Heidenhain VRZ750 problem

My HH VRZ750 DRO is acting up
On the X it displays 0.0.000 at startup
and then it goes to 1.1.025 up to 9.9.995 and them it goes to 0.0.000 again
Anybody had this before and knows how to solve it if possible

It stays on the same X position on the DRO
Swapping scales does not change that



Peter

Do you "reference" on start up?
Try turning the power on (usually a switch on back), then press the "REF" key-the display should freeze and the LED next to that key light up.
Then press "REF" again and see what happens.

Thanks
We will try that tomorrow

Peter

Hi Peter,

So far I have fixed 3 HH displays. In all of them, the problem was the power supply. Normally such problems would affect all three axes, but if the power supply is starting to fail, it might first affect one channel. So in your place I would open it up and check the different voltage rails. You want to make sure they have the correct DC values, and noise and ripple values measured in the tens of millivolts. If you have an oscilliscope and voltmeter, this should not take more than a few minutes.

Cheers,
Bruce

ballen said:

Hi Peter,

So far I have fixed 3 HH displays. In all of them, the problem was the power supply. Normally such problems would affect all three axes, but if the power supply is starting to fail, it might first affect one channel. So in your place I would open it up and check the different voltage rails. You want to make sure they have the correct DC values, and noise and ripple values measured in the tens of millivolts. If you have an oscilliscope and voltmeter, this should not take more than a few minutes.

Click to expand...

For my future reference, what components went bad in the Heidenhain power supplies you fixed ? Often in CNC related power supplies it is weak or bad electrolytic capacitors...I've not yet encountered a bad Heidenhain DRO ps problem...but eventually I probably will.

Hi Don,

Milacron said:

For my future reference, what components went bad in the Heidenhain power supplies you fixed ?

Click to expand...

In two older VRZ models it was burned out 3-pin TO3 voltage regulators. The heat sink grease had dried out after 25 or so years. In the ND model it was electrolytic capacitors in the switching supply. One was bad and one was marginal (I used an ESR meter to check) so I replaced all nine electrolytics with low ESR versions. In all cases I got replacement parts at the Hannover Conrad store, cost in each case was under 2€.

Cheers, Bruce


Sent from my iPhone using Tapatalk

ballen said:

In two older VRZ models it was burned out 3-pin TO3 voltage regulators.

Click to expand...

This style ? Interesting....don't think I've ever found one of those bad...good to know they can be a suspect. Re caps, I have an ESR meter as well....wonderful device for finding suspect caps without removing from board, then remove to confirm.

Hi Don,

Milacron said:

This style?

Click to expand...

Nope, that's a TO-220 package.

A TO-3 looks like the photo below. On HH displays they are normally on the back, mounted to an anodized aluminum heatsink. They are under a black plastic cover for insulation, because the metal package is also one of the active electrical connections.



The T0-3 packages are often rated up to about 200 Celsius, the TO-220 are typically rated to a lower temperature because of the plastic case, which melts. (The "mil-spec" ceramic case TO-220 can support higher temperature.) More important, the TO-3 case has lower thermal resistance. Typical TO-3 devices are 3 Celsius/Watt whereas typical TO-220 are 11 Celsius/Watt.

The main annoyance of the TO-3 is that you have to unsolder it or unplug it to remove it from the heatsink. And because the case functions as one of the leads, you either need an insulated screw making case contact, together with an insulating plastic "washer" and heat-sink grease, or a dedicated heat sink that is electrically isolated. (HH displays use the plastic + heat-sink grease solution.)

The lower thermal resistance of the TO-3 case is good for reliability. Let me illustrate with an example. In the first HH display that I repaired (VRZ 753B) the unregulated supply is 20 VDC, and this is regulated down to 12 VDC with a 7812 regulator in a TO-3 package. The current draw is almost exactly 1 Amp, so the regulator is dissipating 8W = (20 - 12) V x 1 A of power. If it had been in a TO-220 package, this would lead to a temperature drop of 11 x 8 = 88 Celsius. So when operating at room temperature (20 Celsius) the device internally would be operating at 108 Celsius. That's within spec, but too hot for long-term reliability. In a TO-3 package the same power dissipation leads to a temperature drop of 3 x 8 = 24 Celsius and hence an internal operating temperature of 44 Celsius. That is much better for reliability.

(I had a quick look. I could not find MTBF numbers for the 7812, but a similar regulator had a Mean Time Before Failure of 22 million hours when operating at 25C, and 4 million hours when operating at 70C. This drops rapidly with further temperature increase.)

Bottom line is that for a device that is dissipating more than a few Watts of power, the TO-3 is a better choice.

Cheers,
Bruce

Peter, I am curious, did you sort this out? Cheers, Bruce

ballen said:

Hi Peter,

So far I have fixed 3 HH displays. In all of them, the problem was the power supply. Normally such problems would affect all three axes, but if the power supply is starting to fail, it might first affect one channel. So in your place I would open it up and check the different voltage rails. You want to make sure they have the correct DC values, and noise and ripple values measured in the tens of millivolts. If you have an oscilliscope and voltmeter, this should not take more than a few minutes.

Cheers,
Bruce

Click to expand...

Bruce, Do you have the expected voltages from the transformer to the board for a HH VRZ750?
I have a bad transformer, and parts are near to impossible to find, so I will need to get a 3rd party transformer made.
Of course, I need the secondary voltages, and I can't find any data.

Regards

Glenn

hasolutions said:

Do you have the expected voltages from the transformer to the board for a HH VRZ750?

Click to expand...

I don't know. Maybe you can identify the output voltages of the voltage regulators from the part numbers printed on them, and then go back to determine the approximate transformer voltages. Or someone here with a HH VRZ750 can open it up and measure the voltages for you.

I'm surprised that the transformer is burned out. Normally these are extremely reliable.