I have been repairing lcd monitors for about a year, and currently my tools are 60w soldering station, DMM, ring tester and cap tester. I have been considering purchasing an oscilloscope and just saw one locally for $75. It is a Elenco S-1360 used scope. I like the price, and that I can try it before purchasing, but I know almost nothing about scopes and don't know if this is a good brand/model for monitor repair. If anyone has any suggestions please let me know. Here is a link to the specs on this model: [url]http://www.tequipment.net/ElencoS-1360.html[/url]
Thanks.I have been...
sceva
Senior Member
Last Activity: 09-26-2013, 08:01 PM
Joined: 02-13-2010
Location: Omaha, NE
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Elenco s-1360
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Re: Gateway FPD1775W fades to white
I got the power supply working again.
I am still not sure if it is the main board or lcd, but I saw a main board on shopjimmy.com and by the time the customer got back to me and I tried to order it was gone. Does anyone have a PWB-0987-04 laying around? -
Re: Power supply problem VS 940bx
I had tried to check voltages in this area before and got readings that I did not understand. Just trying to figure out why.
Another thing I don't understand is if I test the AC volts at the plug or fuse on a power supply I don't see 110-120V. It usually is somewhere in the 60's....Leave a comment:
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Re: Power supply problem VS 940bx
I have replaced the diode and it is working!! Well sort of. I had not noticed that the lcd was cracked before getting the backlights on. Luckily I had another lcd panel to swap it out with. Then I started getting 2 sec 2 black... the ccfl's on this panel were bad, so I swapped the ccfl's out of the cracked lcd and finally it works!!
So this diode converts the power from the transformer to 12v. Can you use a dmm to test the voltage between the secondary of the transformer and the diode?
Thanks for the help.Leave a comment:
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Re: Viewsonic VG800b power supply noise
Thanks for the tips. I did not try the lacquer yet... I did try pushing around on things and resoldering but it did not change, except it might be a little quieter now. I put it back into the case and am letting it test for awhile. It is not very noticeable inside the case... maybe I should put some insulation around the board to further dampen the sound! :-)Leave a comment:
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Re: Viewsonic VG800b power supply noise
I replaced the caps, even the big one, but that did not help. Maybe the transformer?
I just googled around and saw this:
[I]Usually, there are 3 reasons why you're hearing that buzzing sound:
1. Bad filter caps on the input side
2. Bad diodes, leaky capacitors or bad optocouplers
3. Loose parts on the transformer that vibrate because of the transformer's magnetic field.[/I]
I will check some more. Thanks.Re: Viewsonic VG800b power supply noise
...Leave a comment:
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Viewsonic VG800b power supply noise
This one had a couple of bad caps at C4 and C5, and the component to the left of FL1 had a bad solder joint. I replaced the caps and resoldered the joint and it now works. But when it is connected to power and the monitor is turned off there is a ringing(?) noise that seems to be coming from most likely the area in red, but possibly from the area in yellow. I tried the tube to the ear but could not get any closer than that. Are there any common components that most likely could make a noise? Thanks.... -
Re: Gateway FPD1775W fades to white
You may be onto something. I didn't have another ribbon cable, but I was able to swap it end for end and the display looked different. But I did not have time to fully see what happened, as I think the shield on the ribbon cable caused me another problem while I was trying it. The ribbon cable was laying across the bottom side of the PS board and it must have done something. I didn't see any smoke or hear any noise, but the PS is unstable now and it will not turn on.
When the PS is not connected to the main board the 5V looks good,...Leave a comment:
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Re: Westinghouse TW-80001-S024A Flashing red power led
I don't have the datasheet any longer, but here is some info I found that might help in your search:
[B]B3942[/B]
30V/6.9A,
RDS(ON)=25m&@VGS=10V (N-Ch)
30V/5.8A,
RDS(ON)=40m&@VGS=4.5V (N-Ch)
-30V/-6.1A,
RDS(ON)=35m&@VGS=-10V (P-Ch)
-30V/-5.1A,
RDS(ON)=58m&@VGS=-4.5V
Super High Density Cell Design for
Extremely Low RDS(ON)
Exceptional On-Resistance and
Maximum DC Current
SOP-8 Package
By...Leave a comment:
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Gateway FPD1775W fades to white
This monitor works for 10 minutes or so, and then the screen turns white. I figure it is the main board or lcd. I found a replacement main board at shopjimmy.com for $23 and the customer is interested in repairing it. My question is: Is there a process to determine if the problem is on the main board or the lcd?
[B]History[/B]: I have seen a few boards that 'fade to white' after being on for awhile. I had [B]assumed [/B]that it was most likely the main board and I did not try and repair any of them. Well, the other day I was organizing the lcd panels I had taken out of scrapped... -
Re: Power supply problem VS 940bx
I have put it on order. Thanks again for the help.Leave a comment:
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Re: Power supply problem VS 940bx
I pulled the diode at D201. The transformer rings ok now. I think this is a schottky diode and when testing it the left side is always open circuit, which is different from the other side. So it appears to be toast.
I found a datasheet that matches the part number, Attachment 1. Digi-key recommended the part in attachment 2. It has some different specs and I can't tell if it will work or not. If someone could take a look and let me know I will get one on order.
Thanks for the help with this. I have had a few boards...Leave a comment:
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Re: Viewsonic VA902b dim lights, then black
And now for something completely different...
I turned it on, testing pin 12, got 5V when the lamps lit, but the ccfl's went out twice as fast as usual. I turned it off, and back on, and this time got 5V, and 2 sec to black like normal. The next time I turned it back on, NO backlights... I tried several times, no change. then I unplugged it for a couple of minutes and tried again... still no backlights... I am still getting 4.8V at pin 8, so the on signal has not changed. Still getting almost 15V on 15 & 16, but pins...Leave a comment:
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Power supply problem VS 940bx
This board is not outputting 13V. 5V is ok. I haven't done a lot with power supplies yet, other than replacing caps. I tested the transformer before removing it from the board with a ring tester, and the primary side was showing a short. After removing it from the board it tested good. So I think there is something shorted on the primary side. Test around and can't find anything.
I happen to have a replacement transformer that was working in another board, so I try it. Before I removed transformer B from board B, it rang good. So I begin soldering transformer B to board A. Still... -
Re: hp model l1503
I just had an HP 1502 that was doing the same thing. Fortunately I had a spare logic board out of another one that had a bad display. After swapping it works fine. I rarely attempt to repair logic boards...Leave a comment:
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Re: Viewsonic VA902b dim lights, then black
I had seen Timer on some schematics but did not understand how it worked. Thanks again.
Pin 12 is .05V when pin 7 is at .93V.
I don't have a scope. Been looking around for an inexpensive used one, but haven't landed one yet.Leave a comment:
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Re: Viewsonic VA902b dim lights, then black
OK, so that is why when there are bad caps on the 12V PS you get 0 sec to black, and when the problem is with the inverter you usually get the 2 sec to black while it is going thru its startup sequence and failing.
Another good tip. Thanks.
Pin 7 is .93V when off, 1.33V when on, and stays at 1.33V when ccfl's turn off.
I tested some other voltages on the IC while I was there:
Pin 1 and 3: 2.46V when the ccfls are on, and goes to 0 when the go off. Are these not getting...Leave a comment:
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Re: Viewsonic VA902b dim lights, then black
Tried this and no change - ccfl's about 50% and 2 sec to black.
did not attempt, if I destroy the ic we are done!
A little success. When C525 or C527 were removed the ccfl's came on at about 80%, but still 2 sec to black. No change with R501 or R503.
Readings matched as you said. I did not try and remove them yet in case one of the other tests tell you something... but will if need be.
You helped me with one before with 2 sec to black and their were a couple of caps blown...Leave a comment:
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Re: Viewsonic VA902b dim lights, then black
Looks ok, I tested the resistors and diodes around there and they appear ok.
I removed the earlier jumper on r505 and then shorted Q501's gate to ground and got the normal 1/2 backlights and 2 sec to black.
I tested each of the gates of Q501-Q505 when the backlights come on.
Q502 - 2.4V
Q503 - 2.3V
Q504 - 2.5V
Q505 - 2.3V
All of these went back to 0 when the ccfl's turn off.
Q501 was 0 and went to 4.99 when the ccfl's turned off.
...Leave a comment:
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Re: Viewsonic VA902b dim lights, then black
When I jumper R505 the lights come on really bright (slight buzzing sound on the board also) and then off after 2 seconds... Per PlainBill's instructions I did not jumper the other items.Leave a comment:
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