comparison: content/dell2407.rst
content/dell2407.rst
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| 64 | 64 |
| 65 There 2 controller chips on this PSU, the classic pair with a primary PFC | 65 There 2 controller chips on this PSU, the classic pair with a primary PFC |
| 66 controller (L6561D) in charge of providing a nice B+ DC rail for the PWM | 66 controller (L6561D) in charge of providing a nice B+ DC rail for the PWM |
| 67 controller (NCP1200A) driving the main transformer. | 67 controller (NCP1200A) driving the main transformer. |
| 68 | 68 |
| 69 I could easily find datasheets for these 2 chips. But the noce thing when | 69 I could easily find datasheets for these 2 chips. But the nice thing when |
| 70 fixing such a mass produced device is that obviously some other people already | 70 fixing such a mass produced device is that obviously some other people already |
| 71 had a similar failure to fix. | 71 had a similar failure to fix. |
| 72 | 72 |
| 73 It seems that the problem my monitor suffered is a very common one. I found a | 73 It seems that the problem my monitor suffered is a very common one. I found a |
| 74 `long thread <https://www.badcaps.net/forum/showthread.php?t=14882&page=1>`_ | 74 `long thread <https://www.badcaps.net/forum/showthread.php?t=14882&page=1>`_ |
| 75 (obviously on https://www,badcaos.net) where people discuss this flaw and their | 75 (obviously on https://www.badcaps.net) where people discuss this flaw and their |
| 76 quest for fixes. Which led me to a PDF with the full schematic of the PSU | 76 quest for fixes. Which led me to a PDF with the full schematic of the PSU |
| 77 (which is in fact a BenQ brand). | 77 (which is in fact a BenQ brand). |
| 78 | 78 |
| 79 The first stage of the PSU, around the L6561D controller looks like: | 79 The first stage of the PSU, around the L6561D controller looks like: |
| 80 | 80 |
| 90 For the record, here are the typical application schematics from datasheets: | 90 For the record, here are the typical application schematics from datasheets: |
| 91 | 91 |
| 92 .. image:: {static}/images/dell2407wfp/L6561-AN.svg | 92 .. image:: {static}/images/dell2407wfp/L6561-AN.svg |
| 93 :alt: Typical application schematic of the L6561 PFC controller. | 93 :alt: Typical application schematic of the L6561 PFC controller. |
| 94 | 94 |
| 95 As tou can see, it is very similar to the first page of the schematic above. | 95 As you can see, it is very similar to the first page of the schematic above. |
| 96 This later have the extra power button management circuit, and a few details | 96 This later has the extra power button management circuit, and a few details |
| 97 and compenent values are different, but overall, a very close application of | 97 and component values are different, but overall, a very close application of |
| 98 the typical application schematic (as expected). | 98 the typical application schematic (as expected). |
| 99 | 99 |
| 100 And for the PMW stage, I could not find such a typical application circuit more | 100 And for the PMW stage, I could not find such a typical application circuit more |
| 101 advanced than this very basic one (from the datasheet): | 101 advanced than this very basic one (from the datasheet): |
| 102 | 102 |
| 148 some junk parts from a PCB laying around, on which are many APT8075BN: | 148 some junk parts from a PCB laying around, on which are many APT8075BN: |
| 149 | 149 |
| 150 .. image:: {static}/images/dell2407wfp/junk_pcb.jpg | 150 .. image:: {static}/images/dell2407wfp/junk_pcb.jpg |
| 151 :alt: The PCB from which I took an APT8075BN as test Q651 replacement. | 151 :alt: The PCB from which I took an APT8075BN as test Q651 replacement. |
| 152 | 152 |
| 153 The leads qre not exactly the same spacing, but I managed to do something: | 153 The leads are not exactly the same spacing, but I managed to do something: |
| 154 | 154 |
| 155 .. image:: {static}/images/dell2407wfp/apt8075bn.jpg | 155 .. image:: {static}/images/dell2407wfp/apt8075bn.jpg |
| 156 :alt: The APT8075BN used as test Q651 replacement. | 156 :alt: The APT8075BN used as test Q651 replacement. |
| 157 | 157 |
| 158 | 158 |
| 159 Which resulted in a rather acrobatic setup: I did not want to fight to make it | 159 Which resulted in a rather acrobatic setup: I did not want to fight to make it |
| 160 fit nicely enough that I can screw it on the heatsink (plus it is not | 160 fit nicely enough that I can screw it on the heatsink (plus it is not |
| 161 insulated, like the original transistor, so I would have had to find an | 161 insulated, like the original transistor, so I would have had to find an |
| 162 insulator. I have some, but finding them would have required a bit fo digging | 162 insulator. I have some, but finding them would have required a bit of digging |
| 163 in my overcrowded empire of dirt). | 163 in my overcrowded empire of dirt). |
| 164 | 164 |
| 165 The resulting setup looks like: | 165 The resulting setup looks like: |
| 166 | 166 |
| 167 .. image:: {static}/images/dell2407wfp/psu-repaired-1.jpg | 167 .. image:: {static}/images/dell2407wfp/psu-repaired-1.jpg |
| 168 :alt: The APT8075BN used as test Q651 replacement. | 168 :alt: The APT8075BN used as test Q651 replacement. |
| 169 | 169 |
| 170 However, before applying power again, I checked all the silicon components once | 170 However, before applying power again, I checked all the silicon components once |
| 171 more. And I discovered (what I missed the first time) that Q653 was also dead. | 171 more. And I discovered (what I missed the first time) that Q653 was also dead. |
| 172 | 172 |
| 173 The problem was I had no proper SOT23 replacement part for it. THe good news is | 173 The problem was I had no proper SOT23 replacement part for it. The good news is |
| 174 I do have a few 2N7000 that can be used, but are TO92 packages. | 174 I do have a few 2N7000 that can be used, but are TO92 packages. |
| 175 So I did a bit of surgery: | 175 So I did a bit of surgery: |
| 176 | 176 |
| 177 .. image:: {static}/images/dell2407wfp/hack.jpg | 177 .. image:: {static}/images/dell2407wfp/hack.jpg |
| 178 :alt: The APT8075BN used as test Q651 replacement. | 178 :alt: The APT8075BN used as test Q651 replacement. |
| 195 | 195 |
| 196 .. image:: {static}/images/dell2407wfp/alive.jpg | 196 .. image:: {static}/images/dell2407wfp/alive.jpg |
| 197 :alt: It's alive! | 197 :alt: It's alive! |
| 198 | 198 |
| 199 | 199 |
| 200 However, before closing the box, I did a few tests and measurements, for the | 200 However, before closing the box, I did a few tests and measurements, for |
| 201 fun. I found the reason for the properly working 19v rail when unloaded at the | 201 fun. I found the reason for the properly working 19v rail when unloaded at the |
| 202 beginning: in fact, the L6561D PFC chip is only turned on when some load is | 202 beginning: in fact, the L6561D PFC chip is only turned on when some load is |
| 203 detected by the NCP1200A controller. This allows the standby power consumption | 203 detected by the NCP1200A controller. This allows the standby power consumption |
| 204 of the monitor to be very low. I believe this is done via the Vcc1 signal that | 204 of the monitor to be very low. I believe this is done via the Vcc1 signal that |
| 205 goes from the second stage (PWM controller) to the power on circuitry on the | 205 goes from the second stage (PWM controller) to the power on circuitry on the |
