chncI interface board opto relay mca231 ?

Trouble with my chncI, 1985 model with siemens control. The spindle brake won't release. The brake is air solenoid activated. The solenoid is good. Crydom solid state relay that activates the solenoid is good,proven by swap, but does not activate. I'm not getting the voltage to activate the Crydom relay from the Hardinge interface board. I think I have all the drawings on this machine, but of course they don't go into board level detail.

The interface board has a number of GE mca231 opto isolation devices on it in dip 6 pin IC packages. These are all in sockets, not soldered in. I think these are activated by the cnc control and in turn drive the larger solid state relays that activate the various devices like the coolant pump, spindle brake, part chute, etc.

I could probably start swapping them around trying to isolate a bad one but it would be easier if I knew which one activates the brake relay. Another option is to remove all the wires and extract the board so I can trace the copper runner from the output plug back to the socket but this is a 23 year old machine and it falls under the "don't poke around too much with the electrics it could break worse" scenario.

If anybody out there has details on the HIB board and which optos control which devices I would love to hear from you. I am hoping Hardinge service will be able to tell me which one it is but its a $15.00 fix from digikey vs them selling a board so they may not want to talk about it.

Thanks

Tim

It appears to be a darlington output Opto http://www.optoinc.com/datasheets/MCA231.pdf
If you have the prints or at least the output numbers, in some cases you can figure out which opto it would be by the order of the output.
IOW if it is a 16 output card and the spindle brake is 6th output for example, if the opto's progress down the card, pick the 6th one.
If you jumpered pin 4 & 5, you should turn the output on, if the SSR is OK.
Or if they are 25c each, replace the whole works.
I have found that many opto's get weak with age where they are operating just marginally after many years of use.
M.