eBay
This auction is for an extremely rare Jerrold PlayCable unit for the Mattel Intellivision console. It hooks up to the cartridge slot of an Intellivision Master Component.
This is useless today because it depended on a game signal from the local cable company (see the Wikipedia Playcable description below).
The only thing it does is power on to the 'Playcable Catalog' title screen.
The units are very rare to find these days because they were rented equipment and normally returned to the cable company.

This item is used. It came out of my personal collection and has been tested as you can see by the picture.
The serial number etched into the plastic on the bottom of the unit is 171.
The condition is as you see in the picture(s). Feel free to ask me any questions.
This auction is for the PlayCable adapter only.

Terms and Conditions
This item is used and is sold "as is" without guarantee or right of return.

Shipping.
- Domestic shipping by USPS at actual cost.
- International shipping is via eBay's International Global Shipping service. Import duties, taxes and charges are not included in the item price or shipping charges. These charges are the buyer's responsibility. Please check with your country's customs office to determine what these additional costs will be before bidding/buying.

Insurance.
Domestic shipping will include a charge for insurance when the total of all items won is over $100. International shipping will include a similar charge where available. Insurance charges are determined by the amount of your winning bid(s).
 
I'm in the process of selling off my Intellivision collection, so more items will appear soon! 

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From Wikipedia - 
PlayCable was an online service introduced in 1981 that allowed local cable television system operators to send games for the Intellivision over cable wires alongside normal television signals. Through the service, subscribers would use a device, called the PlayCable adapter, to download the games for play on their Intellivision. It was the first service that allowed users to download games for play on a video game console. PlayCable was not widely adopted, due in part to high costs for users and operators, as well as limitations of the PlayCable adapter. The service was discontinued in 1983.