Electronics > Repair

Tektronix WFM601 A E or M NVRAM Replacement & Reconfigure

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Help! i just picked up this Tek WFM-601A SDI video analyser and all i get on the screen is "configuration error contact tektronix service"

quick google says it's the NVRAM and sure enough there's the usual Dallas job inside.

Replacing the Dallas is easy enough, but what about the recalibration and configuring?

has anyone fixed one of these before?

I would like to restore back to working condition

had a lot of help thrown at me through my twitter and discord so i thought i'd sum up.

Internal Dallas DS1643 NVRAM should be easy fix, there's a direct equivalent in the ST M48T08 or i might attempt a battery hack

Calibration software has been located, i have attached it in case anyone ends up here with the same issue. The service manuals are easily available online.

I will attempt to repair, recalibration might be another matter as i don't have the equipment to do it, but i will post up here when something happens

I have a non-working WFM-601A that I could try to read the NVRAM from if it helps. 

I also have a 1755A that I would like to locate the calibration software for.  It's currently working, but the CRT is tired, and I would need the calibration software if I replaced the CRT.  I already replaced the Dallas NVRAM with an FRAM chip.


After must effort i have some answers on the NVRAM chip and how it's used and configured in the WFM601 Waveform Monitors and what it all means...

What NVRAM is used?
The NVRAM used in these waveform monitors is a Dallas DS1643, it's a 8k NVRAM with clock, the DS1643 is no longer available but ST Micro make an alternative in the M48T08.

What's stored in the NVRAM?
The NVRAM stores the model, serial number and calibration data for the monitor, although some adjustments are made with physical adjustment pots most adjustment is made with software and stored in the NVRAM.

What happens when the NVRAM goes flat?
When the battery goes flat the Monitor will no longer boot and will report 'CONFIGURATION ERROR CONTACT TEKTRONIX SERVICE'

How do i fixed a monitor with a flat battery?
Step 1:
You will need to remove the old one and replace it or perform a battery hack to remote locate an external battery onto it.

Step 2:
Using the UPGRADE.EXE software running under DOS or the Windows98 command prompt in DOS mode you need to configure the NVRAM with the correct model, serial number and date. A RS232 cable is also needed between your PC and the monitor.

To do this type:

--- Code: ---UPGRADE -C
--- End code ---

This will clear the NVRAM and configure it enough to boot. But it will be completely un-calibrated, although you will be able to see everything working you will find much of it will be so far out of specification it's essentially unusable as a reference instrument!!

Can i re-calibrate the monitor?
Yes it can be re-calibrated but it does involve 100s of steps and a very good selection of electronic test equipment (oscilloscopes, signal generators) and broadcast test equipment (SDI test pattern generator).

I have a working monitor, can i make a backup of the NVRAM?
YES! Using the UPGRADE.EXE software running under DOS or the Windows98 command prompt in DOS mode, A RS232 cable is also needed between your PC and the monitor.
To backup type

--- Code: ---UPGRADE -S
--- End code ---

To restore type

--- Code: ---UPGRADE -R
--- End code ---

Can the original Dallas be battery hacked so i don't need to remove it?
Yes it can be battery hacked if you want to keep the original and save yourself some £/€/$. The battery is located on in the potting compound slightly to the right hand side of the device.

Is there any official documentation on all this?
Yes, all software and documentation is attached file with the exception of the service manual which is easily available online (it's too large to attach here)

So with all this info i was able to remove the NVRAM, hack on some temporary batteries and get it back up and running.

Lack of calibration though is a major issue, this is far worse than using something that has been 20 years since it was calibrated, because the chances are it would be pretty close to calibrated but with some drift but with an instrument with factory defaults it is so far out it can't be trusted for anything other than making pretty patterns!  :-\

So if you have one of these monitors that is working, MAKE A BACKUP OF YOUR NVRAM!


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