Film-Tech Forum ARCHIVE: Strong 2020 turret R10 resistor q.

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Posted by Rick Long (Member # 213) on 05-22-2001, 12:10 AM:

Gotta question perhaps some of you electronic whizzes out there can answer for me.

Reference: Manuals Section;
Simplex 35 Model PR1060 with TU2020/2030 turret parts (Oct.93)

Manual page 35 (turret controller schematic)

I have been having some luck working on repairing these things lately. While searching the schematic, however, I have to wonder about the purpose of resistor R10.

Basically, it is placed at the output of the bridge D6 and (to my way of thinking) does nothing but dissipate heat.

Further it is only on the output feeding the 5-volt regulator, there is not one on the 12-vot side.

While testing this circuit, on the repair bench, I can see no reason for its existence, other than burning my thumb when I turn the board over to press the buttons on the board .

My son feels that it may be necessary to discharge the capacitors prior to the regulator, after powering down. Not sure if I agree.

Any ideas?

Posted by John Pytlak (Member # 331) on 05-22-2001, 07:54 AM:

I would agree with your son. It's probably there to discharge that large 1000 microfarad filter capacitor (C3) on shutdown. But why isn't there a similar load on C4? Maybe Pat Moore has more insight into the design.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
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Posted by John Walsh (Member # 168) on 05-22-2001, 12:17 PM:

I think it is to load down the 1000uF cap, which reduces the DC ripple into the voltage regulator, thus improving it. I understand that adding a resistor there would usually make the ripple worse, but since it is on the input, the ripple is still above the 5v. The 5v is pulling more amperage, and I'm guessing that after the circuirt was done, they found the ripple too high, and this was a quick fix. There isn't a 100 ohm resistor on the other (12v) supply, because it requires less amperage, and was smooth enough.

Or, maybe they found that there was a race-condition "glich" when powering off, (the turret motor would start to spin just a little, or the solenoid would unlatch, for example) and wanted to kill the 5v quickly.

What I'd like to know is what the code is in that programmable part, so I can figure the turret operation out.

Posted by Gordon McLeod (Member # 33) on 05-22-2001, 06:08 PM:

I believe it is there to load down the transformers secondary so that it probably has a problem with the regulator presenting to little load.
If it is accross the cap for filter reasons it is making the ripple situation worse since the current level that the cap is filtering is higher. Also the regulator would discharge the cap and as such doesn't need aloading resistor

Posted by John Walsh (Member # 168) on 05-22-2001, 09:01 PM:

You're probably right about the ripple, Gordon. Although, I still think it may be to prevent race-condition "gliches" when powering off or on.

Either way, I'd bet it was added late in the design stage.

Posted by Steve Guttag (Member # 268) on 05-24-2001, 05:12 PM:

Ok....here is Steve's guess...

R10 is, for sure, a bleed off resistor...it isn't to help with charging the capacitor (it would be in series then) nor can it help with ripple.

I think the answer lies in pin 1 of IC 1...it is labled "Reset". R10 probably forms the "reset" on power off...without R10...there is VERY little stuff to bleed off the 1000uF capacitor (the regulator, oscillator and IC1)...the size of R10 was probably choosen such that it will achieve an active low on a typical power cycle.

Steve

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"Old projectionists never die, they just changeover!"

Posted by Rick Long (Member # 213) on 05-25-2001, 09:59 PM:

Thank you all for your replies.

Steve may be right on this, although I am beginning to harbour (harbor?) a suspicion that this may have been a cheap and dirty way of preventing spike or unusually high line voltages from exceeding the input parameters of the 7805 regulator by loading down the input.

Posted by Steve Guttag (Member # 268) on 05-26-2001, 03:41 PM:

A couple of flaws in that reasoning....

First, if one wanted to "load the input" then the resistor should be on the output of the trasformer, not the diodes....why would you load your diodes (and make them heat up more) without reason. Furthermore, diodes are can fail from spikes as much as anything...often there will be a supressor capacitor across the input of the rectifier to clamp said spike (typically low capacitance but high voltage).

The only logical reason for R10 is bleed off the main filter cap at a fast enough rate. Since I don't see it in the parts listing (ie what is it's wattage) I suspect that it was added after "field testing".

Do you know what the output of the transformer is? The 7805 with proper heatsinking can take a lot. It also doesn't seem to be loaded very heavy.

Steve

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"Old projectionists never die, they just changeover!"

Posted by Rick Long (Member # 213) on 05-26-2001, 08:02 PM:

That is sorta my point. The 5V circuit is not loaded much at all, thus the output of the transformer will be somewhat higher than if it were loaded (I did measure the voltage, but forget exactly what it was, but it is the same as the output for the 12V side). I agree with your point about if loading was the reason, it should have been placed directly across the secondary winding.

BTW, the 7805 just sits there in mid-air with no heat-sink. It was the 7805 that I had to change on the first unit I repaired.

Posted by Ken Layton (Member # 133) on 05-26-2001, 09:14 PM:

What is the value and wattage of R10? I'd like to write that down in my manual, since it's not listed.

Posted by Rick Long (Member # 213) on 05-27-2001, 03:17 AM:

As I recall it's 1/2 watt, and gets hot.

Posted by John Pytlak (Member # 331) on 05-27-2001, 06:12 AM:

If it gets "burning" hot, consider using a resistor with a higher power rating, if it fits.

Posted by John Walsh (Member # 168) on 05-27-2001, 10:06 AM:

This is a spec sheet for that voltage regulator (I think.) There is no actual listing for a "VR7805" although it seems like a standard part.

CLICK HERE TO DOWNLOAD

Posted by Gordon McLeod (Member # 33) on 05-28-2001, 12:20 PM:

the VR means Voltage Regulator and the 7805 is a standard from many manufacturers.
It also is about at its maximum input range as they really don't like much above 12volts input

Posted by Steve Guttag (Member # 268) on 05-28-2001, 12:36 PM:

From an engineering standpoint, the concept of putting a loading resistor in circuit is just plain silly (unless it is required for stabilization...some IC amplifiers are designed for low impedance outputs and must be loaded in order to not oscillate themselves to death).

If the goal was to drop the voltage the other safter solutions are many...including series resistance (since the load is known and the regulator gives wide range)...a series zener diode can also drop the voltage well and again current load on the output isn't high so it needn't be huge (heck Strong's igniter circuits work using said zeners to drop the open circuit voltages).

I'm sticking with simple bleed off.

Steve

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"Old projectionists never die, they just changeover!"

Posted by Rick Long (Member # 213) on 06-01-2001, 11:25 PM:

Sorry, been out of town the past week.

Yeah, thinking about it, I beleive you're right, Steve.

Damn, means I owe my son a case of beer.

Posted by Steve Guttag (Member # 268) on 06-02-2001, 10:00 AM:

I did happen to pop open my PR-2000 book and though the circuit is almost identical...the resistor R10 is not there! It is a different transformer though...the mystery continues.

Steve

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"Old projectionists never die, they just changeover!"

Posted by Ken Layton (Member # 133) on 12-06-2002, 11:26 PM:

I've recently had one of the 5172002 Rev B boards in for service. Resistor R10 is a 100 ohm half watt for those interested (it's not listed in the parts list).

Posted by Shaun Flichel (Member # 1435) on 12-07-2002, 09:05 AM:

100 ohm, 1/2 watt. Thanks Ken, every resister ive looked at in that system was black and crusty. Another problem I had with that wonderful system is during a show, the turret would just go ahead and rotate. Replaced Photoswitch on turret itself and it was ok after that. Also when replacing the main board, there are soldiered jumpers for the style of apperture changer you have. Just so all of you know.

Posted by Ken Layton (Member # 133) on 12-07-2002, 09:23 AM:

Shaun:

Quite right about those jumpers! If you get a replacement turret control board always double check the jumper settings for what your particular turret motors are (either AC or DC). The jumpers are located to the left and below relay "RL5". Some of the boards have the jumper settings silkscreened on the board above diode D5. Be aware that I found one turret control board that had the connector "J7 Photo Board" soldered with the locking tab reversed!

The "photo board" has indeed caused some random turret changes and some failure to index when you push the format change buttons on the control board. The photo board contains surface mount components and for the average person would not be practical to repair---you have to order the whole assembly (cable, pc board,and mount).

Posted by Shaun Flichel (Member # 1435) on 12-07-2002, 09:26 AM:

Sorry about that Ken, I said the apperature motors, but I think there is a jumper for that also isnt there??? Something gets me that one time I changed a board and the apperature didnt work, then I found the jumpers.