EIIIx front panel slider calibration...

[xuulan]

I'm currently restoring an EIIIxp (which has been upgraded to an xs), adding an OLED display, SCSI2SD drive, and upgrading the RAM. Currently there is an issue with the front panel sliders (volume and data). When using them to adjust values, the value doesn't change until the slider is about half way up. It's not 'jumping' to the mid point value, it's like the entire value range is compressed from the 50% point on the fader to the 100% point. The issue remains after replacing both sliders. I'm guessing that the fault may lie with the ADC that reads the front panel sliders and its calibration, or possibly an external voltage reference that it uses. Anyone have any experience with this?

Thanks in advance.

[dr.c]

Considering the pot position, are the values starting from "zero" at the middle, and increase untill the end,
Measure the voltage between the two extreme points of the pot. Is it +5V ?
Look at the connectors and cables bringing the +5V to the pots, the solderings, etc...
After then, measure continuously  the voltage on the cursor of the pot while you move it. Is it changing normaly ?

If the four LSB bits are missing over eight bits (just an example), the processor will "see" only the MSB bits starting at the mi-course of the slider !

[xuulan]

I've done some more research. Both sliders are configured as rheostats (only 2 terminals used), not a voltage divider. I've traced the signals to a HC4051 multiplexer IC on the main board, which then goes to a HCT14, then to a custom IC. I really hope it's not the custom IC that is bad...

[xuulan]

Never mind, I'm dumb. It was under Master/Special/Recalibrate.

[dr.c]

Its okay, this gives a human dimension to your genius...   

[scokljat]

The issue remains after replacing both sliders.

Hello,

What value of sliders are originally in EIIIXP? 10K linear 50mm? Or? Do you maybe have PDF service manual?

Best regards

Suad