Oscilloscope question = testing

slimecity

slimecity

Super Member
Hi -


I'm thinking of getting a Syscomp Circuit gear mini for testing and diagnosing a Technics SU-V10 integrated (and learning how to use a scope as I go....). It integrates with your computer and will run with my Mac. This seems like the best cost/benefit option for me.

Most scopes seem to have a DC limit on what they can test - this one has an upper limit of 40VDC. The voltages in the circuit I will test are up to 60VDC. The manual says: “Warning Our recommended maximum input voltage on the AC coupling setting is 40 volts DC. Exceeding this may cause damage to the electronic switch that selects between AC and DC coupling. You cannot use the AC setting to block DC voltages larger than this value……If you need AC coupling where the DC component of the signal is larger than 40 volts, you should put the coupling in the DC position and connect an external capacitor of the appropriate voltage rating in series with the input.”

Any help on how to do this, and what cap value to use for this application would be appreciated!

Cheers
 
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I think 1uF x 250V, polyester, is OK. This will block any DC, you'll see only the AC. Useful to see audio signals, and ripple, but you won't be able to check real voltages on the fly.

You could always build some voltage divider, like a 1/10, of the appropriate wattage and very high resistance (so you don't drop the voltage when measuring). I think something like a 47K-4K7 resistors, or better, 100K-10K, should do the trick.

Oscilloscope probes use to have a "10x" switch, to do this, so I think you won't have problems if you are careful and use regular scope probes. They should attenuate the DC 10 times, so you'd be able to measure up to 400V. PLEASE CHECK THIS 2 TIMES WITH THE DEVICE USER MANUAL.
 
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It appears that this device does is not supplied with an oscilloscope probe. The easy solution to your issue is to purchase a switchable 1 to 1...10 to 1 oscilloscope. In the 10 to one position it will divide the voltage seen by a factor of ten, so 60 volts would appear to the oscilloscope as 6 volts. One must remember to multiply the scope display by a factor of ten when using the oscilloscope probe in the 10 to one mode.

Edit:

I took a look at the accessory package and it includes the probes and they may be 10 to 1 probes, but I did not see any mention of this. Contacting the seller may help with this.

In any event switchable probes allow you to look at higher voltages in the 10 to 1 position and the 1 to 1 position allow you to view lower voltages.
 
BTW, this device has an upper frequency limit according to the manual of 200 Khz, which is sufficient to look at basic audio signals, but, while it may not be common, it is possible to have unwanted oscillations at frequencies much higher than audio frequencies.

If you become more active in servicing, you may want an oscilloscope with a wider bandwidth.
 
I see this scope, with all the kit, is almost as expensive as a regular scope with a much higher bandwith... Look a bit before buying. The "best" scope is the one that can measure what you need to measure... I'm dealing right now with a 3MHz oscillation in an AKAI amplifier...
 
I would consider buying a real analog scope over the Syscomp. You can buy a good Hitachi 15-20 MHz scope for around $100
 
IMHO, you can do much better for almost $100, you're into 60+ MHz Tektronix price range at that price.
 
20-60mhz is more than sufficient unless you are getting into FM alignments. Lots of good used scopes in this bandwidth out there as so many labs had to upgrade to 1+ghz capability.
 
The OP's location may have a lot to do with what he can find for a Franklin.

I would suggest that you make a list of oscilloscope features, and add in the minimum level that you think you need right now. Then go thru that list and place an asterisk by the ones you may need to improve in the future and an "X" by the ones you don't think are important at this time. Your results may surprise you, and you will learn a bit more about scopes than you do now.

Good Hunting - - -
 
Thanks a lot for your detailed responses guys. I am trying to achieve a limited spend as well as using a scope that I can integrate with my Mac if possible. The thing is that at this stage I am only after a fairly limited function scope to signal trace thru the various stages of my amplifier, to see where the signal dies at which faulty component - so that is the primary thing I am after - and hoping that this scope will do the job. I'm always happy to shell out more for a "better" scope if I think I will need this down the track.

The other thing is that the scope market in NZ is very limited and shipping stuff here costs a fortune. The next step up is scopes from Aliexpress (like "Hantek", with free shipping!) but I am looking at around $260US for one and Im not convinced I need a scope of this (slightly better) standard for the work I need to do on the Technics.

Thoughts?
 
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slimecity said:
Thanks a lot for your detailed responses guys. I am trying to achieve a limited spend as well as using a scope that I can integrate with my Mac if possible. The thing is that at this stage I am only after a fairly limited function scope to signal trace thru the various stages of my amplifier, to see where the signal dies at which faulty component - so that is the primary thing I am after - and hoping that this scope will do the job. I'm always happy to shell out more for a "better" scope if I think I will need this down the track.

The other thing is that the scope market in NZ is very limited and shipping stuff here costs a fortune. The next step up is scopes from Aliexpress (like "Hantek", with free shipping!) but I am looking at around $260US for one and Im not convinced I need a scope of this (slightly better) standard for the work I need to do on the Technics.

Thoughts?
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I would suggest get a real scope. You will use it for many things. Rigol is a good brand for cheap new scopes. Otherwise get old Tektronix from ebay for around $200. You will nee a pair of probes though.
 
Hey mate;

Vintage gear testing for the ps and sub circuits.. so we are looking for a clean ac in and dc out basically without sub amps. In NZ is the power clean enough to warrant a scope or would you be looking at noise anyway? Dim bulb tester might help and be accurate to say it's fudged.. in the mains but a good dmm can diag a lot, too.

can't say in NZ for an app.. might hit apple forums engineers? search?
 
a basic amplifier with a capacitor for coupling makes a nice simple cheap signal tracer . for anything more a second hand scope of 30mhz or even less is a good tool to have and wont break the bank .
vintage audio doesn't need anything fancy .
 
slimecity said:
Thanks a lot for your detailed responses guys. I am trying to achieve a limited spend as well as using a scope that I can integrate with my Mac if possible. The thing is that at this stage I am only after a fairly limited function scope to signal trace thru the various stages of my amplifier, to see where the signal dies at which faulty component - so that is the primary thing I am after - and hoping that this scope will do the job. I'm always happy to shell out more for a "better" scope if I think I will need this down the track.

The other thing is that the scope market in NZ is very limited and shipping stuff here costs a fortune. The next step up is scopes from Aliexpress (like "Hantek", with free shipping!) but I am looking at around $260US for one and Im not convinced I need a scope of this (slightly better) standard for the work I need to do on the Technics.

Thoughts?
Click to expand...
if you just want to trace audio signals, you don't even need a real scope, with a probe like this one, with a 10x voltage divider if needed,

plugged to your sound card (or better, buy those cheap chinese crappy sound cards, just in case you burn it), you can trace signals with a free oscilloscope software. "Visual Analyzer" is one of them, for windows, but for sure there are Mac substitutes.
 

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I am not a big fan of using a computer sound card for trouble shooting. They will have a limited input voltage range (the signal in an amplifier may range from a few millivolts in a phono stage to many volts at the output of the amplifier) and digital noise may ride along the ground connections to the device being tested, not always but I have run into this.

I am not saying do not try it if you want to, just be aware of some of the gotchas.
 
yes, it has some limitations, specially th einput voltage , you need to be very careful, use voltage dividers all the time until you are sure the signal is low enough.

But to trace audio signals or see the wave shape is OK. You can burn your sound card as I did, if you are not careful.

I wouldn't use it on the output of a power amplifier, I'd measure at a headphones output.

Anyway, if you plan to continue with this kind of jobs, you'll end buying a real scope, so you could do it now (if you have the $ to invest) and save some years of using the computer...
 
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