Issue with DELL 1545 IO CHARGE BOARD --SCHEMATIC-- (explained with images)

[gjgib]

Hello, need help identifying a DIODE that's right at the start of DC_IN line in this small IO BOARD. (DR1 08530-2 48.4AQ03.021).



I have the boardview for this small board 08530-2.rar but it doesn't specify any components, just 'D1', 'Q2,Q3', etc. That's why I'm looking for the -schematic-. PS: It's in some paid sites.




The blown diode that came in this board was this one: CH9k-B14A

So I bought a tape of 50- 1SMB14A LK and replaced the blown one with a new 1SMB14A LK but the diode gets too hot. Did I purchase the wrong diode?

Would appreciate any help. Thanks in advance!

[piernov]

Original diode is P6SBMJ24APT, a 24V TVS diode, for rudimentary protection against voltage spikes/overvoltage.

[mon2]

Yes, you have purchased the wrong diode. Each serves a different purpose.

The original was a shottky diode and is used to prevent the wrong polarity of the external power adapter from killing the logic board. That is, on the older laptops, there is a coax / barrel connector used to power the board. The center of the barrel is often the '+' polarity and the outside of the barrel = '-' or ground. There are some kooky power adapters where this is reversed. For this reason, the engineer applied this shottky diode to just not function while not killing the board if the polarity is reversed.

The diode you have sourced is a zener diode which has a cut-off voltage. Once this cut-off voltage is reached, it will shunt the voltage to ground. So consider a zener diode like a firewall for voltage. Once this trigger or threshold is reached, it will cut off the voltage. However, this PCB is expecting a shottky diode here and not a zener.

If in a pinch - would you have an old PC style desktop dead power supply? If yes, there should be 4 of such diodes onboard but they will be through hole. While it may be ugly, they will serve the purpose.

Just solder in place with band to band like before and you are all set.

[gjgib]

Oh, thanks so much for the info.

I don't know if I could've known which one was it. Since I didn't have the board schematic and I couldn't find anywhere on the internet the original diode (CH9k-B14A).
Is there a way to know which one is it when you don't have enough info? - Is it depending on where they are placed? Like almost -all- diodes placed right after VIN jack are supposed to be Shottky and so on(?

I tested the laptop's adapter barrel connector with my multimeter and noticed it's reversed and that may have caused the original diode's death. (Meassured inside with red probe and it gives me -voltage even tho specifications say it is - C +.

I'll look out for those diodes inside an old PSU like you said. You mentioned 4, I assume they are rectifying(?

Sry if many questions, I'm apprentice. Thanks so much for all the insight. Very useful.


PS: Would the proper diode replacement be something like this one or(?

[piernov]

Original diode is P6SBMJ24APT, a 24V TVS diode, for rudimentary protection against voltage spikes/overvoltage.

[gjgib]

Wow, they just have so many different names that's like impossible to get the right one with just the inscribed nomenclature they have. Jesus. Thanks a lot!

PS: Now I'm confused. Is it Zener Trascient Voltage Suppresor or Schottky? Can it be both? Schottky TVS is possible? I think I bought Zener TVS and it's the one not making proper function in the board.

[mon2]

I was unable to locate the original diode from your board but we can agree that the diode is a SMB14 sized component. That is an industry standard used by all vendors.

Proceed to review the wiring of the diode to nail this down.

1) If the part is a schottky diode then the back of the arrowhead in the schematic symbol (anode) will be fed the power adapter '+' voltage. The band markings of the diode (cathode or '-') will be towards the power rail of the logic board. The purpose of this type of diode is to prevent reverse polarity wiring of the power adapter. Only a 'center positive' style of power adapter can power the logic board.

2) If the part is a zener diode, then the back of the arrowhead in the schematic symbol (anode) will be to GROUND. The band (cathode) will also be to the logic board but the purpose of this diode is different and will be to clamp the voltage if the rating of the zener diode is exceeded. Acts like a firewall or OVP (over voltage protection).

In both cases, the peak operating voltage of the diodes is important. Review the wiring using diode mode to study the intent of this component.

[gjgib]

In the description I did on this post at the start, I show an image of how I found the diode. So, since the cathode is linked to the DC_IN line and the anode is linked to ground, it should be Schottky as you said(?

[mon2]

So, since the cathode is linked to the DC_IN line and the anode is linked to ground

It is a zener diode and used for clamping higher than normal voltages from the power adapter. Apply as per post # 4. If your power adapter is well behaved then this part is not required. The part is used on the board from a too high of a power adapter voltage.