advice choosing servo amplifiers. Brushed DC motors, +-10V signal input

Or maybe there is a chance to repair the drive that I have.

There are two resistors on the top circuit board which look as though they have been hot. They are labeled 5W 2.5k Ohm but when I measure them I get 3.15 kOhm and 2.08 kOhm, could this be the problem?

I've attached a couple of photos. One of the legs on the transistor mounted behind them also looks suspicious.

Measuring resistances of installed components can be tricky, because readings from surrounding items will screw up your readings. If you had reading even remotely close on a resistor like that they are likely ok. Resistors usually die by going open. But you should probably re-flow those solder joints, and any others that look like they may have gotten hot.

Tom_R2E3 wrote: Hi Jon, thanks for the info and suggestions. I didn't realise it would be such an expensive exercise to replace the drives. For something with 35-40A rating i'm looking at £800+ for the three, probably more like £1000

There are some old NC400 drives listed on ebay with varying prices, maybe that's a better option for this machine. Don't want to spend too much at the moment, because I plan to upgrade to a better machine when I can.

Thanks, Tom

I would NEVER use the NC400's due to the HORRID whine. I go to great lengths to protect my ears from damage.

There is an outfit that makes drop-in replacements for later model Bridgeport servo amps. Unfortunately, I am not going in to work much right now, and can't access the company name. They very well might have a replacement for your servo amps, too.

Otherwise, you can browse eBay and look for AMC and similar servo amps. They still have all their old manuals online, so you can look up the specs and wiring info for those models. Yes, high-power servo amps are expensive.

Jon

Tom_R2E3 wrote: Or maybe there is a chance to repair the drive that I have.

There are two resistors on the top circuit board which look as though they have been hot. They are labeled 5W 2.5k Ohm but when I measure them I get 3.15 kOhm and 2.08 kOhm, could this be the problem?

I've attached a couple of photos. One of the legs on the transistor mounted behind them also looks suspicious.

You might resolder the leads on these resistors, sometimes after long periods of running hot, the solder "crystallizes" and you get bad contacts. But, those resistors don't look like they got hot enough to go bad. Most likely one of the power transistors failed. And, that may have taken other parts with it.

Jon

I have to agree with Todd and Jon, the first order of business is to resolder all those joints, they look tired.
And those drives look nice in the sense that i would still be able to fix them despite diminishing eye sight !

Todd Zuercher wrote: Measuring resistances of installed components can be tricky, because readings from surrounding items will screw up your readings. If you had reading even remotely close on a resistor like that they are likely ok. Resistors usually die by going open. But you should probably re-flow those solder joints, and any others that look like they may have gotten hot.

I've just been comparing it to the X axis drive (which still works) and the working drive looks much worse. When I measure those resistors they measure 1.5kOhm.

Jon, it's the power rating which surprises me. It's only a series 1 Bridgeport but 40A seems bigger than most of the drives I've looked at so far. Is it because the motors are old and inefficient? There are loads of Amps in the range of 15A constant and 25A peak.