EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: Specmaster on February 08, 2017, 01:36:58 pm
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Hi all,
As some of you may be aware, I have been asking questions about various scopes and I thank each and everyone of you for your kind assistance so far but yesterday I made a purchase (from eBay) and got myself a rather sorry looking Iwatsu SS5710 that was advertised as needing calibration, for £40. I made the purchase because it is a 4 channel device, 60Mhz (a sizable jump from 25Mhz), working, cheap and from a top notch maker as well, so worth a punt I thought.
I collected it and got it back to my lab and set about cleaning and sorting out the obvious faults like the handle nearly falling off etc.
Powered it up and after learning how to drive it (a bit more advanced then my basic scope) it seems that it does need a few settings tweaked but before that all the switches and controls need thorough cleaning as they shows signs of being very dirty and may well cure the small errors once done.
The circuit boards at the top all seem to be covered in a sticky layer, is it safe to leave the PCB's situ and give them a little brushing with some alcohol? Leaving it on will add to any overheating issues although none have so far been noticed.
The power led is not working and I'll be investigating this shortly but by far the worst thing I have noticed is that the timebase variable control which part of a 3 control system seems to be ever so slightly bent. If the control is clicked into the CAL position, no problems, move it out of the clicked position then rotating the B time control also rotates the variable as well. I was wondering if anyone has successfully cured a similar problem without having to replace the complete assembly which I doubt is available now?
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Carefully bend the shaft. I had a 100 MHz version with dual time base and built in DMM. I really liked that scope, but the HV transformer started to leak and I did not know how to fix it so I sold it.
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I did try bending the shaft, but it is not a visible bend so I'm unsure if I'm making it better or worse really. If it had a visible bend, I'd know which direction to go in. Just wondering if it could be dust in the shaft, it was in a sorry state when I collected it. Thinking about standing it on its feet and squirting some WD40 down the shaft and giving it a few twists at the same time. Just a bit worried about getting WD40 inside the pot though?
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Don't use WD-40. Use a good contact cleaner on all the knobs and switches. You might want to remove the case (very easy to do) and get at the works from the back with a spray contact cleaner. I would opt for IPA (rubbing alcohol, isoprophyl alcohol) before WD-40. Work the knobs and switches as you spray them to help dislodge any dirt, then wait for it all to completely dry before introducing power.
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I'd just use IPA and stay far away from contact cleaners. They contain acid which eat away the rest of the contacts and the wiring wicks the cleaner anywhere it shouldn't go making things way worse in the long run. Contact cleaner is great to make equipment work for a couple of days before replacing it. A contact consists of a base metal and a contact layer. Once the contact layer has worn off the only real solution is to replace it.
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I have already removed the covers yesterday when I gave it the close scrutiny looking for any tell tale signs of leaking caps etc and could find nothing. Considering there are no slots / holes on the top cover I was surprised that all the PCB's mounted on the top of the chassis on the right, trig and the amp stages for all 4 channels are covered in a sticky substance. Was wondering if it was safe to gently brush this away with a soft paint brush dipped in isoprophyl alcohol and left to dry would A/ remove this substance and B/ help to prevent thermal issues in the future by allowing things to dissipate heat more efficiently?
Further investigation showed that the pot on the time base switch is some distance from the front panel and that the centre spindle for that pot only appears to run through the centre of the A and B time base shafts/tubes for a short distance so I have applied a little 3 in 1 oil to the tip of the shaft and worked it into the tubes. Time will tell if it helps, but there is virtually zero chance of the oil gaining entry to any pot as a result.
It is now airing to make sure that there is switch cleaner remaining to cause problems before switching it on and testing.
I've removed the front control plate for cleaning behind the control knobs and that along with the knobs will be cleaned before replacing.
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Ok, switches and pots all cleaned, also removed all knobs, and thoroughly cleaned them along with the front legend plate, all tested and most of the calibrations seem to have cured themselves, so they were just down to the build up of dirt and grim inside the case. Still have the same issue with dual time base control moving the variable pot, but thats livable with, just need to remember that it does move the variable when changing time settings.
The only adjustment that really needs to be done, bearing in mind that the precise measurements on the screen at this stage for me aren't critical is channel 4 triggering is slightly off and always scrolls to right very slowly. All the on screen measurements from the test calibration point of .3v are spot on.
I'll tackle that another day, so on the face of it I grabbed a real bargain
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.....I was wondering if anyone has successfully cured a similar problem without having to replace the complete assembly which I doubt is available now?
I had some great support one or 2 years ago for some very old (30years) Current probes from Iwatsu Japan, so I would ask them.
Michael