# HG changeset patch # User David Douard # Date 1571437938 -7200 # Node ID fb878b77337784a09654d6b1b5e05c399cd6f88d # Parent 6d0820cef44624a730a55feb24867bed2b584a01 new post: fixing the Dell 2407 diff -r 6d0820cef446 -r fb878b773377 content/dell2407.rst --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/content/dell2407.rst Sat Oct 19 00:32:18 2019 +0200 @@ -0,0 +1,209 @@ +====================== + Dell 2407WFP Monitor +====================== + +:author: David Douard +:Category: Electronics +:Tags: LCD, Display, PSU, Dell, 2407WFP + +A had a non-working Dell 2407WFP LCD Monitor in my stash for quite a long time. +I recently decided to see if I can fix it. It is a quite old but pretty nice +24" LCD monitor, with a 1920x1200 resolution. + +The symptom was the nice kind: dead. No light, no LED, no power consumption. + +Presentation +============ + +The enclosure is reasonably easy to disassemble: 4 screws on the back, then the +usual plastic clips to unclipse all around the enclose. The result is a very +standard view for these LCD monitors: a big metallic enclosure: + +.. image:: {static}images/dell2407wfp/back.jpg + :alt: Back of the Dell 2407WFP + + +When removed, the also very classic view on the boards: + +.. image:: {static}images/dell2407wfp/back-pcbs.jpg + :alt: PCBs of the Dell 2407WFP + +Since there is nothing at all, the first and most probable place to start +looking is the PSU: + +.. image:: {static}images/dell2407wfp/psu.jpg + :alt: PSU of the Dell 2407WFP + + +Diagnostic +========== + +Inspecting the PSU, the first culprit (and the probable origin of the failure) +is pretty obvious: + +.. image:: {static}images/dell2407wfp/badcap.jpg + :alt: Bad cap on the Dell 2407WFP + +This one is dead, right, but the question is if it died alone (very unlikely) +or if it took a series of other parts with it. + +Using the multimeter in diode mode, I immediately found a dead fuse (good sign, +might have done its job and protect some other parts on the PSU... or not), but +also a dead MOSFET (Q651, the one on the PFC stage) and maybe more: + +.. image:: {static}images/dell2407wfp/dead-parts.jpg + :alt: First batch of dead parts on the Dell 2407WFP PSU + +At this point, finding datasheets for the controller chips on this board looked +like a good idea. Most of the time, these PSU designs are very close to the +application circuit described in the datasheets. + + +The schematic +------------- + +There 2 controller chips on this PSU, the classic pair with a primary PFC +controller (L6561D) in charge of providing a nice B+ DC rail for the PWM +controller (NCP1200A) driving the main transformer. + +I could easily find datasheets for these 2 chips. But the noce thing when +fixing such a mass produced device is that obviously some other people already +had a similar failure to fix. + +It seems that the problem my monitor suffered is a very common one. I found a +`long thread `_ +(obviously on https://www,badcaos.net) where people discuss this flaw and their +quest for fixes. Which led me to a PDF with the full schematic of the PSU +(which is in fact a BenQ brand). + +The first stage of the PSU, around the L6561D controller looks like: + +.. image:: {static}images/dell2407wfp/psu-schematic-p1.svg + :alt: Schematic of the first (PFC) stage of the PSU of the Dell 2407WFP + +And the regulation stage: + +.. image:: {static}images/dell2407wfp/psu-schematic-p2.svg + :alt: Schematic of the second (PWM + secondary) stage of the PSU of the Dell 2407WFP + + +For the record, here are the typical application schematics from datasheets: + +.. image:: {static}images/dell2407wfp/L6561-AN.svg + :alt: Typical application schematic of the L6561 PFC controller. + +As tou can see, it is very similar to the first page of the schematic above. +This later have the extra power button management circuit, and a few details +and compenent values are different, but overall, a very close application of +the typical application schematic (as expected). + +And for the PMW stage, I could not find such a typical application circuit more +advanced than this very basic one (from the datasheet): + +.. image:: {static}images/dell2407wfp/NCP1200A.svg + :alt: Typical application schematic of the NCP1200A PWM controller. + +However some interesting details and circuit improvements can be found in this +`application note `_. + + + +Dead parts +---------- + +Having Q651 dead, I started looking for other victims of the deadly C605 +electrolytic capacitor. I quickly found a few more parts, especially R670 +(0.22R 3W). From there, I bought a bunch of parts, obviously the one already +mentioned plus a few more references that were listed by a few people on the +thread list on badcaps (15v zener diodes, 4148 (SMD), and PMBT2907 (PNP) +transistor for Q602). I also ordered a few replacement parts for IC601 and +IC651 since they had also probably suffered from the failure. + + +I first replaced the obviously failed components (Q651, C605, R670 and the +fuse). I probed all the transistors and diodes I could. Even the controler +chips did not seem obviously wrong (no short legs). + +I applied gradually power (via an autotransformer) watching at power +consumption. Nothing wrong, no magic smoke. And even 19v on the output rail! + +More dead parts +--------------- + +So I attached a bunch of power resistors to the 19V output rail, which made the +PCB rapidly start to smell and smoke. + +Something was wrong, not catastrophic (no big explosion nor massive smoke, but +still). + +I finally found the smoke was generated by... the earth wire which was touching +the input NTC! This later was getting very hot. + +So, it looks like it worked fine as long as I did not load the output. +Interesting. From there, the MOSFET transistor driving the PFC stage (Q651) +was dead again. + +So I decided to replace IC651 (the PFC controller, L6561D). And since I had not +that much spare STP10NK60ZFP transistor for Q651, I decided to try first with +some junk parts from a PCB laying around, on which are many APT8075BN: + +.. image:: {static}images/dell2407wfp/junk_pcb.jpg + :alt: The PCB from which I took an APT8075BN as test Q651 replacement. + +The leads qre not exactly the same spacing, but I managed to do something: + +.. image:: {static}images/dell2407wfp/apt8075bn.jpg + :alt: The APT8075BN used as test Q651 replacement. + + +Which resulted in a rather acrobatic setup: I did not want to fight to make it +fit nicely enough that I can screw it on the heatsink (plus it is not +insulated, like the original transistor, so I would have had to find an +insulator. I have some, but finding them would have required a bit fo digging +in my overcrowded empire of dirt). + +The resulting setup looks like: + +.. image:: {static}images/dell2407wfp/psu-repaired-1.jpg + :alt: The APT8075BN used as test Q651 replacement. + +However, before applying power again, I checked all the silicon components once +more. And I discovered (what I missed the first time) that Q653 was also dead. + +The problem was I had no proper SOT23 replacement part for it. THe good news is +I do have a few 2N7000 that can be used, but are TO92 packages. +So I did a bit of surgery: + +.. image:: {static}images/dell2407wfp/hack.jpg + :alt: The APT8075BN used as test Q651 replacement. + + +Fixed +----- + +Applying power again, the 19V is back when no load is applied to the 19V rail. +And stays alive when I draw current (1A). + +I plugged it back in the monitor, the green LED lit as well as the display +itself showing the 'No signal detected' message box! + +.. image:: {static}images/dell2407wfp/alive-1.jpg + :alt: It's alive! + +I replaced the temporary Q651 transistor with the proper reference, checked the +result, then put everything back together. + +.. image:: {static}images/dell2407wfp/alive.jpg + :alt: It's alive! + + +However, before closing the box, I did a few tests and measurements, for the +fun. I found the reason for the properly working 19v rail when unloaded at the +beginning: in fact, the L6561D PFC chip is only turned on when some load is +detected by the NCP1200A controller. This allows the standby power consumption +of the monitor to be very low. I believe this is done via the Vcc1 signal that +goes from the second stage (PWM controller) to the power on circuitry on the +PCF stage (Q654, R678, R656 and the transisor part of the IC652 optocoupler), +which only applies power to IC651 (the L6561D PFC controller) when needed. + +A nice monitor. Definitly not for my desk ;-) diff -r 6d0820cef446 -r fb878b773377 content/eip545b_firmware.rst --- a/content/eip545b_firmware.rst Thu Oct 17 00:13:50 2019 +0200 +++ b/content/eip545b_firmware.rst Sat Oct 19 00:32:18 2019 +0200 @@ -13,8 +13,8 @@ fix a few issues I have encountered in my unit, as related in previous `previous part <{filename}/eip545b.rst>`_. -**It will be updated** as long as I make progress on disassembling and -understanding the firmware. +**It will be updated** as I make progress on disassembling and understanding +the firmware. Original Firmware diff -r 6d0820cef446 -r fb878b773377 content/images/dell2407wfp/L6561-AN.svg --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/content/images/dell2407wfp/L6561-AN.svg Sat Oct 19 00:32:18 2019 +0200 @@ -0,0 +1,1482 @@ + + + +image/svg+xmlNTC2.5 +83BRIDGE W04M +R1750 kC11 µF400VR310 kC29 22 µF 25V +FUSE4A/250V +R4180 kD81N4150D2 1N5248BR14100 C5 12 nFR668 k +T +56 +L6561 +7 +21 +R733 +MOS STP8NM504 +R11 750 k +C6 47 µF 450V +Vo=400V Po=80W +- +Vac(85V to 265V) +R9 0.411WR13 9.53 k +- +C4100 nFC210nF +D1STTH1L06 +D3 1N4148C710 µF35 VR15220 R1691 k +R50 12 kC3 470 nF +R2750 k +R5180 k +R10 0.411W +R12 750 k +C231 µF + \ No newline at end of file diff -r 6d0820cef446 -r fb878b773377 content/images/dell2407wfp/NCP1200A.svg --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/content/images/dell2407wfp/NCP1200A.svg Sat Oct 19 00:32:18 2019 +0200 @@ -0,0 +1,449 @@ + + + +image/svg+xmlEMIFILTER +UNIVERSALINPUT+ ++ +NCP1200A ++ +V +OUT +AdjFBCSGND +HVV +CC +Drv12348765 +1N4007* + \ No newline at end of file diff -r 6d0820cef446 -r fb878b773377 content/images/dell2407wfp/alive-1.jpg Binary file content/images/dell2407wfp/alive-1.jpg has changed diff -r 6d0820cef446 -r fb878b773377 content/images/dell2407wfp/alive.jpg Binary file content/images/dell2407wfp/alive.jpg has changed diff -r 6d0820cef446 -r fb878b773377 content/images/dell2407wfp/apt8075bn.jpg Binary file content/images/dell2407wfp/apt8075bn.jpg has changed diff -r 6d0820cef446 -r fb878b773377 content/images/dell2407wfp/back-pcbs.jpg Binary file content/images/dell2407wfp/back-pcbs.jpg has changed diff -r 6d0820cef446 -r fb878b773377 content/images/dell2407wfp/back.jpg Binary file content/images/dell2407wfp/back.jpg has changed diff -r 6d0820cef446 -r fb878b773377 content/images/dell2407wfp/badcap.jpg Binary file content/images/dell2407wfp/badcap.jpg has changed diff -r 6d0820cef446 -r fb878b773377 content/images/dell2407wfp/dead-mosfet.jpg Binary file content/images/dell2407wfp/dead-mosfet.jpg has 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+F601250V 4A +R678 +10K ++ +C6242.2U K +10V +1 +2 +Q6512SK3502 +D +G +S +R670 +0.22 +C6250.1U K +C6300.1u +R674 +8.25K F +C6210.01U K +C626470P K +D655LL4148 +A +K +L6561D +IC651L6561D013TR +VCC +8 +MULT +3 +COMP +2 +GND +6 +CS +4 +INV +1 +GD +7 +ZCD +5 ++ +C622 +<Spec> +1U 100V +1 +2 +C6290.1u ++ +C6232.2U K +10V +1 +2 +R672 +232K F +R677 +1K J +L601 +19MH +1 +4 +2 +3 +C6281U +R660 +1M F +C6010.22U M +RIP +RIP +Vcc1 + \ No newline at end of file diff -r 6d0820cef446 -r fb878b773377 content/images/dell2407wfp/psu-schematic-p2.svg --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/content/images/dell2407wfp/psu-schematic-p2.svg Sat Oct 19 00:32:18 2019 +0200 @@ -0,0 +1,6885 @@ + + + +image/svg+xml4 +3 +2 +1 +GND +N5 +N8 +N11 +N7 ++19V ++19V_IN +BURST_ADJ ++19V_IN +Vcc1 +C7101000P K +R719 +10K +Q6012SK3548-01SC +D +G +S +ZD603TZMC27 +A +K +R609 +1M F +R612 +47 +D607LL4148 +A +K +D602EGP10D-LF +A +K +L612 +Z45/100MHZ +Q6022N3906S +C +E +B ++ +C611 +50V +47U +1 +2 +R615 +0.22 +R625 +10K 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