Rebuilding my old analog console

[Greg]

Here is the chopper driver card schematic from a package of documentation for the Mk4 received from John Tilp. My ability to read schematics is less advanced than some here, so I'm not sure exactly what the circuit described does. My understanding is that the chopper was a scanner, not a spinning motor. Is that possibly an astable multivibrator in the upper left?

Where it says 100% adjust looks like it is generating a +-15V adjustable offset. It would be interesting to know what potentiometers the operator used as chopper controls, and if a useful square wave generator is shown here.

[Kevint]

Laserist. I totally agree and that is the goal. You are right, ever since I started this thing, it continues to evolve and get more complex - which I love. The summing amp I have in mind has 12 inputs : 4 quadratures, KQO, Sq, circle, triangle, star, sqr wave generator and 2 extra. 8 summing amps in total for 4 XY scan heads. I'm still hoping that something like this is possible. The signals going to the summing amp would not all be on at once. There would be a selector section inbetween to choose various combos.

[Kevint]

Greg, thanks for posting the schematic. I haven't even gotten around to thinking about what to do with chopping yet. Do you know if there is any info on what feeds the various inputs to this circuit?

[Greg]

Greg, thanks for posting the schematic. I haven't even gotten around to thinking about what to do with chopping yet. Do you know if there is any info on what feeds the various inputs to this circuit?

I don't. That is part of what I'm posing as a question to the community. I have been using the ramp generator which I sent you, also called the colormod2 circuit, for both chopper and colormod effects. When needed, I also use the PDM signal from the spiral board for retrace blanking. For more complex intensity and color control effects I will use processor generated signals. Obviously since optical modulation devices are not needed with diode lasers, these effects become much simpler to implement.

[lasermaster1977]

Here is the chopper driver card schematic from a package of documentation for the Mk4 received from John Tilp. My ability to read schematics is less advanced than some here, so I'm not sure exactly what the circuit described does. My understanding is that the chopper was a scanner, not a spinning motor. Is that possibly an astable multivibrator in the upper left?

Where it says 100% adjust looks like it is generating a +-15V adjustable offset. It would be interesting to know what potentiometers the operator used as chopper controls, and if a useful square wave generator is shown here.

The missing variable potentiometer could be most any value where its full resistance plus the 3.3K Rin to the 2nd op amp and it's .22uF feedback resistor makes up an integrator that generates a triangle-like waveform. The triangle wave is feedback to the positive input of the first op amp thereby creating positive feedback to the integrator's input resulting in oscillations.

The output of the integrator is further modified by the parallel cap and 10K resistor and serves as one of three inputs to the 3rd inverting summing op amp. This op amp sums two inputs all the time, the Intensity input, which must be a voltage (variable? who knows) and the 100% Adjust voltage. The integrator's output signal is summed with those two signals whenever the Q2 FET is turned on making it in effect a short circuit between and connecting the 10K/.01uf input resistor/cap combo as a third signal to sum with the other two. The Chop EN signal turns ON Q2 to connect the integrator output as an input to the summing op amp.

Edit: Try putting a 100K or 1M pot across "8" and "10" (wiper on "8", one end of pot on "10") and see how the signal output at pin 7 of A1 changes in frequency as the pot is turned.

A lot depends on how the galvo is used mechanically or optically to achieve chopping.

Seems like there would be an easier way to do this if the Chop Output is driving a G120D or similar.

At least that's my best guess.

[laserist]

The Mark IV & Mark VI projectors used a big old non-feedback galvo that looked like a G330 for chopper. The Mark IV used the same galvo for scanners. The chopper was a slotted can. It was relatively slow with soft edges. If I was designing something today I'd make it capable of higher speeds and make the soft edges optional and adjustable. Maybe make the "off" intensity adjustable too. The upgrade to AOM on the MarkVI had several options including a multiplex effect that was clever, but very "distinct". By that I mean the audience could see it as "just more of the same"...

[lasermaster1977]

The Mark IV & Mark VI projectors used a big old non-feedback galvo that looked like a G330 for chopper. The Mark IV used the same galvo for scanners. The chopper was a slotted can. It was relatively slow with soft edges. If I was designing something today I'd make it capable of higher speeds and make the soft edges optional and adjustable. Maybe make the "off" intensity adjustable too. The upgrade to AOM on the MarkVI had several options including a multiplex effect that was clever, but very "distinct". By that I mean the audience could see it as "just more of the same"...

@Photonlexicon used a nice solution that he shared with me. I thought I had posted this before (maybe I did but I couldn't find it so here it is again. I used this "inverse" of the slotted can solution with both G115 open-loop and G120PD closed-loop scanners. No question it worked best with the G120PDs for fastest blanking speed. It was very simple, made from beer or soda can aluminum material and had two different lengths shown here. This usage was used immediately prior my working out the optical bench setup for using RYGB AOMs for high speed blanking, acquired when @photonlexicon and I bought all the laser gear from Showco in 1980.


We just epoxied one on to the end of a galvo shaft such as a G115 shown here:
By the way, the major grid lines are on .5" centers.


The beam was aligned to pass just between the two vertical tabs (beam ON, TTL=0v) when the galvo was at rest. The opening between the opposing vertical tabs was adjusted by rotating the galvo about its vertical axis. The open gap was set to be the width of the laser beam and just so that neither vertical tab touched the sides of the beam. The galvo amp and TTL blanking signal were adjusted so that the two vertical tabs where directly in the beam path (beam OFF, TTL=5v).

Using a G120PD in this matter allowed very nice blanking with a frame rate around 20-25 Hz as shown in this next photo taken at the Hong Kong Fashion Show in Boston around 1980 or '81.:



copyright 1981

[Kevint]

Thank you all for your help on my quest for a scan amp. I got a very old closed loop Gary Statler scan amp working and the images looked really nice. It's very similar to the laser images LM22SDA. So I kind of morphed the 2 and build a circuit that uses the control part from these designs and my current TIP41/42 open loop amp section as the galvo drive.

It kind of works. I don't have a means to do a test pattern so I used the function generator to generate 2 square waves. I was able to create a square with a diagonal line. The feedback controls for velocity and position are working. I was able to adjust out all the over and under shoot in the corners of the square and had a straight diagonal line when done tuning. The offset and gain worked accordingly. The problem is an audible high frequency sound that shows up in the image as small ripples in the image. For example the square is a square but the lines have fine ripples on it. So some debugging is needed.

I made a pcb for the amp. Here are some photos

[lasermaster1977]

Thank you all for your help on my quest for a scan amp. I got a very old closed loop Gary Statler scan amp working and the images looked really nice. It's very similar to the laser images LM22SDA. So I kind of morphed the 2 and build a circuit that uses the control part from these designs and my current TIP41/42 open loop amp section as the galvo drive.

It kind of works. I don't have a means to do a test pattern so I used the function generator to generate 2 square waves. I was able to create a square with a diagonal line. The feedback controls for velocity and position are working. I was able to adjust out all the over and under shoot in the corners of the square and had a straight diagonal line when done tuning. The offset and gain worked accordingly. The problem is an audible high frequency sound that shows up in the image as small ripples in the image. For example the square is a square but the lines have fine ripples on it. So some debugging is needed.

I made a pcb for the amp. Here are some photos

That looks nice, Kevin.

Can you post some photos of the images with ripple?
Are you looking at "the image" from the laser scans or from the Position feedback signal?
Lots of things can cause the high frequency ripple, such as a poor cable shield Ground on the differential position signals coming from the closed-loop scanner.

[Kevint]

Tried to take a photo but I blew up a transistor I think. One side of my power supply goes into overcurrent mode. I need to fix that side of the circuit channel 1. Now the interesting thing. The noise/ripple on the remaining channel 2 seems to be gone. The line on the wall looks clean and I don't hear the high frequency noise. So I am thinking I need to finish populating channel 3 and see how that channel performs. Channel 1 may just have issues and not the overall circuit design.