Author Topic: Pmdx-120 Breakout Board problem maybe  (Read 2084 times)

callcbm

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Pmdx-120 Breakout Board problem maybe
« on: August 23, 2018, 04:24:20 PM »
I have a PMDX -120 Board like the first built happy with it . But I'm having a problem with one axis will only move one direction no matter the button pushed. then with out doing any thing start working properly. then when cutting to a different spot of the cut, then just move in the same direction. My question is could the buffer chip for a axis malfunction seems voltage effects it as well as higher room temp. Very frustrating have you the machine for 16 yrs only on brown out days would do this know it's doing all the time.There is know loose connection and moving drive it will do the same on the new axis when moved

12strings

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Re: Pmdx-120 Breakout Board problem maybe
« Reply #1 on: September 01, 2018, 11:31:55 PM »
Wow, that's a golden oldie.  As I recall the PMDX-120 has the step and direction driver IC in a socket, so it is replaceable.  Oops - the PMDX-120 manual has a typo on page 19.  It says that the IC is a 74ACT254 - there is no such beast.  I'm pretty sure what they mean is a 74ACT245 (a standard 8-bit bi-directional bus driver IC).

The PMDX-120 regulates the incoming AC to 5VDC for its use.  The regulator can get quite warm, even with the little heat sink on it.  I wouldn't think an AC voltage sag would have any effect on the 5V, but I could be wrong.  You can measure the 5V supply on the 3-pin jumper for step/dir common (JP1).  Heat on the other hand, could be a factor.  Can you put a fan on the PMDX-120 and see if that makes any difference?

If not, you could try replacing the driver IC (check Digikey or Mouser).  Or contact PMDX and see what they say.

callcbm

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Re: Pmdx-120 Breakout Board problem maybe
« Reply #2 on: September 02, 2018, 09:04:28 AM »
I found if I keep the controls at 67 to 72 degree's It works fine if I go lower it malfunctions or higher I was routeing when the temp in room went above 72 and it started acting up. I have a fan with a filter system blowing into my control cabinet for years now but this would show up ever so often hot and cold more so hot. So I was right in thinking this could be the cause and not the UFO or EMI interference as I have been told.
Next question I'm not experienced with replacing chips would it be better to buy a new board or is it a simple job. Thanks

12strings

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Re: Pmdx-120 Breakout Board problem maybe
« Reply #3 on: September 04, 2018, 09:55:23 PM »
Are these temperatures you mention ambient room temperature?  Or temperature that you've measured inside the cabinet somehow?

If those temperatures are "as measured inside the cabinet", failing above 72 degrees is a pretty low "high" temperature.  I would expect maybe something up around 90 or 100 degrees F.  And failing at LOW temperatures, specially when "low" is 67 degrees (F, I presume) is *HIGHLY* unusual.  Electronic circuits usually work better at lower temperatures (to a point).

If those temperatures are room ambient, have you measured the temp inside the cabinet?  And specifically near the PMDX-120?

Regardless, if you don't feel up to trying to swap the IC, as I mentioned before, contact PMDX and see about an RMA.  They may be able to take a look at it and see if there is some other issue, or they may be able to swap the IC for you.  Cou;dn't hurt to ask.