Electronic troubleshooting

[Snapped-off]

Guess I missed that. I haven't been following and just scanned through looking for something more on that. That's a big help to know those things. The voltage isn't going to be high on battery powered toys so that shouldn't be an issue. Only other thing is gain but that may not be critical.

I was just recalling a similar fault years ago on some military gear. The spare circuit card was pulled from stock and didn't fix the problem. Standard proceedure was to just replace cards so they really didn't have training going down to the component level. Wasn't essential gear for the current situation so the team went to bed with it unsolved. I and a buddy had the night watch and I found a transistor that moved more than expected. Cracked lead. Woke up the storekeeper to get the replacement and got it fixed.

The initial problem was a weak or broken lead with the transistor. Some wiggling got it working again. I probably over wiggled it as I found the base lead was broken and everything quit. Since then it's been dead. Hence all the further troubleshooting.

 

[The Cobbler]

I keep following along, each time hoping you got it working!
Cheers & Kudos for your determination.

 

[RPH]

Well that switch wiring is busy. How does the switch activate? The yellow wires show two to the device and two switches with 3 traces on the board proper. Waiting for the scope, we need to look at the signals coming and going out, if any. Don’t quit, look at what you have learned.

 

[Snapped-off]

You drive the train over the red part on the track, it pushes down onto the little grey rubber standoffs and completes the circuit on the board. I can take a picture of it if needed. What kind of switch is this? It's not like any switch I've ever seen.

 

[RPH]

Depends on the cob. But ya, take a pic. How many of the switches can be hit at once? More than one car over multiple switches? Wheels activate them? Magnet? Cam?

 

[dave*99]

You drive the train over the red part on the track, it pushes down onto the little grey rubber standoffs and completes the circuit on the board. I can take a picture of it if needed. What kind of switch is this? It's not like any switch I've ever seen.

There is a chance that switch consists of a printed circuit pattern with 2 electrodes on the main PCB. Under the gray cap may be a black rubber part that is an impregnated rubber part that is "conductive" The electrodes are connected to a high impedance input on the IC. Pushing the conductive rubber down on the electrodes completes the circuit.

 

[Snapped-off]

There is a chance that switch consists of a printed circuit pattern with 2 electrodes on the main PCB. Under the gray cap may be a black rubber part that is an impregnated rubber part that is "conductive" The electrodes are connected to a high impedance input on the IC. Pushing the conductive rubber down on the electrodes completes the circuit.

That's exactly what it is. I've already looked at it. Just not familiar with it and I've never seen one prior to this.

 

[dave*99]

That's exactly what it is. I've already looked at it. Just not familiar with it and I've never seen one prior to this.

Take your TV remote apart. You will see lots of them.

 

[Snapped-off]

Depends on the cob. But ya, take a pic. How many of the switches can be hit at once? More than one car over multiple switches? Wheels activate them? Magnet? Cam?

You just drive over them. You can push them down by hand. Dave's post describes exactly what they are.

 

[RPH]

Ok, just checking. I’ve seen many different creative ways to utilize inputs to generate the output.

 

[Snapped-off]

On this episode of This POS Toy, we're going to learn how to use a scope. It's kind of cute.

 

[Snapped-off]

Gotta figure out how to set this up.

I've played with a real scope before but this ones a little different.

 

[Snapped-off]

Any suggestions on setup as far as input voltage and waveform duration? I'm trying to figure out if I can zoom into the waveform so it's visible.. it's so small it's almost a straight line.

I have black to B- and red to transistor base.

Am I reading AC?

 

[RPH]

No calibration for the probe? Instructions? Start with dc and see what you get.
5 v/div to start is safe, 2.5 most likely to be useful. Time base, start long and keep reducing. Your trigger will be interesting. I have never explored a scope like that. Tektronics, Flukes, and some Sony scopes mainly.

 

[Snapped-off]

No calibration for the probe? Instructions? Start with dc and see what you get.
5 v/div to start is safe, 2.5 most likely to be useful. Time base, start long and keep reducing. Your trigger will be interesting. I have never explored a scope like that. Tektronics, Flukes, and some Sony scopes mainly.

Instructions are just telling what the buttons do. There's a test output on the top I assume to verify calibration.

 

[RPH]

On a normal scope the probe calibration is usually 5v/div @1kHz. What I would be checking is the squareness of that pulse train. Right now get that pulse train displayed and play with the controls to get a feel for it. For the price, what the heck!

 

[RPH]

Just watch the rabbit hole on test gear.

 

[Max]

Vcc is three 1.5V batteries, right? So 2.5V or 1V per division as it’s 4.5V max. And we’re talking audio frequencies - most likely less than 10 KHz. So I’d start at something like 50 ms/div and go up or down from there.

 

[Max]

On a normal scope the probe calibration is usually 5v/div @1kHz. What I would be checking is the squareness of that pulse train. Right now get that pulse train displayed and play with the controls to get a feel for it. For the price, what the heck!

Yep I’d get the cal signal displayed first to validate the scope is working.

 

[Snapped-off]

So it has the 1khz test output. What am I supposed to do with it though when the switch is set to GND, it isolates the input leads from the input signal and grounds the scope.

 

[Snapped-off]

Just clamp one of the leads to it? Cause I'm not getting anything on it.

 

[Max]

Just clamp one of the leads to it? Cause I'm not getting anything on it.

The scope leads are just red and black clips, right? So clip the red one to the cal point. And don’t have the switch set to gnd.

 

[Snapped-off]

Seemed weird. Took it off GND... figured out the test calibration. There's no waveform visible over 1ms. Below that down to micro? Pico? It just gets crazy.

 

[Snapped-off]

Trigger is set to auto. Also has normal and single but they don't pick anything up. I don't think I'm getting any meaningful readings hooked up to the board. The cal test put out a nice square wave, but the board is putting out an erratic sine wave.

 

[Snapped-off]

These are just sitting here hooked up to B- and the transistor base..


No changes when closing a switch.

This should be flat until a switch is closed and the COB sends out a signal right? I'm probably wrong somewhere.

 

[RPH]

Nothing at collector? Drop the voltage do enlarge the trace, and stretch the time out. The beauty of a scope is seeing the waveform.
Transistors are used as a switch or amplifier depending on need. On the npn unit the “P” has to be more more positive than the collector. Only then does the current flow. The more positive it becomes the electrons move until in full conduction. To shut off you apply negative voltage to base. Opposites charges attract = current flow. Like charges repel = no current flow. This is why my questions on the switches and what initiates the cob to output. Not sure if we have done that. Not a bad picture on the scope.

 

[FordTruckWench]

This looks like your picking up wall current. Sensitive instruments will easily pick up the 60Hz AC.

In practice, this means that nothing is driving that point in the circuit. Or you scope isn't fully hooked up.

...

Now that you have the scope, I'm interested in what sort of signal is on the business end of the yellow-violet-yellow resistor. (The end not hooked to B+.) Previously you said that the voltage changed when you pushed the buttons.

 

[RPH]

I did wonder about that 60 Hz.

 

[Snapped-off]

The problem was the waveform wasn't getting bigger or longer while I was adjusting it.

It was working as expected while I was messing with the cal test. I'll get to it some more in a bit. I'm off today.

 

[Snapped-off]

Hooked up to B- and transistor base. Nothing meaningful. I'll try the collector and the resistor as well. Went up and down with voltage as well as duration. Above 50mV just looked flat. Below 50mV didn't look any better.

 

[Snapped-off]

Just some pics of the 1khz cal test. It does seem to work. Also for the above pics. I was closing the switches and not seeing any changes. I'll keep playing with it.

 

[RPH]

Ok, so we have confidence in the scope.
Do you have power into cob? Across the inputs, that change of state thing.
Then probe cob at transistor leads with no transistor in the socket.
All except transistor socket should be dcv. Either it’s present or not.
At this point just verify the conditions.

 

[dogdog]

the thing with these single transistor amplifier is the base is where the sound signal comes in from... maybe try with the transistor unhook... the test lead to the base pin and the ground to ground pin (the E) ? and press the button, it should output something.

 

[Snapped-off]

I've updated the first post in red. I found a cheap and supposedly working track half on ebay. (The half with the circuit board.) Is there any risk in cooking the chip by hooking the scope up to it and messing around with it?

I kind of just want to mirror some testing with the good and bad boards to confirm the original one is toasted. I don't want to ruin the 2nd one though.

 

[Max]

Glad to see that you are still in it.

The ‘scope should be high impedance so no issues there unless you short something with a probe. Just make sure the board gets hooked up ok.

 

[dogdog]

yes, just don't short the legs t to get a click so you know if your speaker works or not

 

[Snapped-off]

yes, just don't short the legs t to get a click so you know if your speaker works or not

I wasn't going to bring it up... but I definitely won't be doing that.

 

[RPH]

For a moment there I thought you were experiencing the seven stages of grief. Just be careful poking around.

 

[Snapped-off]

Got the new track piece in, it works. I definitely get working results on the oscilloscope. I have it hooked up from transistor base to emitter.

The original transistor is in fact a S8050.

 

[Snapped-off]

Couple pics of the scope while closing switches. The last one I pressed it 3 times which you can clearly see. Pretty neat for under $40.