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Old 11-16-2018, 11:19 AM
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Default Today's random project...

I haven't been working on the 911 a lot recently, so not a ton to contribute to the Porsche-iness of the board. However, it seems like at least twice a week there's another repair/restoration/build project I have to tackle in a sisyphean effort to keep all the shit I own in working order.

Today's project was the treadmill. Believe it or not, I do actually use the damn thing. This particular machine does seem to have a design flaw, though - it blows the motor control MOSFET every 200-250 miles of use. This is a shot of the motor control board with the red arrow pointing to the problem MOSFET in question:

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It's become such a common issue that I actually buy the damn things in bulk:

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I've tried plugging the treadmill into a surge protector, unplugging it when not in use, etc. Still blows the damn MOSFET every 1-2 years. Now, replacing the MOSFET is simple enough - I have the tools and experience after all - but its a pain in the ass. To get the PCB out you have to unbolt all 6 transistors from the heat sink, clean up the thermal paste, desolder the old MOSFET, install the new, rebolt everything, and hope that your repeated soldering/desoldering doesn't lift any traces on the PCB. All this when I really just want to go for a 2-3 mile jog.

Last time this happened I swore I'd modify the treadmill to make MOSFET replacement a quick-change operation if it ever happened again. Last night I did just that. I had my son make me a mounting bracket for a TO-247 socket that I got just for this project and attached it to the frame of the treadmill:

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I then wired the socket to the original holes in the PCB and installed the new MOSFET.

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Close up:

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Now if (when) it blows again, I remove the mounting screw, slide the old one out, new one in, reinsert the screw and the treadmill is back and running again in 2 mins.

I was a tad worried during the conversion that the wire lengths would be too long and cause some weirdness, but it doesn't seem like the transistor switches fast enough for this to be an issue. I figured the frame of the treadmill would be a good enough heat sink, but did monitor temps during a test run and everything was good.
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Old 11-16-2018, 11:57 AM
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I love projects like this but never seem to find the time to do them! You may also find that changing the thermal environment will have solved the issue.

Stephen

Quote:
Originally Posted by Jazzbass View Post
I haven't been working on the 911 a lot recently, so not a ton to contribute to the Porsche-iness of the board. However, it seems like at least twice a week there's another repair/restoration/build project I have to tackle in a sisyphean effort to keep all the shit I own in working order.

Today's project was the treadmill. Believe it or not, I do actually use the damn thing. This particular machine does seem to have a design flaw, though - it blows the motor control MOSFET every 200-250 miles of use. This is a shot of the motor control board with the red arrow pointing to the problem MOSFET in question:

Attachment 59109

It's become such a common issue that I actually buy the damn things in bulk:

Attachment 59110

I've tried plugging the treadmill into a surge protector, unplugging it when not in use, etc. Still blows the damn MOSFET every 1-2 years. Now, replacing the MOSFET is simple enough - I have the tools and experience after all - but its a pain in the ass. To get the PCB out you have to unbolt all 6 transistors from the heat sink, clean up the thermal paste, desolder the old MOSFET, install the new, rebolt everything, and hope that your repeated soldering/desoldering doesn't lift any traces on the PCB. All this when I really just want to go for a 2-3 mile jog.

Last time this happened I swore I'd modify the treadmill to make MOSFET replacement a quick-change operation if it ever happened again. Last night I did just that. I had my son make me a mounting bracket for a TO-247 socket that I got just for this project and attached it to the frame of the treadmill:

Attachment 59111

I then wired the socket to the original holes in the PCB and installed the new MOSFET.

Attachment 59112

Close up:

Attachment 59113

Now if (when) it blows again, I remove the mounting screw, slide the old one out, new one in, reinsert the screw and the treadmill is back and running again in 2 mins.

I was a tad worried during the conversion that the wire lengths would be too long and cause some weirdness, but it doesn't seem like the transistor switches fast enough for this to be an issue. I figured the frame of the treadmill would be a good enough heat sink, but did monitor temps during a test run and everything was good.
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Old 11-16-2018, 12:30 PM
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Next step: water cooling...
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Old 11-16-2018, 12:50 PM
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Quote:
Originally Posted by Eplebnista View Post
Next step: water cooling...
Jazz is an air-cooled kinda guy...
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Old 11-16-2018, 01:54 PM
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Quote:
Originally Posted by Eplebnista View Post
Next step: water cooling...
Maybe overclocking?

ed
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Old 11-16-2018, 02:42 PM
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Add lightness, oh that’s how this mess started
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Old 11-16-2018, 07:34 PM
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Brush or brushless motor?
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Old 11-19-2018, 11:21 AM
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I guess the designers never thought someone would use their products more than 6-9 months. ha! Good job, Chris and I like that your boy helped.
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Old 11-19-2018, 12:26 PM
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x2

Most of this stuff seems designed for months of use only. Good work Jazz.
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Old 11-19-2018, 09:10 PM
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Quote:
Originally Posted by Rob in VA View Post
I guess the designers never thought someone would use their products more than 6-9 months. ha! Good job, Chris and I like that your boy helped.
They last much longer as clothes hangers.

Ed
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