[Chrisjh]

I am trying to identify an optocpoupler device on the first generation SX3 Spindle control board. The Part Number is clearly marked 1L6704 on the device (See photo).

I have tried replacing it unsucessfully with a 6N137 (transistor O/P Photocoupler) and a 6N138 (Darlington Photocoupler).

The thing that worries me is the the logo on the IC is the same as the logo on the board which makes me think that it is a "custom" chip.

The chip takes the PWM spindle speed signal from the Interface board via a ULN2003 darlington array on the spindle control board to the 1L6704 I/P which appears to be a photo diode. I have measured the O/P pins 6 and 7 on a known working board and read a DC voltage proportional to the speed requested by Mach3. (typically 1.5VDC @ 500rpm to 3.5VDC @ 2500rpm. So it appears that this chip is more that a photocoupler and may have a PWM detector on board.

Can anyone help?

Regards

Chrisjh

[presslab]

I can't find any info on that part, sorry. However my guess is that it's a high speed opto like the 6N137. Maybe you can take a macro pic of the chip. Any other numbers on it? Is the logo exactly the same as the one on the board? Have you looked at the output pins on the working board with a scope? You probably already know this but measuring a PWM duty cycle with a multimeter will give you a voltage proportional to the duty cycle.

Maybe there is something else wrong with the board. Is there 5V between pin 8 and pin 5?

[samco]

it does look like an opto package... But could it be http://search.digikey.com/scripts/Dk...;keywords=6704

?

sam

[samco]

ah - never mind.. wrong package.

sam

[Chrisjh]

Thanks for the responses.

Last night with the help of a younger brain, we made significant progress. (Thanks Will for the use of your brain)

We managed to subtitute a 6N137 with a jury rigged additional collector load resistor and got the board actually turning the motor. Problem was that the spindle speed worked reverse to how it should work. That is, with 0% PWM the motor runs flat out and with higher % PWM the motor slows down. Obviously the logic is inverted with a 6N137. We trawled the net for hours to find optocoupler with a non inverted output (boy, are such things rare) and managed to find something that most probably will be suitable.

I am very confident that I can come up with a substitute. I am awaiting the new part to arrive so I can test out our theory.

I will keep you all posted when I am 100% sure I have the solution. (Hopefully early next week)

Regards

Chrisjh

[Chrisjh]

I finally got the spindle board working by fitting a "modified" 6N138 Darlington Output Optocoupler rigged in emitter follower configuration. Emitter Followers do not invert the output with respect to the input phase. Looks bloody ugly but it works as intended. That is, I now have full spindle speed control from Mach3.

I fitted a 1K resistor between Pin 5 and ground, connected VCC (+6VDC) to Pin 6, and connected a short wire between PIn 5 and to where Pin 6 used to go. All of this on a DIP8 IC socket. See Photo.

If anyone can identify the original chip, I would be eternally grateful.

Regards

Chrisjh

[Chrisjh]

Following success with the 6N138 Modification, I have made up a piece of Veroboard with a more permanent solution.

I now have 3 working spindle control boards fully calibrated for rpm. (One fitted to the machine and 2 spares).

A schematic of my modification is located at www.cjh.com.au/6N138_ Mod_ Schematic.pdf

Photos of the modification are at www.cjh.com.au/Proto_ and_ Final_ Board.JPG and

www.cjh.com.au/Closeup_of_ Mod_ Board.jpg

I also have some professionally manufactured bare boards made up but I am satisfied with the Veroboard solution.

Regards

Chrisjh

[neilw20]

Zhejiang East Crystal Electronic Co Ltd.
No.555 Binhong Road
Jinhua, ZHJ 321017
China Tel: 86/579-82272001 URL: http://www.ecec.com.cn