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Equipment Discussions >> Classic Telescopes

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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Help getting Tracker Fixed
      #5605037 - 01/04/13 03:34 PM

Anybody know where I can get my Dyna Tracker fixed?
Or does anybody here fix them reasonably? I'm on Disability and things are kind of tight right now, waiting for my next surgery from getting run over by a car!
I've got a great old Sandcast C8 that is fantastic and looks like the day it was made...


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dgreyson
scholastic sledgehammer
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Reged: 11/06/12

Loc: South Carolina
Re: Help getting Tracker Fixed new [Re: orion61]
      #5605077 - 01/04/13 03:55 PM

They are pretty simple, I have one myself. Is it totally dead or what?

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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Help getting Tracker Fixed new [Re: dgreyson]
      #5605129 - 01/04/13 04:16 PM

yep pretty much, plugged it in to use from a battery and smelled THAT smell, looked down and saw a bit of smoke..
now it's ka-put


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starman876
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Reged: 04/28/08

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Re: Help getting Tracker Fixed new [Re: orion61]
      #5605338 - 01/04/13 06:26 PM

These electronic things stop working when you let the smoke out. Every electronic thing I have ever had stopped working after the smoke was let out.

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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Help getting Tracker Fixed new [Re: starman876]
      #5605353 - 01/04/13 06:38 PM

Somethin like rubbing a lamp and Genie? but mine wouldn't look like Barbara Eden (Memba her WOW)
Mine would look like Curley (Jerome) Howard (The 3 Stooges)
and let the smoke out of my tracker as he tripped over it
Nyuck Nyuck....


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dgreyson
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Reged: 11/06/12

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Re: Help getting Tracker Fixed new [Re: orion61]
      #5605506 - 01/04/13 08:18 PM

usually in vintage electronics, the Electrolytic capacitors fail due to age and short out which burns a resistor. Hopefully one of the driver transistors hasnt blown. I will pull the cover on mine and see what the circut looks like.

Rather than just plugging it in and switch it on when it's been sitting a long time unused, you plug it into a variac transformer and slowly bring up the voltage over a day or so to Rejuvinate the capacitors. But some wont form correctly coz they are too dried out and old and blow anyhow. The usual procedure is to replace all the electrolytic capacitors, check for burnt or open resistors and check the transistors and that fixes 90% of the usual problems with such things.

Your smoke came from the Main unit, not the hand controller right?


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dgreyson
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Reged: 11/06/12

Loc: South Carolina
Re: Help getting Tracker Fixed new [Re: dgreyson]
      #5605696 - 01/04/13 10:40 PM

Had it been in regular use by you and failed or did you just buy it with your new scope? Same things would go bad, capacitors have a limited lifespan. just curious.

I pulled the covers off mine and took a look, I would think it should cost less than $20 dollars in parts to fix it, maybe $25 ish if both the power transistors are blown.

The hand controller has a 12v adjustable oscillator made from small signal transistors and ought to be just fine. It pulses 12v through the two power transistors into a transformer that steps it up to near line voltage to drive the motor. I can fix it if no one is closer to you as I'm an electronics tech if you want.

If you have a small phillips screwdriver, unplug the power cord from the wall and pull the main box's lid to see if you can see one of the 3 grey electrolytic capacitors bulged or leaking and if one or more of the three black rectifier diodes have burned.
Hopefully the orangeish large power resistor next to and below the diodes is unburnt as it goes to the power transistors. Also, check the handbox plug to make sure a wire isnt loose or shorted at the plug. the plug cap unscrews if you want to check it but be gentle, dont force it if it's stuck. Has the fuse blown or is it intact?


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DAVIDG
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Reged: 12/02/04

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Re: Help getting Tracker Fixed new [Re: dgreyson]
      #5606374 - 01/05/13 11:24 AM

I have repaired many telescope electronics over the years, just ask TIM53 about all the stuff I fixed for him. Since you said it happened while running off of the battery that sugguests that it is not the AC/DC rectifier used to allow it to run off 110VAC.
What I have found is about 90% of the time on these type of drive correctors is that one of the power transistors has gone bad and is now shorted to ground. This causes all the current to be dumped into the secondary of the transformer, which causes things to heat up and then let the smoke out.
The other common problem is that a wire breaks in the hand controller. The hand controller contains parts which form the oscillating circuit. If the circuit doesn't oscillate what happens is one power transistor is turn on all the time and again all the current is now flowing thru the secondary of the transformer and things get hot.
As Dgreyson sugguests pull the cover off and see what looks damaged and if you can post some pictures I'm sure that we can get a good idea of what went wrong and how to repair it.

All the Best,
- Dave


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dgreyson
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Reged: 11/06/12

Loc: South Carolina
Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5606627 - 01/05/13 01:25 PM

Ah hah, I missed he said he was running on batteries, we are good from the line cord to the 12v socket then.

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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5606644 - 01/05/13 01:38 PM

Thank you all so very much for your help. I have it packed away, I bought a Dynamax DX6 a little over a year ago and it came with it. The first time I tried it, it blew, it looks to have never been used.
I admit I dont know a resistor from a Flux-Capacitor!
I am recovering from my 6th surgery after getting hit by a car, then getting Staff infection,and a Hear attack after a surgery and I threw a blood clot. I thought it would be a good time to have it looked at. I'll try and dig it out.
BTW dont laugh about the Dynamax, it has superb optics!


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DAVIDG
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Reged: 12/02/04

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Re: Help getting Tracker Fixed new [Re: orion61]
      #5606767 - 01/05/13 02:54 PM

Many years ago I heard that Criterion made a mistake when they either designed the drive corrector or when it is built and the power resistor for the power transistors was the wrong value. It could have been defective right out the box and you were the first to plug it in. In any case I'm sure that a bunch of us that know electronics can pretty quickly figure out what died and how to fix it.
If it isn't working off the battery then it the odds are low that it will work off the 110 VAC house current since all the rectifier circuit does is take the 110AC and make 12 volt DC, just like the battery is providing. When you hook it up to the battery the rectifier section is out of the circuit.
Anybody got a schematic ? The guys at Criterion were pretty smart and they also got many of their ideas from the literature of the day so I bet the circuit is pretty close to the Saxon circuit publish in Jan 1975 Sky and Tel.

- Dave


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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5607121 - 01/05/13 06:31 PM

Thinking about it it really does look and untill it Smoked
smelled like brand new, the paint and rubber smelled brand new, and the cords were still sealed in bags.
It fried the first time. Also wont work on AC
possibly should toss it


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dgreyson
scholastic sledgehammer
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Reged: 11/06/12

Loc: South Carolina
Re: Help getting Tracker Fixed new [Re: orion61]
      #5609852 - 01/07/13 10:06 AM

Not when you can fix it for 10 or 20 dollars. another one with shipping still is going to likely cost more than shipping and fixing this one I would guess, unless you get a good deal on it. In that case never pass up a good deal. I think parcel post would be $12 if you dont know how to use a solder gun or a volt-ohm meter and have neither. As a vendor you should have access to discounted shipping rates anyhow. But time is money I know, it is often better to buy another rather than tie up time you dont have to spare.

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DAVIDG
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Reged: 12/02/04

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Re: Help getting Tracker Fixed new [Re: dgreyson]
      #5631427 - 01/19/13 11:55 AM Attachment (10 downloads)

I sent Larry a note that I would be happy to take a look at his Criterion E-6 controller. I have been doing electronics since I was kid and also as part of my job for the last 27 years as a research engineer. I've built a number of drive controller and CCD camera system from scratch and helped Richard Berry with his "CCD Camera Cookbook". I'm not trying to brag just saying that I know which end of a soldering iron to hold without burning myself, most of the time. I'm also a big Criterion fan and I wanted to see how this controller worked. I heard many years ago that Criterion had either made a mistake in the design or when it was assembled which caused the power resistor to easily fail on these units.
Larry packed it up and sent to me and when it arrived I pulled the cover of the unit and took a look. Larry had said that as soon as he plugged it in that it smoked. It didn't take long to see what part had fried. It was the power resistor. Actually it cracked in half it got so hot. Here is a picture showing it still installed in the circuit.

- Dave


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DAVIDG
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Reged: 12/02/04

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Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5631433 - 01/19/13 11:57 AM Attachment (11 downloads)

I dissassembled the case to get to the cooked resistor. I replaced it with Ohmite ceramic one of much better quality.
Here is what was left of the cooked one.

- Dave


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DAVIDG
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Reged: 12/02/04

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Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5631466 - 01/19/13 12:14 PM Attachment (13 downloads)

The next step was to determine if the AC/DC rectifer circuits was OK. I unsoldered the DC connection to the main power transistors and unplugged the hand controller. The oscillator circuit was located in the hand controller and it's job is to turn on and off each power transistor. If the hand controller had a problem or one the power transistor was bad, would usually happens is that one of the power transistor is conducting all the time dumping all the current in the transformer. All the current has to go thru the power transistor which is suppose to limit the current. If it is the wrong size it fries.
So with the transistors out of the circuit I powered up the unit. The rectifier section had no problems and was making 16 volts of clean DC.
The next day I brought the hand contoller into work so I could use the test equipment in my lab. I dissassembled the unit to see what was going on. I flipped over the circuit board and discovered the another resistor was cooked and broken in half. This thing took a real hard hit. Luckly I was able to take the pieces of the resistor and look at them under a microscope and was able to see the what was left of the color coding strips that determine it value. It was 680 ohm and the one right next was also of the same value. I replaced both of them.
Here is a picture of the back of the circuit board and the inside of the case showing were the resistor had burned the paint off the inside of the box and the two new resistors installed on the board.

- Dave


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DAVIDG
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Reged: 12/02/04

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Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5631471 - 01/19/13 12:22 PM Attachment (14 downloads)

I carefully power up the hand controller and was hoping to see two nice sqaure waves coming out of each channel but it was still dead. I little more digging and discovered at 6 volt Zener diode was shorted so it was replaced. Also all the Mylar capacitors looked strange. I never had seen one of these types go bad but on the outside of all of them they had would looked like salt crystals growning on them. Mylar caps are "dry" type so they don't use any liquid electrolyte so I had no idea what was going on. Since I have a ton of spare parts at home, I replaced all the caps. I found one 4.7uf electrolytic cap that when I tested it had 1/2 the value that it should.
Here is a picture of the hand controller board will all new caps and a Zener diode.

- Dave


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Bill Griffith
professor emeritus


Reged: 08/12/09

Loc: Ca.
Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5631477 - 01/19/13 12:27 PM


Dave, you are the epitome of the classic forum! You certainly have given good advise to me.

Congrats Larry,

I'm sure Dave won't stop until the controller is better than new!

Bill

Edited by Bill Griffith (01/19/13 12:57 PM)


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DAVIDG
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Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5631498 - 01/19/13 12:39 PM

With the hand controller still not working, then the issue has to be with one of the transistors. The unit was designed in the late 60 to early 70's and is based on analog radio technology. How it works is that is uses a resistor/capacitor circuit as a time base. By using a variable resistor the user controls the frequency that the unit puts out. The first RC sections fires a transistor which controls another RC/transistor section to make two timing pulses that are 180 degree out of phase. In simple terms when one is on when the other is off. Those two signals then feed another two transistor based circuit that length the pulses to make them squares wave. It these two square waves that turn on and off the two power transistors in the main box of the unit. Those power transistor pulse 12 volts into a secondary of transformer. The transformer then steps up the voltage to 120VAC to make the AC needed to run the motor in the telescope.
The problem is that the transistor (2SB187) used are vintage Japanese germanium units that at one time were very commonly used in radios but not any more. Luckily EBAY comes to the rescue and I found a cheap source there. So when they arrive I'll replace them and I hope that will get this section up and running.

- Dave


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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5633129 - 01/20/13 12:47 PM

I cant tell you how much i thank you.
Dave you really know what you are doing!
There are people in this world I admire, People loke Dave, also Guys that can do Body Work. I've tried and it come out looking like someone threw a handfull of mud on the fender...
Thanks again Dave.. Like you I also Love Criterion I have a great old RV6!
The DX6 Dynamax that tracker came with has outstanding optics, and is in mint "cosmetic" condition. Like that Dyna Track is.. Sure was a lot of smoke coming out of that thing.


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DAVIDG
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Reged: 12/02/04

Loc: Hockessin, De
Re: Help getting Tracker Fixed new [Re: orion61]
      #5654731 - 01/31/13 05:23 PM

I need a little help from anyone who has one of these Criterion E-6 controllers in working order. I've been trying to repair Larry's. I have part of the hand controller working. The circuit is transistor based and is made up of two sections. The top section is a free running multivibrator. One of the transistor was bad in that section. Both transistor were replaced and it is now working fine. The frequency varies nicely from 55 to 65 hz and output is two nice clean square waves that are 180 degrees out of phase just like they should be. Those signals feed to a "flip/flop", again made from transistors. This section is not working and I have triple tested all the parts and they are good. From studing this part of the circuit I don't believe it was made correctly. Either the values of components are wrong and/or there are some missing parts. The original design was modified since there are a traces cut on the board and resistor added.
So can anyone who has one of these unit please take the cover off the hand controller and take some close up shots so I can read the values of the parts and also turn the circuit board over and take a picture of it. It would be of great help in getting this unit repaired and back to Larry. I have traced the circuit and will post it once I get it working so others might be able to repair their unit in the future.

Many thanks,
- Dave


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Datapanic
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Reged: 10/17/09

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Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5654901 - 01/31/13 07:04 PM

If it's based on the same design theory, the October 1970 and January 1975 S&T Gleanings for ATM's columns have the schematics. The 1970 designs used transistors for the flip/flop, the later 1975 design was an improvement and used 555, 7473 and 7406 IC's.

Hope someone steps up with the info ya really need!


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DAVIDG
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Re: Help getting Tracker Fixed new [Re: Datapanic]
      #5655895 - 02/01/13 09:25 AM

Thanks Dan, I'll pull 1970 Sky and Tel. I built my first drive corrector soon after the 1975 Sky and Tel article appeared when I was a kid. Still have it and it still works perfectly. I use it all the time with my RV-6. All these units follow the same basic design. There is a variable frequency circuit that feeds two power transistors. The power transistors feed the secondary of a transformer. The transformer steps the voltage up from 12 volts to 120 AC.
The Criterion E-6 unit is 100% transistor based. It most likely was designed and built in Japan under contract to Criterion. The transistor based Flip/Flop as it is now doesn't make any sense and of course isn't working. I'm sure that either it was built wrong are some component(s) were not installed.

- Dave


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Datapanic
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Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5657344 - 02/01/13 11:14 PM

I built my dual axis drive corrector based on the 1975 article as well. My old, passed away friend Mark Eaton, an electrical engineer at Naval Weapons Yorktown helped tweak it and he was forever mad at me because the box smoked his o-scope somehow...

Anyway, in the 1970 article, there's more discussion about the first corrector diagram in a 1968 S&T Gleanings article. So maybe, you are running into some transistor based flip-flop issues that were later corrected. Or, maybe something isn't properly grounded? Grounding has gotten me once or twice in electronic circuits and I'm sure you've checked, but a reminder doesn't hurt


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Help getting Tracker Fixed new [Re: Datapanic]
      #5657738 - 02/02/13 09:13 AM

Reading this with no knowledge of electronics, I see you claim to be technicians, but I suspect you are actually magicians! Great to see all the help for Larry's corrector.

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DAVIDG
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Re: Help getting Tracker Fixed new [Re: Joe Cepleur]
      #5658010 - 02/02/13 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





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dgreyson
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Reged: 11/06/12

Loc: South Carolina
Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5659017 - 02/02/13 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.


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Masvingo
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Reged: 01/10/12

Loc: Ayrshire, Scotland
Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5659660 - 02/03/13 10:17 AM Attachment (5 downloads)

Quote:

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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Masvingo
scholastic sledgehammer
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Reged: 01/10/12

Loc: Ayrshire, Scotland
Re: Help getting Tracker Fixed new [Re: Masvingo]
      #5659662 - 02/03/13 10:18 AM Attachment (4 downloads)

Now the component side of the board:

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Masvingo
scholastic sledgehammer
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Reged: 01/10/12

Loc: Ayrshire, Scotland
Re: Help getting Tracker Fixed new [Re: Masvingo]
      #5659665 - 02/03/13 10:19 AM Attachment (5 downloads)

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

(woo hoo - post #200!)


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Masvingo
scholastic sledgehammer
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Reged: 01/10/12

Loc: Ayrshire, Scotland
Re: Help getting Tracker Fixed new [Re: Masvingo]
      #5659667 - 02/03/13 10:22 AM Attachment (5 downloads)

And finally another shot of the component side:

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Masvingo
scholastic sledgehammer
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Reged: 01/10/12

Loc: Ayrshire, Scotland
Re: Help getting Tracker Fixed new [Re: Masvingo]
      #5659688 - 02/03/13 10:33 AM Attachment (6 downloads)

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


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Masvingo
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Reged: 01/10/12

Loc: Ayrshire, Scotland
Re: Help getting Tracker Fixed new [Re: Masvingo]
      #5659692 - 02/03/13 10:35 AM Attachment (4 downloads)

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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DAVIDG
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Reged: 12/02/04

Loc: Hockessin, De
Re: Help getting Tracker Fixed new [Re: dgreyson]
      #5659781 - 02/03/13 11:27 AM

Quote:

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


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DAVIDG
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Re: Help getting Tracker Fixed new [Re: Masvingo]
      #5659839 - 02/03/13 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


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Masvingo
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Reged: 01/10/12

Loc: Ayrshire, Scotland
Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5660000 - 02/03/13 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


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DAVIDG
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Reged: 12/02/04

Loc: Hockessin, De
Re: Help getting Tracker Fixed new [Re: Masvingo]
      #5661917 - 02/04/13 02:35 PM Attachment (5 downloads)

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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Masvingo
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Reged: 01/10/12

Loc: Ayrshire, Scotland
Re: Help getting Tracker Fixed new [Re: DAVIDG]
      #5663844 - 02/05/13 04:03 PM

Looking good!

Quote:

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


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orion61

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Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Help getting Tracker Fixed new [Re: Masvingo]
      #5665382 - 02/06/13 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..


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dgreyson
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Reged: 11/06/12

Loc: South Carolina
Re: Help getting Tracker Fixed new [Re: orion61]
      #5665448 - 02/06/13 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.

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DAVIDG
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Reged: 12/02/04

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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
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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
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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

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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

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Reged: 10/20/07

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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

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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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