Falcon NVRam battery replacement
After over 10 years of operation, the builtin NVRAM battery needs to be replaced. There are several method available to do this, and are documented elsewhere on the web. Most of the solution involved the removal of the epoxy mold compound, exposing the internal battery and soldering a new battery across it. These method requires delicate cutting of the mold compound else risk cutting the internal circuit. Other methods includes a direct replacement of the chip itself, and there were cases where removal of such chip also removes the trace itself and one have to repair the trace. Good information about repairing traces are in the web.
There exist a replacement method documented in the the DOITF030 of the DOIT-Archives by Robert Schaffner (http://www.doitarchive.de/index.htm, doitarchive@doitarchive.de - not verified URLs may be obsoleted) under the NVRAM section. This method involves cutting one pin of the NVRAM chip, and soldering a simple diode circuit and battery on to it. This is the motivation of doing this mod as there is little soldering on the motherboard itself.
IMPORTANT NOTE: Please read the note about this mod at the bottom.
circuit schematic from the DOITF030 document
The circuit theory is simple. The replacement battery is placed across the NVRAM. Diodes are used so that current only flows in the correct direction.
When the Falcon power is off, the battery powers the NVRAM. The diode at the +5V Falcon is reversed bias and switches off the NVRAM from the rest of the falcon. This prevents the battery from powering the entire bird.
When the Falcon power is on, the diode at the battery is in reverse bias, effectively switching off the battery. Thus the Falcon power is used to power the NVRAM.
Implementation of the circuit
To implement, we will need to solder 2 diodes to the Vin of the NVRAM at pin 24. To have the a diode between the Vin and the +5V power, we need to cut the leg is pin 24. A sharp cutter is required, making sure that the cut leave sufficient space at the chip leg to solder the diodes on to.
The other end of the battery can be soldered directly onto the ground at pin 12. There is no need to cut the legs here.
I decided to put the diode assembly on a small PCB.
After replacing the NVRam battery, do not forget to reset it by using one of the NVram reset programs or the NVram configuration programs.
Unfortunately for me, putting a 3.6V battery did not work, and the Falcon refuse to boot up.
After sometime, I replaced the 3.6V battery with a pack of 4 x 1.5 AA batteries (similar to my TT030). With the 6V battery over the NVRAM, the Falcon was able to boot AND remember the datetime plus NVRAM setting.
It may be that with 6V across, it is always powering up the NVRAM even when the Falcon is powered on. However, after 2 years the NVRAM still remembers the datetime and settings. Nevertheless, I changed the battery after 2 years, not because it lost it's setting, but just because it's 2 years without a battery change.
Have Fun!!
NOTE:
This mod was mentioned at several Forums, including the one I frequent at the Atari Forums. Hardware gurus there noted that this mod is not a good idea, and that powering up the nvram with 4 x 1.5v AA cells may requires a yearly battery change (with supporting mathematics - amazing stuff!). Other solutions out there are better. This is mention at the following post.
Of course, powering up a chip all the time itself will lead to other issues like hasten the electro migration process of the metalisation & doped regions, but these are all academic stuff and neglected here.
I would also like to point out that the sticky thread DIY: new cell for NVRAM chip provides very good information on how to go about making that replacement of NVRAM possible as well as the other solutions. So look at your options and choose wisely. :-)
See you at
WongCK
created: 11 Feb 2009
modified: 15 April 2011