Combating SE / SE30 voltage drop

[Mk.558]

I bought a Male to Female Molex 14 socket assembly off ebay, but then I found out the original is a Male to Male. Okay I guess mine is now an extension cable instead of a replacement.

Is 20AWG good enough? Just running an Ethernet card, an accelerator may or may not be used, and 20MiB of RAM.

 

[jmacz]

I think the suggestion was to use 16 or 18, but the thing to watch for was wires with thick insulation and less copper inside.

 

[zigzagjoe]

Use 18awg, or 16awg if you are exceeding the stock harness length. Don't act as an extension unless absolutely unavoidable - ie use male to male and adjust length as you see fit.

A badly fitted minifitjr connector pair can introduce some really nasty voltage drop. Even one with good contact unavoidably introduces some drop.

 

[Mk.558]

Noted.

I don't understand the recent obsession with voltage drops: for >30 years we've been doing it all wrong?

 

[cheesestraws]

I don't understand the recent obsession with voltage drops: for >30 years we've been doing it all wrong?

It seems to be the current favourite thing to blame random unexplained glitches on - people want to feel like they've explained something, I think.

 

[croissantking]

It seems to be the current favourite thing to blame random unexplained glitches on - people want to feel like they've explained something, I think.

We're pushing these machines harder now than they were ever designed for, with multiple expansion cards stacked up. So small weaknesses that could have been overlooked in the past are becoming more important now.

 

[Mk.558]

That's true. In the past we weren't really exploring triple stacked expansion cards. Probably also voltage drift over time on PSUs.

I feel like my comment was probably a little harsh, but I didn't intend it to be that way. The difference between 4.89 and 4.76 volts is probably not going to cause a stock system to behave strangely -- like my SE/30 does -- more likely are VIAs or dried up old solder.

 

[zigzagjoe]

Yeah, the stock machine would be just fine with the usual tolerances on voltage.

When you've got a stack of cards... well, power conditions in the SE30 are not great to begin with. Add a stack of cards which is not a topology that does wonderful things for power distribution and voltage ripple.... Top cards get screwed.

Add tight timings on the accelerator logic and you've got room for weird things to happen. It is something I've observed firsthand while developing my cards. You can try to filter the power rail to help this but only so much can be done. On the 30Video cards i resorted to regulating 12v down to 5 in order to get a clean 5v for analog power.

That said voltage related issues usually become evident immediately up until everything is fully heated. It can contribute to long term stability or lack thereof but is less of a primary cause then.