Re: Oscilloscope CRT problem
Are you sure its the CVT, I was also convinced it was that! however it was a component on the output side. I even built a Shorted turns tester to test it as advised on another electronics forum, and it showed the coil as dead! but it really wasn't.
Remember the slightest "drain" on the HV side causes huge current draws on the LV side.
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Re: Oscilloscope CRT problem
Let me know if I can help any any way etc. hope you come right!
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Re: Oscilloscope CRT problem
Ok, just test it and it sits at 20uS per wave, so if my calculations are right this means its runs at 50khz.
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Re: Oscilloscope CRT problem
Stupid question, but can I test the frequency use the scope on itself? sure the grounds must be common?...
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Re: Oscilloscope CRT problem
Its back from the dead !!!!
Don't ask what it was, but here's what I did:
Reassemble the transformer, less one turn on the output side (as I started to strip it...)
Replaced C951, C952 and the Zener.
I cut a "slot" between the tracks on the PCB where the HV had arced before.
Turned it one for 5 seconds and felt Q950, it was cold, so tried it again for 10 seconds, again cold...Mmmm decided to turn it around and look at the screen and I couldn't believe it..... A...
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Re: Oscilloscope CRT problem
Its a Ferrite core transformer, with a E I configuration, it has a small peice of plastic between the ends of the "E" and the "I" creating about a 1.5mm gap.
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Re: Oscilloscope CRT problem
Ok, as I thought, but I'm now wondering if the CCFL inverters secondary winding is also isolated, or if they share the gound? id it does share, could one not just modified the board (cut the track) to isolate it?
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Re: Oscilloscope CRT problem
Looking at the BXA12529 invertor/driver, it can deliver 10ma. rated min:950V typ:1000V max:1050V
pushing that through the voltager doubler should give us a min of 1900V and max of 2100V, surely that should work? only thing that might be a problem is that if the input and ouput use a common GND, then how are we going to get the -2000V? or am I getting myself confused?
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Re: Oscilloscope CRT problem
From what i've seen on youtube and some dead boards I have it should power up. but I not 100% sure.
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Re: Oscilloscope CRT problem
What about using one of these, as discussed above, would they not work?
[url]http://za.rs-online.com/web/p/lcd-display-accessories/5350085/[/url]
...................... Min - typ - max
Output Voltage - 600 - 700 - 800
Output current - 4.0 - 5.5 - 7.0
Or perhaps this one driving directly?
[url]http://za.rs-online.com/web/p/lcd-display-accessories/5350063/[/url]
..................... Min - typ - max
Output Voltage - ... -1500 - ....
Output current - 4.5...
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Re: Oscilloscope CRT problem
Thanks monpirri,
but I've just noticed, the schematic is slightly different to what I have. My looks like the picture in post 78, which I copied from post 40. I think mine if equivilent to the 2120[B]B[/B], and not the 2120.
Does anyone perhaps have the schematic for the 2120B?Re: Oscilloscope CRT problem
Thanks monpirri,
but I've just noticed, the schematic is slightly different to what I have. My looks like the picture in post 78, which I copied from post 40. I think mine if equivilent to
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Re: Oscilloscope CRT problem
here is the schematic of the exact power unit. I would imagine the same would apply for the "voltage doubler"?
So if I turned a new transformer I would need to calculate its output to be about 700V, perhaps 800V for safety, as the voltage reg system should drop it if required?
Is a TV flyback not an option?...
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Re: Oscilloscope CRT problem
Hi monpirri
Must be a common thing with these units then.
Could you elaberate a bit more on your attempt to rewind it! as this is what I was planning on doing!
As it appear the transformer only supply the HV to the rest of the circuit and in not cotrolled by any sort of time from the rest of the system, could one not use a small flyback tranformer from a small 5" B&W TV or something? it could be simply driven from a seperate driver? I'm desperate
Would you perhaps have the complete...Last edited by LightySA; 03-16-2012, 12:45 PM.
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Re: Oscilloscope CRT problem
Ok, so it appear the transformer is toast!
So now to try have have it re-wound.
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Re: Oscilloscope CRT problem
Thanks Agent24
Thought I would just use the same thread as alot of the info in this thread is relevent as its the same "design" and problem. If I don't get any response I'll take your advice and start a new thread!
Thanks again
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Re: Oscilloscope CRT problem
Hi All
I'm new to the forum and wonder if you could please help.
I have the same oscilloscope although re-branded as "Toptronic" that is dead, with very similar faults. (mine is the 20mhz version)
I had used the scope quite a bit, it then went on the blink and I managed to get it working by replacing U950 (741) and the D880 for the HV transformer. it worked for a while before dying again. This time after replace the same components it hasn't helped. I've also noticed that it started to arc on the...
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