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#26 DAVIDG

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Posted 02 February 2013 - 12:02 PM

I looked up the 1970 Sky and Tel article and from it I can see that the Criterion unit was clearly assembled wrong ! A couple of resistors and caps that are part of the flip flop that isn't working were swapped in their positions. No wonder why it won't work.

- Dave





#27 dgreyson

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Posted 02 February 2013 - 10:23 PM

Do you think that was a day one error? It must never have worked. Or had someone serviced it before you and put the parts back wrong?

a schematic of the 555 based version is on the yahoo Cave Telescopes Group in the folders section.

#28 Masvingo

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Posted 03 February 2013 - 10:17 AM

I looked up the 1970 Sky and Tel article and from it I can see that the Criterion unit was clearly assembled wrong ! A couple of resistors and caps that are part of the flip flop that isn't working were swapped in their positions. No wonder why it won't work.


Hi Dave

I've only read the latest postings this morning and it looks like you have found the problem but in case they are of any use here are some pictures of the circuit board from a 1980's era E-6 hand controller which was working just now when I tested the drive corrector on my D8.

It hasn't seen much use as it was (eventually) sent by Criterion to replace the drive corrector that originally came with my D8 which never seemed to work, possibly because when I first set it up fine adjustment control on the hand box was not turned off. The instructions that came with the unit state to make sure the fine adjustment is in the off position before connecting everything up, and also states "Be sure to turn the unit off after use. If left 'on' and connected to power again for next use, unit may not start."

In the meantime I had managed to get a local electronics firm to repair the original drive corrector so I kept it as a spare, luckily, as my original one failed about 3 months ago.

First the back of the board:

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#29 Masvingo

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Posted 03 February 2013 - 10:18 AM

Now the component side of the board:

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#30 Masvingo

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Posted 03 February 2013 - 10:19 AM

Transistor detail: (2 of C2001 and 2 of C1815)

(woo hoo - post #200!)

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#31 Masvingo

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Posted 03 February 2013 - 10:22 AM

And finally another shot of the component side:

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#32 Masvingo

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Posted 03 February 2013 - 10:33 AM

Couple of shots from the failed unit - first:
signs of a hard worked resistor (circled in red)

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#33 Masvingo

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Posted 03 February 2013 - 10:35 AM

second - looks like the local firm replaced a transistor (circled in white) when the unit was originally repaired back in 1981:

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#34 DAVIDG

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Posted 03 February 2013 - 11:27 AM

Do you think that was a day one error? It must never have worked. Or had someone serviced it before you and put the parts back wrong?

a schematic of the 555 based version is on the yahoo Cave Telescopes Group in the folders section.


I'm 90% sure that the unit never worked from day one. When Larry sent the unit to me I found that the fuse had been replaced with a 5 amp one ( he didn't do this) and the specs call for 1 amp one. So I bet that when the original owner plugged it in, the fuse blew and maybe it happened a couple of times so not knowing any better it was replaced with a larger value one. That most likely caused even more damaged and allowed the power resistor to fry along along with some of the parts in the hand controller. Also the circuit board on the hand controller showed no signs of reworking and all the parts were of the correct vintage (mid to late 1960's)
As I said when I traced out the circuit, parts of it made no sense. The circuit uses a monostable multivibrator made using two PNP transistor. That is working perfectly now that I replaced a bad transitor. Those signals feed a typical transistor based flip/flop that is used to control the two PNP power transistor that feed the transformer. The way the Flip/Flop was built made no sense and just couldn't work. My problem was that I was doubting myself and thought that the unit at one time did work and I was missing something. So I checked each part at least 5x in that section of the circuit and spent some time on the Net and digging thru all my electronic references to find a circuit that matched what was in the handcontroller. When I took one look at the Sky and Tel article that DataPanic reminding me of ( Many Thanks) which uses almost the exact same Flip/Flop design it was clear that the circuit in the Criterion E-6 was wrong and multiple parts were flipped around from were they were suppose to be. So it wasn't just one part installed by mistake. It seems like either the instructions given to the person assembling the unit were wrong or they read the schematic wrong vs the part placement on the circuit board.
The other things that are weird on this unit is that the power switch is on the ground side of the circuit and the zener diode section which is suppose to provide a stable 6 volts had no capacitor and no current limiting resistor installed so it won't work as built either. I fixed those problems as well.
On Monday when I get back into the lab I'll see if the ciruit now works with the parts located were they should be.

- Dave

#35 DAVIDG

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Posted 03 February 2013 - 11:54 AM

Many many thanks for the pictures. Your circuit and what is in Larry's units are somewhat different. Your circuit board lacks a number parts that in Larry's unit but they work the same way. Two of the transistors form a multivibrator. It job is to make the variable frequency signal. The other two transistors, one of which was replaced when you had the unit repaired makes a flip/flop that turns on and off the power transistors located on the back of the main box.
The comment by the repair person "Be sure to turn the unit off after use. If left 'on' and connected to power again for next use, unit may not start." is because a transistor based multivibrator in its simple form which is what is used in these units sometimes will "lock up" and not oscillate. If this happens, one of the main power transistors will be on all the time causing all the current to flow through one of the secondary coils on the transformer. If the fuse doesn't blow the power transistor can become shorted as well. If this happens then more current then normal gets pulled from the hand controller hence the slightly burned resistor in your picture.

- Dave

#36 Masvingo

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Posted 03 February 2013 - 01:28 PM

Dave

Thanks for the good description as to how the corrector works, that will be very helpful in getting my failed unit back in operation. i must remember to always make sure the hand controller is switched off.

Having had a look at Robert Provin's site which has some instructions for the Criterion Dyna-tracker from the late sixties I see that Criterion were still using the same typewritten sheet of instructions in the eighties!

James

#37 DAVIDG

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Posted 04 February 2013 - 02:35 PM

Success ! It really helps when the parts are in the correct place in the circuit. Here is a picture of the waveforms coming from the handcontroller. These signals control the two power transistors and pulse 12 volts into the secondary of the transformer to make 120volt AC. The next step is to check the power transistors to be sure one of them isn't fried.

- Dave

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#38 Masvingo

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Posted 05 February 2013 - 04:03 PM

Looking good!

It really helps when the parts are in the correct place in the circuit.

Yes, generally helps! Looks like it should soon be back to new, or better than new in this case!

James

#39 orion61

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Posted 06 February 2013 - 02:22 PM

I have to give you my many thanks, It surely would have been tossed in the Garbage if not for you.
It might make people think twice before bidding on one of these on ebay in the future. It's pretty bad when they go out the door defective..

#40 dgreyson

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Posted 06 February 2013 - 02:54 PM

The new guy at Criterion had celebrated getting his job a little too vigorusly the night before and it took him a few times to remember which hole which wire went in till he finally got it right. Nothing personal I'm sure.

#41 DAVIDG

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Posted 15 March 2013 - 10:24 AM

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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#42 DAVIDG

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Posted 15 March 2013 - 10:36 AM

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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#43 dgreyson

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Posted 15 March 2013 - 11:06 AM

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.

#44 orion61

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Posted 24 March 2013 - 10:52 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

#45 orion61

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Posted 10 April 2013 - 02:22 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

#46 orion61

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Posted 10 April 2013 - 02:27 PM

OOPS forgot the PIC!

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