16 channel Digital Video Recorder Repair
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.
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.
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.
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.
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.
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).
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.
The 3.3Volt can be measured on Capacitor C4.
The 1.8V voltage can be measured on the Regulator in the middle below capacitor C24 as shown in previous Photo.
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.
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.
Albert van Bemmelen, Weert, The Netherlands.
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Note: You can read his previous repair article in the below link: