Xerox xa7-19i - ao4620 failed

[PlainBill]

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).

That's a big help, but it does leave a few questions unanswered. Still, any progress is good.

First of all, could you take ANOTHER picture, just covering the area within the blue box. Don't bother making any marks on it, I'll be supplying plenty.

Next, I've circled three transistors in blue. Your picture is ALMOST good enough to read the numbers on them. What are the numbers?

Third, Pin 2 of the controller IC is Vdd. Where does that connect (Gee, I guess I better let you mark that in.)

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

i don't have my camera anymore to post new pictures, so i have to handle with what i have i have crop and resize one of the good pics.
I'm little bit confused, by datasheet of bit3193 pin 10 (red lines on my pic) is VDD, and pin 2 is error output? I added trace of pin 2, it goes to pin 11 - black lines on pic. Both pin 2 and 11 are zero volts.

other pics are it attach. Those three trans you circled in blue are one that i was so excited yesterday

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

i don't have my camera anymore to post new pictures, so i have to handle with what i have i have crop and resize one of the good pics.
I'm little bit confused, by datasheet of bit3193 pin 10 (red lines on my pic) is VDD, and pin 2 is error output? I added trace of pin 2, it goes to pin 11 - black lines on pic. Both pin 2 and 11 are zero volts.

other pics are it attach. Those three trans you circled in blue are one that i was so excited yesterday

Ahh, crud!!!!I was looking at the wrong datasheet. I guess that's what happens when I'm trying t figure out three different inverters. I saw the tracing you did from pin 10. That 1.9 ohms to ground is probably significant - it may indicate a shorted Zener diode.

One possible reason for the unusual readings on those three transistors is at least one of them (PD) is a P-channel enhancement mode mosfet.

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

Ahh, crud!!!!I was looking at the wrong datasheet. I guess that's what happens when I'm trying t figure out three different inverters.

one step at the time, one step, not three...

Ok, so next step would be to trace shorted zener. Anything else to add?

[emilije]

Re: Xerox xa7-19i - ao4620 failed

think i got it... resistance from pin 10 to gnd is that famous 1.9ohm. When i gently desolder and lift pin 10, from pin 10 to gnd resistance is still 1.9 ohms. From pin 10 lines on PCB to gnd resistance is very high when pin 10 is desoldered and lifted away (140mega ohms). Is this sign that bit3193 is dead?

PS: when pin 10 is desoldered, monitor won't power up (12V present, on 5V there is 1.88V, on backlight and brightness signals there is 1.3V)

if u also think that bit3139 is dead, can u recommend some replacement? i can't buy it in local shops (still i can order it from ebay, but i will need to wait at least 10 days)

[emilije]

Re: Xerox xa7-19i - ao4620 failed

oops, i forgot to mention. This cap (is it a cap?) in blue circle is 5-20-100ohms (oscilating) and little burned up.

correction; without pin 10 and this cap monitor won't power up.

final suggestions, what to use for replacements?

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

one step at the time, one step, not three...

Ok, so next step would be to trace shorted zener. Anything else to add?

But the other two people were getting my help (such as it is) first.

think i got it... resistance from pin 10 to gnd is that famous 1.9ohm. When i gently desolder and lift pin 10, from pin 10 to gnd resistance is still 1.9 ohms. From pin 10 lines on PCB to gnd resistance is very high when pin 10 is desoldered and lifted away (140mega ohms). Is this sign that bit3193 is dead?

If you are indeed reading 1.9 ohms, not 1.9K, yes it is.

PS: when pin 10 is desoldered, monitor won't power up (12V present, on 5V there is 1.88V, on backlight and brightness signals there is 1.3V)

That makes absolutely no sense.

The eBay deal strikes me as the best approach. But you can research if by Googling buy BIT3193

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

Yes, 1.9ohm not kohm, dmm is beeping on 200ohm range!
What do u think about that cap?

[emilije]

Re: Xerox xa7-19i - ao4620 failed

this is getting weird and weird, worse and worse and more complicated
When disconnected from logic board i have 5v and 12V. when connected to logic board, 5V fails to 1.8v... backlight and brightness signals are 1.3V.

monitor is dead, blue led not blinking.Problem at the logic board?
buaaaa. I didn't do anything wrong, just desoldered pin10 and that cap on power suply/inverter board.

on pic there is logic board, only difference is that on my i have three caps (220uF 16V) near conn1

PS i checked every fuse on logic board, they look ok. 12V is normal.

[emilije]

Re: Xerox xa7-19i - ao4620 failed

here are the pic
http://img37.*************/img37/3904/img4559v.jpg

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

this is getting weird and weird, worse and worse and more complicated
When disconnected from logic board i have 5v and 12V. when connected to logic board, 5V fails to 1.8v... backlight and brightness signals are 1.3V.

monitor is dead, blue led not blinking.Problem at the logic board?
buaaaa. I didn't do anything wrong, just desoldered pin10 and that cap on power suply/inverter board.

on pic there is logic board, only difference is that on my i have three caps (220uF 16V) near conn1

PS i checked every fuse on logic board, they look ok. 12V is normal.

Make sure you didn't short something out.

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

tested anything that i could. Nothing. Looking for new video board? Any advice?

[PlainBill]

Re: Xerox xa7-19i - ao4620 failed

tested anything that i could. Nothing. Looking for new video board? Any advice?

Initially you had an inverter problem. Now the logic card has a short. I did not feel we were getting close to solving the inverter problem. Isolating a 1.9 ohm short is just about impossible, so replacing the logic card (yes, I know, calling it a video board makes more sense) is the best way to repair that. HOWEVER, unless you are aware of a Xerox xa7-19i monitor to use as a parts donor, finding that isn't going to be easy.

Much as I hate to say it, it's time to give up. At this point the time to repair would be better spent washing dishes, sweeping floors, or selling blood to earn the money to buy a new monitor.

PlainBill

[emilije]

Re: Xerox xa7-19i - ao4620 failed

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

[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.

[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

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

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

should voltage come from 12V line?

[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