Need Help!- Dead WestAmp Servo Drive - Mid-job, need urget help!

[John3]

Hi All,

Have a WestAmp Servo Board that has two dead H-Bridge output transistors (top and bottom on the same side). They gave up the ghost in the middle of an urgent job I must finish quickly.

One transistor is Open and the other is Shorted. The other components (series diodes & Snubber parts) in the circuit test okay (except a 47ohm resistor which I can replace)

I think my quickest way to get back up and running, possibly this weekend, is to replace the transistors, but I'm not sure what they are and I don't have a schematic. I have a pretty good stock of transistors at my disposal.

Any help in identifying the parts, or diagrams or whatever, would be greatly appreciated.

The particulars are:

Full unit - six axis
Serial # B535
Model # A7216-17F-307
Buss Voltage 170 VDC measured

Axis Drive Modules: 33026-5 SN: 1724S

PC Board: ASSY 33010-1 AW33008 REV C

H-Bridge Transistors: Q501 - Q504
Labeled 29065 - 240 TO-3 case

A picture of the board is attached.

Judging from board layout, associated components and audible PWM frequency, I'm thinking that these are NPN Darlington Power Devices....

TIA,

John

[Al_The_Man]

The info I have is for Motorola Darlington MJ11032 Q1~Q4.
I usually end up replacing the whole drives with A-M-C Servo amps.
Al.

[John3]

Al,

Thanks for the suggestions!

My transistors might be a little beefier than the MJ11032's you mention. My Power Supply buss is +170VDC and the MJ11032 seem to be rated for only 120Vce.

But the information is helpful. I guess if Westamp used Darlingtons in other versions there's a good chance mine are too.

Do you by chance have any schematics for these animals?

What are the A-M-C boards you mention?

As always, thanks a ton!

John

[Al_The_Man]

I have the instruction manual which has a schematic, although not in complete form, parts of it show just a conceptual block.
They do show four NPN Darlington's, however.
The boards look identical to your pic.
The drives I have used can be seen at http://www.a-m-c.com/
Al.

[Al_The_Man]

Originally Posted by John3 My transistors might be a little beefier than the MJ11032's you mention. My Power Supply buss is +170VDC and the MJ11032 seem to be rated for only 120Vce.

In an H bridge configuration, would any one transistor be subjected to the full buss voltage though?
Al.

[John3]

Originally Posted by Al_The_Man In an H bridge configuration, would any one transistor be subjected to the full buss voltage though? Al.

I would say sure, all the time, its how they work.

For instance looking at one side of an H-bridge, there are two switching transistors in series across the full bus voltage. When the top transistor is on, the bottom one sees full buss voltage across it, and when the bottom transistor is on the top one sees full voltage across it.

When you start considering dynamic braking, the voltages even go higher than the nominal buss voltage, and the buss voltage itself can rise.

John