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B&K 1570A Oscilloscope

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Penner35

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Can anyone help me find a schematic for the above. I have checked the B&K site but I guess it is too old for them fo list. I need to calabrate one of the vertical channels. Thanks
Bill
 

Sceadwian

Banned
You shouldn't need a schematic to calibrate the vertical channel. Just feed it a fixed voltage from a high precision voltage reference, should only cost a few bucks to get 1% or better accuracy on a fixed point, opamp multipliers and divider networks can derive any voltage you want from the references for a multipoint refrences to determine linearity, but that might get a little more expensive.

I check mine against a 5volt fixed regulator with a light load.
 
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Penner35

New Member
Thanks for the quick reply. But with no schematic or layout i have no idea which pot/cap does what. There may also be a defect but I can't tell. One channel is ok, but with the same input the other is off by about 10X. There are about fifty adjustable components in each channel.
 

Sceadwian

Banned
You might want to actually explain that in your original post then Penner, I think the distinction is kind of important considering you said you needed to calibrate a vertical channel, not that one was faulty and you were trying to trouble shoot it's failure. That has nothing whatsoever to do with calibration.

Some scopes have a 10X selector knob perhaps your should start there since your failing vertical channel is off by nearly that much, perhaps it's stuck on.
 
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kchriste

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Forum Supporter
I have to agree. If it was out by 10% it would be a calibration issue. 10x is a faulty scope or a faulty operator.
The ~10x control is also called VAR on a lot of scopes and, on Tektronix scopes at least, is a 2nd concentric knob on the Volts/Div knob so it is easy to turn by accident if you are ham fisted. Usually there is a warning light to tell you that it is active.
 
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Sceadwian

Banned
Perhaps the 10X works fine and the LED is broken =\
 

Penner35

New Member
Thanks so much Guys. my appologies for neglecting to completely describe the problem the first time. I did not think of the 10X sw. I will try that. This is my first time to be on thes service and being a newbie I messed up. Sorry.
Bill
 

Sceadwian

Banned
No problem, biggest mistake is not enough information. Believe me, you can't bore us with too many details.
 

Penner35

New Member
Looks like no-go. But was a good idea. With 1 Volt input, Ch.1 reads 1.0V on the 1volt scale (1X probe).
ch2 reads 2.2 divisions (0.22V) on the .1V scale. With the 10X pulled out the reading is 2.2 div (1.1V) on the 50mV scale.with about .2 Div. DC offset.
Does this sound like a defect or maybe someone messing with the scope before I got it? I got it used from a service repair shop. I thought I could do some troubleshooting if I had a schematic or a repair manual. Any more suggestions?
This is a great site Had no idea until a few days ago that it existed.
 

kchriste

New Member
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One thing you could do is feed an identical signal into both channels and compare the reading between them at various points. This will only really work for you if the channels are laid out the same as one another. Another scope would be best for this but you may be able to use a voltmeter if it's input impedance is 10MΩ or higher.
 
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