What frequency limit I should plan for when choosing oscilloscope for TV repair?

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

I think I have something which I can work with. This is 0 to 200 VDC. Would this work if I added a bridge rectifier and some filter caps? Well, the better question is would it be accurate, considering there would be losses during rectification. Would that be enough to make a difference? I'm not looking for super accuracy, but within +-2 volts and 0.2 amps would be great.

I can easily tap the secondary winding to get the supply voltage. I can get close to what I need, then make a buck converter.

http://www.ebay.com/itm/200V-100A-DC...IAAOSwDk5UF72X

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

no, when you rectify the voltage it rises.
besides, the current-shunt is also dc so you cant use it to see the load.

this may be good in the input-side.
http://www.ebay.com/itm/400732748294

you may find it cheaper, i just saw it on the bottom of your link.

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

led version
http://www.ebay.com/itm/370986916580

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

digits - more digits!
http://www.ebay.com/itm/380983067718

now if it can be modded for a seperate psu it would be perfect!

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

no, when you rectify the voltage it rises.
besides, the current-shunt is also dc so you cant use it to see the load.

this may be good in the input-side.
http://www.ebay.com/itm/400732748294

you may find it cheaper, i just saw it on the bottom of your link.

Couldn't I also rectify the source before the shunt though?

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

digits - more digits!
http://www.ebay.com/itm/380983067718

now if it can be modded for a seperate psu it would be perfect!

Yes, I wanted more digits anyway. Might be too thick though. I think I'm going to make an entirely new front panel anyway, so maybe not.


Edit: I think the back cover can be removed so maybe it can be made thinner.

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

yes, but then your reostat would have a dc output - good luck using it on much!
in reference to rectifying the output.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

yes, but then your reostat would have a dc output - good luck using it on much!
in reference to rectifying the output.

Right, because it has to be in series. I didn't think of that.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

I'm actually surprised that nobody has one of these which will do what I want without modification. China is really failing me right now.

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

yes, it's not hard for them to decouple the psu input from the sense input so you could power it from a seperate 6-12v transformer i'm sure.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

yes, it's not hard for them to decouple the psu input from the sense input so you could power it from a seperate 6-12v transformer i'm sure.

I ordered the 4 digit one. Found it on AliExpress for $10.12 and free shipping. I'm thinking the easiest way to power it is to tap the secondary winding on the variac at the point where the voltage is just about what I need, and then build a little rectification and regulation circuit. I'll have the new front panel done by the time this gets here. I'm going to move the receptacle to the lower left front, switch and a load side panel mount breaker on the lower right front. Display going across the top. And the power cord and a line side panel mount breaker coming out the lower right side.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

I like this even better. Illuminated switch and 10A breaker in 1.

http://www.digikey.com/product-detai...B529-ND/512633

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

that's nice, they are a lot cheaper than they used to be!

when you get the display, open the casing and lets draw a schematic of the power input.

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

Any idea what the supply voltage will be? I'm looking at these mini buck converters and thinking it may be easier. If I order now, it'll get here about the same time.

http://www.aliexpress.com/item/DC-St...rchweb201560_9

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

This one, with active and apparent power factor, would have been neat too.

http://www.ebay.com/itm/DL69-Multi-f...cAAOSwBahVRtlS

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

I decided to order the one from my previous post as well.I found this thread here which they've modified it to have a separate supply. The outer board looks about like the other one.

[stj]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

i would say those modules actually run from 12v or 5v in the end.
have to wait to see inside one.
they could use a microcontroller or some custom meter chip.

[tom66]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

If you want regulation then you're out of luck with a variac - the voltage varies with the load and input voltage. Most of those modules that generate various output voltages use poor quality components so the output is often oscillating or unstable.

One project you could consider is to use a servomotor or brushed DC motor to control the variac arm, varying the variac voltage set point to keep the output under regulation. That would be an advanced level project--but the bonus is, you could sell it to some audiofools, who buy variac power supplies to ensure the supply voltage to their audio and video equipment is precisely regulated. Fools and their money are easily separated.

http://audiophilereview.com/amps/why...-a-variac.html

[lookimback]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

http://audiophilereview.com/amps/why...-a-variac.html

Yeah, I don't understand the need for such precision. It all sounds the same to me.

[Agent24]

Re: What frequency limit I should plan for when choosing oscilloscope for TV repair?

Most of that article makes sense to me - there's certainly nothing wrong with bringing old equipment up to full voltage slowly with a variac - it's advice I've read many times and seems sensible, especially regarding old (maybe decades unused) valve-based equipment.

If they said they wanted to keep the line voltage perfectly stable to improve audio quality... well that's another thing, and makes no real sense; that's what the filter capacitors in the power supply are for!

Even with the projector I fail to see the point. Sure, variations in line voltage could upset motor speed perhaps, but I doubt it would be noticeable in the picture quality, and any decent design should incorporate something to compensate for such an effect anyway.

It seems however that he uses it to provide protection against potentially damaging voltage variations, and for significant and sustained changes in line voltage the self-adjusting variac would be useful - but I don't see how it could ever be fast enough to compensate for the usual momentary fluctuations - in such a case, an offline UPS or some other device makes much more sense, if you wish to protect your equipment.