Hi PCBONEZ,

that's right, that the traces on the ISA Motherboard (Master) have current limits and when i overpower the ISA Bus from the Motherboard it will burn the Rail on the ISA BUS from the Motherboard.

But:

When i use the Power from the ISA Motherboard (Master) and use the Power from the Passive ISA Extender, this will blow up in a short, because the Motherboard provides Power from the ISA BUS and the Passive ISA Backplane provides Power from the Aux Power Input, or have a passive ISA Backplane Circuits to shut down all ISA Voltages from the Master ISA Mainboard to the Passive ISA Extender ?

Greetings

Dubinius wrote:

Hi PCBONEZ, […]
Show full quote

Hi PCBONEZ,

that's right, that the traces on the ISA Motherboard (Master) have current limits and when i overpower the ISA Bus from the Motherboard it will burn the Rail on the ISA BUS from the Motherboard.

But:

When i use the Power from the ISA Motherboard (Master) and use the Power from the Passive ISA Extender, this will blow up in a short, because the Motherboard provides Power from the ISA BUS and the Passive ISA Backplane provides Power from the Aux Power Input, or have a passive ISA Backplane Circuits to shut down all ISA Voltages from the Master ISA Mainboard to the Passive ISA Extender ?

Greetings

I am not sure what you are asking.
You are concerned about two power supplies in parallel?
.

Hi PCBONEZ,

yes, two Power Supplies in Paralell (because the Host PC provides Power and your have connected a AT Power Supply to the passive ISA Backplane) This Situation is given:

The Mainboard with CPU, PCI and ISA Bus has it's own Power Supply in Form in a ATX Power Supply or an older Computer with a AT Power Supply.
This Situation powered the External Passive ISA Bus with Power from the Mainboard.

Over the Ribbon Cable to the Connection from the Host PC to the ISA Backplane, all Signals + all Voltages are transfered to the ISA Backplane and powered the ISA Backplane from the Main PC.

But my Question is:

Your have already plugged an AT Power Supply to the Passive ISA Backplane and your have the Power from the Mainboard with CPU, PCI and ISA Bus

I think this will short out somethings because your have Power from the Passive ISA Backplane (With the ISA-Slots) and the Mainboard-Power from the Host PC.
Or the Passive ISA Backplane (With the ISA-Slots) have some Circuits to block the Power Rails from the Mainboard to the Passive ISA Backplane when an external Power Supply is connected at the Passive ISA Backplane?

😊

Because in this Situation i think you distribute Power back to the Mainboard and your will burn something 😀
Or i must cut the Power-Lines from the Ribbon Cable, to do not have any Power to the Passive ISA Bus and i can still use the external Power Source from the Passive ISA BAckplane?

Greetings

Dubinius wrote:

Hi PCBONEZ, […]
Show full quote

Hi PCBONEZ,

yes, two Power Supplies in Paralell (because the Host PC provides Power and your have connected a AT Power Supply to the passive ISA Backplane) This Situation is given:

The Mainboard with CPU, PCI and ISA Bus has it's own Power Supply in Form in a ATX Power Supply or an older Computer with a AT Power Supply.
This Situation powered the External Passive ISA Bus with Power from the Mainboard.

Over the Ribbon Cable to the Connection from the Host PC to the ISA Backplane, all Signals + all Voltages are transfered to the ISA Backplane.

But my Question is:

Your have already plugged an AT Power Supply to the Passive ISA Backplane and your have the Power from the Mainboard with CPU, PCI and ISA Bus

I think this will short out somethings because your have Power from the Passive ISA Backplane (With the ISA-Slots) and the Mainboard-Power from the Host PC.
Or the Passive ISA Backplane (With the ISA-Slots) have some Circuits to block the Power Rails from the Mainboard to the Passive ISA Backplane when an external Power Supply is connected at the Passive ISA Backplane.

😊

Greetings

I think I get'cha now.
You are concerned about powering the add-on ISA slots both through the cable and the passive card's power jack at the same time. - Yes?
.
With one PSU using splitters to the passive board should not cause a short because it's the same voltage from the same source.
That's not to say there are no side-effects at all.
The circuit resistance through the traces and cable (small conductors) will be greater than through the splitter (presumably 18ga wire).
Without the splitter the voltages at the passive board would be *slightly* lower than what is available through the splitter or closer to the PSU.
So, with both connected the current is going to prefer going through the splitter. It's a lower resistance path.
- There will probably be a small reverse current from the passive board through the cable back into the mobo.
That's actually not a bad thing as takes some load off some of the motherboards traces.

If you are REALLY worried about it the thing to do would be to disconnect the power through the cable and use only the splitter for power.
That could be done by removing or not connecting the power pins or by snipping the appropriate wires.
.

I do exactly so, break out power lines +5v and +12v between mobo and isa riser (I use isa riser about 5 slots). But my connection is "classic" without soft cables. I tried to use them and got good stability only with one or two sound cards (exactly sound cards, not midi-only synths), even if very short cables. The same results are reached by another man, my friend. And he leaved cable-connection too.

It is sadly, jwt27 doesn't answer how many and which cards he uses.

I think it is better to use one powerful psu for both, mb and isa plane. Or if you use separate power at least connect their grounds very good!

PARUS wrote:

I do exactly so, break out power lines +5v and +12v between mobo and isa riser (I use isa riser about 5 slots). But my connection is "classic" without soft cables. I tried to use them and got good stability only with one or two sound cards (exactly sound cards, not midi-only synths), even if very short cables. The same results are reached by another man, my friend. And he leaved cable-connection too.

It is sadly, jwt27 doesn't answer how many and which cards he uses.

I think it is better to use one powerful psu for both, mb and isa plane. Or if you use separate power at least connect their grounds very good!

Agree. It's best to use one PSU for both.

Break out -5v and -12v too.
Do not break out the grounds though because signals depend on those too. Not just power.
.

Yeah!

Thats the Information that i want 😀 Thanks.
And sorry for my English or Grammatics, i'm not a English man 😁

It's best to use one PSU for both - is right, also to provide some more Power i can add a Aux AT Power to the ISA Backplane and cut all the 4 Power Lines (+5V/+12V/-5V/-12V) out from the first ISA Bracket from Main ISA Mainboard (the Bracket with the Flat Cables) so no Voltages going into the ISA Backplane and can use a secondary AT Power Supply 😁

Because:

I plan to extend my 8 Bit ISA Bus from my Schneider Euro PC II (XT Class Computer) and in the Future i use then a Backplane with an Aux AT Power Source and cut the Power Lines out from the ISA Bracket so no Voltages going into the little XT Class Computer and destroy somethings 😀

Some Off Topic about Power Lines 😊 :

I had a very strange Issue with that Euro PC II and a 8 Bit SCSI Controller (Future Domain 950). When i using a external SCSI Harddisk with his external 12V/5V Power Jack and connect this HDD to my SCSI Controller via the default 50 Pin SCSI Cable so also my Euro PC II is powered on (!) with the Power Switch OFF and no Power from my 18V Power-Brick for the Euro PC II.

Thad was totally crazy, it boots and works ! I found a TE Jumper on the Future Domain 950 Controller that was closed. I think this TE Jumper means like Termination Power and i think:

The SCSI Card provide 5V+ to the ISA Bus (!) and powered this System. I was shocked that a little tiny SCSI Card can power up the System and look at the Traces from the SCSI Card, its so very very tiny and, ... I shutdown my external HDD at about 3 Secs and also the Euro PC II get shutdown 😁 😁 😁 ...

When i set the Jumper TE to disable, so my Euro PC II don't boot and has no power at all, ... CRAZY !!! What the Hell 😕 😀
This was very very confused because the SCSI Card "pulls" 5V Power from the SCSI Cable and also powered the ISA Bus with +5V BUT why my System is booting and starting with that ugly TE Jumper ON only with +5Volts ? The System needs +5V -5V +12V and -12V .....

But still my Euro PC II runs fine and the SCSI Card also 😀 So i had a little problem i thinking, when i use a external Passive ISA Backplane with an external AT Power Supply it also powers my Euro PC II System because all needing Voltages are on the 8 Bit ISA Bus, ... or my 8 Bit SCSI Card has a crazy Layout-Bug, STRANGE 😀

Greetings

I'm not familiar with that equipment or with SCSI so I don't know the answer to that one.
Someone else around here probably does.
.

Hi PCBONEZ,

thank you 😀
That was strange with SCSI 😀

Greetings

really usefull for a small xt-computer like a "Schneider Euro-PC" or a "Tandy 1000 RL"
8Bit Version with an internal Card an a small metal case with PSU would be VERY usefull.

Agree with dr.zeissler 😀

@jwt27:

I had a "nice" to have feature for your awesome ISA-Brackets with the -5V Regulator Supply:
I'd would be "cool" to have a some sort of 4 jumpers to disable or enable all ISA Power Rails like +5V -5V +12v -12v in Case to use for an external AT Power Supply on a Passive ISA Backplane.

-> All 4 Jumpers closed on your ISA-Brackets - All Positive Power Rails going from the Mainboard to the external ISA Backplane
-> All 4 Jumpers open on your ISA-Brackets - No Power going from the Mainboard to the external ISA Backplane but the Ground Rails are still connected (For external Power Supply on the Backplane)

😀

With this function, no User need to have cut down the Power Lines on the Flat Cables to avoiding a short out, when two power supplys are working together (Mainboard Power + Aux Backplane Power also)

Greetings

ISA cards don't draw that much power. You don't need a second power supply. Did you know a 486DX-100 with VGA, Sound and flash drive takes only about two ampere on 5V to run? Ten watts - Plenty of room with a power supply that has a 200W label.

That's a different thing with an external power supply from a EuroPC.

Hi h-a-l-9000,

you're are right on there, that no external AT Power Supply is needed for a Host Machine that provides plenty of Amps. But for a special Thing, the Schneider Euro PC who has a little tiny Power Supply (Or some other little Computer with a 8 Bit Slot or a compact Computer), they need an external Power Supply to handle the new Add On Cards.

I know, the Euro PC XT is just a little small thing and i think no one use that Machine anymore (also some peoples) but i think the Idea with an external Power Supply for the Passive ISA Extender is not so a bad idea and at another footprint: When a User just plug an external Power Supply without enabling his Brain 😊 then they will have a Mess up i think when both Power Supplys are running (Host Computer and ISA Addon Backplane) 🤣

Greetings

Very cool. I spent quite a bit of hours pondering what sort of retro build to do that can fit the 4 ISA soundcards (+some external) and play all the games I like in single setup.

Ended up with looking for 4 ISA slots + ATX. I found a mobo with PS2/AT+ATX power*, 4 ISA and 4 PCI with P233 MMX. I have SCC1 and MT32 that will hook together, then I have external midi keyboard with XG (only final fantasy 7 used this I think), I can both play all the synths myself or the games. I found some supposedly good DOS music sequencers I will be taking a look at. Also my favorite DOS synth AXS will be using a GUS. I haven't yet decided what FM card to use. I gave away all my ISA cards long ago and looks like I end up buying them back as while for example all OPL2 chip technically sound same, each card had different analog configuration. This is why I believe dosbox sounds "crap" - it does not model the analog side of the cards - some cards add noise,overdrive,EQ,stereo width changes. My old gaming setup ran all the sound also through external system with EQ I had set manually. Now I used headphones so I'm like.. I need some way to EQ the headphones but getting an EQ into dosbox is tricky as I'm clueless when it comes to programming that stuff. WinUAE is much better as it atleast has some level of filtering and stereo width choices, attempting to emulate the A500 analog audio side.

*I'll try some ATX PSU first - since I'll likely need -5V rail I'll have to check this out.

h-a-l-9000 wrote:

ISA cards don't draw that much power. You don't need a second power supply.

You need to be careful making blanket statements like that because while it's usually true it may not always be true.
The ISA BUS Standard allows 8-bit ISA cards to draw up to 58.5 watts and 16-bit up to 66 watts.
Those numbers are for each card, not the whole BUS.

I am not saying ISA cards actually use that much, but that they are -allowed to-, so some may exist.
I don't think you will run into any cards that use that much in typical PC equipment either but if you start dabbling with industrial ISA cards you might.
.
I'm attaching a snap-shot of the appropriate page of the ISA Standard.

Hi PCBONEZ,

thank your for you statement and for the attechment to turn a blanked statement to a rock solid 😁

> You need to be careful making blanket statements
And you just love to be right, eh. Enough to dig up some unreal-world example to prove me wrong.
You'll need a strong backplane too if you want to supply the maximum, and a custom power supply for the negative voltages. And don't forget good cooling - 600 watts heat will not be easy to get rid of.

Good point with the Euro PC.
With two power supplies you will have to consider some non-obvious effects though - even if you switch on both power supplies with one switch, they will most likely not start up simultaneously. Problems can arise from this:
- the delay is too long - the mainboard comes out of reset while the expansion is not yet fully powered. It can drag down the bus and cause malfunction.
- One side is powered, but the other not yet: Danger of latch-up effect - the bus lines sink current into the non-powered chips causing latch-up. This can cause damage when the second power supply starts up.
- Using PC power supply, but unbalanced load: Due to their regulation cirquits many PC power supplies need a minimum load on the 12V line. If you put a load only on the 5V line but none on 12V, the 5V will drop and the 12V rise.

I'd rather power the Euro PC and backplane from one strong enough supply. According to Google pictures that has been done already.

h-a-l-9000 wrote:

> You need to be careful making blanket statements
And you just love to be right, eh. Enough to dig up some unreal-world example to prove me wrong.

Guess what - it's not about you.
It's all about making sure other people don't get into trouble.
.
I was a Quality Assurance Inspector overseeing repairs and mods to electronic controls, nuclear plants and submarines.
It was my job to look up specifications and make sure things were done correctly. - It is second nature now.
If I got it wrong somebody died. Possibly a whole lot of somebodies.
.
I'm hardly always right but if i say something technical I've usually verified it beforehand with an authority or a technical document.
.

h-a-l-9000 wrote:

I'd rather power the Euro PC and backplane from one strong enough supply.

Yes, this is the best choice.

If you are going to use two PSUs in parallel you should set up an auctioneering circuit so the voltage regulators are not fighting each other.
The problem with that is auctioneers drop some voltage so the voltage in the slots will be less than the voltage at the PSU.

It is WAY easier just to use a bigger single PSU.
.