Maynuo DC load has lost calibration data

[aix]

I am looking at a faulty Maynuo M9711 DC load (courtesy of Howardlong) to decide whether to have a go at repairing it.

The immediate symptom is that it displays "ERROR CAL.DATA" on startup.  All that the manual has to say is that "EEPROM lost calibration data."

Before go down this rabbit hole, I thought I'd ask how much do we already know about calibration data on these units?

I had a look for a service manual, but didn't find anything.  This video is relevant, but doesn't touch on calibration data.

(I have a working M9712 load, so one option would be to just keep the M9711 for spares.)

[Ordinaryman1971]

I found a manual for itech version of this one...
On BK precision mulimeters the ic holding calibration data is on the display board.
Read the one you have on working one and write it to the non working one... maybe that would save the day.
The calibration on those is done via the software...
I've requested it from BK and they sent me the link, it maybe be a bit different for this brand but.. possibly you can request it.

Another thing that probably doesn't apply to the calibration data but:
According to the manual you can maybe reset it by the this sequence:
 “Eeprom data lost” means parameters of power-on have been lost.Reset them by
pressing (Shift)+4(save)+0

[2N3055]

Maybe these can help..

[aix]

I found a manual for itech version of this one...

Interesting, thanks.  I've not come across ITECH loads before, but that IT8511 does look very similar to the M9711.

[aix]

Maybe these can help..

That's very helpful indeed, thank you!  I've quickly run through the calibration procedure, but would need to get a 60A power supply to do this properly.

After power cycling the unit, it still shows ERROR CAL.DATA

From playing with it a bit further:

• CV mode seems to work, with reasonable voltage and current readouts;
• CI, CW and CR are all busted (for example, CI just goes into Unreg without attempting to draw any perceptible current).

I can hear a relay click when I switch between CV and any of the other three modes.

Presumably CV is the only mode that doesn't need current feedback, so I wonder if there's a fault with that?  Not completely clear how that relates to the calibration error, if at all.

I'll try to have a nose round this evening, but if you have any ideas or suggestions in the meantime, I'd love to hear them.

[aix]

Also, on one of the calibration screens I noticed that the current readout at the top of the screen was in the thousands of amps while unit was drawing hundreds of milliamps.  Maybe another reason to take a close look at the current circuitry.