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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#11
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Jason Bowers wrote:
================== A small 1x 10x probe arrives today at last so I can at least check the scope's square wave output signal peg. See what happens then. The frequency still seems to be showing higher than it actually is though. Even with a 30 Mhz scope like this, should I be able to "zoom" in to see just one or two waveforms? So far, I can't seem to get closer than 4-5 waveforms at 28 Mhz even with the 10x magnifier on. ** Completely normal. 28MHz is at the limit of the scope's range so no detail is visible on a sine wave. Also, the amplitude will by down by 30% or so from that at say 5MHz. 30 MHz scopes are are not "flat" to 30MHz but will be at least 3dB down. ....... Phil |
#12
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On 5/3/21 6:55 PM, Phil Allison wrote:
Jason Bowers wrote: ================== A small 1x 10x probe arrives today at last so I can at least check the scope's square wave output signal peg. See what happens then. The frequency still seems to be showing higher than it actually is though. Even with a 30 Mhz scope like this, should I be able to "zoom" in to see just one or two waveforms? So far, I can't seem to get closer than 4-5 waveforms at 28 Mhz even with the 10x magnifier on. ** Completely normal. 28MHz is at the limit of the scope's range so no detail is visible on a sine wave. Also, the amplitude will by down by 30% or so from that at say 5MHz. 30 MHz scopes are are not "flat" to 30MHz but will be at least 3dB down. ...... Phil Thank you and the others here! The scope seems fine. I was finally able to find out what happened to the square wave test peg. It dislodged during shipping. Reattached and a nice 2V PP 1 Khz square wave. Phil, what you said was confirmed. If I input the signal generator and set for say 10 Mhz, the frequency and amplitude are spot on. |
#13
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Jason Bowers wrote:
=================== ** Completely normal. 28MHz is at the limit of the scope's range so no detail is visible on a sine wave. Also, the amplitude will by down by 30% or so from that at say 5MHz. 30 MHz scopes are are not "flat" to 30MHz but will be at least 3dB down. ...... Phil Thank you and the others here! The scope seems fine. I was finally able to find out what happened to the square wave test peg. It dislodged during shipping. Reattached and a nice 2V PP 1 Khz square wave. Phil, what you said was confirmed. If I input the signal generator and set for say 10 Mhz, the frequency and amplitude are spot on. ** Thanks for the confirmation. FYI: Analog scopes are one of my favorite things. I currently own 5 of them. One I built from new parts when I was 17 - way back in 1970. Uses 5 tubes ( twin triode and triode pentode types ) plus is fully calibrated. I also own a modern Rigol DSO but don't like it much .... ...... Phil |
#14
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#15
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#17
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#18
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Ralph Mowery wrote:
=================== I also own a modern Rigol DSO but don't like it much .... Phil does your Rigol DSO work well in the X/Y mode ? ** Nope. Does Lissajous patterns bout as well as a dog waking on its hind legs. I am like you, for many things I perfer the Techtronic 465B scope I have over the DSO, but for some things the DSO is better for me. ** Yep, I drag it out only for special jobs like one shot events. I did build a 2 inch scope in high school. I think it only had 3 tubes that handled the signals. One for the horizontal, one for the vertical, and one for the sweep generator. Couple of more were rectifiers. It probably topped out not much above the audio range. ** Still better than having no scope. My 3 inch tube scope does 2MHz. ...... Phil |
#19
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#20
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Need some equipment.
I take a DC voltage source and then adjust a square wave generator to that voltage and go up seeing if the amplitude stays with the changing of the V/div. control. And move the position control to see if the waveform is linear at all portions of the screen. Keep going up in frequency, I happen to have a generator that stays stable at any frequency, it is a Wavetek and operates on a different principle than most. Most do keep a square constant, but not necessarily in sine wave. Next you need a freq counter, set the generator accurately to a 1,000Hz square, put the scope on 1mS/div. Adjusting the horizontal position to where the first cycle lines up with the graticule, check the rest. They should also line up and the vertical parts of the square wave should be on graticule lines all the way across. If they run off, the time base or H size is off. To determine which, switch to different frequencies ad time bases, always with the freq counter on it. If they vary it is the time base, if they constantly run off one way or the other it is the H sweep size - or more professionally put - deflection. How accurate you need it depends on price. I got one I don't pay much attention to, the time base or deflection is slightly off but I am not measuring frequency with it. The amplitude reads right and that is enough because I use it for everything. Even DC, it is much quicker because usually I only need to know a source is there. If you need a scope that is totally accurate all the way you need an old Tektronix. |
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