Oscilloscope CRT problem

[Toasty]

Re: Oscilloscope CRT problem

I can see it and I'm old.

Here. I blew it up a bit and pointed to it...

[etnietering]

Re: Oscilloscope CRT problem

well for the lazy bums I've attached the picture again, with the capacitor in question circled and labeled.

I did find a 2.2uF 350v cap in an old CRT monitor I took apart. It's a SAMWHA, and the wrong size, but I can give it a shot. I don't have an ESR meter, I would like one, but I was going to spend at least a few weeks with the oscilloscope first...

toast: I made the pictures big to retain more of the detail - I thought it might be important. Next time I'll only attach them....On that site, I don't see anything in the picture on the right that looks like the anode connection. The picture on the left however has some wires sticking out of the middle. I think these are for the focusing coils or something. My unit has them, and the plug into connector P482, labeled 'T.R' On the picture, this is the small white connector 3 inches down and about half an inch right from the capacitor. There are two there, it is the bottom one, with the red and white wires.

So begins the search for bad solder joints....


EDIT: scratch the part about not seeing the anode connection - I see it now. It really helps to look at things My tube has no such connection.

edit2: my inspection of the bottom hasn't yet yielded any broken solder joints, but I did notice that there's no pin 10 coming from that transformer, so yes I'm now 100% confident that MV950 shouldn't be there.

[Toasty]

Re: Oscilloscope CRT problem

WOW! Them's some big pics! Just attach them from now on, don't link them in the page. Page is really hard to read now...

Did some digging with the new info. Apparently, you're only dealing with 2kV for the acceleration voltage, not the 12kV as thought (or shown by that "almost-kinda-like-this" schematic). The circuit board is probably used in a variety of scopes, so that's why the space for that MV950 is there.

Ran into HAMEG scopes which currently use this tube: (PDF Catalog)


...and this site in the Netherlands: http://www.professionaldisplaysystems.com/crt.htm

From what I gather from that last site, this CRT just uses the 2kV. If you look at the chart there are others that use the 2kV AND 12kV. Those seem to be higher speed and/or brightness models.

Please also note, that in the right hand pic there, there is a tube with an obvious spot for an anode connection.

I would restart this process by unplugging the unit and discharging all connections to the tube. Then carefully go over each connector on every board and make sure they were all tight. Then start looking for bad solder joints or cracks in the board(s) that could have happened in shipping. NONE of the shippers are kind in any way in package handling. Look for broken wires where they connect to boards and switches. Look for cold solder joints near the transformers(s) and where the boards are screwed to the frame.

I doubt the little cap is bad, but checking it can't hurt.

Toast

[i4004]

Re: Oscilloscope CRT problem

>The HV anode cable is usually the one that looks like it has a suction cup on it, going into the top of the tube, right? Well this tube doesn't have one, nor does it appear to have a place for one. The solder pads don't look like they have ever been messed with.

in that case we were looking at wrong schematic diagram and were drawing wrong conclusions about missing parts.

so forget that, back to usual troubleshooting.

>Also, I did find a cap that is ever so slightly bulging. It's C808, the smaller stamped cap in the fist picture. I only noticed because it doesn't reflect my flashlight beam the same way as something flat would. It's a 2.2uF 250V part, unfortunately not something I stock...could this be causing the problems? It is connected to the HV circuitry that's used to control the CRT interface.

i wonder could you help lazier members of this board like plainbill and me? hehe...
now if i could input c808 in acrobat to find me that cap, i would, but as is that's not working..so could you attach image that shows that cap in the diagram?
then again, if we've established diagrams are not for your scope, what's there to look at all?
so try to establish is this diagram is really thing you have on your desk first.

about the cap; if it's bulging, it can't be good for the circuit.
it it REALLY is bulging...but sometimes it's hard to say if it is bulging or not...
only way to know for sure is to measure it with esr meter.

if you don't need/wan't esr meter as you wouldn't find a use for it(beside this problem) then just buy new cap and replace it.
but expect it's not it...hehe...murphy's law...

if xtraelectronics has same thing he should be most helpfull to you.
you can compare voltages on important places and that should be usefull to investigate why you don't seem to have HV supply to the tube.
edit/scrap that, seems he has different scope.

oh yeah, be carefull....don't touch any metal parts of scope while it's plugged in.
better safe...

[xtraelectronics]

Re: Oscilloscope CRT problem

Unfortunatly I have reassembled my scope. Don't remember the tube #, but it was manufactured by Toshiba. Your scope is very different from mine. I would check the smaller value rsistors near the HV, and def. replace that bulging cap. A circuit tester, that electricians use contains a neon lamp. This is what I used to check fo high voltage @ the flyback. Just hold it close the the transformer, if there is high voltage, it will glow. Good luck. I'll check in again tomorrow to see if you made any progress.
Dan

[etnietering]

Re: Oscilloscope CRT problem

Ok I sent a message this morning to the seller through the ebay messaging system - haven't gotten a response yet. I'll keep everybody posted.

Toast: Here's the pictures:

front half:


back half:


close up of HV part:


same picture, outlined in red is approximately where MV950 is supposed to go, and the blue line is the approximate path of the trace coming from pin 10 of the transformer.


The HV anode cable is usually the one that looks like it has a suction cup on it, going into the top of the tube, right? Well this tube doesn't have one, nor does it appear to have a place for one. The solder pads don't look like they have ever been messed with.

xtraelectronics: I don't see any really big resistors (1/2W tops), but I'll check them anyway. This tube, like yours, doesn't appear to have a place for the usual suction cup type anode connection (if indeed that is what it is). What is the model number of the tube in yours? Mine is D14-363GY/123 made by CRT Heerlen B.V. in the netherlands. Thanks for the info!

i4004: I hope I don't have to scrap it and start over...I sent a message to the seller to see what I can do about it. I did a quick google search for MV950, and everything that came up were things that ran at 950 mV or other non-helpful things.

Also, I did find a cap that is ever so slightly bulging. It's C808, the smaller stamped cap in the fist picture. I only noticed because it doesn't reflect my flashlight beam the same way as something flat would. It's a 2.2uF 250V part, unfortunately not something I stock...could this be causing the problems? It is connected to the HV circuitry that's used to control the CRT interface.

Thanks so much everybody for all your help! I really appreciate it! Hopefully we'll get this sorted out soon...

[Toasty]

Re: Oscilloscope CRT problem

@xtraelectronics: You may be correct. The part may not be in his unit either. Until we see the "whole" picture, we can't be sure.

@etnietering: Also, pull the board where the MV950 looks to be missing and see if the solder pads look like it was removed.

@Krankshaft: The pic of the scope working was my fault. It's the wrong auction. His auction was the other one and he linked it. I was attempting to have him set all the knobs the same as the picture I posted to see if he got a trace.

Toast

[xtraelectronics]

Re: Oscilloscope CRT problem

I might have overlooked the part about MV950. The 2120 has no such component, or a typical HV anode lead. All connections are made via the end socket on this tube. Hope I didn't cause confusio!

[i4004]

Re: Oscilloscope CRT problem

scavenging?
hehe...

well, it defenitely won't work without mv950...
to that extent this malfunction is not fun(not fun to repair something with missing parts..)

first see if something can be done via ebay to return it...as toast says
(scope with no hv is not worth the dime, let alone 120$...but given that you knew there was no guarante...well, you should of find one with some sort of return policy etc.)

if it can't, start searching for mv950, i guess....

[xtraelectronics]

Re: Oscilloscope CRT problem

Ok, found R549 in the flyback cct open. It is a 47 ohm, 2 watt resistor. The scope now has HV and a trace. Tested the small caps in the area, they are marginal. Probably tolerated by the cct, but I think I will replace them anyway, just to be safe. There are a few others elseware in this scope that are def. bad. Hope this helps you
Dan

[xtraelectronics]

Re: Oscilloscope CRT problem

I have almost the same scope. 2120. (no B) It's a bit older, but when I went to use it today, I was surprised to find the same sympton as you. No trace. I appears HV is missing. The scope acted "funny" the last time I used it, about a month ago. I will test some components, and keep you updated on this so maybe we can get to the bottom of this.
Dan

[Bob Parker]

Re: Oscilloscope CRT problem

Is the timebase running? Is the trace centered? It's best to check the basics before looking for complicated faults.

[Krankshaft]

Re: Oscilloscope CRT problem

Wow no HV anode lead geez.

Basically you need 5 things for a CRT to display a sharp image filament voltage, high voltage anode (electron accelerator voltage), screen voltage, focus voltage (both derived from the flyback via a resistive divider in most cases), and deflection drive (to deflect the beam into something useful).

Even without deflection you should still a get a green dot without focus a blurry green dot .

This is why I went with a Tektronix 475 they're hard to kill and are built like rocks built in the late 70s - early 80s in Oregon no made in Taiwan here . I'd be careful with the dials on this unit especially the volts / div and time / div they don't look as solidly built.

If that pic on e-bay is of the scope working and the anode wire is missing this is textbook fraud. No way you're getting ANY image without anode voltage.

The HV anode feeds the acceleration grid in the tube if the electrons don't strike the phosphors hard enough they emit no light.

[Toasty]

Re: Oscilloscope CRT problem

MV950 appears to be a voltage multiplier block. One end is the anode to the CRT, the other to the flyback, and ground.

When you take the pics, would you take top down shots of the whole chassis? Or, maybe 2? 1/2 the front the other 1/2 the back?

Is the HV anode lead connected to the CRT?

If that part (MV950) was there and removed, the anode lead went with it. If the lead to CRT is missing and there is a hole on side of tube where it should be connected, this guy ripped you off. You'll have good reason to complain and void the whole deal and get him to pay return shipping.

But, I might be getting ahead of myself.

Toast

[etnietering]

Re: Oscilloscope CRT problem

OK i'll send them a message tomorrow - I need to get to sleep!
Also, now that it's completely dark, I turned it on with all the lights off, the power LED is definitely on, there is definitely an orange glow in the back of the tube, but not so much as a hint of illumination on the screen.
It still strikes me as odd that that part is missing...I'll try to take a picture tomorrow.

[Toasty]

Re: Oscilloscope CRT problem

Ok. Thought it was this one:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=190331062094

Look at that one and try setting the controls like this picture:
https://www.badcaps.net/forum/attach...id=11537&stc=1

Yeah, I think he carefully worded that to NOT say it was working, just that it was Like New.

I'd still bitch. You at least might get some $$ back.

Furthermore, always use a credit card with PayPal. If they stonewall you, you still have recourse through the credit card.

Toast

[etnietering]

Re: Oscilloscope CRT problem

Thanks for the tips guys, I'm not going to try it until tomorrow though, it's too late for me to being working with 12kV...
I do have a question though: what is the best way to find out if it's working? I don't have a neon lamp, and my cheapy voltmeter only goes to 500v.
From what I can tell, by looking at the schematic and the traces on the board, the output from pin 10 of the transformer doesn't go anywhere. the trace is connected to a pad that doesn't have anything soldered to it. There's space for something with 2 leads into the board, 'IN' and 'G'. Could this be the MV950 thing? and it's just not there? Seems odd that it's not there...and it doesn't look like it was once and it was removed...hmmm....

Edit: toast, the pictures don't actually show it working...here's the link: http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWNX:IT all it says is 'like new condition' and I payed with paypal

[Toasty]

Re: Oscilloscope CRT problem

How did you pay for this? PayPal? Credit card (I hope!)?

I'd complain to the seller through the eBay message system (so there is a record). The item is NOT as advertised. i.e.- working display

You'll have to ship it back and pay for that, but you can file with PayPal or your credit card for defective merchandise.

'As Is' sales showing a working devices that are not working upon receipt are valid claims for returns & refunds. No damage to the shipping box, I trust? Well packed?

Keep everything until this is resolved.

Fight!

Toast

[PlainBill]

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?

That's it. It's unlikely that the current would be high enough to kill you, but 12KV would be enough to alter your outlook. A simple neon lamp should glow if held close to the transformer. I'd also check the output voltages of the power supply.

Again, do this with caution.

PlainBill

[loudnproud59]

Re: Oscilloscope CRT problem

Yes that is the correct location but take great caution the flyback voltage is about 12000 volts, if you are not sure on what to do take it to someone who knows like a tv repair shop,again be very careful.