Help:) Voltage readings incorrect on some scales

[Paul]

Hi there,
Firstly, thanks for producing and supporting a great product - I’m sure you have made hundreds of “workshop tinkerers” very grateful and happy!

I have couple of problems with my new DSO Shell 150 (15001)- I’m hoping that you may be able to give me some help to fix it up..

Using the on-board signal generator, I get unexpected voltage readings on some of the V/Div scale settings.
The scales that seem to be working okay are 5, 1 and 0.5V and the 50, 10 and 5mV The other scales seem way off.

The reported values agree well with the actual amplitude/divisions on the trace..
It seems like the 20V/div setting is not outputting any signal at all, as it gives random large numbers that vary continuously.- I get the same readings when I completely disconnect the analogue board.
The 0.2V/div also seems to be reading random noise
I get a similar issue if I use a constant DC voltage input (e.g. from a 1.5 volt battery)
All other functions on the instrument seem to be working 100% fine.

When I was researching the issue, I found a test chart on another post that gives expected values for the SENSEL0,SENSEL1,SENSEL2 & SENSEL3 with the various scale settings. When I performed the checks, I found that my SENSEL0 is always reading 0 Volts… even when it should be high. I'm guessing this is the problem, but don't know how to proceed to correct it.

I have triple-checked all my resistor values by meter and have re-flowed all solder joints that I made, to be sure that I do not have a dry joint.
I have inspected both boards with a microscope and cannot see any obvious soldering faults or missing components
I am powering up the unit using a lab power supply at 9.0V.

Any assistance with fixing this issue would be much appreciated.
Thanks very much
Paul

[jye1]

The pin SENSEL0 might have been damaged. This pin stuck at 0V. That explains the issue you observed. The pin is neighboring the V+ pin and might have been shorted to it accidentally. Mainboard replacement is required. A couple of reports of the same problem have been received. We are making change to the mainboard to add protection against this.

[Paul]

Thanks for the analysis jye1.
What a shame it requires a replacement board to fix the problem.
Is this likely to be caused by something that I did wrong, or would it be a fault in the manufacturing of the main board?

[JerryS]

Mine is doing exactly the same thing, in my case I think I may have misaligned the conector between main and analog boards, doh! I am going to have a go at replacing the STM32 chip on the main board and flashing the firmware.

[jye1]

@Paul: It was more likely being damaged after shipment since each board was tested before packing. But the design should be more robust to prevent the damage considering that many users are not professional electronics guys.

[Paul]

Thanks for the reply jye1. I understand, there is always risk in buying kit-form devices.
Sad, because I would love to have this instrument working, but I can't justify buying another kit at this point.
Thanks again for your feedback. Glad to hear you guys are continuing to improve the product

[JerryS]

Update - have fixed mine now. It had been damaged by me by misaligning the two boards resulting in erroneous voltage readings on some scales. (SENSEL0 port was shot). I replaced the STM32 chip on the damaged board and then flashed the firmware. The chip can be sourced for around 5 dollars on eBay. It is not easy to solder, took me two goes as I damaged the first replacement chip. I found the easiest way was to use hot air to remove the old chip then tack down two corner pins using an iron with a very small bit, then use solder paste and hot air. Worth checking with a magnifying glass for any bridges.

Hope this helps someone!

[Paul]

Thanks Jerry, that sounds do-able. Fun to have a go at it anyway.
I'll have to read up on how to flash the firmware....