Xerox xa7-19i - ao4620 failed

[emilije]

Re: Xerox xa7-19i - ao4620 failed

dear friend(s) sorry for my delay.
I replaced Q101, 102, 103 and my monitor is now working like a charm.

So thank you all, and especially thanks to you PlainBill for helping me to fix my monitor.

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

Bill, i don't think that is worth to further investigate this situation. Monitor is working, that was primary objective. I know that permanent 5V is not elegant so can i put a shrack relay to workaround this "problem"? What i meen is, take a relay for powering on/off bit3193, i only don't know from where to take power for relay? (12 and 5V are not trigerred by power on/off switch)

I would make another suggestion. Troubleshoot the existing problems.
1. 14 volts does not get to the source of Q101.
2. When 14 Volts is supplied via jumper, Q103 cycles on and off. What happens at the base of Q103, and the gates of Q102 and Q101?

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

Bill, i don't think that is worth to further investigate this situation. Monitor is working, that was primary objective. I know that permanent 5V is not elegant so can i put a shrack relay to workaround this "problem"? What i meen is, take a relay for powering on/off bit3193, i only don't know from where to take power for relay? (12 and 5V are not trigerred by power on/off switch)

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

Dear PlainSeriousBilly,

I put jumper from 14V (actually i measured 14.90V) to "our" pin 5 and there is some strange activity while that jump is connected; i have 7.8V on zener 103, i have 7.6V on VDD pin 10 of bit3193, but i don't have backlight on? I didn't have more time to investigate. Any further ideas?

PS: i don't know is this is coincidence or measurement error, but i've noticed that voltage on vdd pin drops from 7.6 after few seconds to 0.2V after few second back to 7.6....and so on

I don't understand that either. I've attached a complete schematic of the board; it appears the other one had errors, or they are different revisions.

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

Dear PlainSeriousBilly,

I put jumper from 14V (actually i measured 14.90V) to "our" pin 5 and there is some strange activity while that jump is connected; i have 7.8V on zener 103, i have 7.6V on VDD pin 10 of bit3193, but i don't have backlight on? I didn't have more time to investigate. Any further ideas?

PS: i don't know is this is coincidence or measurement error, but i've noticed that voltage on vdd pin drops from 7.6 after few seconds to 0.2V after few second back to 7.6....and so on

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

Oh gee, PlainBill can smile, it takes 50 posts for him to do it

Just because I'm smiling doesn't mean I'm happy.

Ok now serious, here are the readings, and you also have the photos:

Q102:
PIN1: blue led off: 0V and when blue led is on: 3.08V
PIN2: blue led off: 0.01V and when blue led is on: 0V
PIN3: blue led off: 0.74V and when blue led is on: 0V

Q101:
PIN4: blue led off: 0.74V and when blue led is on: 0V
PIN5: blue led off: 0.69V and when blue led is on: 0V
PIN6: blue led off: 0.06V and when blue led is on: 0.03V

Wahoo!!! A smoking gun. According to the schematic, pin 5 should be at 14 volts - a direct connection. This could be due to a bad solder joint or a cracked land (trace).

Q103:
PIN7: blue led off: 0.21V and when blue led is on: 0.24V
PIN8: blue led off: 0.06V and when blue led is on: 0.03V
PIN9: blue led off: 0.72V and when blue led is on: 0V

ZD103:
PIN10: blue led off: 0V and when blue led is on: 0V
PIN11: blue led off: 0.06V and when blue led is on: 0.03V

Codes of transistors are shown in pic.

PS:

from practical reasons, this is my "blue led off"



this is my "blue led on"

//serious off:


Hmm, i did, and you said "The transistors (more likely dual diodes) you are getting so excited about are part of the voltage and current sense circuitry"

<Serious mode on.> On a typical day I am TRYING to help anywhere from one to more than half a dozen people.

At one time I managed a test area with upwards of 50 production lots in test or expected to arrive within the next five days. Each lot could require as little as ten minutes of time to several man-days. Part of my job was making sure everything was completed on time. Think of a small railroad marshaling yard where incoming cars must be switched onto the proper tracks so they wind up in the proper order for the outbound trains. This was done without the benefit of a computer. That was then.

Today I have neither the concentration nor the energy to multitask. When I am pursuing a particular train of thought, nothing is more frustrating than finding my 'eyes and hands' are off on something else. I have to make a decision to either continue with the process I was following, jumping to another area, or simply leaving the person to fix the thing by himself. <Serious mode off>

So I was wrong. It was bound to happen sooner or later.

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

Oh gee, PlainBill can smile, it takes 50 posts for him to do it

Ok now serious, here are the readings, and you also have the photos:

Q102:
PIN1: blue led off: 0V and when blue led is on: 3.08V
PIN2: blue led off: 0.01V and when blue led is on: 0V
PIN3: blue led off: 0.74V and when blue led is on: 0V

Q101:
PIN4: blue led off: 0.74V and when blue led is on: 0V
PIN5: blue led off: 0.69V and when blue led is on: 0V
PIN6: blue led off: 0.06V and when blue led is on: 0.03V

Q103:
PIN7: blue led off: 0.21V and when blue led is on: 0.24V
PIN8: blue led off: 0.06V and when blue led is on: 0.03V
PIN9: blue led off: 0.72V and when blue led is on: 0V

ZD103:
PIN10: blue led off: 0V and when blue led is on: 0V
PIN11: blue led off: 0.06V and when blue led is on: 0.03V

Codes of transistors are shown in pic.

PS:

The first will be with the jumper to Vdd removed, monitor plugged in, and power LED off.

from practical reasons, this is my "blue led off"

Next, with the power LED on and active (blue or green, whichever this monitor uses) and a video signal being fed to the monitor, measure the same 11 points.

this is my "blue led on"

//serious off:

Hmm, I had asked you to measure those transistors back in post 36..

Hmm, i did, and you said "The transistors (more likely dual diodes) you are getting so excited about are part of the voltage and current sense circuitry"

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

Dear Plain Bill... your nightmare is almoast over, but only almoast

I've just replaced bit3193, and there was still no voltage to vdd pin. I took 5V directly from conn1 to vdd pin and voila... monitor is working perfectly!

So, obiously problem is somewhere three transistors that we mentioned earlier; by schematic Q101, Q102, Q103 or maybe zener 103 (i didn't measure voltage yet)

New schematic of this board is here; thanks to Skhoda:
https://www.badcaps.net/forum/attach...7&d=1283432613

PS: to be honest, it's not problem to me not to have stby function so can i simply install switch at the bottom of monitor for turn on/off monitor?

Thanks to Skhoda.

Hmm, I had asked you to measure those transistors back in post 36...

SO: While taking 5V directly to the Vdd pin will work, you may want to go with a more elegant solution. With the schematic (Thanks, Skhoda) it's fairly easy to locate the faulty component.

I've numbered the pins of the three transistors, and of the Zener diode. I will want you to make two sets of readings. The first will be with the jumper to Vdd removed, monitor plugged in, and power LED off. Measure the voltage from ground to each of the 11 points. Next, with the power LED on and active (blue or green, whichever this monitor uses) and a video signal being fed to the monitor, measure the same 11 points.

Now for the fun parts. Those transistors have 'package codes' on the top. The one with terminals 4-5-6 seems to be 'PD' and two more letters at right angles. What are the codes on all three? For extra credit, which is Q101, Q102, Q103? Hints: Q101 has one pin tied directly to N/F. Q103 has one pin tied directly to U103, pin 10.

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

Dear Plain Bill... your nightmare is almoast over, but only almoast

I've just replaced bit3193, and there was still no voltage to vdd pin. I took 5V directly from conn1 to vdd pin and voila... monitor is working perfectly!

So, obiously problem is somewhere three transistors that we mentioned earlier; by schematic Q101, Q102, Q103 or maybe zener 103 (i didn't measure voltage yet)

New schematic of this board is here; thanks to Skhoda:
https://www.badcaps.net/forum/attach...7&d=1283432613

PS: to be honest, it's not problem to me not to have stby function so can i simply install switch at the bottom of monitor for turn on/off monitor?

[emilije]

Re: Xerox xa7-19i - ao4620 failed

@posty

You may find this schematic useful...if you have Lien Cheng board.
PS: I'm still waiting my parts....

[retiredcaps]

Re: Xerox xa7-19i - ao4620 failed

I had a look for any obvious short circuits and there arent any. any idea what it could be?

https://www.badcaps.net/forum/showpo...15&postcount=2

[posty]

Re: Xerox xa7-19i - ao4620 failed

Hi, i have a problem with the same monitor, but my problem is that it blows the power when you turn at on. I've looked at the power board and apart from a fuse that had blown. so i replaced that and plugged it in, it did the same. I had a look for any obvious short circuits and there arent any. any idea what it could be?

Thanks
Adam

[emilije]

Re: Xerox xa7-19i - ao4620 failed

OK i'll try to trace. Anything else to do in a meantime while waiting 3193?

PS: i was asking because only that i can trace from pin is always leads to BL and N/F pins, over a transistor or resistors. but ill do another check

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

should voltage come from 12V line?

I don't know. The recommended voltage is 4.5 - 8 volts; 9 volts is the maximum. One simple design is a 470 - 1K ohm resistor from 12V to pin 10, with a 5.6V zener bypassed by a .1 - 2.2uF cap to ground. Another would be to hook it directly to 5V, a third would be to use a FET to switch it to 5V.

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

should voltage come from 12V line?

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

yes except this - I didn't solder new bit3193 yet, i just ordered it. Old bit3193 was removed from PCB. I measured voltage to vdd and on/off pins on "empty" pcb, without bit3193. What i want to ask is this: is it normal to have no voltages on these pins without the chip? Is sensing circuitry around chip "feeling" that no chip is there so no power is provided?

PS: from earlier testing with DMM diode test (and on 200ohm range), none of this components you circled was not shorted. Any other method of testing?
(i will measure voltage on this zener and post results, voltage results for trans you already know from earlier posts)

Designs vary. Usually voltage would be present at pin 10 whenever the monitor is plugged in. It's not unheard of to switch the power to the BIT3193.

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

Let's see if I can summarize. Pin 10 of the original BIT3193 read 1.9 ohms to ground, and Vdd was not present. You fixed the problem with the logic card (blown fuse) and replaced the BIT3193, but Vdd still is not present. Is that accurate?

yes except this - I didn't solder new bit3193 yet, i just ordered it. Old bit3193 was removed from PCB. I measured voltage to vdd and on/off pins on "empty" pcb, without bit3193. What i want to ask is this: is it normal to have no voltages on these pins without the chip? Is sensing circuitry around chip "feeling" that no chip is there so no power is provided?

PS: from earlier testing with DMM diode test (and on 200ohm range), none of this components you circled was not shorted. Any other method of testing?
(i will measure voltage on this zener and post results, voltage results for trans you already know from earlier posts)

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

PlainBill, your nightmare is back

I did a little experiment - connected logic board to external regulated power supply with 5V, GND, 12V and voila - 5V did not failed. But blue led was still off. OK - i replaced three caps on logic board, and i got blue led working as it should be. I said OK, let see this: ill connect display (still with alternate power supply) and with flashlight i will check picture. Yupeeeee - i saw xerox logo! It is only a backlight (inverter problem) now. So what went wrong last time, why 5V failed when it was connected to logic board? I checked inverter board again and again and i found a dead fuse (F3) on 5V line, because i (by mistake) shorted these pins with DMM probe while power was ON. Replaced fuse - everything OK.
So, we have a progress - picture is here, only backlight is not working. I ordered new bit3139.

Final question - i desolderd bit3193 but there is still no voltage on pin 10 (VDD) and pin6(0n/off), does this make sense? When 3193 is removed, there is no 1.9ohm on PCB. When i measure resistance on 3193 chip between vdd pin and GND it is 1.9ohm (not Kohm)

thnx

PS: it's not a problem to buy a new monitor, i just wanna learn something new. I have some experience with electronic repair, but not so much with LCD monitors.

Why do I feel like 'The Charge of the Light Brigade'. "Theirs not to reason why..."

Let's see if I can summarize. Pin 10 of the original BIT3193 read 1.9 ohms to ground, and Vdd was not present. You fixed the problem with the logic card (blown fuse) and replaced the BIT3193, but Vdd still is not present. Is that accurate?

The most likely event was that the short on the BIT3193 destroyed either a transistor or a resistor in the supply circuit.

I've circled three transistors and a diode in the attachment; check that none of these are shorted. Also look over the area outlined in yellow for resistors, diodes, and transistors that look like they were overheated.

If those steps prove fruitless, start by retracing the signal flow for the oN/oFf signal as it goes through those transistors.

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

PlainBill, your nightmare is back

I did a little experiment - connected logic board to external regulated power supply with 5V, GND, 12V and voila - 5V did not failed. But blue led was still off. OK - i replaced three caps on logic board, and i got blue led working as it should be. I said OK, let see this: ill connect display (still with alternate power supply) and with flashlight i will check picture. Yupeeeee - i saw xerox logo! It is only a backlight (inverter problem) now. So what went wrong last time, why 5V failed when it was connected to logic board? I checked inverter board again and again and i found a dead fuse (F3) on 5V line, because i (by mistake) shorted these pins with DMM probe while power was ON. Replaced fuse - everything OK.
So, we have a progress - picture is here, only backlight is not working. I ordered new bit3139.

Final question - i desolderd bit3193 but there is still no voltage on pin 10 (VDD) and pin6(0n/off), does this make sense? When 3193 is removed, there is no 1.9ohm on PCB. When i measure resistance on 3193 chip between vdd pin and GND it is 1.9ohm (not Kohm)

thnx

PS: it's not a problem to buy a new monitor, i just wanna learn something new. I have some experience with electronic repair, but not so much with LCD monitors.

[emilije]

Re: Xerox xa7-19i - ao4620 failed

Point taken. Thanks for all help that you provided to me.