UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Tandy 200 portable computer

TonyDuell · 2nd Mar 2018, 5:02 pm

One nice thing about Tandy machines is that technical or service manuals (or both) were availble, with full circuit diagrams. I've just looked in the one for the Model 200.

The cassette interface pinout is the normal one for Tandy machines (also used by the original IBM PC!). All you need is the normal 5 pin DIN plug (even though its an 8 pin socket on the machine). On the 5 pin DIN plug, pin 2 (the middle pin) is ground as usual. Pins 1 and 3 are to control the tape recorder (they connect to the contacts of a relay in the Model 200, that's the click you hear). Pin 4 is the input to the computer from the earphone socket of the cassette recorder. Pin 5 is the output from the computer to the Aux socket of the cassette recorder.

As Ancient Greek said, the cassette data signal comes from the SOD (Serial output) pin of the 80C85 processor, though an inverter and an RC network to the connector. So see if there is anything on the SOD pin of the CPU (if not, replace it, I've had 8085-type chips fail in odd ways). If you have data there, then trace the signal through the inverter and the RC circuit.

Incidentally I think (I have never used the Model 200, but have its older/smaller brother the Model 100) you can use the terminal application to transfer ASCII files (text editor documents and basic programs saved in ASCII) via the RS232 port.

2nd Mar 2018, 5:02 pm	#3
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,214	Re: Tandy 200 portable computer - need help One nice thing about Tandy machines is that technical or service manuals (or both) were availble, with full circuit diagrams. I've just looked in the one for the Model 200. The cassette interface pinout is the normal one for Tandy machines (also used by the original IBM PC!). All you need is the normal 5 pin DIN plug (even though its an 8 pin socket on the machine). On the 5 pin DIN plug, pin 2 (the middle pin) is ground as usual. Pins 1 and 3 are to control the tape recorder (they connect to the contacts of a relay in the Model 200, that's the click you hear). Pin 4 is the input to the computer from the earphone socket of the cassette recorder. Pin 5 is the output from the computer to the Aux socket of the cassette recorder. As Ancient Greek said, the cassette data signal comes from the SOD (Serial output) pin of the 80C85 processor, though an inverter and an RC network to the connector. So see if there is anything on the SOD pin of the CPU (if not, replace it, I've had 8085-type chips fail in odd ways). If you have data there, then trace the signal through the inverter and the RC circuit. Incidentally I think (I have never used the Model 200, but have its older/smaller brother the Model 100) you can use the terminal application to transfer ASCII files (text editor documents and basic programs saved in ASCII) via the RS232 port.