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Equipment Discussions >> Classic Telescopes

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DAVIDG
Post Laureate
*****

Reged: 12/02/04

Loc: Hockessin, De
Re: Help getting Tracker Fixed new [Re: dgreyson]
      #5733933 - 03/15/13 11:24 AM Attachment (6 downloads)

I've been working on Larry's drive corrector as time allowed and I finally got it working like it should. It took replacing both of the power transistors, adjusting the biasing resistors, added pull up resistors and changing out some wiring in the hand controller that was intermittent, to finally get it working like it should.
The final count on the parts that were bad were, a fried power resistor, two PNP transistors in the controller, two PNP power transistors, a couple of capacitors, a zener diode and installing the parts in the correct positions in the circuit vs were they were originally.
Here is a picture of the waveform of the output that will run the telescope. It is a rounded off square wave which is typical of what these drive corrector produce, at 108 volts RMS and with frequency of 60.0Hz. The unit draws about 1/2 amp.

- Dave


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DAVIDG
Post Laureate
*****

Reged: 12/02/04

Loc: Hockessin, De
Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5733949 - 03/15/13 11:36 AM Attachment (6 downloads)

One of the design flaws in the unit was that the pull up resistors were installed in the hand controller. What this meant was that if the hand controller wasn't plug in or if it failed, one or both of the power transistor could turn on, this would dump all the current into the transformer, and most likely fry the power transistors and the power resistor. This looks to be what originally happened. What the pull up resistor do, is force the power transistor to be fully turned off until a signal from the hand controller turns them on. By moving them from the hand controlled, to directly onto the power transistors, which are located in the main box of the unit, even if the hand controller is not plugged in or it fails, the power transistors will be fully turned off and not fry anything else.
Here is a picture showing the pull-up resistors installed directly on the power transistors.

- Dave


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dgreyson
professor emeritus
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Reged: 11/06/12

Loc: South Carolina
Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5733995 - 03/15/13 12:06 PM

I have the same model tracker. I need to put it on the bench and check it out now that my Cave Astrola is nearly ready to use. Ive been thinking of putting relays across the faster and slower buttons to use it with my autoguider. Do you know if a standard sbig ST-4 guide port like on a celestron or orion guider uses dry contacts or logic level voltages to output guide signals? I was thinking of using the trackers 12v through the relay coils to the guide port pins 3 move RA positive (faster button) and 6 move ra negative (slower button) and back from the guide port pin 2 ground to my 12v ground. If the guiders expect 5v logic level signals I'd need opto isolators to interface it to the relay I guess.

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orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Help getting Tracker Fixed new [Re: dgreyson]
      #5755249 - 03/24/13 11:52 PM

Well one thing good was it was around the 4th of July when I plugged it in for the first time and got to see all the pretty smoke coming from it... EWWH...AHHH.....
Thanks dave for a job well done, And doing a guy a solid..
looking forward to using it.
Larry


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orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Help getting Tracker Fixed new [Re: Masvingo]
      #5790552 - 04/10/13 03:22 PM

ITS BACK!!
Wow dave did a great job, system tracks great.
I just wonder how many of those there are out there like mine
that were put together wrong in the factory?
I was going to toss this in the Garbage but thanks to Dave
its going strong.. Moral of the Story..
DynaTracker without Dave....Garbage, DynaTracker with Dave...Priceless..
Thanks so much


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orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Help getting Tracker Fixed new [Re: Masvingo]
      #5790563 - 04/10/13 03:27 PM Attachment (3 downloads)

OOPS forgot the PIC!

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