| Electronics > Repair |
| Rigol MSO5074 Knob Repair |
| (1/1) |
| Russ_A:
I was working on a project using my Rigol MSO5074, which I’d fully unlocked thanks to the EEVBlog Forums, and hooked up my current probe to channel 4. It wouldn’t let me adjust the vertical scale on that channel using the knob. I could do it via the touchscreen only. So after some Googling and not finding anything I decided to run the panel button test mode, and lo and behold that knob wasn’t working at all. So I got to work taking it apart to get at the panel and hopefully find something obviously wrong. The scope is very easy to take apart and put back together because, like marriage, every screw is the same. Once I got to the button PCB it was obvious what had happened. Best I can figure is that some time in the past six months or so I had banged that knob from the side and half torn it off the PCB. Perhaps manufacturers could take note that through-hole components are far more robust than surface mount, especially for knobs and dials. Anyway I had torn three solder pads right off. I got to work doing the shittiest solder job possible to get them reattached but that didn’t work. Since the pads had been torn off there no longer was connection to the proper traces and vias. I was able to easily bypass one of the connections because I could see where the trace went. But that didn’t work either. That’s when I discovered that one of the pads ripped off probably connected with a via and no amount of mucking about with flux and solder could make a connection. I grabbed some jumper wires I had sitting around and, being the idiot that I am, connected them backwards. Cue the magic smoke as one of the wires overheated and melted its insulation. Good news though as after hooking it up correctly it still worked! Phew! So I got to work probing the other knobs to see where they connected to on the board. I started probing around on the board, using the other knobs to see where pins were likely connected on the board. I discovered that my bad pin was probably connected to the controller chip. Now I just had to find out which pin. I took a test lead and used a resistor lead to fasten a thin poker. With the oscilloscope powered on and in the key test mode I got to poking. Every now and then I’d poke the wrong spot and the display would go blank but it’d reboot fine. The key with this is that you have to poke each pin on the chip without shorting it to its neighbor, which is pretty hard. I did see a spark once because of this, but again, a reboot worked fine and all the other buttons tested ok. I must have run through the button test ten times. Eventually I found the right pin! And even better I found that it connected to a nearby test point. I soldered a wire onto it, threw some hot snot in there for support and did more shitty soldering. [ Specified attachment is not available ] PS, I expect I'll have to edit this post a few times to get the images working as I really don't know how to work around the bugs yet and there's no working preview. |
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