Electronic troubleshooting

[Max]

you might have to break out that oscilloscope there to verify if the signal to the base of that transistor is still good... you might have shorted the IC in one of the poking.

Unfortunately I agree with you. Unless something else is affecting U1’s output it doesn’t look good.

 

[Snapped-off]

What's out there for a cheap scope? I'm not opposed to buying something to learn with. Even if I never use it again, I'm ok with that.

 

[dave*99]

Research Oscilloscope apps. There are apps that use your PC (some use the sound card in the PC), apps that use an external A/D converter and your smart phone or the smart phone mic input. Lots of cheap options. There are old scopes on FB marketplace, craigslist, eBay, ham fests.

 

[gpiggaz]

I have no personal experience with this one, but It would probably do an ok job for seeing any waveform that board could create https://www.amazon.com/dp/B08832JX4H/?tag=atomicindus08-20

 

[Snapped-off]

Any benefit to analog over digital or digital over analog? That meter isn't priced too bad. I've already got 2.. (no scopes)

 

[RPH]

I thought you stated that a fluke was in use as the meter? If so, what model? Frequency and duty cycle features may get you through this.
Cheap are just that cheap but for learning it would work. Expect prices to start around $200 and go up.
Probes could be another hundred for a cheap set. The scope will give you much better view of the workings of the circuit.

 

[Snapped-off]

I thought you stated that a fluke was in use as the meter? If so, what model? Frequency and duty cycle features may get you through this.
Cheap are just that cheap but for learning it would work. Expect prices to start around $200 and go up.
Probes could be another hundred for a cheap set. The scope will give you much better view of the workings of the circuit.

Yes, a 289.

 

[Snapped-off]

Without going and looking at it, I don't believe it does duty cycle.

Actually looking online I guess it does. I'll check it in a bit.

 

[dave*99]

I believe this toy plays music of some sort. So frequency and duty cycle will change a lot. A multimeter that can read values of F and D.C. will not likely lock onto a rapidly varying audio signal.
O-Scope is needed.

 

[Snapped-off]

I believe this toy plays music of some sort. So frequency and duty cycle will change a lot. A multimeter that can read values of F and D.C. will not likely lock onto a rapidly varying audio signal.
O-Scope is needed.

Yes, I previously said it plays music for 5-8 seconds, but it actually plays a few different tones of bells for like 3-4 seconds. I had to go back and watch the video I recorded of it.

 

[Snapped-off]

STARTO Handheld Digital Oscilloscope Kit 2.4” TFT with BNC-Clip Cable Probe and Power Supply: Amazon.com: Industrial & Scientific

STARTO Handheld Digital Oscilloscope Kit 2.4” TFT with BNC-Clip Cable Probe and Power Supply: Amazon.com: Industrial & Scientific

www.amazon.com

What about this one? Cheap dedicated scope.

 

[Max]

STARTO Handheld Digital Oscilloscope Kit 2.4” TFT with BNC-Clip Cable Probe and Power Supply: Amazon.com: Industrial & Scientific

STARTO Handheld Digital Oscilloscope Kit 2.4” TFT with BNC-Clip Cable Probe and Power Supply: Amazon.com: Industrial & Scientific

www.amazon.com

What about this one? Cheap dedicated scope.

I’m not sure. On paper it has good enough specs - 5mV/div sensitivity and bandwidth of 200kHz. The display is only 320x240 so things displayed will be rough. But the price is right. Note that half of the reviews seem to be on a heat shrink connector kit so who knows.

Another option is here: https://www.amazon.com/dp/B0728GCBLD/?tag=atomicindus08-20

Its the same thing but cheaper.

 

[Snapped-off]

Next episode on Tuesday when the scope comes in...

 

[dogdog]

talking about determination. LOL

 

[RPH]

The fluke 289 can measure frequency to 999.99 kHz. I would look at the base to see if any indications of a varying signal. If it’s flat line then we have bigger problems.

 

[Snapped-off]

The fluke 289 can measure frequency to 999.99 kHz. I would look at the base to see if any indications of a varying signal. If it’s flat line then we have bigger problems.

This is the most in depth I've used this meter. It was my grandpa's. I'll try out the frequency with it today.

 

[RPH]

It’s a great meter, I started with the 87 and moved up to the 189, last meter was 289. I would expect to see a change in frequency. The output of the cob has to be limited in frequency. Most likely 1kHz to 15kHz, flatline is not good.
Explore the meter, you would be surprised what it can tell you. I didn’t always carry a scope but my fluke went everywhere.

 

[Snapped-off]

So this fluke will do frequency, duty cycle, and pulse width, among other things.

 

[Snapped-off]

Tried both AC and DC Hz from B- to the base. We have 0 both up and down. Am I measuring correctly?

 

[Max]

Most accurate would be base to emitter voltage.

 

[Snapped-off]

Not getting anything with the leads on the base and emitter.

 

[FordTruckWench]

Not getting anything with the leads on the base and emitter.

Do you have an assortment of resistors? In days of old, Radio Shack would sell a tub of ~100 random resistors. Reason I ask is that we need to test if anything is hooked to / driving the base. To do that, we need to inject a signal, but it needs to be current limited. Hence a need for resistors. Exact values aren't important. We just need some with the 3rd band being red, orange, or yellow. (The 4th band would likely be gold or silver.) The test resistors could even be pulled off some old electronics.

 

[Snapped-off]

Do you have an assortment of resistors? In days of old, Radio Shack would sell a tub of ~100 random resistors. Reason I ask is that we need to test if anything is hooked to / driving the base. To do that, we need to inject a signal, but it needs to be current limited. Hence a need for resistors. Exact values aren't important. We just need some with the 3rd band being red, orange, or yellow. (The 4th band would likely be gold or silver.) The test resistors could even be pulled off some old electronics.

What do I need to do? I can get some. I don't think I have anything I can salvage from though.

 

[FordTruckWench]

What do I need to do? I can get some. I don't think I have anything I can salvage from though.

I'm still thinking of the exact tests to do. Values in the range 1000 ohms (brown-black-red), through 10K (brown-black-orange), through 100K (brown-black-yellow), and a bit higher would work. Exact values are not important. I'd probably choose 10K.

I mentioned salvaging so that we can avoid shipping delays. Maybe a local Goodwill has something you can take apart.

 

[RPH]

This has been a challenge but a fun one. Things to consider with all that’s been thrown at it.
Cob alive or dead ? This is a distinct possibility of death.
Inputs active to cob? Are we telling it to do something? Unknown.

Per Fluke “To avoid damaging the circuit under test, be aware the Meter sources current up to 10 mA at an open circuit voltage up to 20 volts.”
Did we kill it?

 

[Snapped-off]

This has been a challenge but a fun one. Things to consider with all that’s been thrown at it.
Cob alive or dead ? This is a distinct possibility of death.
Inputs active to cob? Are we telling it to do something? Unknown.

Per Fluke “To avoid damaging the circuit under test, be aware the Meter sources current up to 10 mA at an open circuit voltage up to 20 volts.”
Did we kill it?

It's a shame because it was working for about 5 minutes... I'll probably throw in the towel after I get to play with the little scope. With the 0 readings on the dmm, I don't have much hope.

 

[RPH]

Well if it is dead then do a post mortem on the unit. See what you find but it isn’t dead until you say it is. It’s a good project to play with the scope.
Check power to cob.
Check inputs to cob for function.
Check output of cob for function.
It seems to come back to the cob at this point.
Good luck!

 

[Snapped-off]

Well if it is dead then do a post mortem on the unit. See what you find but it isn’t dead until you say it is. It’s a good project to play with the scope.
Check power to cob.
Check inputs to cob for function.
Check output of cob for function.
It seems to come back to the cob at this point.
Good luck!

How would I check the I/O? Would the output be the leg that goes to the transistor base and the inputs all the other connections to the cob?

 

[Max]

How would I check the I/O? Would the output be the leg that goes to the transistor base and the inputs all the other connections to the cob?

Pretty much, yes. I’d also check power and ground to U1.

 

[RPH]

Either the switch sends a high signal to an input or the input is pulled low by the switch. What you want to see is a change of state and when does it flip back.

 

[Snapped-off]

Either the switch sends a high signal to an input or the input is pulled low by the switch. What you want to see is a change of state and when does it flip back.

Could it operate off both? Seeing changes both up and down in DC voltage probing different inputs while closing the switches.

 

[Snapped-off]

I think there's something going on at C1 and C2. I need to remove them and check.

 

[Snapped-off]

C1 and C2 seemed fine. Both 2.6 nF. I think I was looking at their points in the circuit wrong.

Back to the switches. SW4, the 2 grey wires at the top. With the switch closed I'm getting 1 V.

I'm currently going over all the switches. I should be getting 4.5V when they're closed right?

 

[Max]

Maybe. There could be dropping resistors in the switch path, or other loads like lights that would give you that. You could remove the batteries and ohm out each switch and its wires.

 

[Snapped-off]

I'm not sure what the voltage drop should be.
While closed I'm getting the following:
SW2 1.7V
SW3 1.0
SW4 1.0
SW5 3.1
SW6 4.6

Is any of this useful?

SW2 are the 2 directly on the board. 5 and 6 are equal distance. 3 and 4 are equal distance, and the furthest from the board.

 

[Snapped-off]

Maybe. There could be dropping resistors in the switch path, or other loads like lights that would give you that. You could remove the batteries and ohm out each switch and its wires.

I guess that will be next. There's nothing in the switch circuits but the wires. 3 of them have little boards and have ?contact? switches just like SW2 is on the main board. Just little satellite versions. There's nothing on the board but the switches and 2 wires.
SW3 is a little different. It's a physical switch.

 

[Snapped-off]

I've labeled them their respective colors on the main PCB. SW2 is of course directly on the main board. SW1 is the battery/power switch and unlabeled.

I'm bored I guess.

 

[Innovate1]

Generally you can use an ohmmeter to measure the BE and BC junctions. One direction will show low resistance and the other high resistance as you are testing the diodes at the junction. Depending on which direction is low resistance you can determine NPN or PNP.

Unfortunately looking at the pics it looks like the leads were cut off of the original transistor. So measuring it is out. And since you don’t know the transistor type for sure, you also don’t know which pins are the emitter, base, or collector either.

The good news is that we can probably figure it out from the schematic. You need to follow the traces from each lead of the transistor and see where they go. One will likely go to a speaker, the other to the plus or minus of the battery, and the other to the IC. There may series or parallel resistors in the oath as well. Can you draw a schematic?

Measuring it isn't out. With some pointed probes and something to hold the part steady the remains of the leads flush with the package could be easily probed. With that you could determine NPN or PNP and what pins were what. There are at least 2 different, common pin outs.

 

[Snapped-off]

Measuring it isn't out. With some pointed probes and something to hold the part steady the remains of the leads flush with the package could be easily probed. With that you could determine NPN or PNP and what pins were what. There are at least 2 different, common pin outs.

The original transistor was determined to be NPN with the base in the middle. I was able to test it with some skinny leads.

It's been a pretty long thread. There's been a lot of info and data spread around in here. A couple guys have been following along and assisting from early on so they're more up to pace. I may clean up the first post or 2 to update where everything is at currently.

 

[Innovate1]

The original transistor was determined to be NPN with the base in the middle. I was able to test it with some skinny leads.

It's been a pretty long thread. There's been a lot of info and data spread around in here. A couple guys have been following along and assisting from early on so they're more up to pace. I may clean up the first post or 2 to update where everything is at currently.

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.