Problem installing 2.04 ROM in A500

[BGary335]

I seem to be having some trouble getting a 2.04 ROM chip working with my A500, and am hoping someone can tell me what the problem might be. My A500 has the Rev. 5 motherboard. When I put the 2.04 chip in I get a red screen when I boot the computer up. I've done a bit of research and it appears that this red screen indicates a bad ROM chip. I seem to remember that the Rev. 5 board was a little different than the others. Is there anything special that has to be done in order to get a 2.04 ROM to work on a 5A board, or should it be as simply as just putting it in the socket?

Thanks in advance for any help!

[Matt_H]

I'm fairly certain that 5A boards need a jumper wire between pins 1 and 31 of the ROM. See Aminet, or search for ROM installation instructions.

[BGary335]

Wow, that's something I'm not experienced with at all. Where would I get a jumper wire? How does one install a jumper wire correctly?

[banzai]

I just finished installing one on my Rev5. You'll need TWO jumpers, actually.

It all boils down to putting the address lines of the chip to the right spots in the socket. The earlier REV boards (<=5) need two wires, the REV 6 needs one, and later boards (>=6a?) don't need a jumper at all.

The only things you'll need are a soldering kit (Radio Shack has a basic one for about $8-10) and some thin (24-30 gauge) wire, about 6" (18cm) long, cut to a 2" (5cm) section, and a longer 4" (10-12cm) section.

Step 1: Remove ROM from socket. If there's a wire jumpering pins 1-31, then unsolder the wire from pin 1, leaving the connection to pin 31 for the next step.

Step 2: Bend out (or up) pin 31, and solder wire from this to pin 21. (This jumpers the A18 to VCC.)

Step 3: Solder wire to pin 1, making it about 3-4 inches (~9-12cm) in length, to help with the next step (it's tricky!). Leave other end free, but stripped of ~1/4" (6-7mm) insulation.

Step 4: We're done soldering, so you can unplug the thing and let it cool. Now, place the ROM close enough to the socket, as if you were going to insert it. See where pin 31 would've gone in had we not bent it out of the way? That's where the wire from pin 1 is going to go. So, carefully wedge the wire into the socket at pin 31 (this is why we used an extra long jumper). Once in, you can now insert the ROM into place, making sure that the pin 31 of the chip DOES NOT make contact with the wire we just wedged into the socket's pin 31. (This jumpers the ROM's A19 to the socket's A18).

Step 5: Double-check your work. The ONLY pin sticking up is pin 31. The gap in the socket at pin 31 should be used by the wire to pin 1, and the "stuck-up" pin 31 should be wired to pin 21. Once verified, cross your fingers and power it up.

It only took me about ten minutes, including the time to warm up the iron, to do this mod. It worked the first time (after using an unjumpered ROM, the standard jumpered ROM, and finally finding this tutorial for REV 5s).

Good Luck...

banzai

[wlemonds]

Installing KS 2.04 in A500/A2000

You can use a short thin wire and either solder or hook the ends to the pins. Making sure the wire isn't touching any other pins.

Edit : Yea, what Banzai said

[BGary335]

That sounds fairly simple. Just one question: where would I get the wire? Also at Radio shack?

[BGary335]

Anyone know where I can get the wire? I assume Radio Shack sells that too?

[amigakit]

You could use a Kickstart ROM socket such as:

http://amigakit.leamancomputing.com/catalog/product_info.php?products_id=676

We can provide the appropriate wire free with this. Connect the pins then plug the Kickstart ROM socket into the motherboard's Kickstart ROM socket and finally the ROM into the modified Kickstart ROM socket. This way you are not soldering directly onto the ROM.

[BGary335]

About to begin this project, but have one question before I do so: I assume that pin 1 is the pin that has the small groove above it on the chip. If that's the case, then how do I count the pins so that I find pins 31 and 21? I want to make sure that I solder to the right places!  :-D

[wlemonds]

With the small groove as the top and pins facing down. Pin 1 is top left, pin 21 is top right. You count vertically.

I don't have a camera or scanner and I can't get this text editor to format a diagram. I hope that helps.

[BGary335]

That helps very much, and it explains why it didn't work. I found what I thought was an accurate diagram of an OS 2,04 chip, only what I found showed pin 21 down near the bottom right side, and pin 40 at the top right.

[rkauer]

BGary335 wrote:
That helps very much, and it explains why it didn't work. I found what I thought was an accurate diagram of an OS 2,04 chip, only what I found showed pin 21 down near the bottom right side, and pin 40 at the top right.

 PIN 21 IS IN THE BOTTOM RIGHT SIDE!!! With the groove mark on top, the top left pin is 1, count the pins counter-clockwise.

 This is the standard for DIP chips (DIP means Dual Inline Package). Some wikipedia can helps a lot in those cases... :roll:

[wlemonds]

Yep, sorry, my mistake.

I was looking at a diagram from AirRom Kickstart switcher manual and I read it wrong.

[banzai]

I should also note that pin 31 is the only pin bent out - pins 1 and 21 remain in position for inserting into the socket. In fact, it won't work otherwise.

Yes, ANY wire will do, as long as it's not too large in diameter (I used some scraps of CAT-5 lying around). You want to first "tin" the wire ends by lightly hitting them with the iron tip and a dab of solder, just enough to lightly coat the wire with solder. Then do the same to pins 1, 31, and 21 of the ROM. Now that there's a small coating of solder on each, it'll be a snap to "tack" solder them up, since the solder will seem to melt almost instantly, and will cool just as fast (without damage to the chip, as AmiKit is worried about). Just be sure NOT to let the tip of the iron lay on any chip pin (wires are okay) for more than 3-5 seconds, or you risk heat damage. The soldering kit I mentioned earlier was a 15-20 watt model, and you shouldn't use anything higher than 30 watts for this project.

banzai

[BGary335]

Alright, then I had it right then. Hmm...my soldering job was probably botched somehow then. I haven't soldered since high school! I went to Radio Shack last night and picked up a 25 watt iron, a small spool of 24-gauge wire, and a small spool of solder, so I believe all the equipment I bought is suitable. I assume that all the wire is run across the top of the chip i.e. the wire from pin 21 to 31 is run from the top of pin 21 to the top of pin 31, and the wire from pin 1 is soldered to the top of pin 1 and run across the top of the chip to the place where pin 31 would normally go. If that's not the case, then that would be where I messed up.