How To Replace An Eprom

By Craig Anderton

Hardware units with microprocessors use EPROMs to store instructions of how the unit should function. It is possible to rewrite old instructions, and/or add new instructions, then store these on an EPROM that replaces the older EPROM. The new instructions could fix bugs, add new features, or both.

It's not that difficult to replace an EPROM. There are really only two points to remember:

• If the thought of opening up a unit and changing a chip sounds even remotely scary, get someone else to do it.
• Work very slowly and carefully; if you're careless, you could wreck the unit.

Here's the procedure.

Fig.1. A chip puller makes it easy to pull out a chip.

Fig.2. Keep the EPROM protected from static electricity.

Fig.3. Make sure you don't build up any static charges.

Fig.4. Note the position of the chip's notch.

Fig.5. Pull out the chip slowly and carefully.

Fig.6. Make sure the pins are completely straight and unbent.

Fig.7. Push equally on both ends of the chip. If you feel any major resistance, stop and make sure the pins are going in properly.

Fig.8. Confirm that all the pins are inserted into the socket.

1. Find an uncluttered work space, and throw a towel on top of it to prevent scratching the gear. Then, read any manual that pertains to the upgrade! There may be a crucial tip that spells the difference between success and failure.
2. Gather your tools. You'll need whatever is necessary to open up the box and access the chip (screwdriver, allen wrench, etc.) and a chip puller (Fig. 1). The chip puller has two little hooks on the end that go under the chip itself to pull it up from its socket. In some cases the EPROM may be exposed enough that you can pry it up with a screwdriver, but unless you're really careful, this is asking for trouble should the screwdriver slip.
3. Locate any screw holes and disassemble the case. Some gear is sneaky, and hides a screw hole under a warranty sticker; or the disassembly process may require a service manual if the job is particularly nasty. Hopefully, any documentation with an upgrade kit will fill you in on what to do.
4. Keep the chip with its pins sticking into a conductive foam block (Fig. 2), or wrapped in its conductive plastic bag. Static electricity can fry chips, and this provides protection during handling.
5. Discharge yourself of any static electricity by touching something metal, such as the ground point of a jack (Fig. 3). Conductive wrist straps are also available that go around your wrist and clip to a ground point. This insures that you are grounded at all times. Do not do anything that can build static electricity back up, like running your feet on the carpet.
6. Now take out the old chip, but first, note the orientation of a notch or dot located at one end of the chip (Fig. 4; there may be a matching notch on the socket underneath). The notch or dot on the new chip will need to be oriented the same way.
7. Hook the ends of the chip puller underneath the chip ends (the sides without pins—see Fig. 5). Slowly pull up and out. A slight rocking motion may help.
8. After discharging yourself of static electricity, remove the new chip from its protective foam or bag. Check that all the pins are perfectly straight in a line (Fig. 6). If any are bent, carefully straighten them so they are in the same plane as the other pins.
9. Set the pins into the matching holes in the socket, making sure that each pin is sticking directly into its corresponding socket. If all the pins are lined up properly, push down by applying even pressure at both ends of the chip (Fig. 7).
10. Check where the pins meet the socket to make sure that no pins are bent under the chip, or otherwise out of place (Fig. 8).
11. Once that's done, re-assemble the unit, check it out, and hope that everything turned okay.

Troubleshooting

If there is a problem, it will most likely be due to one of the following.

• It is possible to get a bad EPROM, but that's very rare.
• The chip is not oriented correctly (you did check the notch orientation before pulling the old chip, right?
• All pins don't go straight into the socket.
• There was static electricity damage during installation.

Odds are, though, all will go perfectly and you'll have a brand new set of features.