• Please review our updated Terms and Rules here

Something Different - DECTalk DTC03

I actually went ahead and obtained the last one. I figured that it would be wise to get a known working one; that way if I end up fixing the bad one I can have two or sell the other one. If I can't fix it I will at least have one for spare parts, save whatever is malfunctioning. Plus it would be a very interesting learning experience to compare the two and/or try to reverse engineer the bad one.

As for reseating the eproms, how do you recommend that I go about that? I have a chip puller I got from Radio Shack, but it does not go under the whole chip. Since the chips are ceramic I am afraid of damaging them and the board because they fit snugly in the sockets.

Unfortunately I do not have a chip burner. That is probably something I should get one day. Knock on wood, bit rot has not seemed to affect any of my other computers.

This might be of help in diagnosing the problem. I noticed that there was around 10v DC on some of the serial lines. I know that is in the range of the RS-232 specification, but wouldn't the voltage be absent if the board is not communicating with a terminal?
 
If you don't have a chip puller and don't feel like getting one, I've found that you can (very gently) use a pair of flathead screwdrivers to pry a chip out of its socket. (If you do this, be very careful to do it gradually and keep the positioning as even as possible so you don't bend the pins.) Theoretically this might cause problems if the plastic of the socket is very brittle, but I've worked on machines back to the early '80s and never had this happen. Still, take my advice with a grain of salt.

As for chip burning, I imagine several folks here probably have EEPROM burners; I do, and if you'll cover chips and shipping I'll burn anything you want, as long as my burner is compatible with it (it should be.)
 
I use John's technique also for pulling chips. It works fine for me all the time. The chip puller is to much trouble for more than a 16 pin dip.

I would think you should see -10V when nothing is going on. In the idle state, the transmitters should be in the mark state, which should be negative with respect to ground.

There are some really cheap prom burners out there these days. I still use my old Needhams PB-10 that I bought in undergrad, but I see some now on ebay that are about $50 and have USB interfaced for modern PCs. One I keep eyeing is the TOP853. I almost bought one last time I was in China. Maybe next time.....

At any rate, this weekend I will dump the eproms for good measure.

Lou
 
Thanks for the advice guys! I will definitely start to look into the eprom burner.

The 10v was negative so that must not be bad then.

Good luck with the dumping the eproms.
 
Unfortunately re-seating the chips did not solve the issue. I tried every chip in a socket, not just the eproms. I remember another thread that discussed microfiche. I am going to see if any of the people talking in that thread might have a print set.
 
The other module just arrived in the mail today. It passes its power on self test, and the user initiated test. The only thing I can't seem to get it to do is to talk. I have yet to make an amplifier to see if it works, but I presume that the SP light would activate when it talks. Does it echo the input back to the terminal?

With all the dip switches on (how it came in the mail), what should my terminal settings be?
 
All switches on is 9600 baud, 7 data bits, ignore parity. This is stated explicitly on page 154 of the manual.

When the self test is really passed, you will hear a string of DTMF tones. The SP light does blink while the DTMF tones play.

It will not start talking until it sees some kind of pause (comma) or end of sentence mark (period.) A carriage return will not necessarily make it start talking. Also, when you do end the sentence, it still will not talk right away, it will need to think for a few seconds.

It does not echo back to the terminal. I am not the best typist (as can be attested to by many here), so I set my terminal for local echo.

You can buy LM386 and everything else to make a little amplifier at RadioShack. However I saw recently that discount stores (like BigLots we have here in the east) have amplified PC speakers for $5. Pretty hard to beat the whole speaker with amplifier in an enclosure for that price. When I was messing around on the bench with the dectalk, I had it connected to some amplified speakers that I bought about 20 years ago to use with a tape player that are about the same idea as today's amplified PC speakers.

Lou
 
Thanks. I can confirm that it makes the DTMF tones because the SP light flickers for a little bit after the test.

Thanks for pointing out the switch settings. I was a bit confused because the switches seem to be opposite of how the board appears.

I will be sure to look into the speakers. I am unsure of what I will settle on because I have yet to pick out or design a case.

I think that I might have discovered what could be a part of the problem for my bad unit. I was working on the good one a few minutes ago, and it suddenly started to give me the same error code that the other one gives me. I thought that I had damaged it, but the -12v connection was broken. I turned it off, and when I re-connected it and turned it back on it worked again. Maybe the other board is somehow not getting -12v.
 
Last edited:
Okay. I was hoping that that might have been the cause. Could something be wrong with the part of the system that uses -12v?
 
There isn't much that uses the -12V supply. We know that the 1488 does. I'd have to pull the cover off the unit, but I think the only other parts that could use it are op-amps in the audio processing section. I would think that the digital sections wouldn't know a thing about any problems in the analog audio sections. I still would check the eproms for bit rot first.

Lou
 
If I can find an eprom burner, I will definitely dump them.

I have fully confirmed that the other unit makes the DTMF tones upon power up because I connected it to my computer speakers. The only problem is that I cannot seem to get my terminal to communicate with it. I am going to double check the serial lines again. I am using my VT-101, and I can confirm that it is in full working order, loop back tests pass and connections to other devices work.

Thank you so much for all the advice. I really appreciate it.
 
Forgive me if I am pointing out the obvious, but the VT101 connector on the back is DB25M DTE, and the pinout I showed in my tables for the DTC03 brings the lines out to a DB25M DTE also. One needs a null modem cable to connect the two devices.

My favorite tool to avoid destroying 1488s is the little box with the LEDs at the far right of this picture: http://www.vintage-computer.com/vcforum/album.php?albumid=180&attachmentid=11437 (pay no attention to the wiring to the cardedge connector, it's wrong!). I plug it into the ends of the cable (or device) one at a time and see who is transmitting on pin 2 and make sure that the other is transmitting on pin 3.

Lou
 
That box is sometimes called a breakout box, or LED box. It's trivially simple. Each line passes through the box, it has a DB25M on one end and F on the other. Pin 1 to 1, 2 to 2, etc. Each line (except grounds on 1 and 7 of course) has two leds connected to it. One lights green on mark, and the other one (red) with opposite polarity to the first, lights on space. The leds are connected to ground through resistors. You could make your own pretty easily. This one was my father's that he carried as a field engineer.

Perhaps you could/should check out your existing cable with your ohmmeter (test light, bell set...). If pins 2 and 3 don't cross in your cable, then indeed you need a null modem adapter (like the one in your link.)

Lou
 
Old Computers said:
What do you call that box? It sounds like it might be a handy tool to have.
Click to expand...

Lots of different names: {Serial, RS-232, DB25} {tester, checker, line monitor, breakout box}

This one is cheap at $4 plus shipping:
Check Tester ( Green/Red light)
http://www.monoprice.com/products/product.asp?p_id=1209

This one looks nicer for $15 shipped:
Black Box QuickTest RS232 Line Monitor w/ D9/D25 Adapters
http://www.ebay.com/itm/400388309068

Oh, just found the same one Lou has in his picture, $20 shipped:
Datatran MT-41 Mini Tracker Plus DB25 Cable Signal Monitor
http://www.ebay.com/itm/400388307904

If you want to be able to use jumpers to custom wire the connection you usually want a breakout box, example $25:
Pocket-Sized RS-232/Serial Break Out Box
http://www.ebay.com/itm/280852483299
 
Thanks for all of the info guys. I might actually go with building my own box just for the learning experience, but I might go ahead and buy one of the ones on the internet.

As for the cable I just checked it, and cardedge pin 2 side A goes to the DB25's pin 2, and cardedge pin 1 side B goes to the DB25's pin 3, so I will need the adaptor. I think that I will probably go ahead and modify the cable. Or would you recomend that I construct a null modem adaptor?
 
That Black Box line monitor looks really sharp for the price. It has a little protective case and nice adapters for the ends. Black Box stuff is always really expensive, so you know that device was way more expensive when it was first bought. If I didn't already have one, I'd get that one!

As for making your own adapter, or re-wiring your cable, it's all a matter of your time, your skill, and your funds. If you are cheap (and have a well stocked junk box), if you consider that this is a hobby so time is irrelevant, and if have good skill with the soldering iron, then make your own adapter or rewire the cable. If any of the above don't hold true, go to radioshack (frys, microcenter, ...) and buy a null modem adaptor.

Lou
 
That is a nice piece of equipment. That will probably be the one I will choose if I decide to buy one.

I am probably going to make my own adaptor. That way I can use it for other things when I am not using it for the DECtalk, and it is more fun than buying a pre-made one. Hopefully I can get the parts tonight and work on it this weekend.
 
I made my own null modem adaptor, and it works. Thank you for all the help! When I make a case for it I will be sure to post some pictures. I think now I might make a program to make the synthesizer easier to use instead of using a terminal.
 
You must log in or register to reply here.
Back
Top