I acquired a very clean, working TRS-80 Model I Level II unit, and the only repair it needed was resoldering one of the keyboard switches. I have the cassette cable (which has been tested) hooked up to a CTR-117 cassette recorder.
For many months, I was able to CSAVE programs to cassette, and successfully CLOAD them. Listening the recorded program, the audio was very clear. It only took me one try to get the volume setting right, and then saving and loading worked 100% of the time.
Suddenly, and now consistently, programs recorded to the cassette have a very loud constant hum, and I can hear the program signal very faintly in the background. No adjustments to the cassette controls were made between when it worked and when it started behaving this way. The relay to control the motor works perfectly. And I can save a program, but can't load it because of the loud hum, faint program that was recorded on the tape. No adjustments to the volume help. (I inadvertently erased my tape containing earlier good program recordings, and I don't have any commercial software tapes, so I don't know if I can still load well-recorded programs. But I suspect that when I solve the bad recording issue, I'll be able to read tapes again. At least, that's my hope.)
I remember from my original system that there was a ground loop problem, which I fixed with a little switch box that would effectively break the ground on either the input data or output data cable, depending on whether your were writing to tape or reading from tape. (You'd throw a switch on the box to choose which operation you were about to perform.) I built one of these, but it's long gone. While the loud hum is reminiscent of that issue, I don't think the ground loop is the issue here, because it worked just fine and then suddenly stopped working, without any changes to cabling or cassette settings. And I haven't changed where everything is plugged in.
I suspect some part of the TRS-80's cassette recording circuit suddenly failed, but am not sure where to start looking. I do have the technical reference manual available, if we need to refer to specific components.
Any advice on steps to troubleshoot this issue? My test equipment is limited, and I'm mainly a software person, so be gentle. (That said, I am willing to use this issue as an excuse to purchase some additional test equipment.)
Thanks.
For many months, I was able to CSAVE programs to cassette, and successfully CLOAD them. Listening the recorded program, the audio was very clear. It only took me one try to get the volume setting right, and then saving and loading worked 100% of the time.
Suddenly, and now consistently, programs recorded to the cassette have a very loud constant hum, and I can hear the program signal very faintly in the background. No adjustments to the cassette controls were made between when it worked and when it started behaving this way. The relay to control the motor works perfectly. And I can save a program, but can't load it because of the loud hum, faint program that was recorded on the tape. No adjustments to the volume help. (I inadvertently erased my tape containing earlier good program recordings, and I don't have any commercial software tapes, so I don't know if I can still load well-recorded programs. But I suspect that when I solve the bad recording issue, I'll be able to read tapes again. At least, that's my hope.)
I remember from my original system that there was a ground loop problem, which I fixed with a little switch box that would effectively break the ground on either the input data or output data cable, depending on whether your were writing to tape or reading from tape. (You'd throw a switch on the box to choose which operation you were about to perform.) I built one of these, but it's long gone. While the loud hum is reminiscent of that issue, I don't think the ground loop is the issue here, because it worked just fine and then suddenly stopped working, without any changes to cabling or cassette settings. And I haven't changed where everything is plugged in.
I suspect some part of the TRS-80's cassette recording circuit suddenly failed, but am not sure where to start looking. I do have the technical reference manual available, if we need to refer to specific components.
Any advice on steps to troubleshoot this issue? My test equipment is limited, and I'm mainly a software person, so be gentle. (That said, I am willing to use this issue as an excuse to purchase some additional test equipment.)
Thanks.