Ingelen trv111 am portable radio repair with video
As a hobbyist, I don’t claim to know everything. As soon as you think you know everything, you stop learning. I know that I will never stop learning. This Ingelen AM radio was a challenge, due to the fact that I don’t have too much knowledge of its operation. So, when I discovered the fault, it was more due to dumb luck, but I prefer to say it was a diagnosis after a thorough visual inspection.
The owner of this radio has had it since he was a teenager and wanted it repaired for the memories, rather than a fully restored unit. As you could imagine, the batteries were long gone and needed replacement. But, I didn’t want to purchase new batteries until I was sure I could repair the radio.
After realizing that this radio uses 2/ 4.5 Volt supplies, I decided to create 2 separate power systems. One was easy – just using my adjustable power supply gave me the first required 4.5 Volts. The second one required a little more imagination. By connecting several AA batteries together in series, I was able to produce the needed voltage.
After connecting both supplies together, I was able to achieve the needed 9 Volts.
Naturally, it was more than just a flat battery! This is where my careful visual inspection comes in. By wiggling various components, I was able to get the radio to come to life! The suspect revealed itself – a faulty variable resistor. I confused myself for a while, not being sure if it was a potentiometer or variable resistor.
A potentiometer uses 3 legs to create the varied reading. This is commonly used on Throttle Position Sensors in cars to provide the data needed by the Electronic Control Unit (ECU) of the throttle position or in other words, how far your foot is on the accelerator pedal. This is done by the ECU providing a 5 Volt reference and a sensor ground and then the varied control signal is sent back to the ECU for processing.
However, this component can be used as a variable resistor simply by using one of the legs as well as the terminal leg from the resistive element.
I should have looked at the wiring diagram earlier to see that the potentiometer was actually being used as a variable resistor. Both the resistance element and one side of the component were connected on a single pad on the circuit board.
Fortunately, the resistance rating was noted on the schematic. I measured what the resistor was set at – 15.65 KΩ. Paint had been place on it to lock the trim measurement into place.
I did consider using a trimpot to replace the resistor, but due to the location, it wasn’t the best solution. After removal of the resistor, I could see that the contact points of the legs were poor and by ‘tweaking’ them as well as soldering them into place, I was able to reuse it without replacing it.
After testing the operation of the radio, I noticed that the tuning buttons were very stiff due to dust contamination. All that was needed was some Circuit Board Cleaner to clean up contacts as well as lubricate the slides of the knobs.
So after fully reassembling the radio and thoroughly testing its operation I could pass it back to the customer. Only 2 AM stations were able to be picked up by the radio, but that is the way things are – most are now FM stations. The gentleman was very happy with the result and could listen to the local AM station and take a trip down memory lane with his newly repaired, old radio.
If you are interested in this repair, you can see a video on my channel following the link below:
This article was prepared for you by Mark Rabone from Australia.
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Note: You can check out his previous repair article below: