Yet another treadmill controller board (DCMD75)

Thread Starter

Exxie

Joined Nov 15, 2019
4
DCMD75.jpg


Got a DK City treadmill from the neighbour just before he was going to put it out on the lawn for the upcoming garbage collection.

He told me it would work OK for a few minutes and then shut down.

So I powered it up and, yes, it powers up and the display panel lights up and then after a few seconds it shuts off (no display).

With the cover off, I can see that after about 12 seconds, the board LEDs light up, then shut down. Display board also shuts down. Power cycling will start the board up again but it will only stay on for a few seconds. Leaving it off for longer makes it stay alive a little longer on the next startup (temp related?).

My troubleshooting so far:

- Visual examination of all components under the hood - controller board, EMI filter, choke, main motor, incline motor. All looked OK. Motor is free/not seized.

- Disconnected all plugs on controller board - incline motor board, main motor, speed sensor?. Powered it up and same deal. LEDs stay on for 10 or so seconds and turns off.

- Pulled board out - Visual check of components looking for bad caps, resistors, damaged tracks, etc. Nothing obvious. Put it on bench with only choke connected. Powered up the AC (240V). Same deal.

- Checked diodes. Checked bridge rectifier.

- Replaced all the medium-sized (physical size) electrolytics. Didn't replace the 2 large caps (are these just for starting the motor?). They are in parallel, but capacitance measures right. Still shuts down after 10 seconds.

- Measured temperature of some components after fuse/AC with temp gun. They warm up slightly (a few degrees C), but don't get very warm before it shuts down (30 deg C). Rest of the board stays at ambient.

Is a component failing due to increase in temperature or current allowing it to stay on for a few seconds? Any clues to what component could cause this?

Where to now? Thanks in advance.

PS. Skills are limited. Only have multimeter. Being as careful as I know.
 

SLK001

Joined Nov 29, 2011
1,533
Is the relay clicking off when it shuts down? Does the DC voltage at the bridge go away at shut down? It looks like the bridge and two large devices at the top edge of the board are meant to be on a heatsink. Do either of these two parts get hot? What is the voltage on the cold side of the switching transformer at shutdown?
 

twohats

Joined Oct 28, 2015
34
Are there any dry joints on the underside of the board?
The board could be flexing slightly as it warms up.
Good luck..
 

Thread Starter

Exxie

Joined Nov 15, 2019
4
Is the relay clicking off when it shuts down?
No, relay doesn't sound like it's activating when power is applied and no clicking when it shuts down.

Does the DC voltage at the bridge go away at shut down?
No, DC voltage is there at shut down.

It looks like the bridge and two large devices at the top edge of the board are meant to be on a heatsink. Do either of these two parts get hot?
Yes, they were on a heatsink. None of the heatsinked parts move from ambient before or after shutdown.

What is the voltage on the cold side of the switching transformer at shutdown?
Voltage drops off upon shutdown.
 

Thread Starter

Exxie

Joined Nov 15, 2019
4
Are there any dry joints on the underside of the board?
The board could be flexing slightly as it warms up.
Good luck..
Board looks to be in good condition, but I haven't run over all the joints yet. Nothing seems to move more than a few degrees before it shuts down.
 

SLK001

Joined Nov 29, 2011
1,533
Voltage drops off upon shutdown.
You problem appears to be in your power supply. There is nothing that should shutdown the PS output on the board. It is possible that the TOP222P IC is the culprit, but measure the voltages before and after shutdown. It could also be one of the feedback optos for the PS. Also, I don't see the switching transistor - could it be on the back side? It should be close to the transformer.
 
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