Help driving GSI 120DT Galvo motors

[mixedgas]

Ok, you have removable mirrors. There are clamps on the shafts and the mirrors are glued on to the clamps
The needed low pass filters are on the connector board, confirming my suspicion.
If it gets here by the weekend, if its working with no damage, it would ship on Monday after reverse engineering and test.
You need a real oscilloscope and a bench power supply for this. (20 Mhz oscilloscope, preferably two channel)

I'll reply later this evening, I have to attend a meeting. Let me work out a test procedure for the galvos.

What is the connector on the factory Galvo amp board, DB what? Need a picture...

Steve

[thorson14]

Hi Steve,

I have a multi-channel 20MHz oscilloscope available to me here.

Here are some additional pictures:
Connector to the factory galvo amp board (DB15M):


A better picture of the connector board inside the scan head:


The reverse side connection of the factory galvo amp board and its connection inside the controller tower (topmost connector):


Power connection to the tower. This may not be useful but I was wondering how I would power the factory galvo amp board:


Let me know if you need any further photos.

Thank you,
Todd

[mixedgas]

OK, the feedback signals must ride on individual tiny coaxial cables for shielding inside the cable. two coax per galvo.
!
I have plenty of the required cable.
!
The DB connector is easy enough, I have them. Digikey has them, too.
!
Are you using the backplane connectors in the tower? Can you use the factory power supplies for the Galvo?
!
Where are you located?
!
Steve

[thorson14]

Hi Steve,

I'm located at the University of California, Irvine.

Glad to hear the connections look familiar to you. I have full access to the control tower components if needed; whatever is necessary to get these scanning motors functional. I don't have any other power supplies for the Galvo motors at this point. Can the motors be powered through the backplane connectors in the tower or are there General Scanning power supplies out there that might be simpler? I'm not sure where an external power source would connect to the factory amp board.

I have the 20MHz multi-channel oscilloscope available whenever I need it. Can this be directly wired to the G120s for testing? Do you have guidance for testing the G120s? We need to make sure the motors are still functional, if this can be done independently.

Thank you,
Todd

[mixedgas]

Testing will be connecting suitable power to the feedback connectors on the galvos, which need +12V TIGHTLY regulated with no turn-on spikes from the power supply.
Then tapping into the feedback signals, after the low-pass filters on the connector board, load resistors are connected to the feedback signals and ground. The scope is placed in " channel one minus channel two" differential mode and the feedback signals are monitored while ever so gently turning the mirrors wearing white cotton gloves. If you turn the mirrors too far, the torsion rods inside the galvo will snap. If you do not have a A+B or A-B mode on the scope, don't fret, you can look at one signal at a time, but it will be buried in some noise.
What your looking for is a weak signal with a lot of noise that clearly correlates with movement of the galvo shaft.
!
So start reverse engineering the connector card...
!
We need to ground a few pins on the galvo to get started, as well.
!
Which pin goes where... I'm assuming you may have most of this from your previous attempt.
!
I NEED TO FIGURE OUT THE VALUE OF THE LOAD RESISTORs. They will be at least 2.2 Kohms, maybe more. My 84 year old mom was in a car accident, and I'm behind this week.
!
REMEMBER TO TAP THE FEEDBACK SIGNALS AFTER THE LOW PASS FILTER! At the DB15s....
!
Steve

[thorson14]

Hi Steve,

I'm so sorry to hear about your mother. I hope she is recovering well.

The connector board diagram that I had previously figured out with a voltmeter is shown here:


Note the G120DT connector wire colors in the table match the colors from the pinout diagram you have referenced and that their connecting pins on the DB15M connection then correspond in pin number to the same pinout diagram. No thermistor, heater, or AGC output connections found.

Thank you for the motor testing procedure. Looking through what I have and the instructions, everything looks okay except the shield and the Violet wire (pin12 - AGC output). I am not sure where or what the shield is, and my AGC output pin does not connect to a G120DT pin through the connector board. Do I still ground Pin 12 from the DB15M connection?



Could you guide me with your procedures for reverse engineering the galvo amp board when you can find the time? I might be capable with your help on this and my PI's abundance of equipment.

If this proves futile, I could send you the board if you're still willing to test it for me.


Thank you so much,
Todd

[mixedgas]

The shield is a Faraday shield in the feedback cable.. If the shield is there on that model you'll find a metal braid around the wires under the black cloth outer layer. That braid gets grounded to keep the drive signals and RF from things like cell phones, and EMI from things like fluorescent lights out of the signal path. Signal Integrity, SI, is something you need to learn about if your going to do this. What you may see is a jumper to the shield, covered by heat shrink tubing and grounded.
!
If the AGC (violet) wire is not brought out, its connected to ground on the connector expansion board by default.
!
See if your campus library has The Art of Electronics, by Horrowitz and Hill, 2nd Edition. You need to read some chapters, its designed for teaching electronics to Grad Students who are not EE majors. It then became the best selling Ellectronics Text ever. 3rd edition not so recommended, at least by me.
!
Google Faraday Shield, Quiz Monday!
!
BEAMS lab Eh, some PIs get all the really cool acronyms.
!
I'll look at your wiring diagram at lunch. I'm supervising some new Confocal users today, and keeping an eye on a six KiloDollar oil immersion scanning objective.
!
I need a zoom pic of both sides of the board in the area indicated, good enough to read the part numbers on the chip and see the traces. That way I can possibly isolate the analog input to the scanner amp. Also ask your PI to contact Technical Instruments Inc. by phone and see if he can get a copy of Schematic 660-00081-01. That way the board can stay in Kali... And I wont have to figure out how to bill your university for such a simple task.

!
Steve

[thorson14]

Hi Steve,

Here are zoomed in images of the board, top side and bottom side. Let me know if you need better images and I can try to take very zoomed in pictures and stitch the area of interest together. Hopefully these are legible though:


I am heading to our science library this afternoon to check out The Art of Electronics (thanks for the great recommendation) and I'll have my PI get try to get his hands on the board schematic.

Hopefully that nice objective stays in tip top imaging shape after today for you. I have some imaging to do myself this afternoon with a 60x oil immersion objective.

Please let me know if you will require better images.

Thank you,
Todd

[thorson14]

P.S. Note that in the pictures of the boards, the orientation is the same. The left side stays the left side (i.e. I flipped the board vertically).

[mixedgas]

What is the part number on the Burr Brown Chip, U14? I cant make it out without doing some serious image processing. (Note, after serious image processing, I still cant read it!)

Its the digital to analog converter that actually positions or commands the galvos.

I cant see the number in the picture. Note that this is a "Multilayer" circuit board, so while visual clues help, it takes probing with instruments to verify the circuit. In other words, it looks like a 3 or 4 layer board.


Steve