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Thread: Something Different - DECTalk DTC03

  1. #21

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    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?

  2. #22

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    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.)
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  3. #23
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    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

  4. #24

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    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.

  5. #25

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    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.

  6. #26

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    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?

  7. #27
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    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

  8. #28

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    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 by Old Computers; January 22nd, 2013 at 04:32 PM. Reason: Added more info

  9. #29
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    If the original board was not getting -12V, then you would not have seen -10V on the RS232 transmit line. The problem is something else unfortunately....

    Lou

  10. #30

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    Okay. I was hoping that that might have been the cause. Could something be wrong with the part of the system that uses -12v?

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