CX6325 amp for driving G120DTs

[sheral]

Hi Steve,

I've been trying to understand my galvo connections because the ones I have don't have a DB15M terminal. These galvos end in a 10-pin connector. I've been able to figure out most of the wires, but there are two that are white with brown stripes that I'm having trouble with (shown in the pictures, Pin 3 and 6). Have you ever seen these? My hunch is Pin 3 might be for the AGC and Pin 6 is for the position output common. Do you have any suggestions on how to test this without ruining the galvos if I'm wrong?

Thanks in advance for your help!

DB15M connector

Pin Number	Wire Colour	Signal Description
1	Red	Drive Coil (See notes 1 & 2)
2	Yellow	Drive Coil (See notes 1 & 2)
3	Black	Position output (-)
4	Orange	Position Output common
5	Red	Heater - T-Type (See note 3)
6	N/C	No Connection
7	Red	Heater - T-Type (See note 3)
8	White	Oscillator supply voltage (+)
9	Green	Drive Coil (See notes 1 & 2)
10	Black	Drive Coil (See notes 1 & 2)
11	Red	Position Output (+)
12	Violet	AGC
13	Brown	Oscillator supply voltage common
14	N/C	No Connection
15	Blue	Thermistor - T type (See note 3)

NOTES
1/ To wire drive coils in series, connect Black to Green and drive Red to Yellow. Series wiring is recommended for use in position sensing (closed loop) mode.
2/ To wire drive coils in parallel, connect Red to Green and Black to Yellow. Use parallel wiring only when driving the galvo in open-loop mode.
3/ Heater blankets are mounted only on the G120DT type galvos and are not commonly used in light show applications.

[sheral]

Yes, my galvos have the heater with two red wires coming out of it (see attached photo). Do you think the white/brown wire alongside the 4 coil wires relates to the heater wires?

And sounds like the white/brown cable on the position feedback cable is the shield, am I understanding that correctly? So it should be grounded when connected to an amp?

Thanks so much!!

Do your galvos have the heater (orangish circle on the outside with two wires)? Can you upload a complete photo of the galvos? (never mind, you stated earlier you have G120DT galvos)

The G120PD or 120D has two cables, one for the four wires of the coils and one for the 5 wires (one is the shield) that connect to the position feedback circuit, The G120PT adds two more wires for the heater.

[lasermaster1977]

Yes, my galvos have the heater with two red wires coming out of it (see attached photo). Do you think the white/brown wire alongside the 4 coil wires relates to the heater wires?

And sounds like the white/brown cable on the position feedback cable is the shield, am I understanding that correctly? So it should be grounded when connected to an amp?

Thanks so much!!

I deleted my original reply since I felt it possible I was missing something. The G120DTs had a heater blanket (two wires - voltage input) and a thermal sensor (one wire and common ground - voltage output), the two working together to provide thermal regulation.

You connector has 10 wires and therefore may be only for the coils and position feedback circuitry. Your photo appears to show the heater blanket (and thermal sensor on the opposite side?) to be in a sheathed cable all their own. Is this right?

The normal G120Ds w/DB15 connector only used 10 pins, which was a modified connector version of the earlier G120PD version.


G120PD cable details


Lower left of this image shows connection details of G120PD which used a 5-pin Amphenol connector just for the position feedback circuitry.
The G120D combined the coil and position feedback wires into the one DB-15 connector.

[sheral]

Here’s a better picture. The heater blanket wires are fed back into the place where the drive coil cable emerges (the thicker cable). I don’t see any wires for the thermal sensor on the galvo.

I also have the feeling that perhaps the heating isn’t being used as there’s only 10 pins. But I would assume they chose the DT model for a reason, especially inside a confocal scan head. I’m quite confused what that white/brown wire on the drive coil cable is for.

I deleted my original reply since I felt it possible I was missing something. The G120DTs had a heater blanket (two wires - voltage input) and a thermal sensor (one wire and common ground - voltage output), the two working together to provide thermal regulation.

You connector has 10 wires and therefore may be only for the coils and position feedback circuitry. Your photo appears to show the heater blanket (and thermal sensor on the opposite side?) to be in a sheathed cable all their own. Is this right?

The normal G120Ds w/DB15 connector only used 10 pins, which was a modified connector version of the earlier G120PD version.


G120PD cable details


Lower left of this image shows connection details of G120PD which used a 5-pin Amphenol connector just for the position feedback circuitry.
The G120D combined the coil and position feedback wires into the one DB-15 connector.

[lasermaster1977]

@sheral thanks for the photo. Well it is certain that the sheathed cable opposite the heater blanket orange wires contain the coil wires +1 (white/brown).
I've never dealt with the G120DT before. The position feedback sheathed wires are ("appear") associated with it. The thermistor must be embedded in the galvo, would be my guess.
Certainly the use of the heater blanket must be optional, connect it or not, as it would have minimal affect the tuning and use of the position feedback scanner itself.
I'm still reviewing the CX-660 manual.

The position feedback circuitry for the G120PD and G120D had a +12v and Power Gnd wire, plus the Position + and Position - wires with orange wire/shield signal Gnd. Power and Signal Grounds were the same (but recommended to be separate with signal ground tied to the shield and the metal frame of the scanner) so maybe they combined these two Gnds into one wire. (?) That would be easy to test with an Ohm meter. Find the pin where the scanner connects on the scan controller board that ties to the power supply common or GND to see which pin that is on the scanner connector(s).

mixedgas no doubt has more experience on these G120DTs than me.

[mixedgas]

My best guess without an ohm meter is brown-white on the feedback bundle is a grounded shield connected to braid. Based on the heat shrink.

On the feedback cable, Brown, White, Red and Black are just enough to use a G120 a position sensor if they did something with orange and purple in the cable or at the factory..

A little peeling of the shrink will confirm.

The coil cable looks perfectly normal with yellow, black, green, and red, with a customer added shield as white-brown.

Steve

[mixedgas]

The two oranges are the heater. Usually an internal thermistor is present, which is a bit of a baffle for me, but I bet white/brown is a shield and may carry a ground signal. Thermistor is blue-blue on heated G120 galvos.

My guess is the existing amps are not using the AGC or the purple AGC line is grounded at the shield, disabling AGC. Who knows, they modded the factory cable one way or another,. The factory cable is usually a fireproof fiberglass cloth jacketed material , not heat-shrink.

Time to reach for a scalpel and do a little exploring. remove the shrink, starting at the connector end, progress further if it doesnt make sense. . A replacement Shield can be made by removing the copper braid from a short length of RG-58 RF coaxial cable, which is around a Dollar a foot from a amateur/r ham radio or two way business radio communications radio shop.

If not, I can spare a pair of classic G120s and you can reuse the existing mirror mounts. While not quite yet paperweights around here, I have a lot of them, and knowing a pair went to academic laser microscopy would be a blessing, I have a soft spot in my heart for graduate research. I enjoyed visiting UT, once upon a time, too.

G120 cable conductors are usually a tough teflon wire, grasp with pliars when removing insulation as they pull out of the Galvo fairly easily.

Shoot me a picture of the circuit card the galvo connectors meet up with. There just are not that many g120 driver circuits in the world, it may be recognizable.

US Patents 4142144 and 4135119 will give you a clue, about how this functions, one problem being the 1 Mhz voltage is around 100V Pk to Pk if you open up the galvo case, so working inside the galvo, which is partially filled with epoxy and pitch, can be a bit shocking. Thus while often repairable, it is not wise to open up a G120.

If you don't know about SAYAL for odd electronics materials, you should, I miss Canada.. I used to love attending laser conferences in Mississauga. Usually we'd raid SAYAL, A-1 electronics, and the Toronto Surplus Stores as part of our trip.

https://sayal.com/

Steve (Formerly Senior Technician, Major University)

[mixedgas]

Oh, the horror, working on a G120 without much of a visual clue, well, here is a thread with some internal pics.

https://photonlexicon.com/forums/sho...highlight=g120

I don't suggest opening them.

Steve

[sheral]

lasermaster and Steve, thank you both for taking a look and explaining it to me! Much appreciated.

Sounds like both of the brown-white wires I'm looking at are shields. I'm going to see if I can get any more clues on what modifications they made from the factory model by peeling back the shrink and opening up the cables little by little. My hunch is that the AGC is grounded, and must not have been used on the amp that originally came with the scan head. I don't have the original amp, and the circuit card that connects the galvos is just a filter for the signals (see picture). I'm going to use an ohm meter to try to see how its all connected. Hopefully by the end of this, I'll understand the connections well enough to hook them up to a CX660 properly.

Steve, also super cool to hear you've visited and enjoyed the area! Toronto is a great place. I haven't heard of SAYAL or the other stores, but might have to pay a visit when I have some free time haha. Thanks as well for your offer of some classic G120s -- I'm going to try my hardest to get these ones running if I can first.

[lasermaster1977]

In an earlier post in this thread there was reference for GSI position feedback scanners to have their coils connected in series while open-loop scanners their coils should be connected in parallel. The primary difference is 4 Ohm vs 8 Ohm load impedance along with their inductance differences. More power required for the 4 Ohm load of course put a higher risk of higher heat loads on the amp current driver transistors and scanners and/or burning out coils, etc. (In days of yore, we always used parallel coil connections in the G120PD/D scanners.) Never had an issue.

It might be worth noting that while this may be a recommendation, the early A600, A601, and later GSI CX position feedback scan amps used parallel coil connections as did Laser Media LM22SDA dual scan amps. (I don't know whether some GSI amps expected series coil connections.)

I recently had the opportunity to compare the GSI CX660 Model CX6325 and CX6120 scan drive controllers for the G325D/DT and G120D/DT scanners. The DB-15 connector on the scanners have no connection between the two coils (pins 1,9 and 2,10) but the two coils are tied in parallel on the circuit board where the CX controller's rear panel DB-15 connects via a flat ribbon cable to an IDC PCB connector.

It makes me wonder why GSI and GSI Lumonics CX controllers stayed with parallel coil connections for these scanners.