So I took the ground from the PSU to the shifter, and turned on the machine. The pot now works properly. I haven’t run a job yet, but I feel like that’s a good sign, since it was being really wonky before. The question now is, is it even possible that the ground to the shifter was causing issues?
@K1111 according to @Alex_Krause the level shifter cannot be grounded (although I do not understand why :)).
What is H and L of the power supply connected to?
The L is to the PWM. I had originally said it was the IN, but I now remember that I couldn’t get PWM to work on that pin, despite LightObject saying that was the PWM pin. H is not connected to anything. I cannot get the laser to fire without grounding both sides of the shifter. Also, I spoke to soon. It’s being weird again. The pot is again being squirmy and when I hold the test fire for a second the meter will jump up then back down to where it was set.
@K1111 how is the test fire connected? Try disconnecting the level shifter totally and then see if the pot and test fire works better?
The test fire is going to L & Ground, the Laser Arm button is going from WP to G (that’s also where I’ll put the interlock). I disconnected the shifter totally from the PSU, and I still get wonky behavior. At this point I’m wondering if either the pot or the PSU is messed up.
@K1111 well the smoothie/level shifter is out of the circuit so it can’t be that?
Do you have the right pot?
I had to buy a different pot from the stock 10 turn 1K 2W pot. Here’s what I bought: https://www.amazon.com/gp/product/B0087ZBS92/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1, and here is what they recommended: Power control VR is 5K ~ 10K 1/2Watt at this link: http://www.lightobject.info/viewtopic.php?f=16&t=18
@K1111 LO uses 5K (looked at the PS manual) but according the specs 10K should work. Crappy or worn pots can be noisy. You can take it out and connect it to a meter and watch to see if the resistance is erratic when you turn it… it may or may not show you if its noisy.
It does seem flaky. When I measure it as I;m turning the knob, especially when it gets to the top end it will jump down then back up. I thought I had another one around here somewhere, but I can’t find it, so I just ordered a 5K, 1/2W pot. I guess I didn’t understand the specs. I thought 5K~10K meant a pot in that range.
+Don Kleinschnitz That must have been a bad pot. I found my other 10K pot and it goes up to 10k, whereas the one I have on the machine only measures up to 3.9ish. Question on the better one, as I keep my multimeter probes on the connectors and I spin the knob it occasionally fails to read when there’s a biggish jump from one number to the next. Is that normal?
Well, disregard. I had my machine totally powered down when I tested the old pot, but the pot was still plugged in. When I completely remove it from the PSU, I get the same results as the spare pot. It goes to 10 K, but the readout blanks from time to time as I spin the knob.
@K1111 sometimes poor quality digital meters will pause and read open when the reading is changing. However it sounds like a poor quality pot to me.
Do both pots act the same?
It wouldn’t hurt to get a better quality one that is a 10 turn wire wound pot. Its not obvious to me what else could be wrong. Also make sure that all connections to the supply are tight.
@donkjr Both pots do sound the same. I’ll take a look for a better pot. Thank you for all your help!
@donkjr one more question… when the pot was attached to the powered off PSU why was the upper limit 3.9k, and what would make it jumpy? When it’s disconnected completely it doesn’t jump up and down and it goes to 10k.
if that does not work see you back here :0.
@K1111 I cant tell you because I do not know what the pot is connected to inside the ps, however if there is capacitance in the circuit it can give strange readings.
This is an example of why I want to understand what is inside these supplies:). You probably also should be on the LO forum and tell them of the trouble you are having.
How important is the wattage? I’m having a devil of a time finding a 5k 10 turn wirewound pot that’s also 1/2w.
I just looked at my K40 and it has a 1K 2w. BTW it reads half that when its in the circuit.
I don’t think it has to be 2W (which would be .4A) because according to what I have found so far the pot controls an internal PWM generator in the supply, but again I really do not know exactly what it is hooked to.
This one got moderate reviews (problems with shaft size?).
Here is a 5K version.
This one gives you a vernier dial as well and there is a 10K version.
https://www.amazon.com/gp/product/B01KMAEWZ6/ref=pd_sbs_328_3?ie=UTF8&psc=1&refRID=HRFYE2KV4EY6WVKAB3E2
https://www.amazon.com/gp/product/B01KMAEWZ6/ref=pd_sbs_328_3?ie=UTF8&psc=1&refRID=HRFYE2KV4EY6WVKAB3E2