Kikusi COS 5060A repair and calibration help

[cncman]

Hi All,

   My name is Ben and I'm setting up a beginner electronics tinkering lab in my basement. Using Dave's tips and tricks from EEVblog #498 I just got a Kikusi COS 5060A oscilloscope that I purchased from E-Bay. I got it for $30 USD plus $16 S/H and IT WORKS! It came with the original probes and the full operation/service manual with schematics. As you can see in the photos I lifted from the ebay auction it looks like something has been dropped on it and it is in bad need of calibration. According to the manual most of the calibration is done with a multimeter, but I do need a function generator and a C-meter. I've bought an FG085 and an LC-100A from ebay as I'm on a tight newbie budget and I'm hoping they can get me close enough to cal for my needs.
   Enough back story. The big question I have. As you can see from the pictures the screen diffuser is cracked. I can't find a relacement part # anywhere in the service manual. Do you know of anything I can replace this with that will be just as effective as an original?

Thanks, and feel free to offer any other advice you think will help me get this up and running.

P.S. I am aware of the -1750V running through the CRT circuit and as I don't yet have a HV probe I will be staying the heck away from it!









photos upload

[singapol]

Welcome,
                 Since scope comes with service manual you have it easy in a sense. Eventhough you have a function gen. you can't really trust it in terms of voltage amplitude only shape of waveforms. For scope calibration and multimeters for that matter, a multimeter is more accurate than a scope where stated accuracy is at best 3%?

That said..the dented cover is only cosmetic so no point trying to flatten or straighten it .If you like just clean it and spray paint a colour that is similar to original or any colour you fancy for a personal touch.

Since it's working try adjusting the focus..if you can get a sharp thin horizontal trace you can just continue to use as is,no need to fiddle with it,at most open the cover to clean of dust and whatever you can see. Also adjust the trace rotation so that it aligns  with the horizontal graticules of the front screen.

For sure considering the age of the scope it's calibration will be off somewhat.You can calibrate using built -in
square wave generator with a 1 volt pk-pk amplitude or whatever amplitude is stated for the 3 channels to give a rough estimate how close you are to the ideal.Also don't forget the timebase frequency accuracy. For DC voltage , you will need to buy a voltage reference diode of various voltages ,buried zener which are generally more accurate and stable or the cheaper band gap diodes. Do some reading first about reference diodes.Worst to worse can just use common zener diodes for just a few cents. Since the scope is not that accurate in terms of voltge amplitude I would not split hairs over the accuracy..just ball park average should do. Follow what is described in service manual for calibration steps..it will probably require an accurate instruements.Read before attempting to calibrate. (The reference diodes is for personal checking other than what the calibration procedures described in SM)).

PS
make sure all the rotating switches are locked with a click to the default positions.

Like I said earlier..if focus adjust can give you a sharp thin trace for the time being you can use as is and later when you are more experienced you can replace the electrolytic caps in the power supply first.Don't  replace eveything at once ,this way if you get problems you can backtrack step by step.If you do it all at once then
you will have troble figuring what you did first. Hope this helps.

Do be careful and discharge the caps with a suitable value (resistance) power resistor.