Re: Viewsonic VA2431wm bad cap replaces, new problem
It seems like every time I replace the 2 AO4620s one of the 2 fail in a few weeks. Not sure if it's excessive heat or if another component is causing an issue. The last time I replaced the MOSfets I made custom daughterboards so the chips rest in an area with more airflow. (And it's socketed so it's slightly easier to replace) I didn't open it yet but the MOSfet that failed is the one that caused the LED to fail to light at all.
Any idea of what could be causing this issue and/or any possible fixes?
Tom-Servo
Member
Last Activity: 02-24-2017, 11:22 AM
Joined: 09-21-2015
Location: PA
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Custom stand alone LED power board question
This post is in a gray area when it comes to which forum to post in. It isn't exactly about LCD TV repair and it's asking about electronic theory so I'm guessing it belongs in this forum. Anyway...
About a week or so someone set a ns-40d510na15 40" LED TV outside of a dumpster. On closer inspection the LCD panel was smashed/leaking but the internal power board, control board, back light LEDs, etc, look perfect.
I did a quick look around and I couldn't find a good price on a replacement panel. Since I wouldn't use the tuner etc in the unit I was thinking of selling... -
Re: Viewsonic VA2431wm bad cap replaces, new problem
After further inspection it seems that one of the 4 CCFL plugs was not in all the way, once I made it snuggly connected it works just fine (had to replace one of the MOSFETs when the black electrical tape didn't hold properly, thankfully bought a 10 pack of AO4620s). It does have a few water spots in it and a bigger one in the top right corner. Is there anything that can be done about that?Leave a comment:
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Re: Viewsonic VA2431wm bad cap replaces, new problem
The power LED stays on and I can see the screen if I shine a flashlight on it. I'll try the Inverter test you mentioned and see what I come up with, thanks!
I remembered that I have a spare CCFL from my SFII/mame cab but it's a F15 and 15 watts, going to have to find or buy a 4 watter or so....Last edited by Tom-Servo; 10-16-2015, 08:55 AM.Leave a comment:
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Re: Viewsonic VA2431wm bad cap replaces, new problem
Replaced both AO4620's and now it turns on though now it's doing 2 seconds to black. Now that I think about it my brother said that's what was happening before until it stopped turning on at all. I was able to get the monitor to turn back on for 2 more seconds when I changed resolution.
Two things that I know about the monitor which may or may not be enough to confirm that the issue is the back light rather than the inverter transformer.
1. The picture when on looks extremely drab.
2. My brother...Last edited by Tom-Servo; 10-15-2015, 02:01 PM.Leave a comment:
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Re: Viewsonic VA2431wm bad cap replaces, new problem
I mixed the MOSFET that was shorted, it was Q805. I removed Q805 and tested the resistance between L904 (+16v rail) and ground. It counted up until 9.400 K ohm then continued to count up after that but rather slowly. I then removed Q806 and pretty much observed the same behavior. Though sometimes when I measured the resistance it started in the M Ohm range and counted down from there.Last edited by Tom-Servo; 09-23-2015, 11:38 AM.Leave a comment:
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Re: Viewsonic VA2431wm bad cap replaces, new problem
OK, will remove the MOSFETS tomorrow, too tired to desolder well tonight. Should I then retest L904 and GND? If so what should the resistance be? Are there good substitutes for AO4620 from what I listed before or any others not listed, or is it best just to order the exact part number from China.
Thanks!...Leave a comment:
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Re: Viewsonic VA2431wm bad cap replaces, new problem
2.6 Ohm from Ground to L904 (both contacts are the same)...Leave a comment:
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Re: Viewsonic VA2431wm bad cap replaces, new problem
It seems that I made a mistake. Before I posted here I tried plugging in the power board with the inverter transformer removed to try to see if the blinking blue LED would stop. When I plugged it in the blue led came on for a second and then turned off. When I resoldered the inverter transformer back on the blue led still doesn't come back on. When I measure ground to +5 volts on the cable that goes to the control board I get 2.8 volts or so.
So is it likely I damaged the power transformer? How can I check it out?...Leave a comment:
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Re: Viewsonic VA2431wm bad cap replaces, new problem
Took too much time to edit my last post so posting another reply.
Using the following filters on mouser:
Category Semiconductors > Discrete Semiconductors > Transistors > MOSFET
Pd - Power Dissipation 2 W
Mounting Style SMD/SMT
Package/Case SOIC-8
Transistor Polarity N and P-Channel | N-Channel, P-Channel
Id - Continuous Drain Current 7A, - 5A
I come up with FDS8958A_F085:
Is that any...Leave a comment:
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Re: Viewsonic VA2431wm bad cap replaces, new problem
The page that lists SI4542DY and SI4542DY-T1-E3 as a "Replacements & Cross References" is:
[URL="http://parts.arrow.com/item/detail/alpha-and-omega-semiconductor/ao4620"]http://parts.arrow.com/item/detail/alpha-and-omega-semiconductor/ao4620[/URL]
I then tried searching for it at:
[URL="http://www.mouser.com/Semiconductors/Discrete-Semiconductors/Transistors/MOSFET/_/N-ax1sf?Keyword=SI4542DY&FS=True"]http://www.mouser.com/Semiconductors/Discrete-Semiconductors/Transistors/MOSFET/_/N-ax1sf?Keyword=SI4542DY&FS=True[/URL]...Leave a comment:
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Re: Viewsonic VA2431wm bad cap replaces, new problem
Oh yeah I just finished testing the MOSFETs and I was typing up the following reply:
Ok I did some readings with my multimeter on Q805 and Q806 (AO4620). Both chips are wired more or less the same with pin 5-8 bridged. Between Q806 Pin 5, 1, 3 and 4 show no resistance, while Q805 does not. So it appears Q806 is toast (and it looks like it is toast from it's appearance too.)
Is there a substitute for AO4620 that mouser or some other US vendor stocks? I did see SI4542DY listed as a replacement...Leave a comment:
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Re: Viewsonic VA2431wm bad cap replaces, new problem
Oh yeah I mean transformers, whoops.
Attached is a picture of the bottom of the board. It does appear that at least one of the ICs near the inverter transformer look like they have blots....Leave a comment:
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Viewsonic VA2431wm bad cap replaces, new problem
Hello. I inspected a power board for a VA2431wm that blue led was constant but wouldn't turn on. On further inspection the cap near PT801 was bulging, so I replaced that cap with a NICHICON - HD Series UHD1E102MHD and 2 other caps that were also 1000 uF 25 Volts.
When I put the monitor back together and plugged it in the blue turned on, but when I pushed the power button the blue led would turn off and on every 2 seconds or so. I removed the board and tried pluggin it in again and I was able to hear a short whistle sound every time the LED went out.
I tested the... -
Re: New Members - please post your introductions here
Hello. I'm a robot with non functioning arms. My Viewsonic VA2431wm isn't doing that hot either...Leave a comment:
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