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Equipment Discussions >> Classic Telescopes

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DAVIDG
Post Laureate
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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

Loc: Tucson, Arizona
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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Reged: 12/02/04

Loc: Hockessin, De
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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Reged: 10/17/09

Loc: Tucson, Arizona
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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Reged: 12/02/04

Loc: Hockessin, De
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
scholastic sledgehammer
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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
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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
scholastic sledgehammer
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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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Reged: 12/02/04

Loc: Hockessin, De
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
scholastic sledgehammer
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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
scholastic sledgehammer
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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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