Xerox xa7-19i - ao4620 failed

[emilije]

Hi to all, i'm newbie here so please have a patience with me

So, i have a problem with my monitor - it powers on for cuple of seconds (max 5) and then goes off. After opening and searching on internet, founded that this is common problem with this kind of monitor. I have detected that one of AO4620 was burned out. My problem was similar to this thread https://www.badcaps.net/forum/showthread.php?t=8155 - we have the same boards, same problem. But... Ordered new AO4620, for precaution also new caps for power supply/inverter board... sucsessfully replaced all components (mosfet and the caps) but now when i turn on the monitor there is no picture on the screen, no xerox logo, lcd is black as it can be (no back picture on a direct light). Blue LED comes ON, and after few seconds goes to blink (that's normal because there is no VGA signal). Without vga signal it still need's to turn on lamps, show xerox logo and the after few seconds go in stdby mode with blinking blue led.
So did i do something wrong? Any suggestion? I measured voltage on pins to logic board and i have 5V, 12V
pics are in attach

(all) caps that i replaced are...1000uF 25V 105C, 220uF 25V 105C, 470uF 25V 105C, 150uF 25V 105C and one (burned) mosfet ao4620

[sceva]

Re: Xerox xa7-19i - ao4620 failed

If before you replaced anything the Xerox logo was appearing (I had a Xerox recently and didn't think the Xerox logo came on unless there was a VGA cable connected, but I can't be certain) and now it isn't, you probably did something wrong. Recheck that you have all the cables connected, that none of the caps or mosfet are inserted backwards, all of your solder joints are good, and that you didn't have any solder flow where it shouldn't be.

If all that is good, I would connect a computer and use a flashlight to see if the image is displaying, but just the backlights not turning on. You can also test the Backlight On signal at the connection between the power board and the video board.

It is frustrating to do all that work and be worse off than when you started, but be patient, do one thing at a time, ask for help here, and you should be able to figure out where the problem is.

[retiredcaps]

Re: Xerox xa7-19i - ao4620 failed

(all) caps that i replaced are...1000uF 25V 105C, 220uF 25V 105C, 470uF 25V 105C, 150uF 25V 105C and one (burned) mosfet ao4620

Even though the other 3 mosfets may visually look okay, they still could be defective. Some of these things likely fail in pairs.

The pinouts for source, gate, and drain are at

https://cdn.badcaps-static.com/pdfs/...2def7e2fd4.pdf

Since you have one "good new" mosfet, measure that first. Then measure and compare the other 3.

[emilije]

Re: Xerox xa7-19i - ao4620 failed

thnx for help.

I double, triple checked my work and everything is OK. Cables are also OK, checked every cable connection three times.
No picture when monitor is connected to PC, lamps are off, no picture in the back (checked with flashlight). But good thing is that monitor detects VGA signal because blue led is constantly ON.
Can u pls tell me which pin is for "backlight on" and what voltage is to expect there? (is it gndb/nf pins, because other are 12v,gnd is twice, and 5V).
i think that major problem is not only in backlight, because there is absolutely no picture.

also, i checked all fuses at the board with ohm meter, all OK. Zeners and resistors near failed mosfet looks good, ohm meter says no shorts

[emilije]

Re: Xerox xa7-19i - ao4620 failed

@retiredcaps

sorry, didn't saw your reply. I will change other mosfets. but must say that i measured them, and they look OK. any other ideas?
Can i put external power supply to logic board (5V, 12V) and check if there is a picture in back of the screen (with flashlight) ?

[Dgtech]

Re: Xerox xa7-19i - ao4620 failed

oops - ignore my post

[retiredcaps]

Re: Xerox xa7-19i - ao4620 failed

but must say that i measured them, and they look OK.
Can i put external power supply to logic board (5V, 12V) and check if there is a picture in back of the screen (with flashlight) ?

If the mosfets measured good, then leave the alone for now. Maybe test the transformers for an open winding?

a) Number the pins on the transformers anyway you like
b) black probe on pin 1, red on pin 2 - record ohm
c) black probe on pin 1, red on pin 3 - record ohm
d) black probe on pin 1, red on pin 4 - record ohm
e) etc
f) black probe on pin 1, red on pin last - record ohm
g) black probe on pin 2, red on pin 3 - record ohm
h) black probe on pin 2, red on pin 4 - record ohm
i) etc
j) black probe on pin 2, red on pin last - record ohm
k) black probe on pin 3, red on pin 4 - record ohm
l) etc
m) finally, black probe on pin last-1, red on pin last - record ohm

I'm guessing the secondaries should read 950 ohm (this will vary for different transformers). The primaries should read 1.3 ohm. Some will be 0L. If one secondary is 950ohm and the other is 750ohm, that would indicate a problem.

This test is not exhaustive as it does not detect all faults. For that, you will need a ring tester to test the coils.

[retiredcaps]

Re: Xerox xa7-19i - ao4620 failed

also, i checked all fuses at the board with ohm meter, all OK.

Is that a fuse just below T102? If yes, did you test that one? It is hard to tell from your picture.

edit: And it looks like there is another fuse F003 near the connectors at CN1?

If you missed either one of these fuses and they are defective, that would explain why you get nothing on the lcd screen.

[sceva]

Re: Xerox xa7-19i - ao4620 failed

thnx for help.

I double, triple checked my work and everything is OK. Cables are also OK, checked every cable connection three times.
No picture when monitor is connected to PC, lamps are off, no picture in the back (checked with flashlight). But good thing is that monitor detects VGA signal because blue led is constantly ON.
Can u pls tell me which pin is for "backlight on" and what voltage is to expect there? (is it gndb/nf pins, because other are 12v,gnd is twice, and 5V).
i think that major problem is not only in backlight, because there is absolutely no picture.

also, i checked all fuses at the board with ohm meter, all OK. Zeners and resistors near failed mosfet looks good, ohm meter says no shorts

So you are getting power to the video or logic board, or at least to parts of it since the power button is working and it indicates when the VGA cable is connected/disconnected. It is possible, but highly unlikely that another component failed independent of the work you did. I would try and concentrate on figuring out what might have changed. The Xerox I worked on worked fine with the power supply that came with it at first, but after testing a few things and turning it on/off, it became apparent that the power supply was failing. After substituting a different power supply I was able to repair the lcd. Just one other thing to consider.

The backlight on signal is usually the last terminal on the connection.

Test to ensure all fuses are good. They should measure 0.3 ohms.

[emilije]

Re: Xerox xa7-19i - ao4620 failed

@retiredcaps

all that fuses are OK, that was the first thing that i checked. Il'l do other testing tomorrow (transformer and backlight on signal). Thank u all guys for your help.

PS: in a meantime better pics are here - this is not my board, but is the same like in my monitor.

https://www.badcaps.net/forum/attach...2&d=1257032499
https://www.badcaps.net/forum/attach...5&d=1257085912

i don't have camera right now to post new, better pics

[emilije]

Re: Xerox xa7-19i - ao4620 failed

OK, here we go;

triple checked all mentioned fuses - all OK

measured transformers, because pins are short circued (3+3) on primary i get these results on both transformers: 0,5 ohm. On secondary there is 750ohm, both.

From connectors CN01 i measured voltage, 12V,5V, BL to GND 0,21V and Backlight ON (N/F mark on board, last pin) signal to GND is 3.8V

I measured voltage on primary of transformer, and there is 0V! No voltage is comming to transformer!

then i measured voltage on mosfets (all 4 have same results) and on bit3193 chip. Here are (interesting) results;
mosfet
G1-S1 0,16V to somewhere 0,6V (on upper mosfet)
S2-G2 0V
D-S 0,24V

on bit3193
VDD- 0V!!!
ON/OFF - 0,078V

any ideas where to continue?

PS: i took all voltage measurements while VGA signal was coming from PC and blue LED was ON

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

OK, here we go;

triple checked all mentioned fuses - all OK

measured transformers, because pins are short circued (3+3) on primary i get these results on both transformers: 0,5 ohm. On secondary there is 750ohm, both.

From connectors CN01 i measured voltage, 12V,5V, BL to GND 0,21V and Backlight ON (N/F mark on board, last pin) signal to GND is 3.8V

I measured voltage on primary of transformer, and there is 0V! No voltage is comming to transformer!

then i measured voltage on mosfets (all 4 have same results) and on bit3193 chip. Here are (interesting) results;
mosfet
G1-S1 0,16V to somewhere 0,6V (on upper mosfet)
S2-G2 0V
D-S 0,24V

on bit3193
VDD- 0V!!!
ON/OFF - 0,078V

any ideas where to continue?

PS: i took all voltage measurements while VGA signal was coming from PC and blue LED was ON

I'd like to clarify something about the way you are writing the voltages. I don't want to seem provincial, but in the US we use a period (.) to indicate the decimal point. I'm aware that many countries use a comma(,) for that purpose. Please confirm that the D-S reading above was approximately one quarter of a volt and ON/OFF was less than one tenth of a volt.

Next, what are the voltages across C101, C011, and C020?

Now, as a final question, what is the number of the component on the top part of the heat sink? The location number appears to start with D, the rest is too blurred to read.

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

@PlainBill

sorry for mess, in Europe we use comma for decimal point. Here are readings with dot. I will measure c101, c011 and c020 voltages in a couple of minutes and tell you number on the top part of the heat sink

G1-S1 0.16V to somewhere 0.6V (on upper mosfet)
S2-G2 0V
D-S 0.24V

on bit3193
VDD- 0V!!!
ON/OFF - 0.078V

thnx!

[emilije]

Re: Xerox xa7-19i - ao4620 failed

C101 - 16.22v
c011 - 16.22v
c020 - 11.82v

for the number of the component on the top part of the heat sink pls look at the pic

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

C101 - 16.22v
c011 - 16.22v
c020 - 11.82v

for the number of the component on the top part of the heat sink pls look at the pic

Thanks, that makes sense to me. They use a 12V regulator to supply 12V for the logic card instead of using unregulated 12Volts.

My next suggestion would be to trace the Backlight On and Brightness signals from CN01 to the BIT3193. There are three lines that go from the CN01 - power supply area to the inverter. The answer is probably on one of them. I'd pay special attention to the three transistors just below the BIT3193, and I'd check ZD003 near CN01

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

Hm, OK, i tracked down those signals, here is what i saw;

- at lower marked transistor from picture here are voltages:

from B-E is 3.08V
from B-C is 3.08V again
from C-E is 0V

Ok, now this transistor is connected to upper transistor - lower's C is connected to upper's B

- at upper marked transistor here are voltages:

from B-E 0V!!!
from B-C 0V!!!
from E-C 0V!!!

this is a little bit strange? Is maybe one of this transistors faulty?
multimeter diode test is also weird on these trans, not like on others;
lower:
B-E (in one direction is infinity, in other, where red probe is on E there is 1.333)
E-C (in one direction is infinity, in other, where red probe is on E there is 1.855)
other combinations - infinity in both directions
upper:
C-E while red probe is on C there is 1.127
other combinations, in both directions are infinity

I did measurement on three lower transistors of the bit3139 (lower left that you mention), and they have no voltage, from multimeter diode test they look OK.

thnx for help, i know that i'm pain in the ass

PS: when i did multimeter diode test, i didn't desolder transistors but i still think that readings are wierd

[emilije]

Re: Xerox xa7-19i - ao4620 failed

sorry, i forgot to add attach

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

You are killing me. The transistors (more likely dual diodes) you are getting so excited about are part of the voltage and current sense circuitry. First we have to figure out why there is no voltage to the inverter controller.

Let me explain what I would like you to do. There are two signals coming from the logic card to control the inverter. One of these in On/Off; the other is Brightness. The pictures you have given me to work with do not allow me to trace those signal lines - I'm not blaming you for this; even a professional photographer would have serious problems. So you must be my hands and eyes.

Start with this photograph. Set up with everything connected together. make sure nothing can short out. Hook the black lead of the DMM to ground, set the DMM on the 20 VDC range. Hook up power to the monitor.

Trace the Backlight On signal from the connector to the logic card to the components surrounding the inverter controller. The easiest way to do this is to hold the probe on a point, hit the power button twice, watching the voltage change. Note each jumper, resistor, capacitor, and transistor you come to. You SHOULD be able to trace the signal to the point where it reaches pin 6 of the inverter controller. Identify that path by marking up the picture.

Do the reverse for pin 10 - Vdd. It may be switched under control of the. Backlight On signal, it may not be. Again, identify the path by marking up the picture. If you are using Windows, Microsoft Paint will do an acceptable job. Use different colors, please.

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

Bill, don't be mad at me

I didn't have time to do detailed measurement, but sure will do it tonight just like you said. I'm not home right now so i will do it later.
I forgot to mention why i was getting so excited about that transistors/dual diodes (btw i think on PCB mark is QXXX for them). Lower trans. with his left down pin (if it is a trans, than that pin is B?) is directly connected to backlight ON signal. Right pin next to left is GND. That's the last spot where i can see backlight ON signal, 3.08V.
But OK, maybe i'm wrong, ill repeat my measurement and tracing signals from con1 to inverter controller.
stay cool for now

[emilije]

Re: Xerox xa7-19i - ao4620 failed

Don't know is this helpful to you, but i put my probes on almost every place near inverter controller. This is what i get, on most spots there is zero volts. From conn1 BL signal 2.65V is constant even monitor is in stdby (blue led blinks) N/F signal is 3.08V only when blue led is ON, otherwise iz zero volts.
i took voltage measurement and with ohm meter to show you how the components are connected near bit3139 from pins ON/OFF (pin 6) and VDD pin (pin 10).