DELL AC power adapter - ID CHIP DIED

15 Jan 2009
Posted by Laptop Junction

Just 2 days after the cable repair of the DELL AC Power Adapter for a DELL Latitude D610, the same problem appears again. During startup the BIOS reports "The AC power adapter type cannot be determined". Murphy's law at it's best!


 
DELL AC Adapter not recognisedDELL ID chip diedDELL design failureInside a DELL battery

 

 
A quick check of the AC Adapter identification wire shows it's OK, no disconnects, it has a solid connection. Two DELL Latitude D610's report the same problem, so most likely its not a power jack problem. Suspicion goes directly to the DS2501 ID chip from DALLAS /  MAXIM Semiconductor in the DELL AC  Power adapter. This chip is an UniqueWare™ Add-Only Memory.
 

Checking the DS2501 UniqueWare™ Add-Only Memory

Measuring the AC Power Adapter ID signal with a scopeThis time the threshold for brute force analysis is reached. A FLUKE digital 123 ScopeMeter is used to follow the communication session through the AC Adapter identification wire. According to the DALLAS / MAXIM "1-wire" communication specification the signal speed is 16Kb/sec. That's very easy to capture with any normal oscilloscope.

When the DELL AC Power Adapter is not connected the signal on the AC Adapter identification wire is dead. No voltage, either AC or DC, nothing.

Connecting the DELL AC Power Adapter to the DELL Latitude D610 raises the DC voltage to 16,5 volts. But nothing happens - no communication session is starting, only a tiny wave is seen which seems to be noise. The amplitude of this wave is too small to go for a solid 16Kb/sec paced communication signal. The controller chip in the DELL Latitude D610 doesn't send out any signal remotely resembling a normal data pulse. Most likely the DS2501 does not respond on power-up.

Conclusion :: the DS2501 ID chip is dead! Two other DELL AC Power Adapters are still working, and both DELL Latitude D610's are still charging batteries with the other 2 adapters.

It seems Murphy's Law has come down on  a poor design and test trajectory for the ID circuitry in the PA-1900-02D2 DELL AC Power Adapter.
 

The DELL AC Adapter power cord

Why on earth connect the DATA pin of the DS2501 memory chip directly to a 2 meter long UNSHIELDED wire.......? I would call the ID wire in the power cord an antenna.
 

The DS2501 ID chip in a DELL AC adapter
The DALLAS DS2501 chip found in the PA-1900-02D2 with revision number REV A04.


At least the input circuity of the DS2501 should have been hardened so it can take a reasonable amount of electromagnetic pollution. 

Knowing there's probably a truck load of DELL AC Power Adapters (PA-1900-02D2) out there with this design, what can be done to prevent blowing the DS2501 ID chip?

The safest is when it's connected to the laptop, so the "antenna wire" is connected / part of a loop.

To further reduce the chance of blowing the DELL ID chip:
 

  1. Replace the complete 3-wire charger lead with a fully shielded cable. (3 leads + 1 shield)
  2. De-solder the DS2501 ID chip and solder it on the motherboard of the laptop.

The shielded cable reduces the chance, strong electromagnetic pulses ruin the chips on both end of the AC Adapter identification wire. Moving the ID chip from the DELL AC Adapter to the motherboard eliminates most of the risk - although the operation is a bit complicated.
 

The DELL AC Adapter ANTENNA wire
The unshielded 2 meter  power lead of the
PA-1900-02D2 with revision number REV A04


A work-around to charge the DELL laptop battery is to use a stand-alone external laptop battery charger.