Altair 8800 Power Supply

[Pete Bartusek]

Question,

When I connect my 8800 Experimenter to USB, the system works fine...but should I also be able to disconnect the USB and plug in the power supply only, and have the unit power up (with the on/off switch functionality?)

Right now, I'm not understanding the use of the power supply..unless it's only for the add-on board.  I have a output register board and ran some test and only got very dim lights, so it almost seems like the power supply isn't assisting that, either.

Any clarity is appreciated! 

Pete

[John Galt]

the Arduino due has an issue where it automatically switches power supply sources. 

when using the USB i recommend installing a USB power blocker.

it just prevents power from being provided over a USB connection and keeps the Arduino using the larger external power supply.

that is the reason the power switch stops working when you plug in the usb for file transfers and also using putty or teraterm as a terminal.

this can also cause issues when you need to cold boot when a crash occurs, because the power switch is bypassed and will only allow warm boots.

if you have a lot of devices attached to the DUE and it goes to usb power instead of external power that can cause a low power situation as the amperage over usb is much lower then using the external power.

[Ralf Daume]

Hi,

@John, I don't think that's the issue here.

The 8800 Experimenter comes with a 9V power supply. There is a barrel jack for that power supply on the "Standard add-on board", but plugging in does not actually supply the 8800 with any power. The On/Off-Switch on the front panel does not change that.

I have the same problem. So I pulled out my multimeter and could follow my 9V from the barrel connector to the pin connectors to the "Standard Exp Conn" of the main PCB. And, by the life of me, I couldn't find any leads on the main PCB connected to the two power pins. I assume that while revising the PCB, these leads were deleted by accident.

This is the Altair-Duino version 2.5.2

I would be glad if anybody could confirm my observation, or if I should get better glasses.

Thanks

Cheers

Ralf

[Ralf Daume]

There's also only one lead connecting to the On/Off Switch, which, in my mind, is not enough for an electric circuit.

Unless, of course, I'm missing something.

[Corrupt Liberty]

I have board revision 2.5.1 and the 9v power supply works perfectly.  The power switch works to control the power only when using the 9v supply.  When USB power is applied the switch does nothing. Maybe this is an issue with the 2.5.2 revision?

[Chris Davis]

The 2.5.2 boards are new, but I have built a couple, so I thought they worked...  Looking at the schematic, it looks like I labeled two connections wrong.  To fix this, run a wire from pin 13 of the "Standard Exp Conn" (second pin from the top) to center pin of the power switch.  I'll get the addendum page updated when I return home tomorrow.

[Chris Davis]

Also, you want to avoid connecting USB and the power adapter at the same time.  Use one or the other.

[Ralf Daume]

Yeah, but the top pin ain't connected either...

[Chris Davis]

What top pin?

I have updated the addendum with a photo: https://adwaterandstir.com/instructions/ 

[Ralf Daume]

Two pins of the "Standard Exp Conn" are supplying the 9V, and if I'm not mistaken, it's the first and second pin from the top (pin 14 and pin 13?). Both need to connect to the rest of the PCB somehow, but both pins lack a trace connecting to them.

So by running a wire from pin 13 to the On/Off-Switch, only half of the electric circuit is done. There needs to be a second wire running from the topmost pin (pin 14?) to some other place an the PCB.

Unless, of course, I'm missing something. I tried to find a schematic of the board online. Is one available?

[Chris Davis]

Pin 1 is also ground. You can go to my site and search “schematic”.

[Ralf Daume]

Ah, I see. Thanks for clarifying. :-)

[Pete Bartusek]

Thank you! I do have 2.5.2, so I'll take a look at the addendum!