PurpleROM Issues on IIsi

[bretwashere]

Hello all! I am seeking help and asked this question on a Facebook Group and didn’t get any replies.

I bought a purple ROM for my IIsi, as I would like to customize the ROM on the machine. After installing it and placing a jumper on W1, I cannot get the machine to boot with lines, or a green/blue screen with no chime. If I pull the jumper and try again, same results. If I pull the ROM SIMM and leave the jumper in, same results as well. If I pull W1 and the ROM SIMM, the computer boots.

Has anyone have any recommendations? I have reseated the chip and applied a little force to see if it’s the socket, and it doesn’t appear so. I inspected the SIMM pins, and all looks good.

The seller stated that the ROM is compatible with the Macintosh IIsi and should be plug and play.

 

[ajacocks]

Welcome to the forum @bretwashere .

As far as the ROM SIMM goes, I'd check to make sure that your ROM SIMM socket is clean, and spray in some deoxit. That's a start.

Also, check for any corrosion or battery leakage on your board. In the second photo, there appears to what could be corrosion on the PCB next to the 74ALS254 (based on the silkscreen) IC, and the one above it. Might just be dirt, but I can't tell.

- Alex

 

[bretwashere]

Thank you. I did blow the connector with compressed air, but I’ll try deoxit and post back.

 

[olePigeon]

Over at 68k MLA it's been discussed quite a bit. I believe it was discovered that Apple used an odd thickness for the PCB when they made the original ROMs, a size that isn't available today. So the custom ROMs that are made are just a hair too thin (the next size up is too big.) People have come up with different ways of making sure it has good contact. The simplest is to use rubber bands to create very light tension on the SIMM, pulling it to a slight angle so the SIMM remains in good contact with the socket pins. Other people added a layer of solder to the pins on the SIMM to thicken it up. One user 3D printed a custom bracket that basically did the same as the rubber bands, putting the SIMM at a very slight angle so as to maintain tension against the socket pins.

In short, try taking it out and putting it back in several times. If you have a couple rubber bands, I'd try that trick, too. If you're certain the ROM is good, then it's probably not making a good connection.

 

[bretwashere]

Hello!

Thank you for the suggestion! I got stuck the other night, as I extracted all the EEPROM chips and individually read the ROMs via my flash programmer. I didn’t really understand how these custom ROMs are built, and was confused regarding them being split four times (512k each totaling 2mb).

Deoxit did not help, and upon further inspection, there is no corrosion on the motherboard, traces, or chips.

I’ll put the EEPROM chips back into the module and try again.

 

[olePigeon]

@bretwashere Ah, I found thread. PotatoFi designed some clips that hold the ROM firmly in place.

https://68kmla.org/bb/index.php?threads/3d-printed-se-30-rom-clips.36241/

You can buy a set here for just US $3.00. Hopefully you're local. You can also download the file and print it yourself if you have access to a 3D printer.

https://www.etsy.com/listing/840042244/macintosh-se30-rom-clips