View Full Version : Is this a mod?

June 6th, 2012, 06:24 PM
i have a 3Com Etherlink II that has a weird little blue resistor on it:
Is this normal or is it a mod?

June 6th, 2012, 06:38 PM
It definitely looks like a mod, but it could be a factory mod--it appears to be very neatly done. What does the resistor connect?

June 6th, 2012, 06:42 PM
It connects a different resistor to pin 5 of a chip labeled dp8393n.

June 7th, 2012, 07:44 AM
Changes like that done at the factory are not all that uncommon... the older the hardware the more often you'll see it.

I have a STACK of TRS-80 color computers and every single one of them has changes like that. Take the Rev NC board unit I use as my primary:


Top right near the RF modulator, resistor soldered in between the modulator input and oscillator output on the MC1372P modulator chip. My other NC board has even more modifications with this mess of capacitors and resistors in the same area... one of my revision E boards has bus wiring going EVERYWHERE, while the other rev E is clean -- no changes. The rev E with the extra wiring will take Extended color basic 1.1, while the one without the wiring will only work with ECB 1.0 (took me a bit of fiddling to go "why isn't this working!?!")

In any case, it's not exactly surprising to open up a 70's or 80's computer and find a some cut traces with wiring, resistors, capacitors thrown in even when they were factory fresh. Mistakes in manufacturing, errors in design, or even just upgrading old manufacturing to match the newest 'model' were all pretty common. You find that adding a pull-down resistor to an input makes it run better, do you throw out a thousand already etched boards, or do you cut a trace and solder it in?