Takisawa TP-3 pulse coder PCB diode broke...machine runs better

[copper460]

Hi All,

I purchased a 1985 Takisawa TP-3 Lathe, FANUC 3T, no extras or addons, knowing that it had some issues. One alarm pops up on the X axis. The machine will home fine, but after moving the axis it will not go home again without an over travel alarm. But the limit switches are not even being touched. Until I turn off and on the machine I cannot reference return. Also have to do P + Cancel on startup. I decided to check the pulse coder on the x axis. The machine is coated in oil, so I thought something might be up. Long story short, it looked good. Someone had been in there before though.

Put everything together again and for the first time the machine ran a program with no errors. Not even an axis error on start up. Homing was no problem. Later on my bench I see a little piece of electronics. Exhibit A. NEC diode (I believe) Then checked the pulse coder PCB. Exhibit B. Position C1 At the top you can see something obviously broke off. My quandary is...the machine is now running...but its technically broke...do I fix it? I'm not sure of the function of that particular piece of the PCB. My only concern is that could it lead to a crash? My experience with alarms is that the machine stops. It really seems that either the diode(?) was bad or broken somehow and shorting out. Why else would the alarms stop.

Any thoughts? Thank you for your help.

 

[Vancbiker]

The part in the picture is a capacitor, not a diode. Typically in this type circuit it would be to filter noise or condition the encoder waveform. I don't have board level schematics for that so can not say for certain. Personally I would not worry much about it.

 

[copper460]

Thank you Vancbiker. I appreciate you correcting my misidentification and giving me your feedback on the purpose. It is much appreciated.

 

[ss_user]

From the spacing of the pads I would assume that is a disc cap to dump high freq noise to ground. Unless things get erratic I wouldn't lose much sleep over it.

 

[Wsurfer]

Filter caps on the power in are a common thing to go out. Especially electrolytic caps. You can put a volt meter on the 5v using the lowest AC setting on the meter (better if you have an oscilloscope) and measure ripple on the DC supply. If you start getting anymore erratic behavior, it's an easy fix.

Just fixed my fridge recently with a bad cap. The fridge was short cycling and i noticed some flickering on the display. I was getting 200mv of AC on the DC supply. The cap was also warm to the touch. No schematic, but swapped out a 25 cent cap and its all good again. A reconditioned control board was $450.

 

[copper460]

Thank you ss_user. From the feedback I will let her loose and see what happens.

 

[copper460]

Thank you Wsurfer. I have a decent multimeter and an oscilloscope. If things get buggy again, I will replace the capacitor and see what happens.

A big thank you again to everyone for the replies. It's much appreciated.