Hello Philippe. If you wish to replace the cartridge battery without using a parity battery to hold save files during the replacement, you can essentially skip Steps 3, 5, 6, 7, and 11.
My advice if you were to decide to keep working on the cartridge would be to firstly replace the resistor that has broken with an exactly equivalent one, with the other piece of advice to test the single capacitor on the PCB.
With voltage seemingly going through the PCB from the battery properly and no other component seemingly at fault, the next step would’ve been to see if there was anything wrong with the capacitor located around the lower middle of the board. I couldn’t see the capacitor bulging from the photos you linked, so the only way to test the capacitor for a fault without first desoldering it from the PCB would be to use some specialised equipment such as an ESR Meter or Smart Tweezers. To test the capacitor with a multimeter would involve desoldering it from the PCB first then testing the capacitor in resistance reading.
If however you do intend to give up on this, I suggest looking for a cartridge PCB on its own so you can install that into your current cart case, making sure it’s an identical PCB
One final test. Check and report the voltage of the following terminals in the image below marked red.
Using the image linked below for reference, check the voltage of the terminals marked in red, and check the resistance of each resistor in the terminals marked blue.
If you are no longer reading continuity between the two battery terminals and there is a voltage reading on the resistor terminals, try testing if the game can hold save data again.
The only advice I can offer now is to find whatever is joining the two battery terminals together as it should not have continuity between them. You will need to find this on your own since I cannot determine what it could be from any of the photos. Good luck.
No. There should be absolutely no continuity between both the positive and negative terminals of the battery. When doing a continuity test on the battery terminals, it should not beep.
A bit of shame on me for not thinking to test this before.
There is continuity between the positive and negative terminals of the battery. There absolutely should NOT be. Somewhere on or around the battery holder is something physically linking the positive and negative ends of the battery on the PCB. You will need to find and cut this link. There could be a number of reasons as to what is causing the two terminals to be joined together. The battery holder may be of poor quality and is joining both ends of the battery itself together, or somewhere (probably under the holder is my best guess from the photos) is some solder or something similar physically linking the terminals.
I am confident that once the terminals are physically separated and there is no longer any continuity between the battery terminals, that power will go to the SRAM chip properly and your cartridge will be able to hold save data again.
If somehow it still doesn’t work, then I unfortunately have no more advice I can offer.
One final check. Test to see if there’s any continuity between both positive and negative battery tabs. If your multimeter doesn’t have a continuity test mode, set it to check resistance.
At this point I would need to see pictures of your cartridges PCB in order to determine if I can offer any further advice. If you are able to, please upload high quality photos of both the front and back of the PCB and post the link to the photos in a reply here.