zigzagjoe
Well-known member
So: Much to my surprise, the SE logic board harness (from the analog board) uses 22AWG for all wires, even the two +5v leads (orange).
In an accelerated SE / SE30, you could be pushing 6 amps over these two wires, which leads to nasty voltage drop! With the original PSUs, you can at least adjust the voltage to compensate, though your 12v line may be 13v when you're done.
However, on a seasonic PSU where you can't adjust the voltage? It's a real problem. In my SE/30, I was seeing around 4.72v at the LB floppy port with a Carrera clone, Asante MacCon, grandvimage card, HDD, and seasonic PSU. Somehow this was stable, despite visual noise on the GrandVimage's output.
Solution is to replace the 22ga +5v wires with 16ga wires. Happily, molex makes a near-exact replacement, gold plated, too! Just a hair longer than the original. After doing so, that same machine is now sitting at 4.85v - a 0.13v improvement! While it's still not ideal, it's a heck of a lot better, and importantly drastically reduced the noise on the external video output.
Molex P/N : 2153402223 , 225mm 16G Red cable w/ gold mini fit jr socket terminators.
Digikey stocks it for $1.39 per: https://www.digikey.com/en/products/detail/molex/2153402223/13144614
You can remove the wires from the original connector with a tactically modified paperclip (pictured above), or the original Molex 11-03-0044 tool.
In an accelerated SE / SE30, you could be pushing 6 amps over these two wires, which leads to nasty voltage drop! With the original PSUs, you can at least adjust the voltage to compensate, though your 12v line may be 13v when you're done.
However, on a seasonic PSU where you can't adjust the voltage? It's a real problem. In my SE/30, I was seeing around 4.72v at the LB floppy port with a Carrera clone, Asante MacCon, grandvimage card, HDD, and seasonic PSU. Somehow this was stable, despite visual noise on the GrandVimage's output.
Solution is to replace the 22ga +5v wires with 16ga wires. Happily, molex makes a near-exact replacement, gold plated, too! Just a hair longer than the original. After doing so, that same machine is now sitting at 4.85v - a 0.13v improvement! While it's still not ideal, it's a heck of a lot better, and importantly drastically reduced the noise on the external video output.
Molex P/N : 2153402223 , 225mm 16G Red cable w/ gold mini fit jr socket terminators.
Digikey stocks it for $1.39 per: https://www.digikey.com/en/products/detail/molex/2153402223/13144614
You can remove the wires from the original connector with a tactically modified paperclip (pictured above), or the original Molex 11-03-0044 tool.
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I'm seeing 4.99V (up from 4.84V) booting a bare board, and 4.88V (up from 4.53V) with the Micron Xceed SE/306-48 installed. Bear in mind, this is with a long ATX extension lead with 18AWG wires on its 5V lines (should probably get those upgraded too).
