My SBIG ST-402 TEC no longer cools the CCD. I’ve disassembled the camera to access the connector that sends power from the internal PC board to the Peltier and I can see the (unloaded) voltage (measured by a DMM) gradually increase from 0v as CCDops indicates the cooling % increases from 0% to 100%, at which time the voltage increases to 1.993v I did not (yet) attempt to load test that power by substituting a resistor for the Peltier for fear of damaging the drive circuit. I then measured the Peltier using a specialized ohmeter capable of millisecond measurements (to minimize heating or cooling the TEC). In the + to +, - to - polarity: 1.7 ohms. In the reverse polarity: 0.7 ohms I then applied power directly to the Peltier with the camera powered on, while monitoring the CCD temperature in CCDops. I used a digital lab power supply set to limit maximum Vout to 1.9V while slowly increasing current to the Peltier from 0A to a maximum of 0.5A. As I slowly increased current in 20-30mA steps, I noted small temperature decreases. When the temperatures stabilized (after each current increase), I increased current again until 0.5A current maximum flow was achieved. The power supply Vout was 1.0V at 0.5A. At 0.5A(1.0V) CCDops reported 16.9C which was a temperature decrease of only 8C. I believe the Peltier may have failed or degraded. I’m hoping someone with ST-402 camera knowledge can corroborate my conclusion. If so, I’m hoping for guidance in disassembling the heatsink and cold finger to the CCD. I’m also hoping for guidance or information about the Peltier device SBIG used to cool the CCD of this camera. Perhaps my conclusion that the Peltier has failed may be incorrect. Perhaps the TEC driver circuit which powers the Peltier is the culprit. I believe there is a power module beneath the heatsink along with a MOSFET which power the Peltier. Without at least removing the heatsink from the Peltier, I can’t identify those components (although I can see partial part numbers thru small openings in the heatsink. Once again, I’m hoping someone can provide me guidance.
What were the original symptoms? What is the camera serial number? Normally people contact us for repair assistance when they have a problem, instead of tearing apart the hardware.
Hello Colin - thanks for the reply. Previous owner reports the original symptoms were that the cooling function stopped working. I can’t really provide more details than that. And as for the steps I’ve taken so far, they’ve been quite non-intrusive, other than removing the camera covers to visually inspect it’s internals and disconnecting the power connector to test the peltier and measure the TEC drive circuit open circuit output voltage, I’ve not disassembled anything else - in the off chance that there was a repair option. After reading thru many postings in the legacy cameras section, I didn’t believe sending the camera in for repair would be an option. Hopefully it is an option ! But I’ll get you the camera serial number. And so you know - I reached out to “@Tim” this morning. Thanks again ! Michael Lang
If you would like to send it in for service, please fill out this RMA form: http://diffractionlimited.com/request-rma @Tim will get back to you with instructions.
Update on my ST-402: I received RMA instructions from Tim (thank you !) The complications of sending my camera to Canada with all the confusion and uncertainty (madness) regards tarrifs and such motivated me to revisit a few potential causes for this cameras cooling failure. The first area I addressed was to load test the power supply that I had been using to power the camera. It’s a very small 12v 3A (rated) switcher type power supply. Open circuit output is 12.1V. Under a 1 amp load: 11V. At 3A load: 8V. Eureka ! Or not. So I powered the camera using a bench supply set to 12.7v, current limit set to 3A. The camera powers, and when I enable cooling, I noticed a short duration current increase displayed by power supply current display. Temperature decreased a few degrees, and then warmed back to slightly above the staring ambient temperature. This made me suspicious of the heatshrinked splices in the red and black wires from the peltier to the connector that plugs into the camera PCB. Those splices didn’t appear to be factory installed. They’re just too “rough”. So I attempted to “manipulate” each of those splices while enabling cooling. But the results were inconclusive. So I removed the heatshrink on each wire to inspect the solder joints and found those to be rather questionable - one looked almost like a cold-solder-joint. So I resoldered them and applied new heat shrink. Long story short, I can make the camera cool to 20 degrees below ambient if I set it to cool in small 5 degree steps. If I try to get it to cool from ambient to 20 below ambient in one step, it will stop cooling. After cooling achieves 20 below ambient, I can get it to slowly cool to almost 30 below ambient - but it seems that’s about all it can cool. So I may have “fixed” the issue. I say “may have” because in order to activate cooling, sometimes I have to cycle the cooling on/off/on command several times. And if I make big temperature decreases that require 100%, cooling ceases. So I’m going to keep “exercising” this camera to see if it’s useable as-is, or not, before making the leap into sending it to Tim for servicing. I’m worried about the risks of receiving a huge bill for tarrifs or duties, or never seeing the camera again if it’s seized by federal agents. Now back to my ST2K 0-pixels project. Michael Lang
Michael, a couple of points: When new, the ST-402 has a Delta T of approximately 25C - so it will cool at most 25 Celsius below ambient, which is very close to what you are experiencing. The camera was built in February 2005, so it's 20 years old. Capacitors and the Peltier itself degrade over time. If it is not cooling well, I'd suspect the power supply socket pins have become compressed, or a bad power supply. You can use a tiny flat jeweller's screwdriver to spread the two halves of the centre pin in the power socket. Regarding sending it in, Tim would supply instructions on the proper documentation - there is a special code used for customs on items being shipped cross border for repair. For the most part, our products meet USMCA (formerly NAFTA) rules, so would not be subject to duty or tariffs, unless this changes again. You might have to pay local/state tax and fees.
