General > General Technical Chat
Problem with rigol scope knob
wd5gnr:
Well it turns out I didn't have it completely apart last night which is why it looked like something was missing. Unfortunately, it still didn't clean so I'm going to try ONE MORE TIME.
The attached picture is the encoder apart (enhanced to show detail so a little grainy). The green part is the switch. What I had last night was that off but the black body of the encoder remained attached! Duh. You have to get the board lock legs spread apart to get the black part off.
I Q-tipped the encoder wheel (16 pads so I guess its 32 pulses per revolution?) an sprung the contacts a little with a screwdriver.
A few notes about taking the whole thing apart:
1) The white cable is in a ZIF socket. You have to release the two black tabs at either side of it and then it just comes out with no force. If you are pulling the cable you don't have it unlocked. It should just "float" out with no force.
2) The reason I mention this is that getting it back in is HARD. It is very hard for me at least to keep the ZIF lock open on both sides. The best method is to flip the scope upside down or at least tilting down in the right way so that the lock wants to fall down. Then once you get the cable in (should be none of the exposed metal showing) you can flip it back and push the locks down with a small screwdriver.
3) As far as I can tell the power supply bundle of wires has to come off the main board. I don't think the connector on the power supply comes off.
4) If you see an LED "broken" on the front panel board don't panic. Its for the logic analyzer and you don't have it (well, if you do, then panic). Looks like they make all the boards and just pop the unwanted LED off with a pair of dykes or something.
I'm going to try again. I'm getting pretty good at putting it back together.
Correction. I think it must be 24 pulses per rev. There are 3 contacts. So for 1/3 of the rotation any given contact is the common contact, the A contact, and the B contact. So per rev terminal A has 3 contacts brushing 8 pads for 24 pulses per rev. The good thing about this is I have figured out all the stuff I never knew about mechanical encoders.
Mechatrommer:
be carefull not to damage the parts, as the problem might lies outside it, not in the encoder. the device seems easy to clean/repair.. clean the contact pad and push the 3 contacts lever a bit outward, but not too much to avoid misalignment. you must have a way to verify that the signal is something like the pic below (from your EC11.pdf) (ie 3 phase signal). if you have verified the signal is ok, then i think the problem is not the encoder, it must be something else. Happy hacking ;)
wd5gnr:
Yeah I thought the same thing. But I still think it is the encoder based on occam's razor and the fact that it got worse over time until now it is unusable. The last encoder I mentioned from Digikey looks like it should fit ok and the only real difference is it has detents. If it doesn't work than I will have to look at what's reading it. I did think of swapping two of the encoders but decided it wasn't worth the trouble since I have a new on en route. But if the swap caused the problem to stay it would have to be the circuit not the encoder.
Mechatrommer:
if you cannot verify the 3 phase signal, then easier for connectivity test for each pin while rotating the knob.
wd5gnr:
Well it turns out it was both.
When I started out the encoder was "flaky" but you could coax it. Then eventually it got to where it would just "jitter" and just flop around the current position when you turned the knob.
I replace the encoder with Digikey 987-1195-ND. The fit was exact and since I'd had the other one open I knew it had the right number of pulses per rev. However, it has detents so you get a little click as you turn it. Otherwise perfect.
Replacing the encoder made it "flaky" again. You could get it to move but mostly only in one direction and sometimes randomly the other way. I opened it back up and there are two diodes behind each encoder. One of them read open both ways. I don't keep SMD diodes around (I have started keeping a bunch of SMD resistors around) but I managed to remove one off something I am not using. It was a Schottky diode (the one in there was something like a 1N914 I'd guess from measurements of the other ones) but judging what the circuit was doing I didn't think the forward drop was going to matter. Now it works like brand new!
Rigol has offered to send me a new UI board under warranty which is SUPER of them. Haven't got it yet though. I did buy from a US distributor, by the way.
I posted pictures of the tear down.
https://www.eevblog.com/forum/index.php?topic=2092.0
I don't remember if I mentioned in the notes but the only thing holding the back shield on is the jack nuts for the DB9. Be very careful as the metal work is not so good. I have a top shield screw that will no longer tighten, and one of the bottom case screws chewed some plastic and won't go in well either. But the case is a tight fit so you really can't tell. In fact, I've been leaving out the screws under the handles and can't tell the difference. I suppose if you had it bouncing in the back of a truck, maybe. But mine sits quietly on a bench.
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