Oscilloscope CRT problem

[etnietering]

Re: Oscilloscope CRT problem

I have an update - I believe what's under that box is the flyback circuit. It has a transformer and some blue capacitors and such.
Also - I found what I believe is a schematic. According to some people on the electro-tech-online forum, it's from a different oscilloscope but the schematic is the same. Here's the link: The part of it that's under that box is in the bottom corner of page 6 - the stuff connected to the MV950. Is this the correct place to look?

[etnietering]

Re: Oscilloscope CRT problem

I've taken apart regular CRT monitors...are the flyback transformers the giant things with the huge wire coming out of the top? I don't see anything that looks like that, or even like a general transformer, other than the main power transformer. It might be hiding under the box where it says 'H.V. DANGER!!' on the circuit board...I'll take a look.
Also, it has a plastic protector in front of the screen, so I won't be able to tell if there's any static on the screen.

Thanks for the help! I'll check for the flyback transformer.

[lucky13]

Re: Oscilloscope CRT problem

Yeah after I wrote that I looked and it in indeed keyed...I should have looked before I asked! I do see a very small yellow-orange glow coming from what looks like a filament in the base of the CRT. No picture on it though...

That's a good sign!

Now, you need to figure out if there is high voltage to the tube. On a regular CRT monitor, if you place your hand on the glass surface in front, you can feel the static build up. On such a small tube, I don't think you can fee that.

Do you know what a Flyback transformer is/looks like?

[etnietering]

Re: Oscilloscope CRT problem

Yeah after I wrote that I looked and it in indeed keyed...I should have looked before I asked! I do see a very small yellow-orange glow coming from what looks like a filament in the base of the CRT. No picture on it though...

[PlainBill]

Re: Oscilloscope CRT problem

PB: no, it wasn't guaranteed nor insured, and the seller won't take returns.
I can't see anything glowing in the CRT tube, but most of it is covered up with metal. Where would the filament be? All of the connectors appear to be seated properly.

Toast: the power light does come on. It also has a calibration feature that outputs a 2v p-p square wave across two terminals on the front, and when I put a red LED across these it glows dimly, which is what I would expect. I've played with all the knobs and switches and nothing changes anything.

There was one thing I did though. The board at the back of the CRT was only seated partially, so I shoved it back in (protecting myself from it, of course). It seems odd to me that this board is supposed to be at an angle (see picture). I have a feeling that it's supposed to be level...what would the risks be in spinning it?

edit: normally I'd go for a seller with a higher feedback, but I got this for $120 shipped, whereas a new one would be $350-400...

A skewed socket board is not a problem - it's supposed to be keyed, and will only fit in one position. The filament is very close to the base of the CRT. You should be able to see it glowing, but try it in a dark room.

PlainBill

[etnietering]

Re: Oscilloscope CRT problem

PB: no, it wasn't guaranteed nor insured, and the seller won't take returns.
I can't see anything glowing in the CRT tube, but most of it is covered up with metal. Where would the filament be? All of the connectors appear to be seated properly.

Toast: the power light does come on. It also has a calibration feature that outputs a 2v p-p square wave across two terminals on the front, and when I put a red LED across these it glows dimly, which is what I would expect. I've played with all the knobs and switches and nothing changes anything.

There was one thing I did though. The board at the back of the CRT was only seated partially, so I shoved it back in (protecting myself from it, of course). It seems odd to me that this board is supposed to be at an angle (see picture). I have a feeling that it's supposed to be level...what would the risks be in spinning it?

edit: normally I'd go for a seller with a higher feedback, but I got this for $120 shipped, whereas a new one would be $350-400...

[Toasty]

Re: Oscilloscope CRT problem

Go back to auction pics and set the controls just like the pic that shows them close up.

Anything? Power light on? As PB said, CRT filament on?

Toast

[PlainBill]

Re: Oscilloscope CRT problem

Hello,

I just purchased a BK Precision 2120B oscilloscope, to help me with my projects and such. I got it from ebay, the seller had a 95+% positive rating, and said that the unit had been used for about an hour, and is as good as new. It arrived today, and needless to say, I was very excited. I couldn't wait to avoid more homework, because I got my new toy I plug it in and turn it on, and the CRT does not turn on. I have no idea how to even begin diagnosing the problem, but I did take the cover off (after unplugging it and letting it sit for a while, of course), and looked for burns/fried components/bad caps. I found none, and apart from a few cobwebs and some dust, the unit looks pretty good on the inside. Some of the caps are from a brand called Engel (ever heard of them?) and the rest have a logo which is a capital A in a rectangle.
They made good use of screws and take-apart-able connectors, so disassembling the unit won't be too much of a problem, I'd just like some advice on what to do or how to start.
I tried to get some pictures of the circuit boards without disassembling it.
I searched online for a schematic and couldn't find one (I did find the manual though). The power light comes on, so I know something is working. I'd be happy to take more pictures, and any advice anybody can give is welcome

Thanks!

Eric

95% positive? Ouch!!! Usually I won't trust a seller who has less than a 98% rating. Well, that's water over the dam. Next step, was it guaranteed to be working or insured?

Assuming the above are not going to be helpful, here's some general ideas. Approach the problem from the shipping damage angle. Make sure all connectors are firmly seated. Does the filament in the CRT glow? If not, pursue that trail.

What happens when you hit the beam finder button. Adjust the brightness. check trigger mode, etc.

PlainBill

[etnietering]

Hello,

I just purchased a BK Precision 2120B oscilloscope, to help me with my projects and such. I got it from ebay, the seller had a 95+% positive rating, and said that the unit had been used for about an hour, and is as good as new. It arrived today, and needless to say, I was very excited. I couldn't wait to avoid more homework, because I got my new toy I plug it in and turn it on, and the CRT does not turn on. I have no idea how to even begin diagnosing the problem, but I did take the cover off (after unplugging it and letting it sit for a while, of course), and looked for burns/fried components/bad caps. I found none, and apart from a few cobwebs and some dust, the unit looks pretty good on the inside. Some of the caps are from a brand called Engel (ever heard of them?) and the rest have a logo which is a capital A in a rectangle.
They made good use of screws and take-apart-able connectors, so disassembling the unit won't be too much of a problem, I'd just like some advice on what to do or how to start.
I tried to get some pictures of the circuit boards without disassembling it.








I searched online for a schematic and couldn't find one (I did find the manual though). The power light comes on, so I know something is working. I'd be happy to take more pictures, and any advice anybody can give is welcome

Thanks!

Eric