Amiga : A501 memory expansion Corrosion cleaning and battery replacement

A501 (Commodore) in a tin can
Introduction Commodore A501 Memory Expansion

Anyone who knows the Amiga from its glory days probably also knows the (later in the famous) A501 Memory Expansion Unit.
A nice canned piece of ingenuity, with memory chips, a clock circuit and a time bomb, or a Varta battery.
If you have properly stored your Amiga in the attic or somewhere in a cupboard, time will do the rest, the battery will leak and even crawl into the Amiga via the contacts if you are very unlucky.
Meanwhile corroding and eating away everything it encounters along the way.
Years ago I opened the A501 and removed the battery, but here I will briefly describe how to open and clean the A501.

If you have the A501 in front of you and you turn it upside down, you will see 3 points where the tin sleeve is soldered.
For desoldering you need a somewhat sturdier soldering iron because it has to heat up quite a bit.
Furthermore, a desoldering pump is also handy, or else desoldering wire, all this to remove as much solder as possible before we take the lid off.
Once you've removed the solder, and the lid doesn't come off, heat it point by point while pushing the can apart in that corner.
Once loose you can let go of the can after a few seconds and go to the next point to get it loose in the same way, when you have all 3 loose you can separate the 2 parts from each other.


If you have separated the 2 parts from each other, pay attention to the protective shield, this is to ensure that the bottom of the print does not make contact against the lower tin shield, SO DON'T FORGET IT!

Look at the battery and be careful when disconnecting it, because the substance that has leaked out of the battery is not good for people and animals, and when you are about to disconnect the battery remember that the PCB has suffered from the acid. I personally always cut off the legs, so that I can simply and clearly desolder the legs without having to work with too much force and heating.

If you are lucky and have parked the amiga in the right way, the A501 itself will be affected.
The damage ranges from green battery pins to holes that have rotted in the PCB.
If you look at the photo on the right, you will see that the damage does not seem to be that bad at first glance, but you realize that it is a process that does not just stop.
What do you have to do to stop the process (unfortunately turning is not possible), clean the spots (and clean around them) well with vinegar (I also read citric acid somewhere)
Scrub really hard, and when the pcb has been stripped of as much as possible corrosion, clean the spot well with alcohol or spirits.

A501 Corroded by battery leakage

If you have measuring equipment, you can measure whether the print traces of your A501 that are in the damaged area are still intact, and possibly also test the area around it with a diagram.
If you haven't encountered any problems, it's time to power up the clock circuit again.
This time not through such a battery, but through a relatively safe solution based on a CR2032.
The CR2032 is 3.0 V, the original Varta battery was 3.6 V, the working voltage of the clock chip is between 2 and 7 volts, so the CR2032 is more than enough to run the circuit without any problems.

This replacement CR2032 battery module has an extra circuit on board, since it is not a rechargeable battery but a normal battery and therefore cannot be recharged by the Amiga.
According to experiences, the lifespan of a CR2032 depends on the circuit used for 1-2 years. This means that the battery has to be replaced every 1-2 years, so it is not really wise to solder the A501 back together, as you will then have to You have to unsolder everything again before you can replace the battery with a simple click.

If you have soldered the battery holder in place, it is wise not to reassemble the memory expansion immediately.
You can easily test the memory expansion first without looking around, and thus be sure that the restore operation was successful.
the expansion memory if recognized will report the extra memory and if a clock is detected it will report that too.


The date reported is incorrect and must be adjusted to the current date and time :
Open a Shell, type in date <and then the date in DD-MMM-YY format >, in this case so : Date 07-jan-21
Then set the time correctly by giving the following command: Date HH:MM:SS , in this case Date 01:08
You don't have to mention the seconds, but it is allowed, you can also combine the command, but you can be clear.
The date and time are saved by the command Setclock Save , if that is done and you don't get an error, and the time and date are kept even after a few minutes of turning off the operation A501 was successful.

I chose not to re-solder the 3 tabs that hold the can in place, but just bend it.
That way you only have to bend them straight and you can detach the memory expansion.
Incidentally, there are many people who don't even put the tin back in, the A501 works fine without the tin house it was in.

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