Restored A Tampered Keyboard And Made A Kid Very Happy
This keyboard was brought to me by a Driver with a request to look into the possibility of restoration, after his elder son tampered with it and spoiled it. His second son was very sad that he could not play on this anymore. Well, such cases should be given priority, as a kid’s happiness is everyone’s responsibility and I accepted the device with an assurance that I would try my best. Went through the pandemic protocols.
First my attention was on the adapter, which was found tampered with. It had three screws, which were found loose. On opening, I saw that the output wire was broken. On testing, however, the DC was present. As you can see from the picture above, it had two controls on the top. One was positive/negative inverting switch and the other selection of 0-12V in steps. After reconnecting the wires, I applied power and found that the Keyboard was making some very weak and distorted sound. So, disconnected the power and opened the back cover. As the other end of the DC wires were soldered inside the key board directly, bypassing the DC input socket, I had to open the set in that condition.
The Keyboard had its mother board soldered to its key pad board and an audio board wired and fit on top. After removing the rubber buttons, which had carbon beneath in the centre for making contact when pressed, I cleaned the board as well as these keys. Retouched the solder of the mother board and the inter connecting strip wire. Replaced the keyboard on its place. Did a dry solder patch up on the audio board. Replaced the TW0 220/10v electrolytic capacitors as the values were out. Replaced the disc capacitor (104) on the mother board, as its value was also wrong. Then powered on the set by applying a 6V DC to its battery terminals.
As this keyboard starts a short music on switch on, it is easy to check the output by just switching off and on. The output was weak but the distortion was very much reduced. Disconnected the speaker wires and tried it on another speaker. It was good. As I was not having the right size speaker, I requested the customer to fetch it, by handing over the defective one. I tried after he brought a replacement. It was ok.
Then, my attention turned to the adapters. I disconnected the +/- and 0-12V switches, as these were found to be defective and making intermittent contacts. After removing the contacts, I refixed the switches with its screws from behind. Provided a 7806 IC, fixing it behind one of the rotary switches, with a 220/25V electrolytic capacitor added on the output and fed the 12V AC wiring it directly to the 4xIN4007 diodes. It had one 1000/16V electrolytic capacitor for smoothing, which was checked to be ok. Then reconnected the output wires to the IC. Reassembled and fixed, and powered on and found the keyboard working fine enough for a cheap keyboard like this.
In my eagerness to deliver the keyboard as soon as possible, I forgot to click these works! Called the customer and he was happy to come and pick it up even though it was almost 8.30 PM. His second son also came along and I was so glad to see the happiness on his eyes, though the mouth and nose were blocked by the mask. A job accomplished with satisfaction in double strength getting added to its collection bag!
This article was prepared for you by Parasuraman Subramanian from India. He is 71 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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You may check on his previous repair article below: