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16 channel Digital Video Recorder Repair

By on September 22, 2016
video-recorder-fixing

 

 

 

 

 

 

 

 

The repair in this article is about a defect 16 channel Digital Video Recorder for video surveillance. Model DVR-6616. It records video on a internal Sata Harddisk.

The owner had reversed the input polarity by using the wrong Power Adapter and/or used a too high input voltage which blew a Mosfet from type IR (International Rectifier) P025H, furthermore blew open an anti reverse PCKE150 Diode right after the input Power Jack, plus made a bulged 470uF 25V Capacitor (C4) useless.




The IR P025H was clearly a normal single SOP-8 Mosfet because pins 1 to 3 (Source) and pins 5 to 8 (Drain) were connected as usual, while pin 4 was Gate. But I couldn’t find any matching datasheet for this one. Also because any following markings on top were lost.

Obviously the Mosfet was completely blackened by a reverse Input Polarity, why the anti reverse Diode was completely broken open. Which as always smells horrible. And although the Mosfet now was a continuously connected component by an internal low Resistance of about 30 Ohm nothing worked. There was no voltage on any of the connectors, so the device was completely dead. Same thing that very often happens to Laptop Mainboards.

digital-video-recorder-repair

The first thing to do is take pictures so any wrong changes while repairing can be watched back. Like when any copper tracks get burned and so on. In this case when removing the blackened IR P025H Mosfet because that needs to be done no matter what. Including the Bulged (C4) Capacitor. And not finding any datasheet made it more difficult going on without any information. And therefore I also made following little schematic to understand how things were connected. Following the quick

drawing of the conclusive connections on the Power Jack input on the DVR-6616 Board as measured with my Digital Meter.

digital-video-recorder-circuit

Next thing is determining what type of Mosfet was used. First I measured the gate voltage which was about +19V. Then I checked the H.264/16 Channel DVR by connecting a P-channel 4407 Mosfet as replacement. I used 3 wires to spare the Copper layout to connect the 4407 to the already damaged Board. The 4407A already connected through on Source and Drain without the gate even being attached yet. While the LAN leds worked when the gate was still left loose, it therefore clearly was not the right Mosfet type. Also because the Mosfet got quite hot while also the Gate was connected.

Because a P-channel Mosfet clearly did not switch, I knew I had to look for a N-channel Mosfet. Which is also logical because the positive Gate voltage requires a N-channel Mosfet to switch through the Drain with Source connections. And a P-channel Mosfet only switches through on a negative Gate voltage (or in the above test at no Gate voltage at all).

And I found that an IRF7831 N-channel SOP-8 Hexfet Mosfet was the right kind of type Mosfet. Because it worked great and didn’t get hot and all voltages were now present while testing. On Capacitor (C4) I measured 3.3 Volt. On the HDD Power connector I measured 5 Volt and also 18.77 Volt.

But cautioned as I was it turned out that the owner had given me the wrong 19V Power Adapter. On the back of the cabinet it clearly stated only to use a model 12V 4A Adapter. And because the 18.77V obviously was much to high for the HDD, I was glad I had not yet connected it to the Board. But the HDD tested previously fine when I had attached the Sata Drive to my PC. On next Photo the badly burned IR P025H Mosfet and next to it the bulged Capacitor are shown, and on the left the broken open anti polarity reverse diode.

bulged-capacitor

sticker-risk-electric-shock

Next Photo show the replacement Capacitor 470uF 25V (C4) and the new Mosfet IRF7831. And following Photo shows the 16-channel DVR on the inside with the removed Board.

bad-capacitors

mainboard-digital-video-recorder

On above Photo the Yellow arrow on the bottom points to the 5V (4H1 17-50 marking) stabilizer. And the black arrow is pointing up to the DS1307 clock/calendar chip.

Next Photo shows the Power Input and other connectors as they are present on the back of this 16 channel Digital Video recorder.

circuit-board-video-recorder

About Mosfets : these are kind of digital electronic switches. And all laptops do have them on their Mainboards. If we inspect the Mosfet datasheet we can learn how they work. For instance an AO 4406 type Mosfet of manufacturer Alpha & Omega switches through Source and Drain when the Gate Voltage is a positive voltage. And a type AO 4407 works completely opposite because it switches through pins Source and Drain when the Gate voltage is a negative value.

And some single Mosfets also have an integrated ESD protection circuit between Gate and Source that protects the very sensitive Gate from high voltages up to 3800 Volt. And of course there are also dual Mosfets that also are placed in the same kind 8 pins SMD housing. Most Laptop Mosfets can only be used up to around 20V and switch through around 20A or less.

After I successfully replaced the bad Mosfet and the bulged Capacitor, all voltages were present on the DVR Board. And I gave the completely to my satisfactory working DVR-6616 back to the owner, by explicitly telling him NOT to use the wrong 19V adapter or another wrong polarized adapter again. Since that now immediately would destroy the internal Sata Harddisk controller Board. Because the 12V comes already regulated from the 12V 4A input Adapter, and 19V easily would kill the Sata Drive since all the input voltages are present again.

Next Photos show the working voltages and the repaired DVR Board. Below the almost 19V on the Molex HDD Connector when using the wrong customer’s Adapter. (He had not given me the right 12V adapter yet. So I didn’t connect it to the Sata HDD yet, as I wrote previously).

digital-multimeter

Previous Photo shows the correct HDD 5V voltage on the Molex Connector. On the left Photo below

the 5V Regulator with Marking 4H1 17-50.

circuit-board-repair

The 3.3Volt can be measured on Capacitor C4.

mainboard-and-digital-meter

The 1.8V voltage can be measured on the Regulator in the middle below capacitor C24 as shown in previous Photo.

multimeter

Since all Voltages previously weren’t present, I was afraid that the 3.3V chips like Memory SRAM and BIOS would be killed in the process. But next Photos prove that the 16 channel Digital DVR Board was working again like new. And it again only cost me a few components (like often is the case if you read my previous repairs) and a lot of time.

Following I will show more Photos of the Device working while connected to my TV (set to PC input) by using a standard PC VGA cable. First Photo shows the VGA screen reporting that there is no HDD connected, and if I would like to continue anyhow. And next Photo shows how the screen looks when I press the Continue YES choice.




But the Digital 16 channel Recorder (with X264 video compression!) came back after my perfect repair, because the owner had not listened and still had kept using the wrong 19V PC Adapter again. While the DVR Board functioned perfectly it now had killed his original internal Sata HDD. Which gave me the opportunity to make this article with the following proving Photos of my successful repair.

Because I didn’t have a Sata HDD to test the DVR-6616 completely I used an old 500 MB IDE (parallel ata or Pata) instead. And one of my great working Sata<->IDE converter interfaces to adapt the IDE HDD drive to the Sata DVR Board. These Interfaces can be bought very cheap in every PC shop and can be used from IDE to Sata or vice versa. After that I was able to connect and format the HDD by using the Menu options of the DVR-6616.

samsung-monitor-factory-mode

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repairing-video-recorder

samsung-monitor

repairing-digital-video-recorder

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The last two Photos show the IDE Drive I used. It was completely 100% formatted by the DVR-6616.

Next 2 last Photos show how the original Sata HDD looked after the owner again did use the wrong Adapter. Although I explicitly had told him to only use the right 12V 4A Adapter. That he finally found and brought to me with the still not working Device because of his own fault! So I could retest my successful repair and was able to conclude that I had done a completely satisfactory job after all.

It indeed had cooked the 12V Power input of the Sata HDD Controller Board as can be seen on the Photos. That’s why I had to retest the Device with my own HDD.

It was an interesting repair that as often is uncertain in outcome. Because Customers do the strangest and stupidest things that cook, burn and stink up every affected component in the Device.

And any Repair Engineer is probably the only one who learns the most from others mistakes! Or as they say: “A smart man learns from his own mistakes and A wise man learns from the mistakes of others”.

Do not do what he did, and you’ll be fine! Until another repair.

burnt-components

 

albert1

Albert van Bemmelen, Weert, The Netherlands.

Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.

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Note: You can read his previous repair article in the below link:

Acer LCD Monitor Repair- 22 Inch AL2216W

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47 Comments

  1. George

    September 22, 2016 at 8:20 am

    Good job Albert.Keep up the good work.

    Likes(3)Dislikes(0)
    • Albert van Bemmelen

      September 24, 2016 at 5:56 pm

      Thanks George. If I encounter new and interesting repair cases I will!

      Likes(0)Dislikes(0)
  2. Parasuraman S

    September 22, 2016 at 8:22 am

    A highly professional, skilled and expert service! My hat's off!

    Likes(2)Dislikes(0)
    • Albert van Bemmelen

      September 24, 2016 at 6:02 pm

      Just like your unbelievable difficult repair cases often are dear Parasuraman S. I'm sure they match every professional repair published easily!

      Likes(1)Dislikes(0)
  3. Mark

    September 22, 2016 at 9:20 am

    Well done Albert,
    Sometimes the biggest fault in an appliance is the customer themselves! It makes our life interesting to say the least. Thanks for the well written and explained article.
    Cheers
    Mark

    Likes(3)Dislikes(0)
    • Albert van Bemmelen

      September 24, 2016 at 6:27 pm

      Very true Mark. Sadly unlike Doctors, Dentists and other medically trained people, the job of Repair Engineer is kind of underappreciated. Customers often do not see the training and years of education we have had before we were good qualified engineers. Which is why it is a good thing that spareparts often are obtainable for a very low price. For instance: I recently bought 100 SOP-8 IRF 7831 Mosfets through Aliexpress for only 10.29 euro. Which makes it possible to repair another 100 or so DVRs as the one described in the article for almost no investment costs.

      Likes(1)Dislikes(0)
  4. Robert Calk

    September 22, 2016 at 12:56 pm

    Good job, Albert. Sometimes people just will not listen.

    Likes(2)Dislikes(0)
    • Albert van Bemmelen

      September 24, 2016 at 6:32 pm

      I hear you man!

      Likes(0)Dislikes(0)
  5. Albert van Bemmelen

    September 22, 2016 at 1:29 pm

    Thank you Guys!
    After I had e-mailed the article to Jestine I got confirmation from the owner that with a new internal HDD everything worked as new again. And the owner was more than happy that his digital 16 channel videorecorder was completely fixed so he could surveillance his business again. I just had to assume that after my repair and test, the videorecording part also would work because I didn't have any cables or guidelines on how to connect the 16 videochannels. But after the owner's confirmation I knew it was a complete and successful done repair job!

    Likes(4)Dislikes(0)
    • Albert van Bemmelen

      September 24, 2016 at 3:35 pm

      PS: I have to add for the sake of completeness that I was very lucky when I still used the wrong given 19V PC Adapter by the Customer after I had replaced the original Mosfet by the maximum 30V Drain-Source voltage IRF 7831. And that was because as mentioned in the article I had measured almost 19V on Gate pin 4 before. When you look into the datasheet of the International Rectifier IRF7831 SOP-8 N-Channel Hexfet Mosfet it explains why if you look at the Maximum Gate-Source Voltage which is only 12V DC like when the original 12V Adapter is used.
      But probably because the Gate also isn't directly attached to the Positive Adapter Vin line, but through a Resistor and the MMBT3904 it kept working fine. Which shows the importance of reading Datasheets! And checking every step of your repair afterwards too!

      Likes(2)Dislikes(0)
  6. similinga

    September 22, 2016 at 1:59 pm

    good work

    Likes(3)Dislikes(0)
    • Albert van Bemmelen

      September 24, 2016 at 6:49 pm

      Thank you similinga, I am glad it was.

      Likes(0)Dislikes(0)
  7. Yogesh Panchal

    September 22, 2016 at 3:07 pm

    Albert,

    Thanks for well explained article and your repair skill.

    Likes(1)Dislikes(1)
    • Albert van Bemmelen

      September 24, 2016 at 6:45 pm

      Thanks Yogesh. It helps having good repair tools around like my now almost 30 years old Ersa MS6000 Solderstation that has never lead me down yet! It wasn't exactly cheap at the time but it was worth every penny paid! Although it were 255 Dutch 'Guldens' then.

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  8. Gerald Millward

    September 22, 2016 at 3:27 pm

    Albert - as usual a painstaking and professional job.

    Likes(2)Dislikes(0)
    • Albert van Bemmelen

      September 24, 2016 at 2:58 pm

      Thank you Gerald. Indeed at first it was a doubtful repair, but the ones I get often are. They surely help me to repair the worst repair cases to come. The HDD controller that got cooked on the 12V Sata Power connector however was too damn difficult to repair because the PCB (likely a multilayer) had turned into one large carbon short circuit.

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  9. suranga Electronics

    September 22, 2016 at 4:01 pm

    Mr- Albert,

    Wow.. Great Repair Job.

    Suranga

    Likes(2)Dislikes(0)
    • Albert van Bemmelen

      September 24, 2016 at 2:40 pm

      I thank you Mr-Suranga for the nice compliment!

      Likes(0)Dislikes(0)
  10. Mark Tembo

    September 22, 2016 at 5:42 pm

    Systematically repaired. Thanks a lot!

    Likes(2)Dislikes(0)
    • cain sibanda

      September 22, 2016 at 9:00 pm

      thank you guy sorted 2 and enjoying money

      cain from zimbabwe

      Likes(1)Dislikes(0)
      • Albert van Bemmelen

        September 23, 2016 at 5:16 am

        Thank you cain. But money is never an important issue. If the owner at least compensates me for the parts I needed to repair his defect device, it is okay.
        Anything extra is a plus and will help me to service the customer's device in the near future if anything goes wrong again. After all new parts need to be ordered and paid in advance also, and having spare parts at hand does cost some money too. cheers!

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    • Albert van Bemmelen

      September 24, 2016 at 6:46 pm

      Glad you liked the article Mark!

      Likes(0)Dislikes(0)
  11. Anthony

    September 23, 2016 at 4:03 am

    Hi Albert, a terrific repair article well written and nice photos showing what you had to contend with. Well done to you for bringing it back to life again ! Kind Regards

    Likes(1)Dislikes(0)
    • Albert van Bemmelen

      September 24, 2016 at 3:10 pm

      Thanks Anthony. It helps that I take my close-up photos (Macro) with a great second hand Canon camera I bought about 15 months ago. A PowerShot A590 with 4 x optical Zoom. It only needs 2 Penlight Batteries to operate which is much better than my earlier camera's that needed 4 penlights. Or my Kodak EasyShare CX7530 Camera that also needed only 2 Penlights but was drained everytime I wanted to take new pictures.

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  12. Gerald

    September 23, 2016 at 8:47 am

    The customer is King and this King is often part of the problem 🙂

    Thanks for sharing Albert.

    Cheers,
    GM

    Likes(1)Dislikes(0)
    • Albert van Bemmelen

      September 23, 2016 at 11:46 am

      Hi Gerald, I once new a Boss who said: "the customer may be King but I am the Emperor". He was soon out of business if I remember it well.

      Likes(3)Dislikes(0)
  13. beh

    September 23, 2016 at 11:53 am

    fantastic repair thanks ALBERT

    Likes(2)Dislikes(0)
    • Albert van Bemmelen

      September 24, 2016 at 12:57 pm

      Thanks BEH (LOL).
      And to Jestine of course who apparently tirelessly takes the time and effort over and over again to publish even our very long (like mine) repair articles on his Blog!

      Likes(1)Dislikes(0)
      • Jestine Yong

        September 24, 2016 at 4:35 pm

        Hi Albert,

        No problem.

        Jestine

        Likes(3)Dislikes(0)
  14. Bulent NUR

    September 24, 2016 at 8:55 pm

    Thanks for share, great job!

    Likes(0)Dislikes(0)
    • Albert van Bemmelen

      September 25, 2016 at 2:27 pm

      Glad you liked it Bulent NUR!

      Likes(0)Dislikes(0)
  15. Andrea Del Corso

    September 27, 2016 at 4:22 pm

    Bravo..Albert,you are the number one!I remember your article on the istrument DUOYI and thank you for that!

    Likes(0)Dislikes(0)
    • Albert van Bemmelen

      September 28, 2016 at 6:12 am

      I very much appreciate your kind reply on that older article Andrea Del Corso!
      Repairing the DUOYI DY294 sure took a lot of investigation, tests and so time. And there was a lot of precision involved with soldering those delicate 44 pins chips about four times over again with my 'normal' Ersa MS6000 solderstation until the DUOYI finally worked. But in the end I was very glad I could finally prove that it was the right replacement chip after all. The DUOYI is a magnificent designed Device with unique possibilities worth saving! The fixed unit I gave to one of my good friends. And I already had bought a second good working DY294 to examine and extract the necessary information from to fix the defect first DUOYI DY294 with.
      After that I bought a third DUOYI 294 Device to compare the values of my second DY 294 with. The given LCD values practical were identical. Because I also wanted to test on any deviations. Half work is no good! After all, when I had quit right after the first 44 controller chip, and the second, and the third chip failed, I would never would have succeeded the repair being only half way. The way I see it is that any fixed device helps me to fix another device too. Especially in the case of the affordable DUOYI DY294.

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      • Robert Calk

        September 30, 2016 at 5:04 pm

        Hi Albert,

        I had trouble soldering small pins with my simple Weller soldering station. Soldering is much easier now with my Hakko and the many various tips that I can buy that fit it.

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        • Albert van Bemmelen

          September 30, 2016 at 11:37 pm

          I only use my S-993A (like your Hakko) Soldergun to desolder the older Sockets and parts from Boards, Robert. Soldering the 44 SMD IC pins of the CS7106GN 3.5 segment A/D LCD controller Chip I do best with my ERSA MS6000 Solderstation that is almost as old as my Tektronix 2465 Oscilloscope. Only when it concerns the newer SMD components on pcb Boards I often use my Hot Air Solderstation. But also than I often still use my Ersa MS6000 more easily. It is no good to use an expensive Desolder Gun for the newer Boards with smaller parts since most parts don't have normal pins anyhow.

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  16. Waleeb

    September 30, 2016 at 12:17 pm

    Many thanks for the article and great job done well

    Likes(0)Dislikes(0)
    • Albert van Bemmelen

      September 30, 2016 at 11:47 pm

      Thank you for your kind reply Waleed! I somehow keep repairing all kinds of expensive Devices with only just a few replacement parts needed.
      I guess every repair engineer knows that good feeling to be able to fix almost anything at almost no cost at all.

      Likes(0)Dislikes(0)
  17. Lad

    October 1, 2016 at 3:37 pm

    Yes, great job, Albert.
    But because I am still a beginner in the repair business, can you please explain a little more how you found out that The IR P025H was SOP-8 Mosfet ?
    It was burnt and various integrated circuits can have 8 pins.
    Thank you

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    • Albert van Bemmelen

      October 2, 2016 at 3:38 am

      Yes of course I can Lad. I already repair about 5 years or so mainboards from different Laptops. So I know about most Mosfets because of it.
      And often the 3.3V, 5V ,12V or Vin (~20 VDC from adapter) Mainboard voltages are not present. Mostly because of bad Mosfets. And if you examine the concerning Mosfet Datasheet you'll notice that they very often are placed in a SMD 8 pins (SO-8) housing.
      They like the ones in the article only have 3 active connections being Gate (always pin4), Source (the three pins 1 to 3 connected) and Drain (the pins 5 to 8 connected with each other).
      So if you look at these Datasheets you also will notice that there are N-Channel Mosfets and P-Channel Mosfets. For instance here for the AO4406 Mosfet:
      http://www.aosmd.com/res/data_sheets/AO4406A.pdf
      It is a N-channel 30V (Max voltage on the Drain-Source part of the 4406) Mosfet. Only if the Gate-Source voltage is more positive than 0 Volt, it conducts current from Drain to Source. And if you examine the curve you will see that this Mosfet will only conduct 10 Amps at a Gate-Source voltage of only 3V. And that is at a Drain-Source voltage of about 5V. And already at a slightly higher Gate-Source voltage of 4.5V and a even lower Drain-Source voltage of just about +1.2V it already conducts currents as high as 60Amps! The Gate makes it possible for the Mosfet to function or not. Like an electronic switch. The Treshold voltage tells us for instance at what Gate-Source voltage our Mosfet stops conducting and becomes an isolator. Our Datasheet shows us that that will happen between voltages from only 1.5V to 2.5V when VDS=VGS. So the higher both voltages, the higher the current through it.

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      • Albert van Bemmelen

        October 4, 2016 at 12:16 am

        Do understand that the Maximum Current possible is limited to a value as is given in the Datasheet. The maximum current for the above given AO4406 Mosfet will be around 13A continuesly, when Vgs = 10V minimum. And only very quickly pulsed the Mosfet will be able to switch higher Drain currents! (upto 100 Amps! at a frequency of about 1MHz). Also understand that a Mosfet only uses some energy when its state changes. Only than the Gate draws some current like changing the polarity of a small Capacitor. In fact a modern Personal Computer Microprocessor/controller has millions of these tiny Mosfets on a few square milimetres. And if they all switch extremely fast, its surface will be getting very hot because of it! Also keep in mind that Voltages and Currents higher than their maximum given values will ultimately destroy your Mosfet to Kingdom come.

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  18. Lad

    October 4, 2016 at 2:27 am

    Albert, Thank you very much for your explanation.

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  19. Albert van Bemmelen

    October 4, 2016 at 6:39 pm

    Glad I could help Lad. Whatever you do, always check those Component Datasheets.
    It helps to understand how they work and when they will Break-down.

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  20. Albert van Bemmelen

    October 4, 2016 at 6:56 pm

    PS: it also explains why most modern Microcontrollers (CPUs or GPUs) work on voltages of around 1V DC or less. To keep the currents through all those tiny Mosfets as low as possible.
    And Mosfets are also extremely sensitive for Electrostatic Discharge (ESD) voltages that easily reach high voltages up to 2kV! And because these Mosfets are normally destroyed above voltages of only above 20-30V (Drain-Source or Gate-Source, depending on the specific type), CPUs and Mosfet containing Electronics are sold in special ESD safety bags/packages.

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  21. ombra32

    October 18, 2016 at 7:20 pm

    Hi Albert,
    I can't understand in what way the N-mos works here.

    From the schematic, if you put an-N channel mosfet on positive pole in that way, you obtain an always on mosfet due to parasitic body diode from source to drain.
    Moreover, to power on an N-mos you need a gate voltage higher than source voltage, and this is impossible without a charge pump.

    Are you sure all is working fine??

    Regards

    Likes(0)Dislikes(0)
    • Albert van Bemmelen

      October 31, 2016 at 5:59 pm

      Good question ombra32, I previously had the same thought about the internal Diode but I am very sure it functions because a P-channel didn't. And more types of Mosfets just are not possible. Except for depletion or enhancement Mosfet types of which the enhancement types are the common used types in Digital circuits. So I probably picked the right one. And the N-channel used here probably switches open when another part of the circuitboard activates the Gate so it becomes an Isolator. The Body-diode of a P-Channel would be completely turned the other way around and that just didn't work. The Gate of the 7831 N-channel Mosfet is here higher and positive opposite Source like you said. And the Photos are proof the Device works. Without a Services Manual or Schematic of a Device it always is hard to tell how it exactly works because we therefore only repair/replace the parts that were burnt or broken. If the chosen Mosfet is still the wrong type than maybe some protection circuit now could not be working. And because the Device did work like a new one and the short circuit was removed my job was done. If you want to know more about those kind of Mosfet types look for instance here:
      https://en.wikipedia.org/wiki/Depletion_and_enhancement_modes
      The Customer was very happy that he got his expensive Device back working, and I haven't heard any complaint since. And if the Customer is happy so am I.

      In addition to your very good question Ombra32, following link explains the differences between all type of Mosfets very well!:

      https://oscarliang.com/how-to-use-mosfet-beginner-tutorial/

      Depletion Mode Mosfets are normally ‘ON’ and can be turned OFF on their Gates. And that site also explains that the internal Body Diode unintentionally may allow current to flow.

      The next link tells us that Depletion Mosfets are just rarely used and the rare cases when they are used:

      http://electronics.stackexchange.com/questions/237566/typical-use-of-depletion-mosfet

      So maybe also a Depletion Mosfet would have worked also, but just finding one isn’t easy.

      Especially the SO-8 types.

      Since the previous Short Circuit was removed, now maybe only the 12V regulation to the HDD Molex connector does not work, if that is why the Mosfet was used for. And that most likely is possible here with a Depletion type Mosfet.

      But since the 16 Channel x264 Digital Recorder works even after the owner used the wrong 19V Power Adapter (twice), I am glad I could repair his expensive Device where others couldn’t or wouldn't!

      Thank you for your very observative question Ombra32!
      Thanks, Albert.

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  22. Albert van Bemmelen

    December 2, 2016 at 1:55 am

    Recently I tested the given Digital Recorder circuit of this repair in TINA version 10. Because that program makes it easily possible to test all possible Mosfets in a clear simulation. In practice a PMOS enhancement Mosfet behaved strangely as explained in the article becoming hot when the Gate was also connected. In the Tina simulation however it turned out to be just working perfectly!It was switched through on Source Drain when NPN transistor MMBT3904 LT1 was triggered by a positive Base signal.
    And the P-MOS Mosfet (I used a IRFF9110 Enhancement P-channel Mosfet in Tina) was open (no 12V out to the Molex HDD connector) when the Base of the Transistor wasn’t switched in by a positive Base signal. In short: Vgate was about 7.79V, and Vout Molex 12V when the NPN Transistor was active. And Vgate is Vin, and Vout is 0V when the NPN Transistor is inactive.
    And even without any HDD attached to the Molex connector the P-channel enhancement Mosfet felt rather hot when also the P-MOS gate was connected in-circuit.

    (Probably because the Mosfet behaves odd when no HDD/Load is connected on its Drain. Which I didn't because of the wrong by the owner given 19V adapter. A Sata HDD drive only works on 12V and/or 5V! Because the simulation also showed that the Mosfet Drain output voltage already was about 3.49V without any decent load below about 10Kohm, even if it wasn't activated by the NPN Transistor or when the Gate wasn't attached. Which means dissipation because the Mosfet is in a wrong state between open or closed !! Where it always should show ZERO output voltage when not activated.)

    Why I chose a N-MOS enhancement Mosfet in practice that never got hot but as another Tina simulation showed always switches Vin through to Molex Vout. So it is never an open connection between Source and Drain. Which also explains that the repair still was successful after removing the Short circuits on the Mainboard, but indeed only the HDD 12V on the Molex is never switched off in practice. Which I couldn't test in the end because I had none of the videocables or control cables necessary. Which was fully tested by the now satisfied customer. So I encourage anyone to use a great program like Tina 10 which now can be bought with a free upgrade to the coming version Tina 11 !

    (I bought the Classic version because of its VHDL and other Language simulation enhancements and many more extra's such as the unlimited design capacity, which is not available in the cheaper/student versions).

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  23. Aman Singh

    February 11, 2018 at 5:09 pm

    Hello Sir,

    I have some issue with a Hikvision make DVR, where few channels showing very low brightness or no video. But few ports showing good. I have open the box and noticed resistance between working bnc input ports the good one have 75 Ohms while bad one have 0 ohm (short). Further I had removed diodes (not sure if they are TVS diodes for ESD protection) on those shorted ports & then measured resistance between ground and input pin. The result was good 75 Ohms & then connected camera input there which also worked perfectly. Now I searched that diode (component) over the internet but couldn't find anything with that label marked (6L H503). Would you please assist me what are those components as I am assuming tvs diodes.

    Thanks

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