Like New NordicTrack Exercise Bike - Dead Console

[vestaviascott]

Here's a few more pics of that gold ribbon cable:

 

[hevans1944]

The only problem I have with that is that one end of the power socket doesn't expose any pins, or perhaps only one. How would you do a continuity test on this?

In the photo that accompanies your text, the cable harness has two wires, one of them red, the other not visible. The round connector with the two nuts threaded onto its body appears to be a "barrel" connector, commonly used to interface with "wall-wart" power supply cables. There should be a center pin visible inside the barrel connector. The outside of the mating barrel plug (connected to the wall-wart) mates with an inside conductive sleeve while a hole in center of the mating barrel plug mates with the lone center pin inside the barrel connector.

There are several approaches to measuring continuity of the complete cable harness, including the barrel connector with the two nuts attached. Firstly, identify which pin of the two-pin connector the red wire is connected to. From the photo, it appears that would be the left pin in the red connector housing. Using a small alligator clip or, better yet, a mating female socket pin, place one test lead of your multimeter on the pin identified as being connected to the red wire. Make sure you do not "short" the alligator clip or the female socket pin to the adjacent male pin!

Attach a small alligator clip to the other test lead of your multimeter and use it to hold a short length of conducting bare wire. A paper clip often works well for this. Now, with the ohmmeter set to a low ohms range, or to continuity mode, touch the short length of conducting wire to the center pin of the barrel connector. There should be continuity if the red wire is associated with the center pin of the barrel connector. If no continuity, move the short length of conducting wire to contact the inside of the barrel connector. If there is continuity there, you have identified one end of the red wire connection.

Now move the alligator clip attached to the male pin inside the red plastic connector housing to the other male pin. Repeat the continuity tests to the center pin and inside conductive shell of the barrel connector to verify that you have successfully identified the two connections.

Often it is not absolutely necessary to include the connector pin structure in continuity tests. Usually continuity problems are caused by broken wires or bad connections, especially poor solder connections which can be real bitch kitties to find. So eliminate the wires as potential problems sources by performing end-to-end continuity tests on just the wires. This is most easily and quickly done with needle probes that pierce the insulation to make contact with the wire underneath. Needle probes used to be "standard" equipment in the 20th Century, and steel phonograph needles were readily available sources of replacement needles. Today, you might consider using a sewing-machine needle instead. These are easily gripped with alligator clips. In performing the continuity checks, you might as well make sketches that identifies how all the wiring is connected. This will come in handy when the real troubleshooting begins.

"From the connector pins on the board". Are you referring to the gold ribbon cable?
"to the individual conductors on the other end of the ribbon cable". The ribbon cable's other end goes under the board. Just want to clarify you are suggesting here to remove the board and test where this ribbon cable leads to or somewhere else?

Yes. The gold ribbon cable does not appear to be connected in the photo. If it is in fact securely inserted in the mating socket, it wouldn't hurt to verify there is continuity from the circuit board connections, the pins on the connector, all the way to the other end of the ribbon cable. This type of flexible, "printed circuit" ribbon cable is not very prone to failure, but the connections to either end can be problematical.

Troubleshooting electronics is a skilled art that is helped immensely by knowledge of electrical circuit theory as well as electronic circuit theory. Back in the day, it was quite common for DIY TV "repairmen" to replace every tube, one by one, in a television set until the got the set working again. Often the "customer" paid for a whole bunch of new tubes that didn't need replacing, if only the DIY "repairmen" knew WTF they were doing. We called this "shotgun maintenance" back in the day, and it was (and still is) common in DIY automotive "troubleshooting" with lots of needless "repairs" being performed by ill-trained or non-trained shade-tree, weekend mechanics. Please don't place yourself in that category. Take it easy. Learn the basics and proceed with some knowledge of what you are trying to do. Best of luck to you!

 

[vestaviascott]

Like your quote indicates, you are very good at explaining things in a simple way, thoroughly so someone like myself who needs quite a bit of direction in these matters, can understand. I'm going to print out your reply and study on it a bit.

Extremely helpful! Thanks.

 

[hevans1944]

Be careful in removing circuit boards to gain access to points you want to check for continuity. It is easy to accidentally stress and break connections. If a visual inspection appears okay, and all the readily accessible wiring tests okay for continuity, then it may be time to "fire that mutha up" and go look at voltages, what we in the business call a "smoke test." Most people already know that most electronics operations are mediated by "magic smoke" and will fail to work if you "let the smoke out" during operation or testing.

It will be virtually impossible to make any meaningful voltage measurements without a schematic diagram to guide you on where to make the measurements, so your next step (assuming you still haven't found and corrected the problem or problems) is to locate a service manual for this bicycle exercise machine. This manual may be available from Sears. Google for it based on the Sears part number. It appears, from the front panel controls, that a variable load can be applied to the pedal mechanism. One common means of doing so is to gear a generator to the pedal mechanism and connect the generator output to a switchable load-bank of power resistors. A conditioned athlete can produce about one hundred watts of power on a continuous basis by pedaling a bicycle. If a generator is used to create a variable load, it may use one or more power semiconductors, mounted on heat sinks, to dissipate the electrical power generated by pedaling.

From the description of the power supply, 9V DC at 2A, it appears most of the power from the wall outlet is used by the digital electronics for display and control purposes. It would help to identify which logic "family" is used by looking up (Google again) part numbers on integrated circuits, assuming the part numbers aren't proprietary, in-house part numbers, or provided the manufacturer hasn't scraped off identifying numbers, symbols, logos, etc. This inspection process, along with certain measurements with test equipment, is called "reverse engineering" and if successful may allow you to draw your own schematic diagrams in lieu of having a service manual at hand. It's usually a last resort that is attempted only when you absolutely must make a repair and insufficient information is available. Because of the difficulty involved, most undocumented electronics today is considered "un-repairable" without excessive expenditure of time and materials. Nonsense of course, if labor and repair materials are cheap enough. Hang onto your stash of Kester 60/40 tin-lead rosin-core solder. It will be worth more than gold after the zombie apocalypse occurs, as warned by the Center for Disease Control (CDC).

 

[vestaviascott]

Thanks again for the thorough and helpful explanations. I'm going to check the continuity on the wiring harness first before I move on to anything further. Baby steps.

For my education, I do have a question about the "Earth Ground" for this bike. Since the power adapter only has two blades, how can it be grounded to earth?

Or maybe it's "magic smoke", lol?

 

[vestaviascott]

OK, after further reading, here's what I found:

This third prong is the ground. Both the neutral and the ground are connected to an earth ground in the main breaker box in your home. The difference between the two is that the neutral completes a circuit with the hot wire and normally carries some amount of current (which is why it’s insulated), while the ground does not normally carry any current whatsoever and is not connected to the circuit at all (unless something has gone wrong). It simply is used to connect the external conductive parts of the device to the earth and, thus, in normal operation is completely unnecessary. This is why you can use a 3-prong to 2-prong plug adapter to bypass having to use the ground line and the device will still work just fine.

 

[vestaviascott]

Update on progress...

With the help of some folks on badcaps forum, I've identified 3 voltage regulator ICs on the board and tested their voltages. I've included a high res shot of the board where you can see the 3 RG chips, RG2 on the lower left, RG1 on the top center and RGA1 on the lower right.

Here are the measured voltages of each:

For RG1 (GH16D), voltages are from left to right:
0.7 (left pin - GND)
7.2 (middle pin - Vout) * I measured this several times b/c I was expecting 5 V
8.7 (right pin - Vin)

For RG2 (3940M3), voltages are from bottom to top:
8.9 (bottom pin = Vin)
0.1 (middle pin = GND)
4.99 (top pin = Vout)

For RGA1 (3940M3), voltages are from left to right:
8.9 (left pin = Vin)
.6 (middle pin = GND)
4.99 (right pin = Vout)

Am I correct to observe that the RG1 chip (of P/N type GH16D) may be faulty by passing >5v to the board on its output pin?

 

[kellys_eye]

The GH16D doesn't have a version that exceeds 5V output so there's definitely something amiss there. If the output really IS as high as you measured then it most likely will have damaged circuitry elsewhere - probably 'fatally'.

 

[vestaviascott]

I've ordered a new GH16D. While I'm waiting for it to arrive, can you suggest a way, short of hotwiring the 3.3volts to the board, of testing the upstream circuitry for damage?

 

[kellys_eye]

Unless you have another way of deriving the 3.3V (separate PSU?) - which you'd then apply to the place on the board where it is normally generated at (by removing the damaged component) - then there is no other way to do it using the existing circuitry (without knowing the intimate parts of it and that requires a schematic).

But you'd need a current limited supply to be safe although if the 'upstream' circuitry has been receiving 7V when it should be getting 3.3V then there's no way it will have survived.......

 

[vestaviascott]

...if the 'upstream' circuitry has been receiving 7V when it should be getting 3.3V then there's no way it will have survived.......

OK, the output pin of the bad chip (RG1 on the board capture pic below) is the center pin, GND is pin 1 and input is pin 3. How can it be that it doesn't appear that the output pin is connected to any visible trace on the board?

 

[kellys_eye]

The 'large' green area is the trace carrying the output voltage - it seems to go off to the left, diagonally upwards..... and diagonally down to the right to a 'thru-hole' pad.