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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 2nd Mar 2018, 1:36 pm   #1
ct92404
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Question Tandy 200 portable computer - need help

Hi all,
I recently bought a Tandy 200 portable computer. It was made in 1985 and I guess it could be considered an early laptop computer. It still works! I've been playing with it for the past few days, typing some documents on the simple word processing program that came with it built-in, and I made a couple of simple BASIC programs so far. Amazingly, the little computer runs on only 4 AA batteries! (It can also run on a DC power adaptor, but I prefer batteries). It's actually kind of cute. It's about the size of a 3-ring binder.

But I did run into a problem. The ONLY internal memory it has is RAM. It does have a back-up battery on the motherboard, which apparently recharges from either the AA batteries or the power supply. (And amazingly it is still able to hold a charge!) But once both are dead, any data you saved will get wiped out! The little computer of course doesn't have any kind of internal hard drive. It has a tape cassette interface using a DIN cable, which is what I planned to use to save files externally. I don't have the original cable to hook up a tape recorder, so I made one. I connected an audio line out from the cable to my modern laptop to try to save the sound as an audio file. Unfortunately, when I tried to save files from either the word processor or BASIC, it didn't work. I heard a faint click sound from the Tandy, but there wasn't any sound of data being transmitted (beeps, hiss, etc). The other computer didn't pick up anything either.

Does anyone have any idea what could be wrong? I double checked to make sure that I soldered the wires to the right pins on the cable and everything seems to be connected correctly. But even without the cassette cable connected, from what I've read about these computers and the videos I've seen on YouTube, you're supposed to be able to hear the sound of data being sent when you load or save files to casette. But I'm not getting anything.

I don't know if this particular computer was ever sold in the UK, or if anyone here is familar with it. But I'd really appreciate any suggestions!
- Chris

Last edited by ct92404; 2nd Mar 2018 at 1:42 pm.
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Old 2nd Mar 2018, 4:43 pm   #2
Ancient Geek
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Default Re: Tandy 200 portable computer - need help

What pins of CN2 did you connect to? In at least some of the Tandy machines the pin numbers on the connectors did not correspond with the pin numbers in the manuals. It should be relatively straightforward to identify the ground pin(s) and then I'd suggest trying each of the other pins in turn to look for an output. Failing that, if you have an oscilloscope, see if there is any output on the 8085 CPU pin 4, which drives the casette output via an inverter gate.
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Old 2nd Mar 2018, 5:02 pm   #3
TonyDuell
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Default 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.
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Old 3rd Mar 2018, 4:26 pm   #4
dragonser
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Default Re: Tandy 200 portable computer - need help

Hi,
I seem to remember that " some " early computers have quite a low level output signal as they were meant to be connected to the mic socket on a cassette recorder, rather than the aux input. But I am not sure about the Tandy 200
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Old 4th Mar 2018, 8:13 pm   #5
acollins22
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Default Re: Tandy 200 portable computer - need help

Hello,

I suspect (but don't know for sure) that the click you hear is a relay for controlling the tape drive motor. That feature was very common for micros back in the day.

I regularly use my PC or an old mobile phone to store programs for use on my old machines and it works very well.

I wouldn't expect the Tandy to make any noise when it's sending or receiving so I don't think you need worry about that.

Levels probably do matter and usually they needed to be too high to comfortably listen to.

Hope this is of some help.

Andy.
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Old 5th Mar 2018, 8:41 am   #6
ct92404
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Default Re: Tandy 200 portable computer - need help

I just noticed that the "Telcom" program isn't working right
I can select it from the main menu, and it opens. But when I try to select "Terminal," the computer freezes up. I have to press the reset button.
So unless I can find out what's causing that problem, it looks like I won't be able to transfer files to another computer with the serial connection either.

Someone definitely tinkered around with this little computer. I opened it earlier to check the internal condition, and I noticed that someone had installed what looks like custom ROM chips. There's also some other program listed in the menu, apparently what's on the custom ROM. It looks like some kind of software to control a printer. What I'm wondering is if they replaced the original ROMs, and if maybe Telcom is missing? But if that was the case, how did it even open when I selected it from the main menu? How hard would it be to write a small program to transfer files with the serial port? Or I wonder if I might be able to find the original ROM chips somewhere?

About the cassette problem, I don't have an oscilloscope so I don't know how to check if there's a signal coming from the cassete interface.
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Old 7th Mar 2018, 2:08 pm   #7
ct92404
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Default Re: Tandy 200 portable computer - need help

I got it!

I don't know what went wrong before, but I am now able to save AND load with the cassette interface. I connected the Tandy to my modern Dell laptop and saved a file. First I tried a text file. I recorded and saved the data sound as a .WAV file on the dell, and then copied it onto my cell phone. I opened the TEXT word processor on the Tandy again to get a blank file, and loaded the sound from my cell phone. It worked! The text showed up on the screen.

I then tested saving and loading BASIC programs the same way, and it worked without any problems!

For some reason, if I try to play the sound directly from my Dell laptop, the Tandy won't load it. But I had the same problem with other vintage computers using a cassette jack. It must be just something about how the Dell plays sound files, these old computers don't seem to like it. But it works if I play the sound from a cell phone.

I'm just so glad that now I can use the little Tandy computer and save files externally and not have to worry about losing my work if the batteries die!
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Old 7th Mar 2018, 3:56 pm   #8
dominicbeesley
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Default Re: Tandy 200 portable computer - need help

When doing anything like this you may need to fiddle around in the deeper settings for your soundcard. This has caused me grief both on trying to transcribe computer recordings and doing NBTV work.

Computer sound card drivers do all sorts of audio processing (that is supposed) to make things sound better but which messes up anything like this. For instance on my card on windows 10 I need to right click the speaker icon, select playback devices, select the device I am using right click that and in "enhancements" tab [sic] disable everything except "immediate mode", then in the "spatial sound" tab turn spatial sound off.

This works on my machine but your mileage will vary greatly if you have, for instance, realtek driver suite installed which adds all sorts of graphic equalisers, theatre effects etc all of which will need turning off.

Phones I have found tend to be less of an issue probably all that processing would cost battery power though I should think there are plenty of apps/OS settings that can/will mess things up.

I've got a model 100 languishing in my workshop that needs rehabilitating. That one has the separate disk drives and runs (I think) some sort of CP/M

D
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Old 11th Mar 2018, 1:38 am   #9
ct92404
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Default Re: Tandy 200 portable computer - need help

I had another question. I think I'm eventually going to have to replace the original built-in nickel-cadmium battery. (I don't know how in the world It's still able to hold a charge considering it's over 30 years old! But it does!) It looks in mostly good condition, with just a little bit of corrosion on one end. What would be the most appropriate modern replacement? I'm assuming that Ni-Mh would be safer and more reliable. Is there a particular kind you'd recommend?
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Old 11th Mar 2018, 3:17 am   #10
julie_m
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Default Re: Tandy 200 portable computer - need help

Ni-MH will be fine. Just go for the same voltage (number of cells) and the same or slightly higher milliamps-hours capacity. Varta probably is the best-known make, but a generic, unbranded item will be fine.

Don't spend too long soldering it in, and let it cool down fully before soldering the other connection.
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