Re: Mag LT916s Model 900p 19" LCD dropping like flies
Continuity between any pins on a bridge rectifier means it's blown and must be replaced with a possibly beefier one (more current and voltage). The reading of 0.564V is from the only diode that's not blown...
Regenpak
Mr.Power Supply
Last Activity: 07-23-2019, 05:52 AM
Joined: 06-04-2010
Location: Amsterdam
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Re: ViewSonic VX1940w
CHEAPO
(sorry - couldn't help it...)Leave a comment:
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Re: NEC Accusync LCDV9 - no power totally dead
The SG3842 (AKA UC3842) pin 7 fluctuating between 10 and 16 volts means that it hovers between its startup voltage (16 V) and undervoltage lockout (UVLO - 10 V). This could be caused by the capacitor C807 being bad (use of low ESR unit is mandatory). It could also be that there's an overload condition causing it to shutdown and then startup again. A test I like to do is to power the circuit from an external power supply while monitoring the feedback optocoupler I802. If the TL431 zener (next to R825) starts to draw current you've hit...Leave a comment:
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Re: SDT-S-112DMR relay - where to buy in qty = 1
Is it just me or are there two Q901s in this weird amp?!? There's a regulator Q901 (2SA1271Y, page 73, -30V for the display) and the relay transistor Q901 (2SC2785Y, page 76) that switches RY94 (main power) on. Kinda split personality or something.Leave a comment:
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Re: Samsung Syncmaster 940BX backlight problem - Need help please.
Finally got to try the board with the CCFL tubes attached. It was indeed clear that the two transformers should have been in parallel as the OLP kicked in after the dreaded two seconds. When I resoldered the wires I was awarded with a "check cable" message floating across the screen.
Apologies for the out-of-focus connections but I already closed the monitor when I discovered that......Leave a comment:
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Re: Samsung Syncmaster 940BX backlight problem - Need help please.
Actually, it's quite simple. The circuit will adjust itself so that EA_IN is at 2.5 volts. Which means 5.2 volts at FB. If it doesn't get there it goes OTP (Open Tube Protection). I'll try tying the primaries in parallel after all. And use an external power supply starting at a lower voltage.Last edited by Regenpak; 06-09-2010, 01:39 AM.Leave a comment:
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Re: Samsung Syncmaster 940BX backlight problem - Need help please.
No, I already tried that and that didn't work. The primary inductance seemed too low. But maybe it has to be that way anyway. The display as it is now seems too dim.
In any case, to make things a bit easier to understand, this is the original schematic:
So nice of Suntronics to keep the component numbering......Leave a comment:
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Re: Samsung Syncmaster 940BX backlight problem - Need help please.
So I made one of the most geek-esque fixes in my thirty-year career of repairing electronicks. I swapped the offending transformer out with two (!) transformers liberated from a donor board. No idea where that came from, prolly from a monitor with a cracked panel or something:
According to the [url=http://www.alldatasheet.net/datasheet-pdf/pdf/135703/FAIRCHILD/FAN7314.html]datasheet[/url], the output transformers are symmetrical. The Suntronics board uses one transformer with two secondaries,...Leave a comment:
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Re: Samsung Syncmaster 940BX backlight problem - Need help please.
Oh. This happens very often. Thought I was onto something new. Still going to try if I can fix it. I have 0.10 mm wire ready.Leave a comment:
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Re: Samsung Syncmaster 940BX backlight problem - Need help please.
Sonofabitch... it's the transformer. This is unexpected. The PSU board is Suntronix model # SIP-U5F(M) FWIW. It's nice of Suntronix to have followed the Fairchild FAN7314 datasheet almost to the letter, even using the same component numbering as the application schematic. The AP4525GEH half-bridge MOSFET is fine, although the PCB is a bit discolored. The DC values of the XFMR are OK, primary zero, secondaries 1.2k. Even so, using 390k/1W resistors as dummy load for the CCFLs and an external 15V PSU the OLP gets triggered....Last edited by Regenpak; 06-05-2010, 07:59 AM.Leave a comment:
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Re: Samsung Syncmaster 940BX backlight problem - Need help please.
I'm just starting here myself... I already checked the caps and they're fine, I believe it's a matter of a blown tube or something. This weekend I'll do more testing. The 2 sec symptom suggests an OLP (Open Lamp Protection) trip. See the datasheet for an example schematic, very helpful. My display is a 940N though.Leave a comment:
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