ballen
Diamond
- Joined
- Sep 25, 2011
- Location
- Garbsen, Germany
My 1965 FP2 came with a non-functional 3-axis Heidenhain DRO, model VRZ 753B. The control unit displayed 5 on all three axes and was non-responsive. The sealing lips on the scales had disintegrated into a sticky mush, and the insides of the scales were full of dust and grease.
Probably I should throw it out and start over, but I'm not good at that. The system seems to date from the early 1980s and appears to have been professionally installed. The mounting hardware is machined and blued, with fiduciary dowel pins. The wiring is in armored waterproof flexible conduit with gasket-sealed connection boxes. The scale covers are heavy-duty steel with matching gray hammer-tone paint. So rather than trashing it I'm going to try to fix it.
As a first step, I took apart the control unit. The three unregulated DC power supplies, 5, 10 and 20 volts all were working OK, but I changed their electrolytic capacitors because these tend to dry out with time and heat. Cost 5 Euros. The problem turned out to be with the 12 volt regulated output: the three-pin 12 volt regulator (MC7812 in a TO3 package) was defective. I replaced it (cost 3 Euros) adding some Arctic Silver 5 thermally conductive grease to help keep the temperatures down . The regulator is supplying 980 mA of current, and has an 8 volt drop across it. So it is dissipating around 8W of heat and will eventually cook (again) if not cooled properly.
Here is a photo of the old regulator sitting on top of the heat sink, just next to the mounting location (under the black plastic cover).
This fixed the control unit!
Then I turned my attention to the glass scales (all are LS803). I've started with the shortest one (220mm) from Y. I took out the reader head, removed the remains of the rubber lips, and cleaned the scales and the reader head with alcohol. For motivation and to be sure I was on the right track, I reassembled this and tested it with the display: everything works correctly, as far as I can tell. The rubber sealing lips were crimped into place, so now I need to open up the crimping slightly to get the new lip seals into place (I bought 4m of material). I also want to make sure that I clean the read head properly. So here is my first question. What is the best way to clean the read head? Should I, or could I immerse the entire head in cleaning alcohol? Here is an annotated photo:
I am particularly concerned about dust or dirt that has gotten in between the pea lamp and the glass window/reticule. I'm afraid to clean it with compressed air, as that would probably break small wires and throw off the optical alignment. Any suggestions? Or is it not important to clean out this area thoroughly? My goal is to do it well enough that the scales give accurate and correct results, and work reliably for some years to come (this is a home shop, so not heavy use).
Cheers,
Bruce
Probably I should throw it out and start over, but I'm not good at that. The system seems to date from the early 1980s and appears to have been professionally installed. The mounting hardware is machined and blued, with fiduciary dowel pins. The wiring is in armored waterproof flexible conduit with gasket-sealed connection boxes. The scale covers are heavy-duty steel with matching gray hammer-tone paint. So rather than trashing it I'm going to try to fix it.
As a first step, I took apart the control unit. The three unregulated DC power supplies, 5, 10 and 20 volts all were working OK, but I changed their electrolytic capacitors because these tend to dry out with time and heat. Cost 5 Euros. The problem turned out to be with the 12 volt regulated output: the three-pin 12 volt regulator (MC7812 in a TO3 package) was defective. I replaced it (cost 3 Euros) adding some Arctic Silver 5 thermally conductive grease to help keep the temperatures down . The regulator is supplying 980 mA of current, and has an 8 volt drop across it. So it is dissipating around 8W of heat and will eventually cook (again) if not cooled properly.
Here is a photo of the old regulator sitting on top of the heat sink, just next to the mounting location (under the black plastic cover).
This fixed the control unit!
Then I turned my attention to the glass scales (all are LS803). I've started with the shortest one (220mm) from Y. I took out the reader head, removed the remains of the rubber lips, and cleaned the scales and the reader head with alcohol. For motivation and to be sure I was on the right track, I reassembled this and tested it with the display: everything works correctly, as far as I can tell. The rubber sealing lips were crimped into place, so now I need to open up the crimping slightly to get the new lip seals into place (I bought 4m of material). I also want to make sure that I clean the read head properly. So here is my first question. What is the best way to clean the read head? Should I, or could I immerse the entire head in cleaning alcohol? Here is an annotated photo:
I am particularly concerned about dust or dirt that has gotten in between the pea lamp and the glass window/reticule. I'm afraid to clean it with compressed air, as that would probably break small wires and throw off the optical alignment. Any suggestions? Or is it not important to clean out this area thoroughly? My goal is to do it well enough that the scales give accurate and correct results, and work reliably for some years to come (this is a home shop, so not heavy use).
Cheers,
Bruce