[SOLVED] Reverse eng of a PCB: unknown components and polarity...

[auato]

Hi all.
I have an Aethra ADSL tester. Currently it runs with a battery but I would like to use it with an external power supply. Kinda I'm looking for identify two poles for the power supply. There are 4 pins on the power-in DIN-type connector.





Looking the PCB some doubt are arisen about the components which I highlighted with a pink circles. I think that the small component with over the letter P looks like a fuse, and the qaudripole in bottom right corner seems a transformer or a filter... but I don't find any information about that TSOP labeld D236.

Anyway a similar schematics seems like this:



Maybe watching the PCB, you can help me to find two poles or maybe you already have a similar power supply for a similar instrument or to help me about those strange components.

Regards
Ciro

 

[FvM]

Fairchildsemi has a clear marking scheme which suggests that D236 is the fab and date code (none lead free 2012-36) and 8304 the type. Obviously it's discontinued NDH8304, dual 20V/2.7A PMOS. Fairchild has cancelled both the package for MOSFETs (most likely due to lead-free solder temperature problems) as well as the type number. Unfortunately discontinued devices are completely hidden on the web site.

Generally I don't exactly understand your question. The instrument has an external power supply connector, but you neither have the original power supply nor know it's specification?

"Reverse engineering" can take advantage of intelligent multimeter usage to find out trivial things like polarity.

 

[auato]

Fairchildsemi has a clear marking scheme which suggests that D236 is the fab and date code (none lead free 2012-36) and 8304 the type. Obviously it's discontinued NDH8304, dual 20V/2.7A PMOS. Fairchild has cancelled both the package for MOSFETs (most likely due to lead-free solder temperature problems) as well as the type number. Unfortunately discontinued devices are completely hidden on the web site.

@FvM, thank you very much, finally I discovered it is a PMOS array.

Generally I don't exactly understand your question. The instrument has an external power supply connector, but you neither have the original power supply nor know it's specification?

Exactly. I want to use an external power supply but I don't know the polarity and I am afraid to blown the instrument. I know instead the specs (6VDC 850mA).

"Reverse engineering" can take advantage of intelligent multimeter usage to find out trivial things like polarity.

I don't know this way. Please, teach me how to recognize quickly the polarity with a multimeter or other tips

 

[FvM]

The basic idea is to locate the junctions of diodes and transistor by a continuity measurement and use this information to determine the type of the respective part, e.g. NPN/PNP, NMOS/MOS etc. In most cases, at least the supply polarity will be obvious after identifying a few elements.

 

[auato]

OK, this afternoon I done my first attempt. Looking the part of diagram rewritten above, in my opinion, the pole + and the pole - is like drew in the previous picture. Result: no power on :-(
... but if I connect the battery, it turns on. The Max 1775 runs fine and even the next stage of PMOS/NMOS after the Maxim IC (8928A) runs fine (the component in yellow) since I found the correct voltage on pins 5, 6, 7 and 8. Now I have to proceed my troubleshooting but without a diagram, I see hard. Anyway, somewhere the rail of battery and the rail of the ext. power supply cross each other.



- - - Updated - - -

Solved! There was my mistake to identify the negative pole. The negative pole is the shield of Din connector. The right pinout of Aethra D2061's external power supply is represented in the new picture


Thanks all!