Dell DA2 12V 18A PSU repair P/N M8811

[technicalspecialist]

I have aquired a Dell SX280 from a friend that wasn't working.
I opened the external PSU (part number: M8811) and found that some SMD transistors on a small daughter board are fried.
Its part of the feedback circuit. I think some pins on it got shorted to the metal shield/heatsink.
They're so badly burned I can't identify the part numbers.
I bought a replacement DA2 on eBay for £10 with the intention of looking inside to try and identify the components so I could fix the other PSU but the little daughter board in it is different.
The part number on the case of the working one is N112H. The computer works fine with the new PSU.
Does anyone have a working DA2 PSU with part number M8811 that they don't mind opening to get the part numbers of the components on the little daughter board. That would be much appreciated I have attached some photos showing the fried components.

Simon

[Behemot]

Re: Dell DA2 12V 18A PSU repair P/N M8811

I don't think it matters a lot, these tiny transistors would not be much different one to another. Just get the right type (PNP/NPN). Check the zeners, one may went bad thus burning the components.

[technicalspecialist]

Re: Dell DA2 12V 18A PSU repair P/N M8811

I think it does matter. There are 100s of transistor types out there all with different specs.
The side with the 4 pins and the burnt transistors is on the primary high voltage side. They're not likely to be just any 2SC, 2N or BC548/558 type. They probably need to be high voltage ones. Q201, Q202, Q203, R201 and ZD201 are what is burnt. R201 is completely black. The value of that resistor matters.
I couldn't find any schematics on the web of this PSU. OEM is Delta.
The model number of this little board is STDC-003.

The other working PSU doesn't have those tiny transistors. The components on it's daughter board are completely different. There is an IC and an opto-isolator as well as the transformer. The side with 2 pins on this is 3 pins on the other working PSU.

[Behemot]

Re: Dell DA2 12V 18A PSU repair P/N M8811

I am sure they cannot be on high voltage themselves. The electrodes are so close it could arc, you can simply not make HV transistor so small as this SMD package. And as for power, the same - they are so small they cannot carry any significant power so it does not matter much. I bet the transformer is there to galvanically separate HV and LV and these are only the low-side feedback.

[stj]

Re: Dell DA2 12V 18A PSU repair P/N M8811

check every resistor and semi with a meter - these type of things are a bitch.
and check the ceramic caps for shorts.

and the soldering on the vertical pins is cracked btw.

[Antronics]

Re: Dell DA2 12V 18A PSU repair P/N M8811

Well I,ve got a Dell 12V 18A DA2 like yourself. Maybe you can reverse engineer it. I looked and measured my own and these are the clues.

The Primary Side has 4 pins. The grounded innermost pin as 0V reference and the pin closest to the PCB edge is 310V, I didn't measure the two inner pins.

The Secondary Side Components are a measured 7V93 Zener in a cylindrical orange SMD package marked 882 (I think). The SOT23 package is marked NGV1 which I think is a BD49L55 but maybe it is just V1 then its is a ELM9751CBB which measure 5V1 voltage detect as well. Or it could be a Zener Diode DZ23C2V7 but since there is already a 7V93 Zener it is unlikely.

The Primary Side Switching transistor on the other side of the PCB is a 2SK2845, but since your package is a TO92 I would use a BRS1N80 for the main switching or equivalent. The K2845 is rated at 900V whereas the BRS1N80 is 800V, both 1A.

The Primary Side has two types of SOT23 transistors. 2 marked 2X which are MMBT4401 NPN Transistors for sure. The other SOT23 transistor is marked 702 which is an N-Channel MosFET 2N7002. The other cylindrical orange SMD diode measures 14V55 when the PSU is on.

The 3 pins on my secondary measure 0V 7V and 15V where the 0V is the last pin closer to the other side of the PCB edge and is common with the 0V of the 12V secondary output

So firing up the daughterboard off the Main PCB through a 220Vac light bulb on the 300V side and getting those secondaries right might indicate its working OK.

The SOIC8 on the primary side is marked DAP7A; which I don't know what it is. [Maybe is a DAP7ADR2G but you'd have to check the pinouts. UTSouce says: DAP7A is an 8-pin SOP (Small Outline Package) transistor manufactured by ON Semiconductor. It is a PNP transistor with a maximum collector current of 500mA and a maximum collector-emitter voltage of 80 V. Description: The DAP7A is a PNP transistor designed for use in general purpose switching and amplifier applications. It features a low saturation voltage, high current gain, and a low collector-emitter saturation voltage. Features: Low saturation voltage High current gain Low collector-emitter saturation voltage Maximum collector current of 500 mA Maximum collector-emitter voltage of 80 V Applications: The DAP7A can be used in a variety of applications, including general purpose switching, amplifier circuits, and other applications requiring high current gain. It is suitable for use in automotive, industrial, and consumer electronics - no datasheet] But I see your PCB has no IC/SOP-8 transistor that I can see so maybe you don't have to trace this component. My daughter board is also marked Delta [who actually make very decent variable frequency motor drives.] Dell must have subcontracted to them I guess.

So there is only one 300~325Vdc High Voltage track [on my daughter board] which loops round to the pin on the small switching transformer and out to the drain of the 800~900V/1A switching N-Ch FET if you are concerned with the high voltage section. If you are using 120Vac it would sitting at about 170Vdc rectified.

The two inner pins between the +300V and 0V, [I am pretty sure], supply sense voltage as to whether the mains supply is ON or not because the wired remote pins sits at about 15Vdc, and even if the main supply storage cap is fully charged up it won't switch on the 12Vdc when the 15Vdc Remote pin is grounded to tum on the Switching Supply when the mains is OFF. Oddly enough the other thin red wire, is wired to a lone solder pad in between the +12V and 0V, so I guess one could short it to either voltage, if required.

[Antronics]

Re: Dell DA2 12V 18A PSU repair P/N M8811

Correction: - Zener Voltage : The Secondary Side Components are a measured 9V Zener in a cylindrical orange SMD package marked 882 (I think). The SOT23 package is marked NGV1 which I think is a BD49L55 but maybe it is just V1 then its is a ELM9751CBB which measure 5V1 voltage detect as well. Or it could be a Zener Diode DZ23C2V7 but since there is already a 9V Zener there, it is unlikely.

[Antronics]

Re: Dell DA2 12V 18A PSU repair P/N M8811

I've worked out what the NGV1 is from its function although I don't know its original manufacturer number. It is a P-Channel Enhancement Mode MOSFET in a SOT-23-3 package. The gate and drain are connected by a 100kΩ resistor and the source is connected to the supply voltage of 15Vdc unloaded. The drain is connected to the the output pin supplying all the components. When the Remote Wire, connected to the gate, via a 100Ω resistor is shorted to ground, then +15V supply switches to +12Vdc when the drain outputs +12V to the control circuit and also activates an opto-coupler photo-diode side, feeding back to the primary side on the photo-transistor side.

NGV1 is possibly an AP2311GN, which would work fine.

[technicalspecialist]

Re: Dell DA2 12V 18A PSU repair P/N M8811

Thank you Antronics. Its been 9 years since I posted this. I thought no one would ever reply.
I still have the power supply and the daughter board. What version is yours? Is it M8811?

Looking at my original photos, all I need to know is what R201, ZD201, ZD202, Q201, Q202, and Q203 are supposed to be.
The rest of the power supply looks ok. Nothing burnt. But i'll check the rest of diodes and transistors for shorts anyway.

[technicalspecialist]

Re: Dell DA2 12V 18A PSU repair P/N M8811

The Secondary Side Components are a measured 7V93 Zener in a cylindrical orange SMD package marked 882 (I think).

Which Zener do you mean? There are 2, ZD201 and ZD202
There are no components on the secondary side of the little board, only 2 pins from the transformer.

"The SOT23 package is marked NGV1 which I think is a BD49L55 but maybe it is just V1 then its is a ELM9751CBB which measure 5V1 voltage detect as well.

Which SOT23 is marked NGV1? There are two SOT23 transistors, Q201 and Q202. Which one do you mean?

"The Primary Side Switching transistor on the other side of the PCB is a 2SK2845, but since your package is a TO92 I would use a BRS1N80 for the main switching or equivalent. The K2845 is rated at 900V whereas the BRS1N80 is 800V, both 1A

Ive got a scrap board with some 4N50's in a TO-251 package on it. 4N50 are rated 500V 4A.
One of those will fit in place of the 2SK2845 TO-92. Of course I will check they're ok first. Ive got a transistor tester.

The Primary Side has two types of SOT23 transistors. 2 marked 2X which are MMBT4401 NPN Transistors for sure.

Ive got some 2X SOT23 transistors.

The other SOT23 transistor is marked 702 which is an N-Channel MosFET 2N7002.

What other SOT23 transistor? There are only 2 SOT23 transistors on the daughter board, Q201, Q202.

The other cylindrical orange SMD diode measures 14V55 when the PSU is on.

Which "other" SMD diode are you refering to? ZD201 or ZD202?