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mike_z

TI99 will not read cassette tape

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I thought I'd start a new thread, because the title does not apply to the current problem (TI99 no sound). I have recently re discovered my old TI994A that I purchased for the kids a long time ago. I got it working, having trouble with the video cable etal. Currently, I'm attempting to get the tape recorder to work, in order to save programs. My first tries sometimes resulted in storing programs, at least I knew that sounds were recorded. But I only once successfully read a recording back to the TI99. The first problem was the cable. The 9 pin connector had some problems. I cut it off and installed a new DB9 connector. This helped but still had trouble recording. I replaced C403 and C407 and now the records work (at the sound) seem to be OK. But I still can not read the tape. I checked at the 9901 pin 30 and using my scope I can see plenty of vpp and frequency pulses. So I suspect that the tape recorder and the interface circuits up to the 9901 are working. I have seem some documents regarding how the 9901 work. When the TI99 starts to read, it masks all the interrupts so that it can read a tape from beginning to end. The 9901 uses CRUIN, pin 4, to send the data to the CPU. When reading a tape I can see activity on pin 4, but am unsure whether what is there is good data.
Also, both the read and check programs do not work, so this seems to lead me to think the 9901 is at fault. The fact that I can record means the timer must be working. I'm assuming that the timer is the same one used in record and read, but am unsure right now. I'd like to think up a better test to see if the 9901 p11 is working. Any Ideas? Thanks for the help, Mike

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Well...... I backed up and thought that I'd try and verify that the recording, the part I know is being done, is correct. I dragged out my logic analyzer and looked at the 9901 pin 28, while saving a program. I get a bunch of 690 cps pulses that are the zero's. These apparently are used to figure out the speed of the tape recorder motor. Then there is 8 pulses of 1380 cps. This apparently is the data mark. This should be followed by 64 bytes of data and the LSB of the checksum.  Then the next record is sent. I appears that a record is about 1/2 second long. Mike

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Ensure that the ground lead for both the tape in, and tape out are connected to each other.

 

There is a known circuitry faux-pas that has the tape input circuit's ground line floating.  Apparently, TI assumed that the cassette recorder would bridge the grounds as a common ground internally.

 

This is not always true.

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Yup, the commons are tied in the tape recorder. Mike

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Well..... I think I may have the reason why I'm having trouble with reading the tape recording. True, I'm recording, BUT.... I believe that the o-ring drive belt is causing the tape speed to vary way too much. When looking at the leader, the bunch of leading zeros, they are not similar, the ones and zeros highs and gaps are all different. I think the TI99 is reading the input, but is becoming confused at the varying pulse widths. I'm going to have to either find a new drive belt or a different tape recorder. Maybe that will clear this up. Hopefully, it is the tape recorder and the TI99 is OK. Thanks for the help, Mike

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Posted (edited)

Put some tape around the motor, then put the belt back. Take up the..10 thickness that the belt stretched. 

Poor Man solution, PMS

Edited by GDMike
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1 hour ago, GDMike said:

Put some tape around the motor, then put the belt back. Take up the..10 thickness that the belt stretched. 

Poor Man solution, PMS

like when I was a kid.  we could use panty hose as a belt for the motor!   American ingenuity at its finest!

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Sometimes a large o-ring can substitute for a belt. I've even used rubber bands, but they tend to stretch from the torque. While in there, look around for dry bearings, grundge or reasons for dragging other than a loose belt. Oil sparingly if at all, I put a drop on the end of a toothpick to help apply the minimum to where it's needed. Don't need oil on the belt or tape path! Clean the head also. Head alignment won't be an issue with tapes made and played back on this same machine. Tapes themselves can bind too, especially if played a short bit, rewound, played again, etc.

 

Have you tried recording voice or music and just listening to it? You may also be able to record to your computer or phone. Even an old VCR if you have the adapters to RCA plugs.

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You may try placing the belt in some boiling water for a minute or two, then let it cool, may tighten it up some. Saw that trick once before.

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Or try connecting a phone to the computer and download a .wav file...

Ok, who kicked me...

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Thanks for all the suggestions. I'll try the hardware store maybe later today or tomorrow. I believe they have a good selection of o-rings. I'm sure that I can find something that will work.

 

This morning I've been reading about using Audacity instead of the recorder. I downloaded a copy and have been playing with it. The problem remains the same. I can record and obtain a very similar sounding recording, but can not read that recording. Also, interestingly I compared the pulses seen on the 9901 pin 30 using the tape recorder and the Wave file. They are very different. The tape recorder produces a relatively square wave, although there are jiggles in the timing, which I believe the recorder is making. Then when I look at the pulses the wave file makes, it is mostly a high signal with many short 10 uSec pulses instead of the square wave. I'm wondering if I'm using the Audacity wave file correctly? Am I sending the TI99 a digital file?

 

One other question. I read somewhere that when the TI99 is reading a file from tape, the monitor will produce the sound of the tape, is that correct? I can not remember. Anyway, my monitor, although it beeps and can play sounds does nothing when I'm reading a tape or wave file. I still would like to see if I can write a BASIC program that would test the port11 of the TI99. Thanks for the help, Mike

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I have to take that back about not hearing the recorder sound on the monitor. I had the volume turned down. I can hear the tape recorder, but maybe not the wave file. I think I can hear something when playing the wave file, but it is faint. I have amplified the wave file to 0db and when I play it on my speakers it is loud, but not thru the TI99. I'm getting confused, time for a break, Mike

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One other question. I read somewhere that when the TI99 is reading a file from tape, the monitor will produce the sound of the tape, is that correct? 

 

Yes, that is correct.

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2 hours ago, mike_z said:

I still would like to see if I can write a BASIC program that would test the port11 of the TI99.

If you have a MINIMEMORY, you can read/write the 9901's ports, manually, by using EASYBUG.:pirate:

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I cranked up the volume on the Audacity wave file. I can hear the wave file sound on the monitor. Not as loud as the tape recorder. I see that there is a 15 ohm resistor across the input, quite a load, maybe my PC can not drive that very well? The fact that the recording sound can be heard on the monitor kinda tells me that the recording is getting through the 9901, but somehow does not make it to memory. I have to dig some more.

 

Star, No I do not have minimemory or easybug. I'll look into those, but again I'm wondering if the 9901 is good or not. THanks Mike

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1 hour ago, mike_z said:

Star, No I do not have minimemory or easybug.

 

           S.T.A.R..jpg.69ebd2fdb8095450e17909e35d36d8f4.jpg

 

                       S.T.A.R. ...At your service!

 

 

How about Editor/Assembler, Extended Basic?

 

Some PC's, only have line level output.

 

Usually the cassette output has to be turned up nearly all the way.

Tone set all the way towards the high end.

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Star, I did some experimentation with the recorders volume and watching pin  28 on the 9901. If the volume is too low, the pulses are miss formed. I need to have my recorder volume at 9 - 10 to obtain nice square waves.

 

Somehow the OS must grab the recorder data from the 9901 and incorporate it into the video signal. This seems to work. The OS also has to grab the data, and information in the header in order to store the data in memory. Since I think the data is coming out of the 9901, either there is a part failure or the data stream is faulty. The CHECK program does not place anything in memory, it just compares what is received with what already is in memory. Whereas the READ program deposits what comes in, into memory. Therefore I'm still thinking that either the data is corrupt or the CPU is fumbling. Somewhere I saw some documentation regarding the recording data stream. Maybe I can verify that my recording is correct. Mike

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Yes, to use a computer output, sometimes it's too low to drive the TI99. I've had to use an auxiliary amp to boost it. I routed the PC sound output into the cassette recorder mic input jack, put it in record mode, then drove the TI from the cassette's earphone and that boosted it back to normal levels.

 

I made a little dongle to monitor sound level using an old recorder's level meter, a diode and a few wires and plugs or jacks. That has been really handy to help set correct level and you can watch the needle wiggle as it loads. Sometimes a tape dropout could be seen when the needle would suddenly drop for an instant. With practrice, I could bump the volume right at that point and get a poor recording to load. Once loaded, I'd reSAVE it to a new tape. It's in one of my old posts, I'll dig it out.

 

 

 

 

LoadMeter cassette.jpg

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I wonder if it could be just low signal level.

 

What I just did was to monitor the INT REQ on the 9011. It is an active low. I see 4+ volts while the TI99 is idle. Then when I read a tape, once the sound starts I see low pulses. After the recording ends, the interrupt requests continue, as if the READ program is looking for more. Kinda hints at bad checksums? Mike

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