Rotary encoders in Lecroy WavePro 7000A series

[dufflespank]

Some of the encoders are unreliable in my LeCroy WavePro 7300A, and was wondering if anyone knows which encoders are used in the front panel assembly?

I actually pulled the whole thing apart to see if I could get some part numbers off the encoders.  Unfortunately, no part numbers to be found, but I did take a number of measurements, which I think most closely match Bourns PEC16 series. 

Any idea if these are the right ones?

I'm also going to try popping the encoders apart and cleaning/lubing with deoxit before going through the trouble of desoldering and replacing. 

Thanks!!!

[DaJMasta]

Just keep spinning!


In all seriousness, I've worked on two WP7k scopes with encoder issues - where a turn in one direction makes a seemingly random number of steps in either direction or doesn't register at all - and the fix every time was just using them a lot.  A couple minutes spinning a knob back and fourth will usually get it coming good.  I assume that means deoxit or similar contact cleaner will likely do as well, but unnecessary if you've got the time to spin them.

There's a thread with a fair bit of info on this series of scopes, so there may actually be replacements found as well.

[klausES]

...I'm also going to try popping the encoders apart and cleaning/lubing with deoxit before going through the trouble of desoldering and replacing...

Then slightly increase the spring tension of the grinders again, then they should deliver clean signals again.

[nctnico]

I just replaced all of the encoders in my 7300A. It had several knobs which didn't work well. Read to the end before ordering though!

Replacing the encoders is fairly easy. With some Chemtronics Soderwick the pins are extremely easy to desolder. The holes aren't plated! I'm a bit dissapointed though that the board is hanging from the encoders (with their single layer pads) and isn't screwed onto the chassis directly. Also the board hasn't been plated using either tin or gold which leaves the vias as bare (exposed) copper. There is even one trace which sits in a place where the board touches the chassis. There is a bit of polyimide tape over it. I can't say this board has been designed with care.

Without detent:
https://uk.rs-online.com/web/p/mechanical-rotary-encoders/2651723

With detent:
https://uk.rs-online.com/web/p/mechanical-rotary-encoders/2651739

These seem to be the original parts. However, replacing the encoders didn't solve my problem at all. After taking the encoder board out again and some probing with the power on it turned out some of the signals didn't go through to the scan lines (the front panel is a typical X/Y scanned matrix). So I checked all the diodes using a DMM and much to my surprise it turned out about 10 of the diodes had failed open.  I don't think I've seen this failure before. The diodes are market COT but I have no idea about the specs but the scan frequency isn't so high that the speed of a diode is going to matter. Based on the forward voltage of the working diodes I assume the diodes are Schottkys and I replaced the faulty ones with BAT54C because I had the most of those (BAT54 and BAT54S will also work).

After this the knobs seem to be working again. I'm still puzzled what the failure mode is. In most cases a diode fails as a short. My unit has been in a moist place; could it be the diodes rusted on the inside??

[Elasia]

High humidity will cause water to invade most thermoplastics over time, the biggest discussion around them these days is usually 3d printed material

You could have anything from internal shorting to parts getting popd from steam release, same reason you see notices to bake certain chips if they have been exposed to too much humidity because when you go to solder them they can just explode instead due to high heat

There is usually a notice on the spec sheet of sensitive parts

A good conformal coating will usually deal with humidity for anything that needs left in moist places for long periods of time.  Some people also leave certain equipment running so they stay heated to keep it out as well

Now was it the humidity specifically? Hard to say but certainly didnt help your cause

[hpw]

I have also some issues on the 8600A timing encoder, just jumps forward and backwards not to forget to clean the surrounding dust

So IMHO it looks like a decoder issue as some golden parts are with dust or oxide ..

So order now as mention on RS, as on mouser obsolete..

 

[maxwell3e10]

To owners of Wavepro 7300A: I am wondering if you could do a simple test for me on how fast the scope can average data. It looks like an inexpensive high-bandwidth scope with switchable 50 Ohm/1 MOhm inputs that I would like to get, but this is a crucial parameter.

To test the speed of averaging just use a 1 Hz sine wave as an input, a short time base, minimum number of waveform points and auto trigger. Then switch acquisition to averaging mode and keep increasing the number of averages until the amplitude of the 1 Hz waveform oscillating on the screen reduces by 1/2 (the waveform appears as just a straight line going up and down).

This is for continuous averaging mode. For stopped averaging mode (not sure if it has one), can just time how many samples can be averaged in 1 sec.