-5V in SE/30 power supply

[aeberbach]

I've been powering a SE/30 board from a power supply that has 5V, 12V and -12V. I simply left it disconnected and no issues.

So far on the schematics the only place I can see it used is Vee on UE12, a 26LS30 line driver. Serial communications. Is that the only place it is used?

 

[cheesestraws]

So far on the schematics the only place I can see it used is Vee on UE12, a 26LS30 line driver. Serial communications. Is that the only place it is used?

That's plausible; on the LCs, at least, it's only used for serial communications, and at that only differential signalling, so you could probably even get away with doing RS232 without it.  You need it for RS422 and LocalTalk.  So while I haven't really looked in-depth at the SE/30 schematics, it wouldn't surprise me if it was the same.

 

[superjer2000]

-5v?  Where do you see a reference to an SE/30 PSU supplying -5V?  LCs for sure but not SEs or SE/30s.

 

[superjer2000]

-5v?  Where do you see a reference to an SE/30 PSU supplying -5V?  LCs for sure but not SEs or SE/30s.

Unless you're powering the logic board independently of the analog board?  Is one of the connectors from the analog board to the logic board -5V?

 

[superjer2000]

Actually - that's pretty awesome.  I was planning on modding one of my ATX PSUs to power my IBM 5150 I just bought - I was looking at ways of adding a -5V and had pretty much settled on using a 7905 voltage regulator.  I see in the schematics for the SE analog board they used a 7905 and the caps. etc used are all there too so I might just copy that, adjusting the resistor value to match the current limit of the original -5v line on the IBM PSU.

 

[aeberbach]

I do have my SE/30 out of its case because I am doing some hardware things, when it is in the chassis you can’t access much. To keep it safe I made a 3D printed base with power supply mounted on one side. Because I have all the connectors handy I made a cable from a Mean Well +5/+12/-12 supply direct to the logic board. A lack of -5V wasn’t stopping anything from working, I just wondered if there was anything I hadn’t tried other than serial that it could affect.

 

[superjer2000]

I do have my SE/30 out of its case because I am doing some hardware things, when it is in the chassis you can’t access much. To keep it safe I made a 3D printed base with power supply mounted on one side. Because I have all the connectors handy I made a cable from a Mean Well +5/+12/-12 supply direct to the logic board. A lack of -5V wasn’t stopping anything from working, I just wondered if there was anything I hadn’t tried other than serial that it could affect.

To follow-up on this, I did end up replacing my IBM 5150's power supply with the same Seasonic I use for my SE/30s.  I used a 7905 and a couple of caps and a resistor on the -12v rail to get -5v and it's working great.  Might be an option if you did want to get -5V going so you have the complete set of voltages.