Dell Latitude D620 laptops
I bought a couple of Dell Latitude D620 laptops and they have given me quite a few problems.
One of them has a bad external microphone connector which would cost way too much to repair and I
resolved the issue with an external USB audio device which works fine but takes up a USB port.
It seems the connectors on Dell laptops are generally not very good and give many problems as we
shall see later with the power supply.
Dell Latitude Power Supply Unit (PSU)
Dell laptop power supplies often have problems, often caused by bad connectors, either on
the cable from the PSU to the computer or the connector on the motherboard itself.
I found I could not use generic power supply units (PSU) because these DELL computers have a
special connector with the two power supply contacts but also a third signalling connection.
So I decided to investigate.
but the power supply pack supplied with it says it supplies 19.5 V at 3.34 Amps (65 W).
The computer says it requires adapter model pa-10 or pa-12. The PSU says it is "model pa-1650-05d2, 65 W AC adapter PA-12 family". Another similar adapter I have says it is model hp-OQ065B83. It seems these power supplies are used with many different models of Dell laptops including Latitude, Inspiron, Dimension, etc.
Searching online I find that many people have problems with the 65 W power supply which are resolved by using the 90 W PSU. It seems the way it is supposed to work is that the computer knows what PSU is connected and will limit its power usage. If the more powerful PSU is used then it will run at full blast and charge the battery at the same time but if the less powerful PSU is used then it will not charge the battery while the computer is in use and will wait until the computer is turned off.
The computer and the PSU communicate through the third conductor and if you connect a generic PSU with no third cable then when the computer starts up it will display an error message saying "The AC power adapter type cannot be determined. This will prevent optimal system performance". It seems the computer assumes a very low capacity PSU and will not charge the battery and will throtle back the speed of the processor to conserve energy.
I decided to do some tests of my own even if very limited due to the limitation of the means and tools at my disposal. Maybe someone with better tools can do better.
I determined that
One possible cause of problems is the signal line not making a good connection because the pin is bent or broken. This should be relatively easy to fix. Another, more serious, problem happens when the 19.5 V wire is shorted to the signal wire due to an aging cord. Then the signaling circuitry at the computer is fried and the computer will no longer recognize any PSU.
More information on the power supply, the battery and the signalling can be found here, here, here, and here. Those pages refer to a Dell D610 and the battery pack looks physically different but electronically it looks like everything applies.
Because of the signalling I cannot use a generic 12Vdc power supply and I am forced to use a 12Vdc to 220Vac converter and then the regular Dell PSU. At 12 V it uses about 3.5 A if the battery is fully charged but about twice as much if the battery is charging.
The problem with this approach is that it requires much more power than strictly necessary. For one thing the two conversions (12 Vdc - 220 Vac - 19.5 Vdc) are wasteful but also the laptop feels it is being supplied power from the mains and goes at full speed and the screen at full brightness whereas when it is working from the internal batteries it saves power by slowing the processor and diminishing screen brightness.
Battery Pack PC764
The battery pack stopped working so I decided to open it up and investigate. Cracking the case
open was not easy. It snaps closed and it was also glued. As I could not find any easy
or obvious way to open it I ended up cutting it open with a utility knife. I found it has six
Lithium - ion cells type 18650 (18.0 x 64.5 mm). Each cell provides about 3.7 V and they are
connected in two parallel strings of three cells each in series which makes a nominal 11.1 V.
A1 and A2 in parallel form the lower cell with the negative directly connected to the computer negative. B1 and B2 from the middle cell and C1 and C2 form the upper cell which is connected through a software controlled switch to the + power pins. I measured voltages and found the two upper cells had 4 V each but the lower cell was dead. No voltage and infinite resistance. Now I need to decide whether to replace the entire pack, replace all six cells or replace the two faulty cells. I am inclined to try replacing just the two faulty cells because there is a risk that the controller circuit might have some problem so the risk is minimal.
The battery pack connector has 9 pins numbered beginning at the far end from the battery cells. Pins 1 and 2 are the + power output which is connected to the battery through a semiconductor switch controlled by software. Pins 5, 8 and 9 are connected to the computer ground and directly to the negative end of the batteries. I am not quite clear on the purpose of pins 3, 4, 6 and 7 although the seem to be used for some kind of signalling. From information gathered from other Dell battery packs I gather it may be that pin 4 might be SM bus signalling and pin 7 may be an on/off signal. Pin 6 is labeled "PESS" and pin 7 is labelled "alert". I guess the alert signal may be used by the battery pack to signal to the computer that the battery is low. In the photo you can see pull-down resistors to ground.
I replaced the two dead cells but the pack, in spite of having the right voltages, still did not work with the laptop. I investigated the control circuit and found some damaged components so I think this is probably the cause of the problem. The control circuit is quite complex. As you can see in the photo it has some ICs with many pins. After looking over the circuit very carefully I detected some damaged or missing components which I have marked in red.
It looks like two SMD resistors are missing and a black component (diode?) next to them is damaged. I have no idea how this could have happened because I was very careful when I disassembled the pack and because the components are located in a location quite protected by other components but, at any rate, it seems this is beyond my capability of repair because I do not have the schematic. It's time to buy a new battery pack.
I first wrote this page in early 2012 and it has rained a lot since then. One of my Dell laptops was stolen and the other one gets very little use and is on the way out so this issue is only of academic interest to me now. December 2015 Richard Allen emailed me to tell me the charger uses 1-wire protocol and directed me to this page for more information. He built an adapter for his Thinkpad which you can see here.