Hitachi V-1065A Scope Problems...

[Th3_uN1Qu3]

Re: Hitachi V-1065A Scope Problems...

Simple, for someone who has the funds. Just because you afford to get fancy new gear, don't look down on those who bought what in your opinion is a piece of junk. If they learn and hit its limits and desire to stay in the field and keep moving, they will then acquire a better instrument.

But the truth is that most hobbyists are gonna be fine with what you call "junk".

[Spork Schivago]

Re: Hitachi V-1065A Scope Problems...

Just so I understand the animated gif of the 555, pin 8 always has volts going to it. Rb always has juice going to it...Ra is where I'm getting a little confused. Ra only has juice going to it while the cap is charging? I thought capacitors blocked DC voltage and only allowed AC going through. How come when I put a cap in my LED circuit with nothing more than an LED, a resistor, a diode and a cap, the LED wouldn't blink like I was expecting it to? It only powered the LED while the cap was discharging and it never charged back up like I thought it would...what am I missing here?

[Spork Schivago]

Re: Hitachi V-1065A Scope Problems...

Simple, for someone who has the funds. Just because you afford to get fancy new gear, don't look down on those who bought what in your opinion is a piece of junk. If they learn and hit its limits and desire to stay in the field and keep moving, they will then acquire a better instrument.

But the truth is that most hobbyists are gonna be fine with what you call "junk".

You are correct. We don't have a lot of money and I really do want to learn this stuff real bad. It's hard though for me to learn now a days. I have some issues with my brain. Something called global volume loss of the T2 white matter. I also have these wholes in it the neurologist says. It takes me a bit longer to do stuff then it used to. If I can get this down, maybe eventually, when I out grow this unit, I'll have the cash saved up to purchase a more modern scope with additional / better features. For now though, I don't think it'd be a smart investment.

[tom66]

Re: Hitachi V-1065A Scope Problems...

The capacitor can continuously charge through the Ra resistor, if the 555 didn't get in the way.

Remember electric current -always- (except in limited circumstances not important to you) flows from positive to negative. (Conventional current. Ignore electron current for now.)

So, the 555 normally has pin 7 open circuit, which means nothing is connected to it. So the capacitor charges through Ra + Rb. When the threshold voltage of 2/3rds of Vcc is reached (for example, 15V supply, threshold is 10V) the 555 turns on pin 7. Pin 7 becomes a short circuit to ground. So now pin 7 is at 0V, essentially. Current flows from Ra to pin 7 GND (remember positive to negative)... but you don't care about that really. What also happens is current flows from the capacitor through Rb to GND through pin 7, thus discharging the capacitor. When 1/3rd Vcc is reached, for example 5V, the 555 turns off pin 7, and the cycle repeats. This cycling makes the 555 chip, in this instance, a relaxation oscillator. The state of pin 7 is reflected in the output pin 3 as highs and lows.

Note that the capacitor is charged up with Ra+Rb, and discharged with Rb. Therefore, the charge and discharge times are not equal. Can you think of a way to make the oscillator have nearly equal charge and discharge times? Hint; think about how you could use diodes to redirect the charge/discharge current flow, and don't be afraid to experiment!

[budm]

Re: Hitachi V-1065A Scope Problems...

"Essentially, the 1X probe with VOLTS/DIV set to 5V shows the same results as the X10 set to 0.5V and the X100 set to 50mV." That is correct, you have to increase the sensitivity by factor 10 and by 100.
So x100 probe and the sensitivity is set at 50mV (or 0.05V), so 1 vertical division will now represent 5V.

[Spork Schivago]

Re: Hitachi V-1065A Scope Problems...

...Can you think of a way to make the oscillator have nearly equal charge and discharge times? Hint; think about how you could use diodes to redirect the charge/discharge current flow, and don't be afraid to experiment!

I am very much looking forward to this. I cannot do it tonight though, I've had some problems and now I have to go to bed. I will start working on it when I first get up. I have a couple ideas. Thank you!!!!! This is going to be so cool.

[Spork Schivago]

Re: Hitachi V-1065A Scope Problems...

"Essentially, the 1X probe with VOLTS/DIV set to 5V shows the same results as the X10 set to 0.5V and the X100 set to 50mV." That is correct, you have to increase the sensitivity by factor 10 and by 100.
So x100 probe and the sensitivity is set at 50mV (or 0.05V), so 1 vertical division will now represent 5V.

So I can use the X100 probe with this scope? Awesome!!!! My scope's VOLTS/DIV goes down to 2mV. It has a 5mV setting. So I can even use a X1000 probe if I wanted to, right?

[budm]

Re: Hitachi V-1065A Scope Problems...

Your scope should have built-in 1KHz Square wave signal generator test point on the front panel, most of this will put out 0.5V P-P so you can see what happen when you use x1, 10x, and x100 probe.

[Spork Schivago]

Re: Hitachi V-1065A Scope Problems...

Your scope should have built-in 1KHz Square wave signal generator test point on the front panel, most of this will put out 0.5V P-P so you can see what happen when you use x1, 10x, and x100 probe.

I did see that and I ended up using it with all three to compensate the probes. I thought someone said I could never use an x100 probe with it for one reason or another. Thanks for the clarification. I have a function generator but it's broke. I think it's the step-down transformer. Once I get some time, I want to see what happens when I replace it. Night.

[tom66]

Re: Hitachi V-1065A Scope Problems...

The particular someone was talking what we call "bullshit" in these forums. There is absolutely nothing stopping you using a 100X probe on this scope.

[cliff_hootarski]

Re: Hitachi V-1065A Scope Problems...

Sorry to hijack this thread, please indulge me.
I've been thinking about buying a new scope for TV troubleshooting.
What would you veterans recommend?
Tom, would you recommend the Rigol scope you've been using?

Thanks.

[Kiriakos GR]

Re: Hitachi V-1065A Scope Problems...

Thanks guys! I will try that. I think I'm figuring this stuff out, slowly but surely.

Now someone said that my probe doesn't support the X100 probe. Is that true? I measured the 555 timer using the X1, X10 and X100 probe. To get the oscilloscope to show up the same with each probe, I had to change the VOLTS/DIV setting. Essentially, the 1X probe with VOLTS/DIV set to 5V shows the same results as the X10 set to 0.5V and the X100 set to 50mV.

By getting lower in to mV range you have to deal with the input noise voltage of the scope it self.
Which is much higher in this generation of Oscilloscopes and therefore it contributes significantly at getting inaccurate measurements.

The professionals repair man they do favor bullet proof solutions as tools, it is true.

[tom66]

Re: Hitachi V-1065A Scope Problems...

By getting lower in to mV range you have to deal with the input noise voltage of the scope it self.
Which is much higher in this generation of Oscilloscopes and therefore it contributes significantly at getting inaccurate measurements.

This is true, and it is a limitation of ALL oscilloscopes.

A modern DSO typically has a noise of 2~3mVrms, and an analog scope typically has LESS noise. This is because the scope has no quantisation noise, which significantly impacts ALL ranges unlike an analog scope where noise typically only affects the lower ranges. I have owned an analog scope with noise <1mVrms and it cost me $50 US equivalent.

Yes, it's true, some newer DSOs, like the Rigol DS2072 have noise floors of around 0.4mVrms, But this is more the exception than the rule, and you can get analog scopes that are better than that.

Bottom line is: It REALLY doesn't matter! Especially for your repair. And, it has NOTHING to do with calibration!

[tom66]

Re: Hitachi V-1065A Scope Problems...

Tom, would you recommend the Rigol scope you've been using?

Highly. That being said, it's quite expensive. An analog scope may well suffice for 99% of uses.

[budm]

Re: Hitachi V-1065A Scope Problems...

Scope input amplifier signal-to-noise ratio is one of the spec that should be looked at also.

[Kiriakos GR]

Re: Hitachi V-1065A Scope Problems...

Dear Tom I have bad news for you, in Europe everyone will get an GW INSTEK GDS-2000A series scope, because it comes with three years warranty, and there is a true authorized branch (distributor) in its one European country.

RIGOL has a single base in Germany and their after sales service sucks big time, and it is not a mystery as it follows the same path as the mother company regarding firmware releases and direct support.

By the way, after the latest issues with those brand New RIGOL bench-top PSU and their problematic design, it makes me wonder if your suggestions have any value at all.

About the input noise on Oscilloscopes, you have much more to learn.
Before a week time I joined one of those Agilent seminars about this topic.
You better join too when they will repeat it so to open your own eyes.
http://www.ittsb.eu/forum/index.php?topic=584.0

[tom66]

Re: Hitachi V-1065A Scope Problems...

Everyone in Europe? Are you being paid by GW Instek to spin their crap scopes? Obviously they've run out of marketing money for better salespeople...

I have never used a Rigol PSU, and the bad design of the voltage regulator has nothing to do with the 4 year old DS1000E design (agreeably, Rigol quality appears to have fallen, as they've moved from Nichicon to Capxon on SMPS for example.) Besides, I am NOT promoting it! It's a good scope, but it's showing it's age. Nowadays, someone would be better getting a DS1000Z or DS2000, or perhaps one from another manufacturer, though I've not tested any others but high end Agilent -- well beyond a hobbyist's budget.

Input noise DOESN'T MATTER to a guy trying to repair a bloody CRT! Jeez, you act as if everyone needs the best scope in the world or they might as well not bother.

[Spork Schivago]

Re: Hitachi V-1065A Scope Problems...

...Note that the capacitor is charged up with Ra+Rb, and discharged with Rb. Therefore, the charge and discharge times are not equal. Can you think of a way to make the oscillator have nearly equal charge and discharge times? Hint; think about how you could use diodes to redirect the charge/discharge current flow, and don't be afraid to experiment!

Tom66, can you please give me a little bit more help. I just want to know if I need to change any of the caps / resistors (from what you said about Ra && Rb charging the cap and just Rb discharging it, I am 99% sure the answer is no). The main thing was how many diodes I'd need. I was thinking I could do it with just one, however, you used the words diodes implying more than one.

Spork

[tom66]

Re: Hitachi V-1065A Scope Problems...

You can do it with only one diode.

Think about the other solution though, which requires no diodes. If you made Ra very small, its value would be negligible. Why could this not work though?

[budm]

Re: Hitachi V-1065A Scope Problems...

https://cdn.badcaps-static.com/pdfs/...e1308f3f05.pdf

http://www.williamson-labs.com/555-circuits.htm

http://www.ohmslawcalculator.com/555_astable.php