Electronics > Repair
Looking for circuit diagram GSI Galvo servo amplifier (Minisax)
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_Wim_:

--- Quote from: Harry_22 on July 02, 2024, 05:05:40 pm ---Remove jumper W1 to open the loop and apply power.
There are two circuits to monitor. Check them both.
- Pin 4 (Position) of Test Interface (see Page 14).
- Pins 7 an 8 of Signal Interface Connector (see Page 12).
Rotating the mirror shaft should cause the position voltage to fluctuate between +3V and -3V (probably this is between pins 7 and 8. See Page 37 of the manual)

--- End quote ---

- Tested first on pin 4 of the test interface. Signal was larger than +-3V but followed nicely my mirror movement
- Tested on pin 7: lots of high frequency noise/oscillation (+-2.5MHz) but signal track mirror movement. Measured with grounded probe, check with ground from signal interface and with ground from power supply, same result.
- Tested on pin 8: identical result to pin 7
- Tested with differential probe (HP 1141A) between pin 7 and pin 8: same result, oscillation remains present.
- Tested by powering with a lab power supply instead of the switch mode I was using, same result (consumption +-3.5 Watt on +24Vdc, and +-4 Watt on -24Vdc)
- forgot to test between both pins of W1
- checked the easily probable opamps if I could find one with the same oscillation signal, no luck, so it must be one of the opamps that is hidden by the boards on top. Will test this weekend by soldering probing wires to all of this.


--- Quote from: Harry_22 on July 02, 2024, 05:05:40 pm ---Please also check the following areas.

--- End quote ---

No solder bridges were found, was only some minor flux residue and it looked WAY better in real than on the pictures  :o
Harry_22:
Hi!

I prepared the layer diagram for PaintNet (please see attachment).
There are several 78L00 and 79L00 in SOT-89 as well as LM317, LM377. 7V reference U5. Check them also.

https://drive.google.com/file/d/12g5bB9MpHA1xPD8NZRaeOuxLwTiKXTSC/view?usp=sharing
_Wim_:

--- Quote from: Harry_22 on July 04, 2024, 07:51:21 pm ---Hi!

I prepared the layer diagram for PaintNet (please see attachment).
There are several 78L00 and 79L00 in SOT-89 as well as LM317, LM377. 7V reference U5. Check them also.

https://drive.google.com/file/d/12g5bB9MpHA1xPD8NZRaeOuxLwTiKXTSC/view?usp=sharing

--- End quote ---

All voltage regulators measured  OK. The 7V reference was also fine. Measured also with the jumper W1 open an closed:
- open: 0.5V on one pin (changes when I move the mirror by hand), +-7V on the other pin
- closed: +-7 volt on the jumper.

It really seems the LM3886 is at fault, which could make sense it the damage occurred due to high voltage arcing, as the servo cable runs close the the Xenon lamp cables. The replacement LM3886 has not shipped yet (Ebay seller from Germany), so I still have to wait patiently to test if it is really all what is wrong...
_Wim_:
The LM3886 arrived and is installed. Now the galvo is moving again  :), but always to the same direction and goes full stroke  :(. I am now thinking the other LM3886 might also be broken (as the replaced one also showed movement initially), so I ordered a second one (should have done so immediately, but hindsight is a wonderful thing...)

_Wim_:

--- Quote from: _Wim_ on July 14, 2024, 06:38:18 am ---I am now thinking the other LM3886 might also be broken (as the replaced one also showed movement initially), so I ordered a second one (should have done so immediately, but hindsight is a wonderful thing...)

--- End quote ---

Hi, sorry for the late reply, I was away on summer vacation. Meanwhile, the second LM3886 has arrived and is installed, but this did not make any difference (so the issue remains). I have currently some other priorities, but will revisit this later for sure.
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