MAXESP3 - 12v Regulator


markarose@...
 

Hi All, I put together my MaxESP3 board and when checking the 12c regulator I found that the output voltage was around 0.05v. Then I got buzzed by a wasp and slipped the probes and fried the regulator and blew the fuse.
Go another off Ebay which is almost the same but still get the 0.05v on output. Input is fine at 24v. 
Decided to plug in the boards and check various pins, getting 5v at the STM32 and Wemos D1 Pro, 24v on the drivers VM pins but only 2.79v on VDD.
Can anybody help, what should the 12v regulator output be ?


Howard Dutton
 

On Sun, Oct 24, 2021 at 04:24 AM, <markarose@...> wrote:
Can anybody help, what should the 12v regulator output be ?
12V.

Perhaps something is shorted?


markarose@...
 

Either that or something is blown but I really can't see what it might be.


markarose@...
 

As far as I can see from the EDA schematic, the 12v out goes to VM on U4 and U5, diode D2 and capacitors C3 and C9.
At the moment I don't intend to use U4 or U5 so can I just omit the 12v regulator ? 


markarose@...
 

One thing I can try is to cut the trace to the adjuster and bridge the 12v pads on the regulator.


markarose@...
 

Modified the regulator for 12v output as above and with nothing else plugged in all I get on the output is 0.05v. Also the 3.3v line has only 0.93v.
Something must have shorted or the regulator is faulty.
With everything plugged in I get 2.88v output on the regulator and the 3.3v line reads 2.73v except on the Wemos which is 3.29v.


Drew 🔭📷🚴‍♂️
 

On Sun, Oct 24, 2021 at 11:57 AM, <markarose@...> wrote:
With everything plugged in I get 2.88v output on the regulator and the 3.3v line reads 2.73v except on the Wemos which is 3.29v.
The 3.3v is supplied by the regulator on the ESP32 module. It must be plugged in. Any voltage measurements without having your components plugged in is suspect and consistent with what you are reporting.


Ken Hunter
 

Yes, you can omit the regulator if you are not planning on having a Focus or Rotator stepper driver in your build but...
I'd want to know what is wrong as there may be other issues (like the 12V output shorted to another trace that might go somewhere to let out the magic smoke).
Measure the resistance to Ground on the Regulator output. Then switch the meter leads and measure again to eliminate the possibility of a backwards installed diode. I'm betting the regulator is sensing a short and protecting itself. Anything less that 12 Ohms to Ground is likely to shift the regulator into protection mode. Look again at the capacitors on the 12V line and, if installed, the diodes on the backside of the board. Make sure they are all installed correctly. The Black line on the capacitors goes to Ground, Of course if there is a + on the capacitor, that lead goes to the 12V line. The regulated 12V on the MaxESP3 is fairly short as you have seen on the EDA schematic. You should be able to trace it out on the PCB to make sure there are no solder bridges of other nefarious things going on.

Good luck!

Ken


Ken Hunter
 

Looking at my MaxESP3 boards, D5 is there to protect the driver in case the motor windings are disconnected under power.
With the Cathode on the 12V line and the Anode connected to Ground, It wll shunt any NEGATIVE Back EMF voltage to Ground.
If it is installed backwards, it will shunt any POSITIVE voltage to Ground (Like 12V) .  The small surface mount diodes have a line
on the Cathode end. If installed correctly that line will be over the  D5 "D" on the PCB.


markarose@...
 

Hi Ken, the capacitors are black with white line, white being negative and are installed correctly.
Setting the DVM at 200MOhms I get 15.4 one way and 0.6 the other.
The diodes D4 and D5 have 3 scribed lines one end, both of which have the lines on the VM side. Closest to the "D" on each.
No visible signs of shorts or dodgy soldering anywhere on the board.
At a bit of a loss as to what the issue is, I think I'll just remove the regulator and flash the firmware to see what happens.

Thanks for the help, Mark.


Ken Hunter
 

Well, with 2 different readings it ain't directly shorted! Your readings are bogus though. You need to measure across the diode with the meter in Diode mode or the lowest range you can. MegOhms will be effected by the capacitor leakage current and is heading you in the wrong direction. In Diode mode you will be able to Identify the cathode fairly easily.

In my MaxESP's, measuring just across the diodes, I typically see OVER RANGE with the Red meter lead on the Cathode and around 0.2-0.3V with the Black lead on the Cathode end. Of course the other meter lead is on the other end of the diode. BTW, I mistyped the D4 yesterday - the 12V diode is D5 and may be removed if you don't mind fussing with surface mounted devices to do the test.

Since you have 2 different readings, that takes a direct short out of the possibilities and points directly to a semiconductor, the diode being the only one in that circuit.


markarose@...
 

Thanks Ken, I had an inkling that it might have been the diode but the only real way to check is to unmount them. Will look at replacing D4 and D5 if I can find the right parts.


George Cushing
 

I install the SMD diodes for the Max kits as most folks aren't set up for reflowing them. You can check them with you DMM's Ω meter or its diode tester. When the positive probe is in contact with the anode and the common probe with the cathode (the scored end of the diode) you should get a reading. When the probes are reversed the meter should read "OL." The diodes are Schottky 40V, 1 amp. As mentioned their purpose is to handle back EMF from the motors that can trash some drivers.



If your caps are the wrong polarity they would have blown very quickly and with a loud report. I'd check them for a short through the cap. It's possible they were damaged by the short. But there's a short somewhere. Examine the solder points with a magnifier. It doesn't take much to foul things up. If all else fails check adjacent pins for being shorted. I've seen female headers where adjacent connectors were in contact. I recently had a bad driver that caused a short. Went thru 5 fuses before I tracked that down.


markarose@...
 

Hi George, thanks for the reply. Probably not the diodes then, will check again later. I reckon my soldering is pretty neat but maybe some got between the pins under the female headers, Will check adjacent ones for continuity.


Ken Hunter
 

In that particular circuit the caps are connected directly across the diode so you CAN test the diode in circuit... If you read a direct short then get a different reading when you switch the probes... it is not a direct short.  This eliminates the soldering or a shorted capacitor which will give the same results when switching probes. Getting a different reading when you switch the probes points to a semi-conductor being biased on and off when probe switching. The only semi on that side of the Regulator is D5 (assuming no driver is installed as you previously posted). Remove it and your short will disappear. As I said earlier, I  have seen them mis-marked occasionally. You can replace the SMD diode with a similar spec axial lead since the MaxESP3 pcb is set up for both types.

Interesting problem... keep reporting what  you find to help the next guy.

Note: Experience is a GOOD thing... it helps you recognize a mistake when you make it again!


markarose@...
 

Just making a start testing things out on the 3.3v line. Everywhere is showing 2.72v except the Wemos D1 Pro which has 3.3v. Cant see on the EDA where that 3.3v comes from.

With the DVM set at 200 Ohms I read 175 one way and 1(on the left side, presuming it means OL) switching probes.


Drew 🔭📷🚴‍♂️
 

On Tue, Oct 26, 2021 at 02:00 PM, <markarose@...> wrote:
Everywhere is showing 2.72v except the Wemos D1 Pro which has 3.3v. Cant see on the EDA where that 3.3v comes from.
Again, the 3.3v regulator is on the ESP32 chip/module. Pull it and the 2.742v will disappear. The Wemos D1Pro has it own 3.3v regulator, that is what you are measuring there, it has no connection to the main board..

It sounds to me like you have something loading that regulator or a bad ESP32 chip. Look for problems wherever the 3.3v is used. Pull the drivers and see if it changes. Look at the status led (D2) and circuit around J2, for example.


markarose@...
 

Hi Drew, thanks for clearing up the Wemos 3.3v thing, currently checking over everything I can think of especially the 3.3 line.
Don't have an LED in D2 but will check the contact points.


Ken Hunter
 
Edited

[EDITED]

I can see why he is not measuring 3.3V at the anode of D4 or D5...
0.5V seems reasonable considering the Cathode is at GND potential.


markarose@...
 

Checked the board for any dodgy soldering and bridged pins, nothing untowards there.
Powered up with no components and checked voltages, input 24v is fine, 5v is fine, the 3.3v however starts low around 1.6v and slowly climbs. Powered off when it got to 3.5v