Thread: Heidenhain DRO VRZ 753 B dont react when moving axes

Hi

I have bought the Swedish machine Mattson & Zetterlund VF600

The DRO Heidenhain VRZ753 B dont react when moving axes

I have tried to clean one of the scales but dident help

Any idea whhats the problem is ?

Johan

The most likely source of problems in these systems is the power supply. Does the DRO react when (for example) you type in values and transfer them to X/Y/Z? If so, it's probably not the power supplies.


Next thing: check that the lamps are working in the three scales. In a very dark room, carefully pry open the sealing lips and see if there is a dim orange glow coming from the read head. The bulbs are 12V ones but operated at 5V to give them a long lifetime and produce mostly infra-red radiation.

Also, move the memofix switch to the green position for now, otherwise it might generate some apparently strange behavior.

Thanks Ballen

Yes I can whrite in values . The DRO seems to work fine exept nothing happens when mowing the axis

I will try your other advices later . Thanks !!

Originally Posted by Johan.A

Yes I can write in values . The DRO seems to work fine except nothing happens when mowing the axis

OK, if the DRO is responsive then the power supplies are almost certainly OK.

Next step: check that the small light bulbs inside the read heads are not burned out. What model are the scales? Are they Heidenhain LS803?

All three scales with dead bulbs?
That would be some bad luck

perhaps some settings in the DRO are off, see if you can track down the manual, Heidenhain website may have it and see if there might be settings that might make it not read.

Also be aware that scales "could" have LED light sources.....Those will not be visible to your eye.
Cheers Ross

Yes it is LS803 scales

I tried to see any light from the scales in a dark garage .

No light what I coul see

I do have the manual but havent find anything there yet

Check that you have the correct voltage for the lamps at the box...LS 803 pins 3 and 4 at the connectors should be 5v +- 5%.
Cheers Ross

Here is a diagram showing the internal functioning of the LS803 read head (it also applies to the LS803D, LS903 and LS903D).



You can do the following checks with a 15 Euro multimeter that measures DC volts, ohms, and has a diode-check function (displays the forward voltage across the junction).

(1) Disconnect the scale from the DRO

(2) With a voltmeter, on the DRO side, check that you have 5 volts DC across pins 3 and 4. This is the power for the lamp.

(3) With an ohmmeter, check that the scale has around 50 ohms of resistance across pins 3 and 4. This checks that the lamp is not burned out.

(4) With the diode test function, check that pins 1 and 2 show about 0.6 volts with EITHER orientation of the red/black leads, meaning first connect red to 1 and black to 2 and then connect red to 2 and black to 1. This checks the photodiodes for the first quadrature.

(5) With the diode test function, check that pins 5 and 6 show about 0.6 volts with EITHER orientation of the red/black leads. This checks the photodiodes for the second quadrature.

(6) With the diode test function, check that pins 7 and 8 show about 0.6 volts with EITHER orientation of the red/black leads. This checks the photodiodes for the reference mark.

Thanks for all help

A friend comes with measuring equipment and helps me checking the electrical some day

Johan

Don't think i would bother testing the scales at this point....Resistance ,diode test etc....
Highly unlikely that all three scales have failed...
Might not have the supply voltage to the lamps (problem in the box) believe that is a common element to all three axis.......
Cheers Ross

Hi Ross,

As I recall, the 5V supply for the scale lamps is the same 5V supply used by the TTL logic in the DRO. If it had failed, the DRO would not respond to keyboard input, which uses TTL logic. But now that I think about it, the Heidenhain engineers probably would have wanted to protect that 5V supply against any monkey business from the users on the outside. So there might be an internal fuse or sacrificial resistor which protects that supply.

So, if there is no power at DRO pins 3/4, open up the scale and trace that power source back. You will probably find an internal fuse or a burned resistor along the path.

I agree it is unlikely that all three scales have failed in the same way. But it just takes a few seconds with a multimeter to check them, and requires no disassembly or invasive effort. I could imagine a production scenario where the machine was under power for 40 years and eventually the bulbs burned out in all three of the scales.

Cheers,
Bruce

We have measuerd in the connectors and they were dead

The problem seems to be in the box . We cant see anything wrong.

Does anyone have an electrical diagram to this DRO ?

Johan

Just a thought
Do the scales have reference points And do these reference points need to be passedfirst by the readerhead to get any reaction ??

Peter

Originally Posted by Peter from Holland

Do the scales have reference points? And do these reference points need to be passed first by the reader head to get any reaction ??

The LS803 scales do have reference points, 35mm from each end. However they are ignored by the DRO if the "memofix" switch is in the green position. Even if it is in the red position, the DRO will count until the reference point is crossed the first time. Only then will it stop counting. So that's not the problem here.

Originally Posted by Johan.A

We have measured in the connectors and they were dead. The problem seems to be in the box . We cant see anything wrong. Does anyone have an electrical diagram to this DRO?

The bad news: I have never found a circuit diagram for the VRZ-753B. If you find one, please share it.

The good news: this is easy to fix. First check that the on-board 5V supply is working correctly. As I recall there is +5V and +12V. These are easy to spot, three terminal regulators. I am moderately sure that these are OK on your DRO, since the logic board uses 5V and works correctly. Second, trace back the connections from pins 3 and 4 of the scale connector. They are the brown and the white wires. One wire will go to ground. The other wire will go to the 5V supply. Either there is a fuse in series there (burned out) or a resistor in series there (burned out). Or perhaps there is a second 5V supply just for these bulbs, in which case it will probably be a type 7805 3-terminal regulator, which you can replace for pocket change.

PS: here is my thread on this topic: https://www.practicalmachinist.com/v...-scales-284063

I will try contact Heidenhain in Sweden on Monday and ask for a diagram

Good that you think its easy fix .

Originally Posted by Johan.A

I will try contact Heidenhain in Sweden on Monday and ask for a diagram. Good that you think it's easy to fix.

I hope you succeed! Over the years, many people here have tried to get circuit diagrams from Heidenhain and have been told "no".

Anyway, you can easily fix this without a circuit diagram. Just trace back the brown/white wires. One will go to the large ground plane, the other to the power source for the bulbs. I am sure that what is wrong will be quite obvious and easy to fix. Just use a voltmeter to understand why the voltage source is not reaching those wires. You can probably figure it out without even connecting the DRO to power, by tracing the connections and using an ohmmeter to find where continuity is lost.

Hi

I have talked to Heidenhain in Sweden and they dont have acircuit diagram on my DRO he said

They dont even repair DROs this old .

I also got an e-mail answer from them ,
were they tell me they dont give away circuit diagram at all


We found broken components that we missed when we first looked .

Johan

One of the 2200uf is broken.

We shange all three