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Topic: My first Elmo ST-600DM not work!
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Steve Klare
Film Guy
Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003
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posted November 27, 2014 08:28 AM
Hello Darek,
Welcome!
I've e-mailed you two circuit drawings. Someone else e-mailed them to me, so I am passing along a favor.
The question is this: Is the motor getting voltage, and if it isn't then why not?
There are a pair of switches activated by cams on the control knob which reverse the motor voltage and direction. If either of these is not connecting there will be no voltage on the motor.
There is a speed regulator circuit that controls how much current is fed through the motor with power transistors. The later ST-600 used an integrated circuit as a controller. Any of this could also be causing an open circuit.
Then there is wiring, connnections, solder joints and the rectifier circuit that gets the motor voltage from the transformer. (Maybe the transformer...probably not.)
Unless nothing else on the machine works, it shouldn't be the fuse. There's only one for everything.
Since you are an electronic technician, I think you will do OK here!
As I said: it's good to ask questions here. Many times you will find out someone has had a similar problem and they know exactly what to do.
Good Luck!
-------------------- All I ask is a wide screen and a projector to light her by...
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Steve Klare
Film Guy
Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003
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posted November 28, 2014 08:05 AM
Hi Darek,
Your photo looks like you have a sil-pad between the transistor and the heatsink. This is for a good thermal connection, but it is sometimes used for electrical insulation too.
If the transistor is meant to be electrically insulated from the heatsink, the washers between it and the screw can not be metal, they need to be plastic or some other insulator.
When the heatsink is installed, is it electrically connected to the projector chassis? Are there any other devices also on there that the transistor should not be connected to? (rectifiers maybe?)
(-if it is still installed, try an ohmmeter reading between collector and heatsink?)
If any of these is true, then thermal grease is not the right thing, the transistor has to remain insulated.
Just for thermal connection, the white thermal grease is better, but factories don't like to use it because it is messy, expensive and just a little bit toxic too!
It keeps the devices cooler, though.
When I worked on aircraft systems we used this stuff: we hated it, but there was no substitute.
-------------------- All I ask is a wide screen and a projector to light her by...
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