Proud of myself

I have an old Heidenhain VRZ 731 2 axis DRO on my BP and the x axis
stopped working. So after determining that it was a sensor assembly
malfunction by switching the x and y sensors into the readout, I
proceed to open the assembly. The etched glass scale is intact so I
explore the actual sensor. It has some photo-cells a lens/collimator and
( I assume) some form of creating a light beam. I find Heidenhain's
website, and luckily a PDF of the manual for my unit. The only thing of
value in the manual is a pinout, a description of what voltages are to
be found on what pins. 2 of the pins are labeled lamp and carry a 5v DC
at 120 milliamps. So now I trace the circuitry and find a direct
connection to what looks like a grain of wheat incandescent lamp
positioned in a subframe assembly. I rule out a LED, because of the 5v
at 120 mA and no current limiting resistor in the circuit. So I start
making calls and finally get the Heidenhain tech in NY. I ask him if he
can repair my sensor. He says it's too old, not supported and I might be
well served with a newer model for $ 600.00 . I ask him if he knows what
the light is on my unit, he says it's a very special lamp, I ask him " a
5v grain of wheat microlamp?" He says it's a very special lamp and no,
they don't have a replacement, and I should buy the new sensor for 600$.
I thank him and hang up. So I find a 5v grain of wheat lamp in my local
electronics supply house, take apart the sub-assembly, remove the old
lamp taking care to measure where the original filaments where placed,
and superglue in my new lamp in the same position. A little bit of
soldering and pronto I power up the sensor, adjust the collimator so the
beam of light is perfectly centered on the photocells, replace the unit
into the scale and my x axis now works. A very special lamp indeed!
cheers
T.Alan
Reply to
T.Alan Kraus
Loading thread data ...
GOOD ON YA, Alan. I'm always glad to hear of someone actually FIXING something rather than replacing..... Ken.
Reply to
Ken Sterling
That superglue could cause a problem in 30 or 40 years when this bulb burns out.
Reply to
wwsjr
Outstanding, Alan. It wasn't as involved as your repair, but I fumed at paying GM 80 something dollars for an idler pulley on son's Olds. Bearing was shot. Chucked it up in the lathe, removed the extruded plastic retainer, put in a high temp bearing from the local motor shop. Resealed it with epoxy. $11.00 total outlay and my worlthless labor. And I was just as proud of it as you are your intricate repair.
Garrett Fulton
Reply to
gfulton
Great job T.Alan.
I will proceed with my repairs of a dead sensor.
Same type as yours, for a three axis Sargon DRO. I purchased it with a dead Y axis but figured I could swap the good Z sensor over to the Y rail and have at least a two axis DRO. This I have done.
I see all the components, just as you describe.
Now, I would appreciate some ID or more descriptive info on this "Grain of Wheat" lamp. Something I can speak when this plumber walks into the elex parts store. (I have done electronic repairs before but never anything on the Micro-Miniature scale.)
BTW. I discovered a trick for getting the encoder sensor back into the rail and on the glass rod. A popsicle stick shoved into the tail end of the sensor carriage. Then, once the carriage is started squarely on the rod, I pull the stick out and use it to put the sensor the rest of the way in.
Appreciate any info you want to share about this component number.
Thanks.
Steve
Reply to
Steve
Nothing is more satisfying than fixing that which ' can't ' be fixed!
-Dave
Reply to
spamTHISbrp
I got mine from a place that has bins of stuff, some well labeled some not. This lamp came from one that was labeled 5v / 60mA. I found the same in the Mouser catalog (800 346-6873) listed as a type 6833 (catalog # 606-CM6833).
cheers T.Alan
Steve wrote:
Reply to
T.Alan Kraus
Those bulbs are sometimes used in model kits (cars, planes, etc..), try checking with a local hobby shop.
Reply to
reply
Well done! May the arrogant tech be soon replaced with a newer model!
Reply to
Don Foreman
A grain of wheat bulb is a tiny glass capsule which (once) had a filament in it. It is probably blackened inside the glass from the vaporized Tungsten. It will have two tiny copper wires coming out of it. When I say tiny, I mean something like .1" diameter and maybe .3" long at the most.
I would replace these with an infrared LED and a series resistor calculated to draw the proper current for the LED. You may not even need to run full rated current on modern IR LEDs, as they produce so much output. The LED won't burn out again.
Jon
Reply to
Jon Elson
I'll bet you could have used a white LED and dropping resistor. It would use less current than the grain of wheat lamp and last forever.
T.Alan Kraus wrote:
Reply to
Mike Berger
With a cheap Chinese clone of a Polski farmer?
Nick
Reply to
Nick Müller
"T.Alan Kraus" wrote > -Snip-
making calls and finally get the Heidenhain tech in NY. I ask him if he
You should have bought two lamps. One to send to the techie with a note to place it where the sun don't shine. Very special lamp. Good job. Tom
Reply to
Tom Wait
According to T.Alan Kraus :
[ ... ]
I suspect that you could put a white-light LED into it just as well. Add a limiting resistor and you now draw less current, and have a light source which will not be subjet to failure when operated in the presence of vibration. (You may need to adjust the current through the LED to get the right level of illumination to minimize errors.) The real question is whether you have room for that resistor.
It would probably work well with a red LED for that matter. I suspect that they were running a 6V grain-of-wheat lamp at 5V to get longer life from it, so it would be a bit redder than usual.
:-)
Of *course* it is very special. *He* doesn't even know where to get one, so it *must* be special. :-)
Congratulations, DoN.
Reply to
DoN. Nichols
There are things which really CAN'T be fixed, or it makes no sense to fix. This was a case of the manufacturer DIDN'T WANT him to fix it. They sell a lot of new scales and complete new DROs that way. And, the average shop owner has no way to dig into something like a DRO scale and know what is wrong.
Jon
Reply to
Jon Elson
No, most likely not. Most of these old DRO scales used Silicon photodiodes which are mostly IR sensitive. The white LEDs put out NO IR at all, and the sensors would be nearly blind to that light. Most of the DRO scales went to IR LEDs as soon as they came on the market, with no changes to the rest of the sensing head. Most optical scales still use IR light sources today.
Jon
Reply to
Jon Elson
Ok, an IR LED then!
J>
Reply to
Mike Berger
Thanks, another good fact to stash in my noggin. Now if I could only find the space... :)
cheers T.Alan
Reply to
T.Alan Kraus

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.