Radio Shack Project Lab 300 Help/Questions

[BaldGuy]

I bought the project lab 300 about 23 years ago, and finally decided to work on it. LOL.

I still have all the parts and when I did experiment # 1 (makes the speaker sound like a bird), I thought I smelled something burning. Experiment worked correctly and I thought I was just imagining it.

Then a week later I did project # 2. Its a simple AM transistor radio. I put it together, had the ear piece in my ear, turned it on, turned the control knob to tune it, and smoke came out from under the unit. This experiment uses 6 volts of power.

It was a bit funny in some ways but kind of serious in other ways. I thought these kits was 100% safe no matter what I did? I am using Eneloop batteries which I'm sure wasn't available when the kit was bought. But they are 1.3 volts each instead of 1.5 volts. So I would think that would ok. I measured the different voltages coming out with my multimeter and all seems ok.

Enclosed is the different pictures of the lab. You will notice a melted area where the switch is at. That's where the smoke was coming from. As you can see, nothing inside the unit looks corroded or melted, etc.

So questions are:
1. What did I do wrong?
2. If I wanted to do the experiments with a breadboard and such, how would I replace the transformer, terminals, antenna, etc the lab has?

I did order another lab off e-bay, but don't plan to try again till I get some feedback. Also, feel free to ask any questions. I do appreciate any help I can get with this. I know its been a long time coming, but I would like to work thru all 300 experiments, but want to do so safely.

[KMoffett]

Did you use the "control" potentiometer in the AM radio circuit? I would have thought that you would have used the "Tuning" capacitor. I suspect that you connected one end of the potentiometer and the wiper across your battery and then turned it to one end. When I smell smoke from the trainers in our student lab, they invariably have done that and burned up the potentiometer. Use your multimeter and measure the resistance from the pot's wiper to each end. I will bet that one way you will get a varying resistance and the other you will get an open circuit.

Ken

[BaldGuy]

No, I used the tuning knob as shown in the picts. I shouldn't have said control in the post, I just meant the dial they told me to adjust to try to hear stations. I hooked it up exactly as the picts sho other then I unplugged the power for obvious reasons.

I appreciate your reply, but to be honest, I don't understand how to do that check.

Could I have had a fire on my hands?

[KMoffett]

Without a schematic of the circuit and a photo of your setup it's pretty hard to troubleshoot. Did you poke your nose (seriously) around the underside to see what may have burned?

Ken

[BaldGuy]

Without a schematic of the circuit and a photo of your setup it's pretty hard to troubleshoot. Did you poke your nose (seriously) around the underside to see what may have burned?
Ken

Ken,

Enclosed is the schematic and parts list. I actually see some things I did wrong, just didn't try it yet. I hooked way too much to the (-) instead of ground. I got confused on what was ground vs the (-) which can also be called ground.

Still hard to believe, such a easy mistake would cause a meltdown and smoke on a "toy" that is designed for kids 10 and up.

As far as what is burned, you can see that in the other pictures as well as how I hooked the thing up.

Back to an earlier question, what parts could one buy to replace some of the radio shack ones on the kit. Such as transformer, antenna, terminals. Be interesting to see how one can hook up terminals to the experiment if it wasn't in this kit.

O well, will make the changes and see If I can actually hear an AM radio.