Re: HP w2207h Intermittent Misbehavior
I just got one of these with similar symptoms, and it was due to misbehaving microswitches in the button panel. Unplugging button panel stopped this madness. I found a thin film of something inside one of the microswitches which was causing ~30K resistance, enough to make it think that menu or the source select was being pressed. I cleaned this out of the microswitch and it seems to work now. I'd have replaced them but didn't want to try to find a microswitch of the same dimensions (I popped them open by cutting the tops off the melted plastic...
blargg
Senior Member
Last Activity: 04-10-2023, 06:42 PM
Joined: 02-11-2010
Location: Central Texas, USA
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Re: HP W2408H No Power (Surge) Repair - Success
@agie: also, start a new thread, so that this one can be for ones that failed due to the thermistor.Leave a comment:
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Re: Acer X223W - Repair or Replace
I think the person in the YouTube video was mistaken and it's not an LED-backlit monitor, and it wasn't just a year old. That model seems to be from 2008. The wires to the backlights in the video were only a pair, which is very unlikely for LEDs which use several strings and thus several wires. Those were CCFL wires. Back of power board also looks like that of a CCFL power supply, with several far-spaced components on the right side.Leave a comment:
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Re: Would bad caps cause this display?
Yes, feedback is an important part of the repair process, so everyone else (perhaps yourself in a few years) knows what problem these symptoms were a result of.Leave a comment:
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Re: Acer S271HL bid LED monitor goes partly/fully dark, flashlight shows image: SOLUT
Final update: I finally did the proper approach. I cleaned the clogged vias out with a very thin needle. I scraped the green coating off the copper trace around both sides of the via. Then I stripped some 30-gauge wrapping wire and threaded pieces of that through the vias. I trimmed the ends to about 2mm on both sides, bent them down, and soldered them to the exposed trace.
As is most visible in the last picture in the lower-left, I avoided having to scrape the trace bare when the...Last edited by blargg; 10-04-2014, 10:02 PM.Leave a comment:
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Re: Acer S271HL bid LED monitor goes partly/fully dark, flashlight shows image: SOLUT
Backlight mod worked out great to allow lower brightness, and I was able to add [url=http://forums.blurbusters.com/viewtopic.php?p=10171#p10171]strobed backlight mode to greatly reduce motion blur[/url] (sample-and-hold).
I still have gotten occasional momentary black hiccups, I think due to the remaining vias I haven't jumpered. I'm going to order some tiny PCB drill bits and add my own vias next to the bad ones, and remove the jumper wires. I think this will be more reliable and...Leave a comment:
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Re: Samsung T240HD backlight never lights, flashlight shows image
Monitor still working, so I think it's solid. First repair I've done where I actually ordered parts, rather than scrounge something from the junk PCBs I've collected over the years. Thanks again!Leave a comment:
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Re: Acer S271HL bid LED monitor goes partly/fully dark, flashlight shows image: SOLUT
Updated the PCB photos to show the problematic vias I ran jumpers to fix (yellow circled) and ones I didn't run jumpers for (purple). These are basically single vias which carry a signal, where degradation of it can disrupt the signal. This is in contrast to the redundant ones for the ground/positive planes, which just serve as shielding/secondary connection. The remaining purple vias could use redundant jumpers, except the center vertical one (seen on back), which goes to an unused 19V segment...Last edited by blargg; 09-17-2014, 10:49 AM.Leave a comment:
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Acer S271HL bid LED monitor goes partly/fully dark, flashlight shows image: SOLUTION
tl; dr: LED driver board's vias were faulty and would gain tens of ohms when board heated up. Via for ground to resistor divider of voltage feedback would heat up from nearby inverter components, and ground voltage would jump several tenths of a volt, triggering overvoltage and disabling LED strings until all were off. Fix is to run extra ground wire to that point.
I saw this broken Acer S271HL bid monitor on craigslist for $30 and figured I'd give repairing it a shot. First I found that there's very little information about problems, repair, or available parts for this model. The...Last edited by blargg; 09-17-2014, 12:27 AM. -
Re: i-pad 2 16gb model#a1395
You say no LCD/backlight; do you have signs that it is working at all? e.g. does USB cable link to computer and allow access to its files?Leave a comment:
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Re: Samsung T240HD backlight never lights, flashlight shows image
Parts arrived, I tested new 4506GEH MOSFET combo chip to be sure it was good then replaced old one on the board, and replaced and SEM2005, triple-checked everything, and the monitor is working again. The Vref pin of the new SEM2005 measures 4.98V as datasheet shows it should, so the old one was definitely bad. I avoided running it without the CCFLs connected, as I had done when it failed. I think that might have contributed. SMD stuff really stretches my soldering skills/crappy tools to their limits. Will report back...Last edited by blargg; 09-10-2014, 05:40 PM.Leave a comment:
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Re: Samsung T240HD backlight never lights, flashlight shows image
Haha, it failed after five minutes when I turned it on today (ran for about 12 hours yesterday). Opened it up, at some point it started trying to strike the CCFLs, but the sound wasn't as intense before. 4506GEH (U202) drain is shorted to GND (I isolated it to be sure it wasn't inverter transformer). +15V supply was dropping to 8V when it tried to generate a drive to the transformer, due to this short. $2.00 shipped for a replacement from China (pack of two, so an extra in case I blow second one as well), guess it's...Leave a comment:
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Re: Westinghouse LCM 17v8 - CCFL wires had come loose!
Reviving this thread with an update. This monitor worked for a couple of years after the CCFL resolder, but in mid-2012 was having many faint horizontal bands across the screen which as I remember were less intense on lower brightness. I replaced four electrolytics in the power supply (with generic ones from Fry's Electronics, as I was visiting the person and only there for a few days) and it's worked as the main monitor for their PC up to the present (mid-2014). They must have been bulging as I didn't have any tools with me,...Leave a comment:
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Re: Samsung T240HD backlight never lights, flashlight shows image
I'm dumbfounded, but it's working now. tl; dr: I did some lengthy soldering on pin 16 of the chip but didn't modify anything, and it works now.
I wanted to be absolutely sure that the Vref pin wasn't connected to something else that was loading it down (it only supplies 10mA), before I ordered a replacement chip. I decided to desolder that lead to isolate it from the PCB. I couldn't get it lifted well and it got shorted with the lead next to it, and heated the chip a whole bunch (I'm terrible with lead-free...Leave a comment:
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Re: Samsung T240HD backlight never lights, flashlight shows image
Yeah, F301 is good. It's between U201 and the switching supply, and U201 gets power.Leave a comment:
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Samsung T240HD backlight never lights, flashlight shows image
Samsung T240HD 24" LCD monitor. Backlight never comes on, not even a flash. Flashlight shows menus etc. working fine.
See pictures for measurements I made.
Connected each of the four backlight CCFLs individually to another inverter and they run for a quarter second, then turn off. They seem to be running stably for that quarter second, not just flashing for a brief instant when struck by the inverter. I think that they turn off here because they aren't in the metal case that the inverter is in or don't match the characteristics of the inverter, not because there... -
Re: Dell 2000FP Blank screen problem
I've found that the /RESET line to the flash chip is low. Tracing it to a couple of transistor inverters, I find that some control signal is low into the pair of inverters, when it should apparently be high. Holding the /RESET to flash doesn't allow it to boot, so I'm thinking that whatever is making the earlier control signal low is closer to the cause. It may also explain the LEDs delaying coming on if it's been off for a while, some capacitor somewhere discharging. I couldn't find where this control signal goes elsewhere on the board thou...Leave a comment:
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Re: Dell 2000FP Blank screen problem
I've been trying to get my 2000FP working again, now that I have an o-scope. It's followed the same pattern several times:
* When I power on, it shows the logo, then menus work, etc. Works for a few hours, then all buttons stop responding. Still works as monitor (as long as I don't turn it off), showing output from PC. Doesn't resync when I change resolutions. So the CPU has crashed, but all the video stuff is working fine.
* If I unplug it and plug it back in, it generally just lights all LEDs and the backlight never comes...Leave a comment:
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Re: Cambridge BassCube 12 blowing relays
After fighting with this protection circuit all day, mapping it out and seeing how poorly it operates, I just bypassed the relay so the amp is always powered, then put the speaker on the relay and manually switch it in after the amp has been on for a few seconds. This eliminates all popping and nasty stuff, and it works perfectly. I also moved the power resistors from the underside of the board by the zeners to the copper trace side on top, which gets the heat away from the zeners and other sensitives there. Either this thing is way overpowered,...Leave a comment:
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Re: Cambridge BassCube 12 blowing relays
I wonder whether this is relay system is related to detecting large DC on the speakers, and was failing to work. I could always put the speaker on one of the relay switches, as that would have protected it from these stick DC episodes.
I researched the regulator a bit and found that I could use a 317/337 adjustable regulator, which has an absolute maximum drop of 40V from in to out. In this case it'd be dropping 50V to around 16V, a 34V drop. I'll have to see if I can measure how much current the preamp is using, and the amp....Leave a comment:
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