oscilloscope Help!

[miljnor]

I have recently bought a used 465m tektronics oscilloscope.

I am looking for help on calibration and or advice on if its working or not, and if not how much to repair or is it worth it.

when I hook the probe up to the calibration signal in the front of the unit I get a standard digital wave form but it looks more sawtooth than square.

The adjuster on the probe itself allows me to adjust it a little but not enough to make it looke like a conventional square wave.

just to be sure the generator is working I have hooked it up to the parallel port of a computer when mach3 was running the spindle and the sawtooth pattern is still there if not more pronounced..

Is the scope out of calibration and if so is it a DIY fix or do I have to send it out. I only payed 100.00 U.S. for it and if its fixable at a resonable price I will get it fixed. but would like to DIY.

Any suggestions???

[gar]

050912-0704 EST USA

miljnor:

On any Tek scopes I have the calibration signal is a square wave.

Bypass the probe and connect a Y input to the calibration signal and see if the waveform changes. This will eliminate the probe as a cause. Check all Y channels. My 7603 has 4.0, 0.4, 0.04 outputs.

Service from Tektronix is very expensive.

The scope might be fine except for the calibrator. I doubt that the calibrator was designed as a sawtooth generator. One of the uses for the calibrator is to do high frequency compensation of the probe. The square corner of a square wave is best for this.

To check the basic operation of the scope there are other procedures you can use.

.

[One of Many]

A couple things to try:

Make sure the outlet this scope is plugged in to is properly wired for Hot, Nuet, and ground. You should also be using an adapter to go form 3 prong to 2 prong so as to isolate the earth ground from the units cord. Hopefully what you are seeing is not a result of this very condition by the previous user.

You can use a simple jumper wire to go from either channel and connect directly to the cal terminal. The grounding should be internal, so no need for the ground clip. Another device with a square wave might help verify the input or cal signal as the faulty portion.

The probe you have may not be a good match for the input. 10-60 Pf would be reasonable, but some of the cheaper probes can be in the 180pf range. Which can contribute to a slow rise time viewing the signal and never adjust to a see a good sharp leading edge to a square wave.

I'd expect any repair facility will need to go through the unit as a whole. I don't know of any that would just fix one issue. The quote I had for inspecting mine 15 years ago wanted around $900-1200 to inspect, repair and calibrate. Not worth it on an obsolete scope used for basic hobby applications. Far cheaper to find a known good scope at the $500 rate.

DC

[miljnor]

Bypass the probe and connect a Y input to the calibration signal and see if the waveform changes. This will eliminate the probe as a cause. Check all Y channels. My 7603 has 4.0, 0.4, 0.04 outputs.

where are thes outputs as it has been 22 years since I have used a scope . there are several connections in the rear of the scope and of course there are several in the front. 2 in the front are singnal 1 and 2 then on the right hand side there are 2 more all are listed as 20pf and 1m on the front. the ones in the back have various listings.

If this fixes the pattern then I would assume that the probe (which is new) isn't compatable with the scope. OR more likely there is something wrong with the scope. how would I fix it??? Is this something you know how to do?

[EDM_Fixer]

i don't work for them but...... radio shack has a $69.00 i think .. meter.. that also comes w/ 232 port ..with the cable.. w/software and its a scope also .. looks like it would be great for someone starting out ..it even has the yellow rubber bumper cover .. heck i payed $35.00 for the cover alone on my fluke $2,200.00 for my scope.. ahh the speed electronics are advancing.... have fun .. Jim

[miljnor]

originaly posted by OneOfMany
You can use a simple jumper wire to go from either channel and connect directly to the cal terminal. The grounding should be internal, so no need for the ground clip. Another device with a square wave might help verify the input or cal signal as the faulty portion.

direct wired made the square wave practically purfect! So this means that the probe I have is not compatable??? It is a 150mhz probe with a x1/x10 setting and the 18pf inductance cap. Or is it that the probe just has too much resistance for the 1volt 1khz Calibration signal???

what probes would you guys recomend?

originaly posted by OneOfMany
Make sure the outlet this scope is plugged in to is properly wired for Hot, Nuet, and ground. You should also be using an adapter to go form 3 prong to 2 prong so as to isolate the earth ground from the units cord. Hopefully what you are seeing is not a result of this very condition by the previous user.

what problems would the ground wire cause. I have a cheap home depot grand tester and it says the ground is good at the plug. should I still isolate the ground prong? and if so why if it goes to a good earth ground?

[ViperTX]

Check if you are AC coupled?

[One of Many]

direct wired made the square wave practically purfect! So this means that the probe I have is not compatable??? It is a 150mhz probe with a x1/x10 setting and the 18pf inductance cap. Or is it that the probe just has too much resistance for the 1volt 1khz Calibration signal???

what probes would you guys recomend?



what problems would the ground wire cause. I have a cheap home depot grand tester and it says the ground is good at the plug. should I still isolate the ground prong? and if so why if it goes to a good earth ground?

If the voltage scale is set to 1v/div and the probe is set on 1X, The adjustment should cancel out any capacitance created in the cable verses the scope input. Inductance in general, should have nothing to do with this probe.

I would investigate what that probe actually is. It may have a problem or is not a standard passive probe? No or not enough trimmer compensation, from the sounds of it.

Tektronix Probe Tutorial

Not all tests are taken in reference to ground. When checking some circuits/components that are not ground, but some potential above ground. Sparks will fly if the ground clip is attached to anything not at ground potential!

DC

[miljnor]

by ViperTX
Check if you are AC coupled?

I am alot rusty! could you explain?

And I will check the docs I have for the probe and see if the probe is right for my ap and If i cant tell then I will assume that it dosn't have enough compensation!

thanks guys

[gar]

050912-1647 EST USA

miljnor:

As has been said your probe is the problem. Get new probes from Tektronix. These each will cost more than your scope, but are well designed. Get X10 probes.

I just took a look at the Tek web site and it appears useless. I can not find a way to get at specs on probes. There are too many very bad web sites like this. Bit this does not change the fact that Tek probes are good.

If you are going to unground your scope you have to be very careful. In the case of a HAAS machine I have a special socket on the HAAS that derives from the safety ground of the HAAS and this must go back to your service entrance safety ground. See some of my discussion on noise and ground on my web site. www.beta-a2.com and then to NOISE and GROUNDING page.

If you ground your scope to the machine, then use two input channels in differential mode with both amplifiers balanced then you can cancel out most noise.

.

[miljnor]

AFter I got the wire method working I decide to put the probe back on for another try. This time it didn't do anything!

So, I took it back for a replacement and picked up another one of 60mhz just to check it (they have a great return policy and know me pretty well). Turns out the first probe I bought was DOA! and the both of the new ones were perfect right out of the box (or bag as the case may be).

Thanks for the info guys and as always its greatly appreciated!

Gota love this sight!

[unterhaus]

Probes and test leads go bad a lot. If I'm getting bad results, that's the first thing I check. I suspect that a probe from a company like pomona will do what you want.