Horizon RST 5.6 Treadmill/Johnson Fitness JDYF02L Control Board - No Incline

Thread Starter

jahoov

Joined Jan 8, 2024
1
Hello, I'm looking for some assistance troubleshooting a no incline issue on my Horizon RST 5.6 treadmill with the Johnson Fitness JDYF02L (Rev G) control board. I've seen several very helpful threads here regarding these treadmills/boards, so hopefully someone has some insight they can provide.

For context, the treadmill belt motor was not working in addition to the incline, and I've solved the belt motor issue by installing a new 220ohm resistor into R48 on the lower control board, as referenced in this thread: https://forum.allaboutcircuits.com/...rd-johnson-fitness-jdyf02l-revg.110355/page-4

Now, I am onto troubleshooting the incline functionality and have observed the following. I suspect the issue is in the lower control board since I had the bad resistor mentioned above, so that is where my focus is.

Symptom: In normal operating mode, incline up and down have no functionality and no indications of functionality on the lower board (eg no clicking relays)

Findings thus far:
- I am able to manually lift and lower the incline motor by applying external power to the black/white and red/white wires on the 4 pin connector (unplugged from the board when doing this, of course), so the motor itself is fine.
- Raised the incline via external power, and then plugged the motor back into the board. When starting a normal "session", the incline lowered to flat position without issue. (suggesting the down circuit works as expected)
- If I raise the incline via external power, I am able to lower it using the control panel button in Engineering/Test Mode.
- Eng/Test mode also correctly identifies the incline position when raising (via external power) and lowering (via external power or control board), so the board "knows" the position of the incline up and down.

After reading through IamJatinah's responses in this thread: https://forum.allaboutcircuits.com/...-horizon-t900-treadmill.141422/?cb=1704988340
I am thinking that my issue lies within the SMT transistors and/or relay for the "raise" side of the incline circuit. Something in the circuit has failed, so the up/down function appears to have been disabled to prevent motor damage.
My board does not have D14 as referenced in that thread, so that is one less component to check.

Looking for the following assistance:
Can someone help me identify the SMT transistors and any other components for the "raise" circuit (image of board attached zoomed to that area). I believe the outer relay on the board is for the raise functionality, because I can feel/hear the inner relay engage when the motor is lowering in my test scenarios above.
Are there any other components to evaluate besides the SMT transistors and the relay?
Would anyone be able to provide some additional information on what/how to check the components, specifically the SMT transistors in this circuit? The transistors appear to be labelled as "Qxx", but I'm not sure which ones are related to each function. Unfortunately I'm limited to a digital multimeter as my tool for testing, so I've got limited ability to troubleshoot.
I do believe I've got a way to generate +5v from a board for another unrelated project, so I can probably use that to test the SMTs as mentioned in this thread: https://forum.allaboutcircuits.com/...-horizon-t900-treadmill.141422/?cb=1704988340 , but I'm not exactly sure how to go about it (where to apply the +5v, etc.)

I got the treadmill for free, so I suppose I could always replace the two SMT transistors (after identifying which two they are) and relay for a few dollars, but it'd be nice to nail down where the issue lies instead of throwing parts at it.
 

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