88-2SIOR1 and 88-2SIOJP OutPuts LOW ???

Walt Perko

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Jun 30, 2026, 12:44:58 PMJun 30

to Altair 8800

Hi,

Although the 88-2SIOJP drives my SpeechBox just fine with an RS-232 to TTL adapter, I can't seem to get enough direct or with an RS-232 adapter to drive the stepper motor driver board.

Shouldn't the output of the 88-2SIOR1 and 88-2SIOJP be a little higher? Like peaking nearer to 5V?

.

Walt Perko

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Jun 30, 2026, 12:45:49 PMJun 30

to Altair 8800

Hi,

Yes, all the backplane voltages check out slightly higher than 8V, +/- 15V ...

.

Patrick Linstruth

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Jun 30, 2026, 1:55:13 PMJun 30

to Altair 8800

Where are you measuring those voltages?

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On Jun 30, 2026, at 10:45 AM, Walt Perko <r4r...@gmail.com> wrote:

Hi,

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Walt Perko

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Jun 30, 2026, 2:00:05 PMJun 30

to Altair 8800

Hi,

I'm tapped on the end of the RS-232 cable going to the DCE port of both boards to get essentially, the same signal amplitude.

.

Patrick Linstruth

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Jun 30, 2026, 2:09:47 PMJun 30

to Altair

I can’t speak for the JP, but the R1 should be providing +/- 10v.

Double check your measurements. Maybe use a multimeter and verify -10v when not transmitting.

Sent from my iPhone

On Jun 30, 2026, at 12:00 PM, Walt Perko <r4r...@gmail.com> wrote:

Hi,

I'm tapped on the end of the RS-232 cable going to the DCE port of both boards to get essentially, the same signal amplitude.

.

On Tuesday, June 30, 2026 at 10:55:13 AM UTC-7 pat...@deltecent.com wrote:
Where are you measuring those voltages?

Sent from my iPhone

On Jun 30, 2026, at 10:45 AM, Walt Perko <r4r...@gmail.com> wrote:

Hi,

Although the 88-2SIOJP drives my SpeechBox just fine with an RS-232 to TTL adapter, I can't seem to get enough direct or with an RS-232 adapter to drive the stepper motor driver board.

Shouldn't the output of the 88-2SIOR1 and 88-2SIOJP be a little higher? Like peaking nearer to 5V?

.

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Walt Perko

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Jun 30, 2026, 3:21:35 PMJun 30

to Altair 8800

Hi,

My bad, I should have checked the little switch on the oscilloscope lead ... it was moved to 10x ... Now I'm seeing a good big signal:

I wonder if the 4.67V power to the RS-232 to TTL adapter might be the problem. The power is coming from a USB cable on the PC to the Stepper Motor Driver board ... but maybe the PC isn't putting out enough on the USB power?

.

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