DSI temp sensor location

[mldee (Mike)]

I recently bought a used DSI III OSC to experiment with making a TEC system. I have completed the modifications and all seems to work well.

I tested the cooling finger temp using an external digital thermometer and remote thermistor attached to the side of the CCD finger. It reduced from 30C to around 10C in about 10 minutes.

I have reassembled the two-part case with the thermistor still in place. When I run it, the camera works, and the thermistor temp at the finger after an hour or so is around 6.5C and stable.

The finger is well seated on the rear of the CCD with silver-based heat sink compund, and is making good thermal contact. However, when using Envisage or Nebulosity, both show the 'CCD temp' to only very slowly fall about 4C below ambient over a period of 1-2 hours.

I suspect the DSI temp sensor may be located elsewhere on the DSI PCB, and is not seeing the actual direct CCD casing temp, but simply measuring the internal ambient temp. I have specifically thermally-isolated the cold finger from the rest of the alloy casing, so there would be major difference in temps.

Does anyone know what system is used to measure the temp as shown in Envisage, and where the sensor is located on the PCB? There are numerous little surface-mount components, but nothing marked as a thermistor or temp-measurement IC that I can see.

[DavidU (Dave)]

Does anything look lihe a small ceramic cap? They may use a thermistor.
Only way to go is monitor the temp whilst touching selected parts with a soldeing iron to warm it.

[mldee (Mike)]

Originally Posted by DavidU

Does anything look lihe a small ceramic cap? They may use a thermistor.
Only way to go is monitor the temp whilst touching selected parts with a soldeing iron to warm it.

Thanks for the response, David.
No, the only thing in there that looks like a ceramic cap is the 10K thermistor I put in there

BTW, that appears to be the standard value used in most of the little digital thermometers you can buy. I got a Jaycar QM6324 "Mini Indoor/Outdoor Thermometer with Clock" for $20 or so. Lets me measure obs ambient and DSI cold finger temps.It comes with a long lead and big remote sensor on it. I measured that with multimeter at ~7.8K, them measured a 10K thermistor at my ambient and it also was 7.8K. Swapped out the big package with the little one and voila! same temp reading. I then glued the little one to the CCD cold finger. My plan is to use it later as the sensor for temp stabilisation if I go that far.

Everything on the PCB is surface-mount and small. I am hesitant to go barging around in there with my "giant" soldering iron ( and lousy eyesight). May be the last resort though.

I may try a post on CN, perhaps more folks there who have tinkered with cooling these things.

Cheers,

[DavidU (Dave)]

Anything that looks like this?
http://media.digikey.com/photos/Hone...80-SOT-89B.jpg

[mldee (Mike)]

Originally Posted by DavidU

Anything that looks like this?
http://media.digikey.com/photos/Hone...80-SOT-89B.jpg

Yes, lots of them

Actually, there maybe one or two that particular shape, probably a good place to start heat probing. I presume it's a temp sensor IC you've researched.

There's an 8-pin SOT under the CCD, but that seems a bit fancy for a temp sensor.

I've left it running on the scope in the obs as a smoke test for the TEC circuitry, the Envisage CCD temp reading is now down to +21.5, and the finger thermistor is -1.2C! Both obviously decreasing as ambient goes down (6pm).

I'll re-open it tomorrow and follow up your suggestions.

Cheers,