Help With G0768

S

Superjet

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Oct 25, 2021
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Hi Everyone,

I have a G0768 that I bought used that will not get up to speed in the high speed pulley selection. It spins up to 1000 RPM in the low speed selection, but won't go above 70 RPM in the hi-speed pulley selection. I was thinking it was the speed controller as I found a loose ground wire, but after fixing that, it still passed the lightbulb test. I also powered the motor with a 12V car battery and it passed that test as well. The motor does seem to spin faster in the forward direction compared to reverse.

Anyone have any ideas? I'm stumped.

https://imgur.com/HkMSiUn
https://imgur.com/sMBICfo
 
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What does Grizzly tech support say?
 
You should be seeing a distinct lack of torque as well- have you tried to cut any material? The speed control may be failing
Check out www.olduhfguy.com
-Mark
edit: the web address is uhfguy not vhfguy
 
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Yes, because the speed control should have torque compensation over a wide speed range- something is wrong there
Couple things: The machine is used; is it possible the previous owner tweaked some or all of the adjustments on the speed control board?
Also, did he mention replacing any electrical parts like the direction switch?
-M
By the way, be careful with dangling the speed pot out like that- the terminals are at line voltage potential and could cause sparks or a shock
Put some tape on it at least for safety
 
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markba633csi said:
Yes, because the speed control should have torque compensation over a wide speed range- something is wrong there
Couple things: The machine is used; is it possible the previous owner tweaked some or all of the adjustments on the speed control board?
Also, did he mention replacing any electrical parts like the direction switch?
-M
By the way, be careful with dangling the speed pot out like that- the terminals are at line voltage potential and could cause sparks or a shock
Put some tape on it at least for safety
Click to expand...

Thanks Mark,

I don't think the PO tweaked anything, but can't be sure. The machine was sold to me incomplete (missing change gears, BELTS, and some other bits). The motor spun freely with no load on it, so I figured everything was good to go. I later discovered that Grizzly sold this at a local auction when they were in PA as a damaged/incomplete unit, so it's most likely a basket case. I bought it in haste, lesson learned.
 
Well, the worst case you would need to replace the speed control but maybe not if Pete (olduhfguy) can fix it
-M
 
If you don’t have the manual for your G0768 you can find it at:
https://cdn2.grizzly.com/manuals/g0768_m.pdf
The PDF file image is corrupted with bits and pieces of a manual for one of their mills but don’t let that discourage you.
On page 90 you’ll find a schematic and on the pages that follow you’ll find images of virtually everything in the speed control and, if you look closely, you’ll see the markings on the potentiometer in figure 156 (front panel) disagrees with the pot shown in the schematic on page 90 (WX14-12 4K7 +/- 5% vs WX14-12 1k7+/- 5%). In your place I would compare that data with what’s actually in the machine, remove that part and check it with a volt ohm meter to see how linear it is throughout its range of motion.
https://www.bing.com/videos/search?...1B152F78F3D05E5DC1FD1B152F78F3D05E5&FORM=VIRE
Another option, but a bit more expensive, might be to purchase an electronic speed control and install it in place of the control on your lathe so isolate the problem. https://www.grizzly.com/products/grizzly-electronic-speed-control/t32007
At least you’ll have isolated the problem to a specific part of the lathe’s circuitry.
 
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