East Tester ET5411A+ (and ET5410A+) Electronic Load: Schematic reversed...

[morris6]

For your entertainment the reversed schematics of these instruments are added here. There are three boards and an SMPS power supply. The SMPS power supply that is at the backside of the instrument looks rather "generic" so I didn't include it. The instrument itself consists of a large "Main" board mounted to the bottom side of the main heat sink, a "Slave" board on the top side and a "Front" board with the display and the control buttons. The schematic of the main board is spread over 5 pages. So we have a total of 7 .PDF plots of the schematic pages in the .ZIP file.

The schematics were done in KiCad 7. I used the part references as they are silk screened on the boards. Because the part references are not unique for the whole system, they sometimes appear on more than one board, I had to make separate KiCad projects for main, slave and front. For your convenience the schematics are published as .PDF's. And some pictures of the main board. The bottom side picture is marked with the different ground planes and the interconnecting zero ohm resistors.

Comparing the ET5411A+ main board with pictures I found here of the ET5410A+ the only hardware differences are the type of power Mosfets and the value of the resistors that determine the high measuring range for voltage and current. And the firmware is adapted of course to reflect these differences in measuring ranges.

Funny thing is the main board contains in the isolation section all the parts for the double channel ET5420A+ variant, I wonder why that is..?

The input sense section has some nice provisions to cope with the advertised maximum 500V input (ET5411A+). It has isolation slots in the PCB and two ladders of 8 resistors for the voltage input circuit. However, the heads of the board mounting screws have only about 2 mm spacing from the traces. The screws attach the board to the main heatsink, The main heatsink is connected to the V+ terminal while circuit ground is connected to the V- terminal! Even for the ET5410A+ variant that is restricted to 150V on its input it makes me feel a little uneasy. Use with care, keep the boards dry and clean.

I am working on some small mods. I took the encoder out of the front board and soldered it back with A and B pins free of their pads; connected the pins with short wires to the opposite pads. Now rotating the encoder to the right increases numbers, it feels more natural IMHO.

Next is taming the noisy fan.

Another thread here discusses the addition of an external voltage sense connection.
https://www.eevblog.com/forum/testgear/et5410-electronic-load-mod-add-external-sense/msg4837247/#msg4837247
But be aware of the problems that can arise when these external sense wires loose their connection.

Your questions or remarks are welcome. I connected some wires to specific points of the circuits trying to get an idea of the dynamic behaviour.

[andyB2022]

Hi, first I want to thank you for all of your work. Do you won ET5410 (first model)? If so, could you please extract the firmware from the stm32? I've managed to screw my unit...

[morris6]

Hi Andy,

About your request, I don't have the ET5410, the older model.
The newer model, the ET5411A+ I have here, has a different hardware design and also the processor is different. So I am almost sure the firmware is NOT compatible. Also, it has to be seen howfar it is possible to read the content of the processor flash...

[LinuxHata]

Maybe someone is familiar with ET5408/09 models?
They appear to have bigger screen, more buttons and features also appear to be similar to 5010/11 models, but they cost about 20% less. So what is the catch?

[CloverGit]

Hi, do you have the parameters about the second order low pass filter circuit (U7) in the DAC output section with its capacitors C10, C8 (or C5, C3). Also, the values of capacitors C6, C9 and C2 are unknown. I am building my first electronic load and would like to determine if these parts are necessary. Your work has inspired me, thank you for your work!

[morris6]

I did try to measure these values in circuit but gave up due to the inconsistent results. Seems I can't help you.
 
The low pass filter circuits on U7 are for cancelling noise from the DAC in the MCU. These signals are not pwm but dc levels. The other caps you mention are part of the integrator circuits. Maybe try a simulation to determine a value for these?

Have fun, Maurits

[CloverGit]

I spent a few days reversing part of the circuit of the Maynuo M9812B and I found a similar design. the capacitors at C6, C9, and C2 are usually large (several to several tens of nF, even up to 10uF in one case) and use a complex circuit, which I guess may also be related to the op-amp self-oscillation problem.

[cnkz]

Thank you for this interesting re-engineering work.

[modoran]

I am working on some small mods. I took the encoder out of the front board and soldered it back with A and B pins free of their pads; connected the pins with short wires to the opposite pads. Now rotating the encoder to the right increases numbers, it feels more natural IMHO.

Why do you do that ?   Rotating encoder to the right or left can be changed from menu, in which way you want, reverse or forward.
menu -> system set -> knob set.


Perhaps older firmware does not have this setting ?

[morris6]

Checked the menu of my ET5411A , yes, indeed, you can change direction forward <> reverse for the encoder knob. Thanks for pointing this out. It's not mentioned in the "manual".

However, after my modification the knob is working the "right" way and accordance with the menu setting. So, not a totally wasted effort after all.

[KubaSO]

In the output stage, a TL072 drives 3nF of NMOS gate capacitance through a \$100 \Omega\$ resistor. TL072 has a fairly anemic output - about 25mA max. The series resistor doesn't help drive strength either. For a gate driver, that's very anemic. A buffer stage would make things better.

[andyB2022]

Anyone that tried to download the firmware from GD32F303VET6?

[temperance]

In the output stage, a TL072 drives 3nF of NMOS gate capacitance through a 100Ω resistor. TL072 has a fairly anemic output - about 25mA max. The series resistor doesn't help drive strength either. For a gate driver, that's very anemic. A buffer stage would make things better.

Not only the drive current is a problem. The open loop output impedance of the TL072 is 125 R and responsible for a phase shift in the feedback. Good luck trying to compensate that. Or you buffer the op amp or you have to implement a different compensation network.

[Luv2Learn]

I know this thread is old but I have a ET 5410a+ that I'm having issues with. Any help would be appreciated.  It will show the voltage of the source that's hooked up but will not draw any current. There is a bad trace on the main board between p1 and p12 but if I jump it it will start to draw current automatically no matter if it's on or off.  I posted your schematics in the repair thread. I hope that's ok

[enoch247]

@morris6: How did you figure out the pinout of the LCD controller? I am working on an open firmware alternative to the factory firmware. I've gotten the current and voltage regulation working and am now working on the user interface. I can't find any datasheet for the LCD. Thanks!

[morris6]

About the pinout of the LCD module.., the 24 pins interface seems some kind of standard for these panels with 8 or 16 bit parallel data bus to the LCD controller. But what controller is used here, I don't know, sorry about that. Can be a problem when writing your own software for this thing.

[enoch247]

After snooping the LCD bus with a logic analyzer, it would seem that the LCD uses a ST7789 driver (or similar). I base this off my analysis of the LCD initialization sequence on boot.

[enoch247]

I managed to get the LCD to initialize and draw some squares to the screen. See images. I have a two channel unit. Normally the front panel is driven by the bottom board (channel 1). In the image, I have swapped the flat flex cables from the two channels to the front panel and have flashed my own code to channel 2. This arrangement lets me swap back and forth between observing the stock firmware and testing my own. I did have to add a resistor in place of Q5, as Q5 and R106 were unpopulated on channel 2.

I discovered 2 errors in the reverse engineered schematic (at least compared to the channel 2 board I have):
LCD data line 0 goes to PD14 of the MCU, not PB8
LCD data line 1 goes to PD15 of the MCU, not PB7

[ranma]

Is your ET5410A+ also emitting a high-pitched whine in addition to the fan noise?

Looks like I got a different/newer revision, notably the 12V AC/DC converter is now soldered to the main board (and a teeny tiny one at that):

[enoch247]

I have never noticed any noise, aside from the fan, from either of my two units. They were bought at different times from different places. They had different firmware versions, and the plastic knob on the encoder is a little different between the two. I have only opened up one unit, so I can't say for sure if the internals are any different between the two. Yours does look a bit different from the one I have opened up. I also noticed that yours has bus bars connecting the front panel banana plugs to the PCB. Mine has some heavy gauge wires instead. Although that could be a difference between the single and double channel units.

[hp3310a]

Is your ET5410A+ also emitting a high-pitched whine in addition to the fan noise?

Looks like I got a different/newer revision, notably the 12V AC/DC converter is now soldered to the main board (and a teeny tiny one at that):

I don't think that is 12V AC that is coming in, notice the isolaton cut-outs around the connector and the electric shock hazard symbol. I wondered what that was for on my version (which is V1.05 2022.08.07) were it is unpolulated.

The whine likely comes from the ceramic capacitors around the ME7660, it did that on my unit. More info here: https://www.eevblog.com/forum/testgear/brand-new-et5410-emits-high-pitch-noise/msg5799591/#msg5799591

Solution was to replace the caps: https://www.eevblog.com/forum/testgear/brand-new-et5410-emits-high-pitch-noise/msg5841943/#msg5841943

[ranma]

I don't think that is 12V AC that is coming in, notice the isolaton cut-outs around the connector and the electric shock hazard symbol.

Yes, I meant mains AC to 12V DC power supply, sorry wasn't clear.

The whine likely comes from the ceramic capacitors around the ME7660, it did that on my unit. More info here: https://www.eevblog.com/forum/testgear/brand-new-et5410-emits-high-pitch-noise/msg5799591/#msg5799591

Solution was to replace the caps: https://www.eevblog.com/forum/testgear/brand-new-et5410-emits-high-pitch-noise/msg5841943/#msg5841943

Thanks, I should look into that! I was somewhat suspecting the tiny mains supply, but I haven't really been able to pinpoint where exactly the noise is coming from yet.

[ass20]

Hi
 Anybody have firmware update for DС load of east tester ?
i write to after sale support it is... But it is answer ? we do not have firmware.... 

[enoch247]

I don't have any OEM firmware. I did try to read out the stock firmware before erasing the one unit that I am hacking, but the flash was locked. If you do manage to find a firmware image file, I would like to have a copy as well. At this point, I am committed to creating an open source alternative firmware since I have unlocked and erased the flash on the slave board of one unit. Any one else is welcome to join. The pace has been slow only because I'm not in any particular rush to get it done. I think I've figured out all the hardest stuff already. Time to just crank out the code now.

[ass20]

 to enoch247

Are you send to request for fw update to east support?