Sony DTC-700 DAT machine problem

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Dougdoorman

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Hello all,

I have a Sony Digital Analog Tape deck that will not operate due to some sort of "moisture indicator" problem. When I load a tape the mechanism loads the tape normally, then a "caution light" comes on the display panel, which disables all functions of the deck...play, record, fwd, rev, etc. The operation manual says the error is caused by "moisture condensation", and says to leave the unit turned for about an hour and the problem should be corrected. I have tried this, and even leaving the unit in a very dry location with the cabinet cover off for hours, and still no luck. I believe there must be some kind of sensor bad or an open connection in the circuit that controls the light to come on and stop all operations. Can anyone tell me what to look for, or how "moisture or condensation" is detected in a tape deck or circuit? Can I simply jumper out the circuit or sensor that is causing the problem? Any help on this would be very much appreciated!

Thanks
 

For a start it's Digital AUDIO Tape

Basically it's a VCR type machine, with helical scanning - the moisture detection is normally done by a resistive element mounted on or near the head drum assembly.
 
This is what a Dew sensor looks like in a VCR. This particular one reads aprox 800, ohms dry & goes up in resistance with condensation to 4k ohms. With VCRs if there was moisture I used a hair dryer to dry out the mechanism.
 
nsaspook said:
Have you tried a large desiccant bag with the unit inside a 'zip' bag at a warm location. I don't know where the sensor but the people from this link might give you an idea where to look for it.
**broken link removed**
Click to expand...

I haven't tried a bag, but I am pretty confident that there is no moisture present. I have had the unit in a box for a couple years now, and I think any moisture would have dried out by now. I do appreciate your idea, and the link...I will definitely check it out. Thanks so much for your time in replying.
 
debe said:
This is what a Dew sensor looks like in a VCR. This particular one reads aprox 800, ohms dry & goes up in resistance with condensation to 4k ohms. With VCRs if there was moisture I used a hair dryer to dry out the mechanism.View attachment 87202
Click to expand...

Thank you very much! That def gives me something to look for. So it sounds like I can check the sensor with an ohm meter? Is the resistance marked on the sensor? And can you tell me if this is a "dry" contact point? If it is I should be able to "jumper" out the circuit to at least troubleshoot if its causing me the problem? Thank you so very much for your knowledge and information....sounds like that is where I need to start!
 
This is a brief description of a Dew sensor from a National VCR service manual. Its typical of most dew sensors. The values are not on the sensors.
 
Was lucky to find this as ive thrown out nearly all of the VCR & TV service manuals as they took up too much room & don't see them any more for repairs.
 
I will follow up on the pins with a meter, but so far I have yet to find a dew sensor present in the unit. I spent about 3 hours looking for one, if its in there it must be inside the drum. And just for reference, this is not a VCR, although I'm sure its the same principal, but the drum, heads, tape transport, are all very much smaller...more like a cassette deck. I do have the service manual if you are any good with those? If I could find the right circuit to start with it would be so much easier. I would be happy to email it or upload it here. I got it from here, so it is in the data base. I do appreciate your help and effort Debe! I am really stuck with this thing.
 
It should be in the System control circuitry. A starting point if you have the circuit is the System control IC, should have a pin marked Dew, or Sensor stop, work back from there. I knew it wasn't a VCR but these are the only circuit & description I had to go on for Dew sensors.
 
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debe said:
Was lucky to find this as ive thrown out nearly all of the VCR & TV service manuals as they took up too much room & don't see them any more for repairs.
Click to expand...

Yep - all thrown out here long since (as CRT TV manuals ).
 

Well debe, at a dead end again! The only sensors listed in the service manual for the pin locations are the take up and supply sensors for the tape transport. They only list one other sensor in the entire service manual, which is an FG sensor. Any idea what the function of the FG sensor is? Could it be they are using this for moisture detection?
 
It may be setup like this circuit where the processor pin Sens Stop is also being used by the dew sensor rather than having a dedicated pin. FG is usualy Frequency Generator which is some times used to sense that something is actualy rotating.
 
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