[SRT Mike]

I have a mid 80's LC-40 with an OSP5000L control. It was working fine on Thursday night and the next morning on startup it alarms as soon as it starts up with "166 Alarm A - Revolution tool SDU". The manual states the issue is with the SDU (spindle drive unit) for the live tooling.

I open the case and the SDU has 3 green and 4 red lights in a row. The 2nd and 3rd green lights are on, and the 2nd, 3rd and 4th red lights are on. The other SDU (for the main spindle) just has the 2nd and 3rd green lights on.

The red lights mean

2nd - OS (overspeed - manual says to check tach brushes)
3rd - PH (phase loss - manual says check for blown fuses)
4th - IOC (instantaneous overcurrent, check DC motor brushes and check SDU-600W unit)


Any ideas?


I have never used the live tooling. Is it possible to bypass the error somehow? I don't use the live tooling so if the SDU for that isn't working I don't care so much. Perhaps there is a parameter to turn off the control's awareness of the live tooling and associated servo and spindle drives?




Also, this lathe has 2 turrets (upper main turret, lower 8-tool turret). I knew the lower turret didn't work, the seller told me he was told it needed a new servo controller. The lower turret would move in X but not in Z - if you tried to move it in Z it would just immediately alarm on the control and the servo driver had some error lights on. I moved it in X when I got it but haven't moved it since (about 2 years).

When I open the cabinet today, I noticed that the error lights were on the XB servo driver as I expected. I also noticed they were on the ZB servo driver - so that is something new, apparently, although I'd never have noticed). There are also lights on the C axis servo drive. First, I can't imagine why the C axis has a servo drive? I'd have thought it would be part of the SDU for the spindle? But the same lights are on for all three of the servo drivers. The only servo drives that seem OK are the XA and ZA (which are the only ones I use).

But it makes me wonder - are these servo drivs (LDU-600) prone to issues? And if so, what causes the failures? I am very handy with electronics so I have no problems testing parts or replacing components on the circuit board - but I don't know where to start. On my old Leadwell mill, the high-power transistors were known to fail over time. I noticed on the SDU there are several small black things with screw terminals on them with wires... looks like high power transistors. Are these the potential culprit? Anyone got any suggestions on getting diagnosing the drives myself?

Thanks!

[Algirdas]

1. IOC can be because of faulty power modules. Check power transistors of drive unit.
2. Spindle drive is different from C axis servo on old type lathe. Spindle drive makes revolutions on high speed, it ensures torque and revolution stability. The sin cos generator is sufficient for feedback. C axis drive ensures movement synchronization and coordinate accuracy, it works with position encoder. Later architecture is different.
3. All drive units has power modules "at the end", they ensure sufficient current to motor. The power transistors are aging, they loose their parameters, it's quite normal issue. The parameter dispersion causes some errors sometimes.

[SRT Mike]

1. IOC can be because of faulty power modules. Check power transistors of drive unit.
2. Spindle drive is different from C axis servo on old type lathe. Spindle drive makes revolutions on high speed, it ensures torque and revolution stability. The sin cos generator is sufficient for feedback. C axis drive ensures movement synchronization and coordinate accuracy, it works with position encoder. Later architecture is different.
3. All drive units has power modules "at the end", they ensure sufficient current to motor. The power transistors are aging, they loose their parameters, it's quite normal issue. The parameter dispersion causes some errors sometimes.

Thanks for the information. Do you know how to check the power transistors? I have plenty of testing equipment, just not sure what I am checking for.

Are the power transistors still available? Or is there an upgrade parts available?

Thanks!

[Algirdas]

how to check the power transistors?
the diagram is on the body. It's tandem npn with protective diode as usual
I have plenty of testing equipment, just not sure what I am checking for
it's very good if You check beta. Sometimes I don't find any glue and inverter doesn't works after my check. Beta factor could be guilty at that case.
Are the power transistors still available?
Sure yes. They are very popular. Used for acoustic amplifiers and so on. There is "eupec" company, they produce new power amplifiers according manufacturer's specification. The best solution if You can wait a couple of weeks. Best quality for lowest price. These original also are available as replacement parts from various suppliers.

[SRT Mike]

how to check the power transistors?
the diagram is on the body. It's tandem npn with protective diode as usual
I have plenty of testing equipment, just not sure what I am checking for
it's very good if You check beta. Sometimes I don't find any glue and inverter doesn't works after my check. Beta factor could be guilty at that case.
Are the power transistors still available?
Sure yes. They are very popular. Used for acoustic amplifiers and so on. There is "eupec" company, they produce new power amplifiers according manufacturer's specification. The best solution if You can wait a couple of weeks. Best quality for lowest price. These original also are available as replacement parts from various suppliers.

Thanks for the information. Are you an Okuma service engineer? Have you seen a lot of problems with the SDU-600 boards, and is it usually the power transistors?

I had a little time to play with it this evening... I checked many of the components on the top card - the relays, TVS's, diodes. I also checked the test points on the board to ensure the power is what it should be on those places, and everything looks OK... so it appears all the switches and power regulation circuits are OK. I just though I would test the easy part first. I also tested the main power at the transformer, I was getting 200V on all six legs, which is seems should be correct (it is listed as a 200/220V transformer)

So then I looked at the power transistors, there are two kinds.

Two of TM20RA-20 and six of TM55DZ-20. I wasn't able to find the exact part numbers yet but it seems that these transistors cost $100-200 each! Wow! They are expensive! I was thinking I could just change them all to be sure, but at that price, I better test them all out first.

I can easily test them to their schematic on the side... I can test the beta on them also, but I will have to make some kind of little testing unit to do that.

In the meantime, I noticed there was a jumper on the board marked "Alarm reset", so I shorted it and the alarm disappeared. The alarm re-appeared immediately when I turned off the power and on again. So I shorted this jumped again to clear the alarm, then I turned on the control... and it booted up OK, and I can move the XA and ZA axes! So at least I can use the machine for now, even if it is limping


The good news is that the only axes I use are XA and ZA (and the spindle). These are all working OK. The bad news is that the XB, ZB and C axes drives (LDU-600) all show the alarm codes. I noticed there is the same transistors on these axes as well.

When I got the machine about 2 years ago, the ZB was not working. Now XB is not working also. C is not working, but I don't know how long it was like this. The circuit boards are marked from year 1984... so they are more than 25 years old now. So maybe the transistors just start to fail after a time?

Maybe with a little hard work I can fix all the axes and get the whole machine running like new

[Algirdas]

Are you an Okuma service engineer?
a little, yes. Okuma is my favorite
Have you seen a lot of problems with the SDU-600 boards, and is it usually the power transistors?
I don't remember any SDU-600, but not a big difference. All Okuma's drive units from the same age are very similar. Power modules is the first. Okuma provides diagnostic information for power modules even on user manuals sometimes. Contacts is second.
I would test the easy part first
Absolutely yes. The unit was in perfect working condition some time ago, so it can't be complicated.
Two of TM20RA-20
must be for braking only. You can leave them for now.
I wasn't able to find the exact part numbers yet but it seems that these transistors cost $100-200 each!
Sure, if You ask on Farnell or some similar supplier. Ask from eupec and change them all.
Six double are by two for three electrical phases. You can also find some cheaper HongKong or Taiwan based supplier, and it's worth to order from them also. Instant dispatch, good price. The last time I did ordered three pieces from China it costs €50 each.
"Alarm reset"
check big capacitors of power unit. It's good to replace them all - on drive unit also. If alarm reset is enough to start the machine, the power supply problem is most likely.
maybe the transistors just start to fail after a time?
wet capacitors from that age are most likely.
Maybe with a little hard work
and some €3000 expenses