Treadmill motor controller PCB repair, blown bridge rectifier

Thread Starter

RegentFlaw

Joined Nov 13, 2019
3
Hello, I see some threads on my exact board in the past, so hope this is ok to post here.

I want to learn more about PCB repair and possibly save money repairing my commercial treadmill that I use at home. I design and make solid-state III-V optoelectronic devices for my academic research job and I have made simple low-voltage mixed AC and DC circuits for custom testing of my devices, but it's all very simple breadboard-type stuff compared to a complex PCB. Like RC filters.

The story- I replaced my garage 20A outlet with a GFCI and after testing it out on a halogen lamp, I plugged my treadmill into it. After turning it on, I heard a loud pop and knew I had messed up something. I don't know what I did wrong, maybe a coincidence, but it was working fine before I changed the outlet. I put the old outlet back.

Visual inspection revealed that the bridge rectifier on the motor controller PCB labelled DF06 was blown. This board is ~$200 to have repaired professionally. Here is the album with pics of the board with some markup of my notes:
If I understand the service manual correctly, the board takes 120VAC input and doubles to 230 V. It converts to DC, then inverts to 3-phase AC. The microcontroller applies PWM to the both output voltage and frequency. I have not tested the motor itself, I assume I will have to do that but not sure how yet.

I am making parts list to replace. So far, I am going to replace all the electrolytic capacitors since they're probably 20 years old and should be replaced anyway. And the DF06 rectifier. I think the relay too.

That DPDT relay next to the blown rectifier does not work as I expect. I have tested the relay with the power off, it looks to me that one of the connections that should be closed when de-energized is not closed. You see from my notes that 3 of the 4 connections are open circuit, when I think just 2 should be open and then the other 2 are switched to after 12VDC is applied to coil. Could one of the relay poles failed and caused the bridge rectifier to fry?

All components immediately connected to the DC side of the fried bridge rectifier appear ok.

Will the IGBTs be broken? How do I test the IGBT module? I'm not even sure how to remove it from the board yet.

Thank you.
 

MaxHeadRoom

Joined Jul 18, 2013
19,163
I don't recognize the board, but test the rectifier and all the power components IGBt's/Mosfets etc.
Digikey is a source of parts.
Max.
 

Thread Starter

RegentFlaw

Joined Nov 13, 2019
3
Max,
Yes I know digikey, mouser, etc. The bridge rectifier is clearly bad, you can see the huge crack in it in the first photo. I have watched some videos on how to test IGBTs, I will this weekend.

Usually in the videos they are testing simpler IGBT circuits than the entire module I have. The data sheet for the module is in hand so I know the pin outs. I don't think I have to, but, just to make sure, do I have to desolder the module to test it properly? I am planning to look for shorts by clearing any charge on the gates and then testing both polarities from collector to emitter across each of the 3 parallel IGBT pairs. Sorry, my first time testing them, though I could actually make these in the cleanroom had I the funding...

Assuming I find all the broken components and fix them, anyone have any idea what caused the rectifier to blow in the first place? I want to hope that it's just that relay right next to it that failed, but this is probably naive of me. That relay has something to do with the emergency stop switch, maybe it does something more but looks to me like it cuts power to the motor without cutting power to the board.
-George
 

MaxHeadRoom

Joined Jul 18, 2013
19,163
If replacing offending items, I would power up with the motor disconnected at first, and see if it hangs in OK.
The motor itself can usually be tested simply by using an automotive battery.
Max.
 

Thread Starter

RegentFlaw

Joined Nov 13, 2019
3
In case anyone ever google searches this, I was able to get the treadmill working. Terms: Life Fitness A080-92209-B000 9100HR 9500HR

First thing I did was replace the DF06 diode bridge, the relay, and the capacitor and I was able to get the service LEDs to light up for the first time, but only when the emergency off was engaged. The relay I replaced is the real emergency off switch, and it sends some small current to the logic part of the board when the emergency off is engaged.

Once I disengaged emergency-off, I could hear the relay click but the board LEDs would lose power again. So I tested out that side of the relay, and found that there's another set of 4 diodes in a bridge rectifier configuration on the motor side of the relay. Two of those diodes were open circuit, unfortunately these were in the IGBT module itself. Testing the IGBTs in the module without any charge on the gates didn't reveal short-circuits so I assumed the IGBTs were ok.

So, the relay was somehow broken, and the rectifiers on both sides of the relay had blown diodes. On the emergency-off->engaged side current goes through the DF06 rectifier part, to a capacitor in parallel with the RF transformer to power the low voltage logic parts. On the emergency-off->disengaged side, the amps go through the voltage doubler and the motor and ultimately to that same RF transformer to power the logic.

Probably unwisely, I decided to replace the broken diodes living in the IGBT module with loose 20A diodes I purchased from mouser. See in this album, my loose diodes are near the middle of the board:
After replacing those diodes on the motor side of the relay, the treadmill works as expected. I did not try without the motor as the thermal cutout switch has to be connected to get power to anything. I assume, though, I can just short these pins together to simulate the real motor, and perhaps connect the phases to 3 60W light bulbs? I kind of want to do more testing to make sure all 3 phases are working, but for now I'll just test by using the treadmill over the next few days. Maybe my repair will fail due to bad soldering job or if my replacement diodes are not up to par.

Parts replaced:
DF06 Rectifier: $0.50
22uF Capacitor: $1.20
Two 20A diodes: $1.60 each
Relay: $16
 

MaxHeadRoom

Joined Jul 18, 2013
19,163
The module appears to made for a 3phase supply, in this case, just two sections of the 3ph bridge are operating for 1ph mode.
Ideally if replacing the defective diodes, use high speed versions.
Looks as though it could be a BLDC driver.
Max.
 
Top