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    Help Needed to repair a CRT + pictures and info about the problem.

    Hello, my CRT Monitor from my old retro system currently gave up on me, after i tried to find what the problem was without success, i took the monitor to a specialist to check what the problem was to see if it could be fixed.
    He said "there was no components to repair the damages", after awhile... i took it to another specialist..., and he said it was a problem with the flyback and it could only be fixed with a new one and gave me the reference model of it. I searched awhile and contacted the fabricant to check if they had an "HR46500 Flyback model", unfortunatelly they don't have those anymore, i ended-up contacting another shop and they asked me what were the sympthoms. As usual.. i said (Horizontal deflection problem) the image closed from the sides giving me a line from the top of the screen to the bottom. They said it couldn't be the flyback and told me to check the yoke and so did i.. tested the yoke tested the flyback & all good.., any advice, any help would be appreciated thanks in advance and sorry for my "bad english". Click image for larger version. 

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  2. #2
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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Quote Originally Posted by siXence View Post
    image closed from the sides giving me a line from the top of the screen to the bottom
    This looks as though you have a weak power supply to the horizontal deflection or else the horizontal amplifier is not amplifying.

    I have a 'retro' Tektronix scope with CRO and tubes. The power supply produces several outputs at different volt levels. Service manual shows voltage to the horizontal plates draws from sources +100 to +250v and possibly -100V. Current is several mA.
    Inside is a potentiometer adjustment for me to change the width of the sweep.

    If you want to chance the risk of poking around inside your scope, then you can look for a similar adjustment. A dirty or burnt potentiometer is able to create your symptoms. Or if you cannot obtain adequate voltage then one or more power supplies are faulty.

    Even if the power source is adequate, a defective neighboring circuit might be shorted, draining away power which should go to the horizontal plates.
    Suspect circuits include:
    * horizontal amplifier
    * sweep generator
    * sweep trigger


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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Thank you for the quick tips Brad!! I will check everything as soon as im able to in a few hours hopefully finding the culprit

    - - - Updated - - -

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    Can't find any Schematic Diagram of this screen model (Samtron 96P), i have no idea were to look for those, i have a potentiometer in front of the flyback tried to tweak it nothing happens
    Last edited by siXence; 4th March 2019 at 06:57.



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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Now I realize I misunderstood thinking your CRT (monitor) is an oscilloscope (CRO). The principles are not too different anyway.
    Your unit is like a TV set but yours has high resolution. There may be buttons on the front panel. Did you press these to see if you can change settings for scan height and width? It's possible on a deluxe unit.
    However if your monitor is from the 1970's or 80's then it may be the type that has an unlit margin around the picture (it's hard to tell from your photo). Screen size may vary depending on 10 percent tolerance of some component such as a power resistor. I have wanted to increase the picture so that it fills the entire screen, but I was unable to find an easy adjustment. Besides the idea of insufficient voltage to the horizontal yoke, or plates, etc., there is the possibility of arcing. Carbonized dirt, dust, deposits tend to accumulate. Do you start hearing a new buzz which might be rapid sparking in the high voltage coils?


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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    The horizontal output stage MUST be working or there would be no picture at all. The same output stage that produces the scan also produces the HV to the tube and without that the screen would be completely blank.

    Either the horizontal oscillator frequency has shifted significantly or one of the coupling capacitors around the scan coils has gone open circuit.

    CRT monitors are magnetically scanned - oscilloscopes use electrostatic scanning, they are very different to each other!

    Brian.

    [edit - I think the manual for this chassis is 955MB which I have attached but the quality isn't too good I'm afraid]
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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Brad! i had already tried to mess with the panel it opens but i can't see what im doing the image is all broken :/
    betwixt i will dig in that .pdf today thanks for the quick tips in advance!



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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Click image for larger version. 

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    Only tomorrow i have the capacitance meter with me, i don't trust the tests with the multimeter, should i inspected those marked areas? That blue 2kv ceramic disk capacitor i never thought it could be the problem but who knows, another question (do i need to take out the capacitor to test it correctly/preciselly?) thanks a lot for the explanation/.pdf



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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Quote Originally Posted by siXence View Post
    capacitance meter
    ...
    do i need to take out the capacitor to test it correctly/preciselly?
    Yes, the capacitor needs to be tested out of circuit since neighboring components can throw off the readings.

    This would be a good time to check the capacitors (particularly electrolytics).
    There are electronic technicians who routinely replace all electrolytics when they service old equipment. And there are claims it cures the equipment even though objective tests could not diagnose the fault.

    Besides the tendency to change value, electrolytics often become dry, leaky, or develop a problem with ESR (equivalent series resistance). Test capacitors in the area of the horizontal drivers.
    ESR is an important parameter since switched-coil power supplies have become popular.


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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    I will do is as soon as im able to, thanks for the attention/support^^



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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Hello again, managed to test the whole yoke area but not the horizontal circuit, im having 2 problems now, one is cold solder joints somewhere i turn on the screen its all black with backlight, i touch the pcb it opens the vertical and stays like in the pictures, there are no damaged capacitors or resistors in the small pcb on yoke, now what i am going to do probably tomorrow will be searching for broken electrolytics in the main pcb horizontal circuit once again thanks for the support ill keep updating cheers.



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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Quote Originally Posted by siXence View Post
    Hello again, managed to test the whole yoke area but not the horizontal circuit, im having 2 problems now, one is cold solder joints somewhere i turn on the screen its all black with backlight, i touch the pcb it opens the vertical and stays like in the pictures, there are no damaged capacitors or resistors in the small pcb on yoke, now what i am going to do probably tomorrow will be searching for broken electrolytics in the main pcb horizontal circuit once again thanks for the support ill keep updating cheers.
    Hello again, after searching awhile i have discovered what might be the problem, and (im 90% sure its "an IC failure"), the big micom microship. I managed to find the right chassis model of the screen wich is here (http://www.shema.ru/cd/mon/5/data/19mt.pdf) after testing the microship the screen went all black with backlight only, i took it out cleaned it put it back in and the screen was back to its "no horizontal deflection state" the only thing im not 100% sure its ok is the T401 horizontal output transformer, a little yellow and black transformer im not sure how to measure it correctly but i've been watching some videos explaining and it seems to be fine, so all the failure points to the (IC-201) full reference:

    IC201 0903-001194 IC-MICROCONTROLLER 3P863,8Bit,SDIP,42P,600MIL,12MHz,ST,CMOS,PLASTIC,5 V,-,-40to+85C,1040BYTE,48KBYTE

    PN19MT_04 2001.02.19(9F4B) 0317

    If anyone knows where to find one of those, i already tried one with the exact same specs from a 17" (Samtron 76E) wich shows in its service manual that's exactly the same as the one above (IC201 0903-001194 IC-MICROCONTROLLER 3P863,8Bit,SDIP,42P,600MIL,12MHz,ST,CMOS,PLASTIC,5 V,-,-40to+85C,1040BYTE,48KBYTE) and the Power led became on and off tickling sound, installed again the original ic "pn19mt" and tested it, the same no damages, tested the other "ic pn17" in its monitor and all good no damages, can it be a power supply issue also ? Im still thinking its just the IC



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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Quote Originally Posted by siXence View Post
    Power led became on and off tickling sound
    This could be important since the sound might be high voltage arcing near the led. Suppose it's not the led at fault but intermittent cutoff of the power supply? Darken the room while watching for any spark. Look at both sides of the pcb. Look around every component. Check especially the area where you said you you touched the pcb and caused the screen to change.

    Use a non-metallic rod to wiggle components where you think might be a fractured solder joint.

    If you're trying to choose whether to experiment on the microcontroller or the transformer, choose whichever is less expensive, or is easier to fix.


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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Quote Originally Posted by BradtheRad View Post
    Darken the room while watching for any spark.
    Use a non-metallic rod to wiggle components where you think might be a fractured solder joint.
    If you're trying to choose whether to experiment on the microcontroller or the transformer, choose whichever is less expensive, or is easier to fix.
    Hey, i found no signals of arcing just heard the tickling noise, the new problem with the vertical was bad contact with the micom microship, as soon as i cleaned it the vertical opened again with no problems like the normal, I have only the horizontal issue for now. As i said, i changed to another micom microship from a different chassis with the same specs wich didn't work and made all those noises/power led blinking. I tought i had fried it but it is 100% fine, no changes/damages to the tested ic's.
    Is it possible to recover the micro-code from the broken ic and reprogram the new ic with the same specs ? Once again thanks for the attention ill keep updating



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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    I would think it EXTREMELY unlikely to be the multi-function IC. The fault has all the hallmarks of a horizontal output stage failure. Remember that if the IC horizontal output signal was missing or significantly wrong, there would be no HV to the tube and no picture at all.

    Brian.
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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    I will correctly measure the Horizontal output transformer "T401" and all its components and then i will give updates about the work. I really tought it could be the IC201 because i had no image at all only backlight, i touched it and the vertical became opened again, with that i decided to take it out and clean it, and to my surprise after i cleaned it, the vertical was fine again no issues i can touch the board it won't close and open like before. Once again thanks for the tips/attention. Cheers



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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Hello again, after some time away from home i finally got able to test the transformers and some other components, unfortunatelly all seems to be good. My last hope is a Ceramic Disk Capacitor a very small one right on the scan coil plugs on the "H. Section cables" i was measuring in circuit because i didn't took it out, my old man kept saying "those never go bad" (blue ceramic disk capacitors he was saying very rarely go bad) but in CRT's we know they usually work with high voltage and can go bad right?, in result of that i decided to give a small test without taking it out from circuit, and for my surprise it didn't show any values on any scale/polarity, tomorrow i will take it out and test it, but i would like a hint from the masters if im wrong about my guess... it should give readings right ? even if they are wrong readings because its being tested in-circuit it should give values/readings am i wrong ? can anything around supress the readings in circuit ? I don't see anything linked with the capacitor besides the Red Cable on the scan coil plug. From my experience it should give any kind of value even if its wrong ones am i right ? Best Regards



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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    It's easier to imagine a ceramic capacitor going bad due to short. With high voltage it might arc between the plates. What reading would that give on your meter?

    However if it goes open then it could be a broken lead or a cold solder joint. Conceivably a break could occur where the wire is tack welded to the plate? What reading would that give on your meter?


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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    Quote Originally Posted by BradtheRad View Post
    It's easier to imagine a ceramic capacitor going bad due to short. With high voltage it might arc between the plates. What reading would that give on your meter?

    However if it goes open then it could be a broken lead or a cold solder joint. Conceivably a break could occur where the wire is tack welded to the plate? What reading would that give on your meter?
    It's a B-101k 2kv capacitor i took it out of circuit right now, B stands for +0.1Pf and the meter values are 91.3 pf, i think its bad ? +0.1pf tolerance ?



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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    I forgot to mention: The readings are oscillating a lot from 91 to 91.1/91.2/91.3/92 sometimes 95 its bad right tell me this is the issue im losing hope



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    Re: Help Needed to repair a CRT + pictures and info about the problem.

    101 = 10pF
    Make no mistake between my personality and my attitude.
    My personality is who I am.
    My attitude depends on who you are.


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