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Thread: DT25 help

  1. #1
    Join Date
    Dec 2007
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    Default DT25 help

    Hi all,

    Something strange is going on with my DT25s. I bought them 2nd hand. Once I received them I wired them up and pointed my RGV module at them to check everything was working. All worked good. I put everything away safely whilst I ordered ali baseplate and other hardware so I could mount everything nicely.

    Hardware arrives, drill and tap the ali baseplate and hook everything up. Apply power - bugger.

    Only one power LED comes on, on the X side of the driver card. There is a slight bit of motion on the X scanner. The Y power LED doesn't come on and the Y scanner moves to an end stop. Neither scanner has any friction on it if I touch it gently. The Y scanner however bounces back to the end stop.

    I removed the driver amp from the baseplate to see if it was that. The 3 transistor things look to be insulated. I get exactly the same as when it was mounted. The power supply is spitting out +24V and -24V. I have double and triple checked all the wiring. Like I said it was working before. All I essentially did was mount it all to a baseplate. I noticed the middle transistor (larger one, not even sure if it is a transistor) gets quite hot and it was only on for a few minutes.

    I am very limited on test equipment, in fact I only have a multimeter here. All my 'proper' tools are back in the UK.

    Can someone point me in a direction to try and get this figured out.
    Thanks in advance.

    Cheers
    Rich

  2. #2
    Join Date
    May 2006
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    Default

    Rich,

    The two LED's on the board indicate +V and -V from the voltage regulators on the amp. If I remember correctly, they are 7815 and 7915 regulators. Sounds like one of them has failed, it could have been caused by a short. Replacing which ever one has failed may fail again if there is indeed a short. Until the problem is figured out, I would disconnect the scanners to prevent them from being damaged, if they aren't already damaged. Do you have access to these replacement parts?

    Are you in the U.S.? If so, you are welcome to send the set to me for repair. I'll only charge the price of the parts replaced and return shipping. Just about all of the DT scanner sets are relatively easy to repair.

  3. #3
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    Default

    Hi David,

    So the 7815 and the 7915 are the two regulators either side of the larger central 'device'? (I don't have the unit in front of me until tomorrow now).
    I am in Honduras currently so I am guessing these parts will not be easy to come by. The scanners are disconnected, I hope they are not damaged.

    I am looking at heading to the US towards the end of August for a week so maybe I could send them to you then if I cannot get the replacement parts. Then I can get them sent to the shipping company I use to get them back to Honduras.

    I assume the 7815 and 7915 regulate the +-24V supply to +-15V. Should I be able to measure the output voltage with my meter if I look at the datasheet and get the correct pin out? If so I'll give it a go tomorrow when I am in front of the scanner.

    Thanks again
    Rich

  4. #4
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    Rich, the 7815 and 7915 regulators are very common. I'd be surprised if you couldn't find a replacement. Both should be available on ebay if you can't find anything local. Looking at the top of the 7815 with pins down it's input---GND---output. Looking down at top of the 7915 with pins down it's GND---input---output. The LED's are connected to the output of the regulators, one for each, and if the left LED is out, it should coorespond with the left regulator. And, obviously, the 7815 is the positive 15V regulator and the 7915 is the negative 15V regulator.

  5. #5
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    Thanks David, I down loaded the datasheets this morning. I'm going to do some testing shortly. We have no electronic type stores on the island. I may have to pop over to the mainland. So if one is faulty this would explain why one of the scanners is moving to the end stop as it has doesn't have the other voltage to pull it back.

    So the larger unit is a dual op amp. What would happen if this was faulty? Would I just get a bizzare output?

    I've found a friend that is heading back to the US on Wednesday. I will ask if he is ok to take the unit back and mail it on for me. Would it be ok to send it to you for repair if he is ok with it? Do you need the scanners as well as the driver card?

    I really appreciate all the help.

    Cheers
    Rich

  6. #6
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    Rich,

    I've not seen one of the power amps fail in any of the DT scanners, so I can't say for sure what the symptoms would be. Since I don't handle DT sales anymore, I would need the scanners and amp, otherwise I would have had a few spare scanners to test with. Hopefully, you can find the regulators, replace the failed one and be good to go. If not, I'll PM you my address. Let me know.

  7. #7
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    I'll try and get over to the mainland tomorrow and see what I can pick up. I did manage to pick up an opamp for a LW50K amp that had snapped off in transit. So maybe they will have some voltage regs too.

    I'll let you know how I get on. If I can't source them I'll let you know.

    Thanks again
    Rich

  8. #8
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    SO i just measured the outputs of the two voltage regulators.

    7815 output is 13.84V (this is on the 'Y' side which has no LED illumination)
    7915 output is 14.49V (this is on the 'X' side which has LED illumination)

    The driver was only powered up for around 4 minutes and reached a temperature of 110F. The driver was only connected to the PSU and had no signal input.

    Cheers
    Rich

  9. #9
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    Default

    Are you absolutely sure that there isn't a tiny piece of swarf shorting a pcb track or between any pins. Maybe give the board a blast with an air duster to be sure.

    It just seems strange that it was working before you mounted it.
    http://img62.imageshack.us/img62/3985/laser.gif

    Doc's website

    The Health and Safety Act 1971

    Recklessly interfering with Darwinís natural selection process, thereby extending the life cycle of dim-witted ignorami; thus perpetuating and magnifying the danger to us all, by enabling them to breed and walk amongst us, our children and loved ones.





  10. #10
    Join Date
    Dec 2007
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    Default

    Good point. I did look it over and didn't see anything. I will give it a blast with compressed air shortly and give it another go.

    Thanks
    rich

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