Brush Servo Cards

magno_grail · Jan 30, 2015

I have three servo cards from a friend that are burned out. He said that I can have one if I can repair the other two. Since I need a board for the A axis I am thinking of making a new board. I traced out all the circuitry and most all the parts can be replaced with modern (SMT) components or their equivalent. Is there much interest out there for brush servo cards? I realise most have brushless servos now but my VF-1 is a '90 and I expect to keep it for a while.

BGL · Jan 30, 2015

How about you sell them as a you solder kit - like ye olde Heathkit. Good margin for you, economical for me. I'll take three!

magno_grail · Jan 30, 2015

That is possible. I can have the boards made with a solder mask and silk screen labeling part names and positions. You need a fine point soldering iron for the small parts. There is a another way to solder them, provide a mask and solder paste, squeegee the paste onto the board, place the parts on the board then bake in the oven. Saves a lot of hassle with the parts sticking to the iron.

magno_grail · Feb 1, 2015

As you probably know, the drive MOSFETs (IXFM50N20) are no longer available in the TO-3 case but the same specification MOSFET from IXYS is available in the TO-268 case so the mounting plate/heat sink will have to change. The drive transistors are marked for End of Life so they will also be not available sometime in the future. I am looking into rebuilding the drive section with modern parts. There are H-bridge drive ICs that are made for this type of application. They will cut down on the parts count.

magno_grail · Feb 12, 2015

So I have one of the older Rev. D boards working again. R72 and R30 burnout appears to be common between these boards when the drive MOSFETs go. The Rev. D board uses MTM40N20 drive MOSFETs (40 Amp), the Rev. F uses IXFM50N20 (50 Amp). I found the MTM40N20 at xsforsale.com at $7.50 each in case someone needs them.
I bought a PLD programmer so I can reproduce the socketed ATMEL chip. The different Rev versions were due to changing parts that were no longer available, the on-board power supply and fuses. The PLD programming was the same on the Rev. D and F. I found a couple boards have labels on the mounting bracket that say "X, Y, Z AXIS ONLY". I am not sure why this would be as all the boards are limited to 20-22 amperes and there is no circuit differences with the other boards without the label.

magno_grail · Feb 16, 2015

I have the new layout for the servo board using surface mount parts where ever possible. The board could actually be a great deal smaller but I am not sure if the wire cables will reach. Mine do not have much extra length. I left the holes in the board for the heat sink/mounting plate so it can be reused. It will now mount on top of the MOSFETs. Here are the Rev. K board and mine:

tlloyd3817 · Jun 16, 2016

Did you ever get your servo amps repaired? I have four that need repair. Please let me know how you made out

[email protected]

tlloyd3817 · Jun 16, 2016

[email protected]

magno_grail · Jun 16, 2016

Yes, typically it is the output transistors or the output drive circuit but one had the voltage regulators go bad. I got the obsolete output transistors from Jameco Electronics. The early Rev no. boards had 30 amp transistors, the later were 40 amp. I would have to check my notes to be sure. The output drive circuit transistors and voltage regulators are available from mainstream sources (Mouser, Digikey).

npolanosky · Aug 1, 2016

magno_grail said:
I have three servo cards from a friend that are burned out. He said that I can have one if I can repair the other two. Since I need a board for the A axis I am thinking of making a new board. I traced out all the circuitry and most all the parts can be replaced with modern (SMT) components or their equivalent. Is there much interest out there for brush servo cards? I realise most have brushless servos now but my VF-1 is a '90 and I expect to keep it for a while.

Absolutely! Would love to drop a fourth axis on our old VF-1.

moparmuscl · Sep 10, 2016

magno_grail said:
I found a couple boards have labels on the mounting bracket that say "X, Y, Z AXIS ONLY". I am not sure why this would be as all the boards are limited to 20-22 amperes and there is no circuit differences with the other boards without the label.

I just noticed this today on my machine. I was wondering the same thing since they all have the same part number. I need an A \drive board since it was used to replace my burnt Y board. What do you think you would be charging for these boards?

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