The DELL PA-10 AC power adapter has a power plug with 3 connections; +19,5 volts (V+), ground (V-) and power adapter identification. With already 1 AC power adapter with a dead MAXIM DS2501 power adapter ID chip, it might be worth to have a detailed look at the mechanics of the DC power plug.
The DELL PA-10 AC power adapter examined in this case is known as a PA-1900-02D with revision number A04 and part number 9T215. After having a bit of look at several "identical" PA-10 power adapters, the "family" had several revisions already. To name a few other variations "PA-1900-01D3" - P/N: U7809 (REV A0.4) and "PA-1900-02D2" P/N: DF266 (REV A0.3).
Meaning the same "PA-10" power adapter can have different internals. The PA-1900-02D REV-A04 examined here has 2 meters of unshielded blank wire directly connected to the DS2501 "1-wire" data pin. There's nothing in between to protect the chip for this revision of the power adapter as discovered earlier.
Dell DC Power plug variations
Looking at the DC power adapter plugs, two power adapters both a REV-A0.4 had two slightly different power plugs. The outside tube carries the ground wire, the inside tube 19,5 volts, the center pin is the Adapter ID. On the left, the bottom of the power plug tube seems like fully plastic. In the right one there's a metal edge visible decreasing the distance between the 19,5 Volt and the Adapter ID pin. The AC Power Adapter with the dead DS2501 has the power plug displayed on the right. Strange - changing the power plug design must have some reason.....other than production cost?
** Read about the differences between PA-10 and PA-12 AC Adapters **
|DELL DC power plug variations and revisions - small differences - why?
Now looking at the specification of the DS2501 "1-wire" memory chip, the power for this chip arrives through the data wire. It's called "parasite power" supply, feeding on the energy supplied by the "1-wire" communication signal. The DS2501 has 2 power ranges - the normal 2.8V to 6.0V for communications and 11.5V to 12.0V for memory programming with a maximum of 12 mA. (milli-Ampere)
Connections of the worst kind
Now, hypothetically speaking, what would happen to the DS2501 if the 19,5 volts / 4.62 Amps from the power supply would accidentally touch the data pin of the DS2501? Would it survive the treatment? Probably yes, if the Amps rating would be low. However the 19,5 Volt comes with 4.62 Amps (max). The energy released would most likely blow-up the poor DS2501. And in practice it's not so hard to do this, just insert a screw driver in the power plug connecting the inner tube (19,5 Volts) with the identification pin. For the DS2501 it would mean "programming time", however it'll probably die while making the switch to programming mode.
Stepping on a DELL DC power plug
Now, thinking a bit further along the line of more likely abuse. Say the power plug is "accidentally" stepped upon? Not such a strange or unlikely incident. How many times I crawled on the floor to connect the power adapter to the mains and had the power plug laying on the ground? Even so, the plug probably survives the pressure, but how about the internal wiring? Let's have a look at the inside of the sealed plug.
After having sliced open the plastic plug jacket the solder side of the plug becomes visible. As with many plugs with multiple connections, the solder side is always a bit of miniature work of art. How did the manufacturer design the solder side and reducing the risk of individual wires touching each other?
Soldering a DELL DC Power plug
Now the PA-1900-02D with revision number A04 has 3 solder positions as shown below. The soldering in this case is not particularly great and it seems the person who assembled this version had a bit of a struggle with the wires.
This power plug might have been assembled by some-one new to the production line? The power adapter identification pin has a protective cap on one side. Most surprisingly, the function of the cap is unused. The +19,5 volt wire hangs just above the naked identification wire. There's only a small air gap left between the 2 wires.
Now with a sealed plug, it could be so that there's plastic from the sealing process sitting between the wires creating "accidental" insulation. Also soldering the 19,5 volt white wire in this position requires it to be clipped pretty short to prevent naked +19,5 volt wire to touch the already naked identification wire. In this case it was not. Also when removing the soldered plug from the plug seal there wasn't like the wrestling needed to remove any "accidental " plastic from between the wires.
|DELL Power plug internals - possible cause for failure
Imagine stepping on the plug above - would the pressure cause contact between the 19,5 volt wire and the identification wire? It would surely not, if it was soldered in the way I modified it - using the protective cap of the plug design.
Protective circuitry for the worst
Now for this to happen there's a few if's. It means stepping on a power plug which is soldered the wrong way. Anyhow, to get this power plug soldered the right way, one needs to supply good instructions. Specially in using the protective cap of the Adapter ID wire in the plug design. If it's not used, the chance wires could touch would be significantly higher.
Going back to the electronics design of the DS2501, wouldn't it have been a much better idea to just add a bit of circuit protection and make it more robust? If it was only for some-one sticking a screw-driver in the power plug?
In this case, i don't want to know the effects of inserting a "stepped-on" plug with 19,5 volts and potentially lethal 4,62 Amps buzzing on the adapter identification wire. Would it blow any circuitry on the DELL motherboard?