Infiniti VG30 crosstrainer Err4 - fixed!

[mitaux8030]

Came home last night with the good lady pointing at our Infiniti VG30 crosstrainer with UM6609 computer/display unit showing 'Err4' and nothing else. "We will have to get a new cross trainer" was the counsel offered to me.
Nope, not going to happen - won't throw something away especially if it's only a simple problem that is stopping it from working. How hard could it be?
Following up on a clue found from Google where a customer reported Err4 and it had to have a motor replaced under warranty, I started looking in that area.
After removing about a gazillion screws around the flywheel shrouds, inside was a magnetic resistance braking assembly, driven by a small DC motor with gear reduction system. Motor measures 20 ohms resistance - seems about right. Apply external voltage to motor, and it turns OK. Hmm, can't be the motor itself.
The gear reduction system for the motor was turning freely too, so couldn't be that. Ah ha, what's this here? As part of the gear reduction system, there's a positioning sensor to indicate to the computer what setting the magnetic brake is at. It's just a simple 5k ohm pot. Measure the centre wiper - and it's infinite resistance. That's probably the issue. Spray in some electronic grade cleaning solution, exercise the pot from one adjustment limit to the other. Repeat with some electronic grade contact lubricant. Power up the thing and ensure Err4 does not reappear. Reassemble the magnetic brake assembly with it's driving motor, and retest to confirm Err4 doesn't reappear, and that the magnetic brake adjustment limits are correctly set and being driven correctly. Do final test and reassemble shrouds.

One thing that was disappointing to see within the unit was the variable quality of design. Many of the cables have nice little header style plugs & sockets, with some sealant at the back of them for added strength. All soldered joints were covered in generous amounts of heatshrink. BUT, the wiring from the DC motor / pot on the gear reduction assembly had no removable connector, it was soldered in to the wiring harness. To replace it means replacing the main wiring harness through the entire chassis of the crosstrainer (or cut & shut the wiring harness onto new parts). That was very poor design in my view, especially when everything else was so modular and well constructed with attention to detail.

So in the end it was the oldest trick in the electronic repair book that was stopping the thing from working: dirty pot. (And probably saved me from a needless $500 purchase of a new cross trainer)

Hope this might help someone in future years.

[tristen]

Interesting exercise in faultfinding, 6502.

It's good to know you found and fixed the fault. Good work!

Thanks for posting such a detailed description.