Re: Cisco 2960-CX Not providing POE
As far as the source for each FET, all 8 of them have roughly -33v DC being supplied to each FET.
The drains, on the other hand, seems hit or miss. Q4803 & Q4804 are not "on" - fluctuating around 3v output voltage. This is with port 1 powering a POE device.
When I remove the device, nothing changes.
I'll replace Q4803 & Q4804 and see what happens....
fuxxy
Badcaps Veteran
Last Activity: 11-13-2023, 04:53 PM
Joined: 01-15-2013
Location: Houston, TX
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Re: Cisco 2960-CX Not providing POE
oh that sounds logical.
I was thinking they used some weird setup like one fet for each side of the power pairs or something....Leave a comment:
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Re: Cisco 2960-CX Not providing POE
Progress!
Took my multimeter in basic continuity (beep mode), U4701 was the only FET that read short across source and drain. I'm a novice and can't find datasheets, so I'm interpreting source and drain as the two of the three larger sinked pads. These are 8-pin SMD FETs, with 4 pins bridged together, as well as 3 other pins bridged together. The last pin I'm assuming is the gate.
I replaced U4701 (again) and Q4801 with similar components from my donor board. They're not quite exact, but appear to have the same footprint...Last edited by fuxxy; 03-06-2023, 09:48 PM.Leave a comment:
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Re: Cisco 2960-CX Not providing POE
sweet, I can work with that. Let me do some testing...Leave a comment:
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Re: Cisco 2960-CX Not providing POE
Reference board from a Cisco WS-C2960X...Leave a comment:
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Cisco 2960-CX Not providing POE
First off, I'm sorry if this is the wrong subforum - None of the others seemed to fit the description.
I've got this Cisco 2960-CX. It works flawlessly otherwise, but won't provide POE to the ports.
On initial inspection, U4701 (An SI3458) has a physical hole in the die. I replaced with another chip out of a dead 2960, and it immediately popped a new hole.
All I've been able to pull up are datasheets for mosfets, and I'm not quite convinced this is a simple FET.
Popping the die implies an overcurrent downstream, correct?
...Last edited by fuxxy; 03-05-2023, 07:17 PM. -
UN55D6000 - Multiple issues, now no standby light
UN55D6000 I've posted about before.
Initially had bad backlights, of which both entire strips were replaced.
Then TV started not staying off. Every poweroff command was recognized, TV would power off then power right back on, even with nothing attached.
Now, no output at all. No red Power LED, No response to remote. No clicking or coil whine.
From other threads, tested various outputs on the PSU. Noticed that when the mainboard was unplugged, the backlights would turn on.
Backlight Connector CNL802:
Logic board unplugged:
pin...Last edited by fuxxy; 12-23-2022, 08:51 PM. -
Re: (SOLVED) - ONN 100012588 No Power, Then Rebooting After Main Board Change
Sorry, I guess I couldnt be bothered to read the datasheet.
Q306 & Q307 are schottkey barrier diodes. They are tested just like any other diode - They will conduct in one polarity, and insulate in the opposite polarity.
The only caveat for the MBRB20100CT is that there are 2 diodes in one package. Since the board is designed so the anodes are connected, the whole package functions as a single diode. The package would need to be removed from the board to test each diode in the package...Leave a comment:
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Re: Onn 70" Class JE695R3HB9L - No backlight
Found another surge of energy, and read up on some other threads.
currently following [url]https://www.badcaps.net/forum/showthread.php?t=110193&page=3[/url] , since it seems to detail a common issue on these power supplys.
The same is true for my board. R355 was actually two resistors stacked in parallel, both marked 2R20 = 2.2ohm. Removed them and each resistor read 12.2 ohms out of circuit. Tested again a few mins later, now reads 11.6 ohms.
R354 is a single...Leave a comment:
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Re: (SOLVED) - ONN 100012588 No Power, Then Rebooting After Main Board Change
Can you elaborate a bit more on the process that led to conclusion of q306 and q307 being blown?
I am currently working on a similar TV - ONN 65 inch that originally wouldn't show picture - replaced all backlight strips and now all backlight LEDs are lighting uniformly and read the same voltage on my backlight tester. Now I get a single flash from the backlight when pressing the power button.
This TV also shocked the hell out of me when attempting to disconnect the backlights...Leave a comment:
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Re: Onn 70" Class JE695R3HB9L - No backlight
Replaced all 10 LED strips again.
After plugging the set in, I get a single flash from the backlights when powering on, then nothing. Picture is displayed if I shine a light at an angle.Leave a comment:
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Re: Onn 70" Class JE695R3HB9L - No backlight
Finally got all the strips replaced. Accidentally damaged one of the strips while trying to slide it into the slot. Slipped and bent the strip about 90 degrees, breaking the copper traces on top of the substrate.
Fixed it by scratching away the enamel about an inch away from the crack on either side, then soldered a bare wire on each leg. added heatshrink on the wires, then soldered the other side.
FINAL RESULT: TV turns on! Yaya!
BUT WAIT THERES MORE!
The backlights no longer...Leave a comment:
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Re: Onn 70" Class JE695R3HB9L - No backlight
New strips have arrived!
Did some testing, mabye it's useful for others? Hooked up to my benchtop constant-current PSU.
With a single strip (6 LEDs in series) attached to the PSU. Judging from the markings on the power board 100-126v is supplied by the TV. With a generic forward voltage of 3V, I'll assume the two "arrays" of 36 LEDs are wired in parallel. 100V / 36 LEDs gives me a forward voltage of 2.7777 volts. 126V on the same 36 LEDs gives a forward voltage of 3.5V. With only 6 LEDs, I shouldn't...Leave a comment:
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Re: Onn 70" Class JE695R3HB9L - No backlight
Understood and agreed. I have already ordered a set if replacements, figured I'd attempt a compo e t-level repair in the meantime just to see if it worked.
I noticed In addition to a voltage marking 9. the PSU, there's also an amperage for the backlight circuit. Just as a test, and to solidify the hypothesis, I have a regulated power supply I can attach the strips to to measure their current draw at target voltage. Ive seen signs of carbon deposits on the metal behind the strip connections, it's probably as you describe....Leave a comment:
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Re: Onn 70" Class JE695R3HB9L - No backlight
Voltages on PSU board - powered ON
3 large main caps - 370v DC
GND
ADJ - 1.712v
BK - 3.19v
+5V - Not Connected
PSON -2.94v
+5VSB - Not Connected
NC - Not Connected
ND - Not Connected
GND
GND
GND
+12V - 11.98v
+12V - 11.98vLeave a comment:
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Re: Onn 70" Class JE695R3HB9L - No backlight
I've identified about 20 individual LEDs in the backlight array. Only 3 failed to product any light at all (shorted). The others seemed to require more initial voltage to produce light (they were slow to turn on). All of these individual LEDS have been replaced on the existing strips.
The single backlight flash still remains. I"m also getting a red status LED giving a "2-blink" pattern - I'm assuming indicates some sort of error?
I'm still wondering if the PSU itself could be damaged.
...Last edited by fuxxy; 09-29-2022, 03:24 PM.Leave a comment:
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Re: Onn 70" Class JE695R3HB9L - No backlight
Dissasembled the panel. Attached backlight tester.
This panel arranges the backlight LEDs divided vertically - with the left half powered by one connector, and the right half powered by the other.
3 LEDs didn't light on one half. The half that is working normally shows 95.5v on my backlight tester.
Working on removing the white plastic to determine the PCB layout.
Edit Arranged thusly:
Each strip has 6 LEDs in series.
Each strip is connected to the next strip...Last edited by fuxxy; 09-29-2022, 01:47 AM.Leave a comment:
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Re: Onn 70" Class JE695R3HB9L - No backlight
Building up external LCD strips in indeed an option.
I guess there's no need to use actual backlight LEDs when testing via this method? As long as the forward voltage is 3v, I suppose it shouldnt matter if 'regular' 3mm LEDs are used on , say, stripboard.
As you say, as long as they are wired identically to the original.Leave a comment:
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Onn 70" Class JE695R3HB9L - No backlight
This unit will flash the backlights once on powerup. Still responds to remote commands, and plays audio.
I have a backlight tester.
Two backlight connections to PSU. I have them connected opposite of OEM in the picture.
CON301 - Red/White wire - tests 95.5v on my backlight tester.
CON302 - Red/Gray wire - tests 92.5v on my backlight tester.
Is a 3v difference between strips enough cause to tear down the panel? It doesnt trigger any red flags for me. The backlight flash is enough for me to knee-jerk blame bad backlight strips as a first...Last edited by fuxxy; 09-28-2022, 11:27 PM. -
Re: Samsung LN46A850 - Displays image that degrades, then reboots
It's definitely not input related, as the same thing happens in the TV settings menu.
I was expecting to see some bulged caps, but everything appears visually normal, apart from some light heat discoloration. I checked the 2 fans as well and they still spin freely after 10+ years!
I'll check those voltages in the morning and report back.Leave a comment:
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