Lexicon 960L PSU ATX standard?

[flintan]

Hi! I'm having a hard time to gather all the correct pieces of information together here. I'm about to replace the PSU of a Lexicon 960L. The manual says it's a standard ATX PSU and I've seen several people have it successfully replaced with modern equivalents.

However, the stock PSU has the old standard ATX motherboard connector with 20 pins and a -5V rail on number 18. The service manual also says there should be -5V at pin 18 under the section about "Main Power Supply Connector J26 Voltage Level Tests". Most (all?) modern ATX power supplies does not have -5V and there is no cable on pin 18. From the link above:

The -5 volt line on pin 18 was made optional in ATX12V 1.3 (introduced in 2003) because -5 had been rarely used for years. Newer motherboards virtually never require -5 volts but many older motherboards do. Most newer power supplies don't provide -5 volts in which case the white wire is missing.

Is the -5V rail necessary or can I use a PSU without it?  Any help would be really appreciated.

 

[scott2000]

I almost wonder if that -5v rail is just there because the older supply had that and it was just a way of verifying there were no issues with the supply....I just quickly looked through and don't see where -5v is used but, I surely could've missed something....That's a big manual.....

Sorry I couldn't be helpful.....If you say others have successfully used newer ones, why are you doubtful ?

 

[flintan]

I almost wonder if that -5v rail is just there because the older supply had that and it was just a way of verifying there were no issues with the supply....I just quickly looked through and don't see where -5v is used but, I surely could've missed something....That's a big manual.....

Sorry I couldn't be helpful.....If you say others have successfully used newer ones, why are you doubtful ?

Thanks for your input! Indeed the manusl is quite voluminous.

It might very well be as you say that the -5V measurement is just for verification.

I’m doubtful because I’ve just heard about replacement with no specification and old Windows NT computers aren’t really my area of expertise.. The motherboard is NLX form RadiSys SF810 97-9000-03

 

[flintan]

I can now confirm the -5V is just for reference, the unit does not need it. Went with a Seasonic Prime Gold 650W PSU, works perfect. It has the same size as the original 250W PSU and it also has a switch with two different modes for the fan so you can have it rotate all the time and suck out warm air from the rest of the unit even though the thermal sensors in the PSU does not think it's necessary.

 

[scott2000]

That's wonderful! Thanks for the update...Good to know.....

 

[PRR]

I know the history and know there is no way to know.

The original IBM 5150 PC *prototype* needed:

-12V for RS-232
-5V for RAM substrate bias.

The -5V was a simple R-Z drop from the -12V.

As it happened, Intel improved the RAM to not need the substrate bias before IBM got to production. So -5V was already obsolete before the 5150 shipped. However the design was done and -5V was available to all slot cards.

Nobody really knew "who" used the -5V. Maybe somebody did? Apparently this was still unresolved when ATX took over, since it has -5V. And maybe by 2003 it had been decided that any card actually eating -5V could just die (side-sales of new cards is always good business).

Glad it worked for you.