. I would also use Ohm mode to check the leakage resistance between E and C using 2K scale.

[playman]

Re: Testing the c5707 transistors

Using the 2k Ohm gave me open circuit, even tried 2000k which also gave me open circuit.

[Davi.p]

Re: Testing the c5707 transistors

5707 often fails in couple, you have to check even in circuit if there's a short between 2 pins, if yes replace also the other 5707 even if seems good. "that is causing black screen" black with or whitout image (use a lamp by side of screen to see)? with or whitout the backlight (see in a dark room)?

[playman]

Re: Testing the c5707 transistors

Okay I just tested them in circuit.
200Ohm
Black probe on pin(B) red probe on pin(C) = No reading (open circuit) on all four
Black probe on pin(B) red probe on pin(E) = No reading (open circuit) on all four
Black probe on pin(C) red probe on pin(E) = 107.3 on all four

Diode test
Red probe on (B) Black probe on (C) = 706 on all four
Red probe on (B) Black probe on (E) = 706 on all four
Black probe on (B) Red probe on (C) = 1185 on all four
Black probe on (B) Red probe on (E) = 1475 on all four
Black (E) Red (C) = 1390 on 2 of them 1402 on the last 2
Red (E) Black (C) = 160 on all four

Are those readings correct?

The screen is just black, when I put a light on the screen I'm able to make some sight on what the screen is projecting, as in, there is no
light in the screen to light up the screen.

[ecking767]

Re: Testing the c5707 transistors

Okay I just tested them in circuit.
200Ohm
Black probe on pin(B) red probe on pin(C) = No reading (open circuit) on all four
Black probe on pin(B) red probe on pin(E) = No reading (open circuit) on all four
Black probe on pin(C) red probe on pin(E) = 107.3 on all four

Diode test
Red probe on (B) Black probe on (C) = 706 on all four
Red probe on (B) Black probe on (E) = 706 on all four
Black probe on (B) Red probe on (C) = 1185 on all four
Black probe on (B) Red probe on (E) = 1475 on all four
Black (E) Red (C) = 1390 on 2 of them 1402 on the last 2
Red (E) Black (C) = 160 on all four

Are those readings correct?

The screen is just black, when I put a light on the screen I'm able to make some sight on what the screen is projecting, as in, there is no
light in the screen to light up the screen.

normally a transistor will short out or read open on diode test on your meter. on eBay, there are some transistor testers you can buy. This little device work great and it will give you an better idea what going on with the components you are testing.

those reading for that transistor maybe OK. I can't say for sure I don't have a one new

[Davi.p]

Re: Testing the c5707 transistors

"Are those readings correct?" them seems to be correct, for the 160 seems a bit low, but since your testing on post #8 them are good, just to be clear, you don't have to test in circuit, it's only easier to do..

"when I put a light on the screen I'm able to make some sight on what the screen is projecting.." backlight is not working, on the under side of the board there is a chip with 14/16 pins, how is labeled?

[playman]

Re: Testing the c5707 transistors

Thank you ecking767 I'll look into that.
This is a big jungle out there, here are few I found
http://www.ebay.com/itm/Transistor-T...item19e21c8b66
http://www.ebay.com/itm/Peak-atlas-D...item3f1f6efb03
http://www.ebay.com/itm/Transistor-T...item19e734f236
http://www.ebay.com/itm/Mega328-Tran...item1c3f58273d

Should I get the MK-168 or the atlas one, they kinda look
the nicest but are also the expensive ones.

"Are those readings correct?" them seems to be correct, for the 160 seems a bit low, but since
your testing on post #8 them are good, just to be clear, you don't have to test in circuit, it's only easier to do..

Okay thanks, it is quicker and easier to test them in circuit, I just
have to know what I'm looking for

"when I put a light on the screen I'm able to make some sight on what the screen is projecting.." backlight is not
working, on the under side of the board there is a chip with 14/16 pins, how is labeled?

Could that be the TL1451A?
http://pdf1.alldatasheet.com/datashe...I/TL1451A.html

[R_J]

Re: Testing the c5707 transistors

If you suspect the transistors are bad, why don't you just replace them, they are cheep.

[playman]

Re: Testing the c5707 transistors

It's not that I suspect them really, but they have a history of going bad.
It's just that I wanted to know how to measure them correctly, so I can be sure
that they are okay or bad.

[Davi.p]

Re: Testing the c5707 transistors

"Okay thanks, it is quicker and easier to test them in circuit"
This is valid only for this particular board configuration eh!
The datasheet of TL1451 doesn't tell what pins does, from a very similar service manual schematic (DELL E173FP) i can tell you that you can try to power on (with 5707 mounted) with, in order, pin 15 or if doesn't work pin 1 of that chip connected to gnd, this we hope will disable protection, this only for testing purpose! If the monitor works you must dismount the panel, verify that ccfl lamps are with black ends and then change those blacks with new ones.

[playman]

Re: Testing the c5707 transistors

"Okay thanks, it is quicker and easier to test them in circuit"
This is valid only for this particular board configuration eh!

And you just had to burst my bubble
If I buy the transistor checker I have to unsolder them anyway.

The datasheet of TL1451 doesn't tell what pins does, from a very similar service manual schematic (DELL E173FP) i can tell you that you can try to power on (with 5707 mounted) with, in order, pin 15 or if doesn't work pin 1 of that chip connected to gnd, this we hope will disable protection, this only for testing purpose! If the monitor works you must dismount the panel, verify that ccfl lamps are with black ends and then change those blacks with new ones.

The strangest thing happened, I was going to try that out, but I decided to test the screen
before I did that for some reason. Lo and behold the screen turns on and shows me the "Check Video Cable" popup message.
But some strange things are happening, the VGA and DVI ports don't work and the screen is just blank, I put a "carpet"
over it and noticed that there was light, so the lamps work at least now.
And if I press the menu button I get the menu but it doesn't stay on, it just shows for 1 sec then disappears, if I hold the
button the menu stays until I release the button.
What could be causing those 2 symptoms?

And how come the screen works now and not before?
All I did was re-flowing some joints for good measure, could that be it?

[Davi.p]

Re: Testing the c5707 transistors

It seem the mcu gone crazy, that is a chip on the video input board, but all this happenings seems a bit strange. Continue testing it until you can be sure that the backlight works, if yes and if you dont receive any other hints consider to buy another video input board.