Viglen CRT monitor intermittent jumping

[R_J]

Re: Viglen CRT monitor intermittent jumping

It would depend on the circuit, If it was for a supply voltage it would likely act as a short and blow something or just go up in smoke itself, if it was a small value for decoupling or signal coupling it should'nt cause any real problems.

[roadrash]

Re: Viglen CRT monitor intermittent jumping

It would depend on the circuit, If it was for a supply voltage it would likely act as a short and blow something or just go up in smoke itself, if it was a small value for decoupling or signal coupling it should'nt cause any real problems.

Its OK I havent shorted any I just wonderd whatwould happen if a cap was put it wrong way round.

[roadrash]

Re: Viglen CRT monitor intermittent jumping

Well I did everything I said I was going to do. I tried other computers with a EGA output on the subject monitor and there was no display either so that would suggest the computer we are using on the monitor is working ok. I took the PCB out of the monitor again and made a thorough check just to be certain that I didnt get a cap in the wrong way round and I ddin't, they were all OK. I then looked at a picture of the PC before I replaced the caps and i then compared it to the PCB after replacing the caps and it looks like all the caps I repalced were in the right place and I counted 21 original (original blue) caps I removed from the PCB and I count 21 (Black NEW) caps I repalced on the PCB. So all would appear to be right & no mistakes. I then connected up another PC to the scopes (A Dell system 200) which has a EGA output to see what output I got on the scope from that. I spent ages tweaking all the knobs in AC mode and I found sometimes when turning the volts/division knob I almost got a display of peaks & troughs so kept persevering and managed to get a few more patterns althogh it was a bit hit or miss. I am wondering if this other scope I just got has dicky/dirty contacts in the switches & knobs causing a random result when turning the knobs back & forth. Anyway do any of these outputs look like we should be getting? I have no idea what a EGA signal should look like on the scope so its guess work to me.

[R_J]

Re: Viglen CRT monitor intermittent jumping

That second pictue looks like it could be video, The scan on the scope (left to right) would show the video from top to bottom of the screen, (and seems to show 2 and 1/2 vertical fields) The amplitude of the signal would represent the intensity of the video.
I don't know which pins you got that from?
There should be 3 pins (3,4,5) that will look the same, R,G,B. The amplitude of the video should be about 1 volt P/P and the scan should be set to 5ms.
The vertical sync pulse, (pin9) should be around 3-5 volts P/P with time set to 5ms
The horizontal sync pulse (pin8) should be about 3-5- volts P/P with time set to .1ms
These are aproximate depending on the pc scan rate.

[roadrash]

Re: Viglen CRT monitor intermittent jumping

Thanks for that info RJ, nice that i might at last have made some progress with the scope. Think I will give those switches and variable dials a clean with some servisol to clean and lube them. Might make them respond more consistanly. Now I have checked all ive done was alright what should my next move be in tracing what is causing the loss of video display.
It wouldn't be that 470uf 10v cap we replaced with a 470uf 16v one would it because I have the 10v caps now i can put in.

[petehall347]

Re: Viglen CRT monitor intermittent jumping

yep the old switches play up in mine from time to time . i have an old Hitachi 40 mhz that rarely gets used plus another old scope i have on standby . think its telequipment . seems better suited to tv work .

[R_J]

Re: Viglen CRT monitor intermittent jumping

The cap voltage won't make a difference being a bit higher. The switches get oxidized with lack of use, usually as the switches are used they self clean and you don't see much of a problem.

[roadrash]

Re: Viglen CRT monitor intermittent jumping

Your right RJ but it takes time to break through the oxidisation for example a old amplifier volume control crackles for ages. A quick squirt of Servisol and a few turns back and forth and the crackles are gone and the movement feels nice and smooth like its new again.
RJ can you help guide me what i should be testing with this scope now ive got it to find this monitors problem.
I wish I had your knowledge in this field but being a motorcyle mechanic doesnt have much in common apart from basic testing with a mulimeter. Hahhaha lol..

[R_J]

Re: Viglen CRT monitor intermittent jumping

The first thing to test is if you have the rgb signals at the plug on the main board,(the one that comes from the rear jack) They should be there. Then I would check on the plug that goes from the main board to the neck board, the rgb signals should be there also but likely larger in amplitude, if they are not there then the problem is on the main board.

[roadrash]

Re: Viglen CRT monitor intermittent jumping

The first thing to test is if you have the rgb signals at the plug on the main board,(the one that comes from the rear jack) They should be there. Then I would check on the plug that goes from the main board to the neck board, the rgb signals should be there also but likely larger in amplitude, if they are not there then the problem is on the main board.

I am still trying to get to grips with these 2 scopes I now have. I downloaded various howto's & tutorials but cant seem to get the display on the screen as clear as shown in the pictures. What makes it hard in particular is the brightnes/intensity of the vertical line. for example in a calibration test I get the square or should I say oblong pattern and the corners are 90 degree. But it took a long time to see it like this because for a lonmg time it looks like 2 rows of horizonal lines above/below each other. This was because the horizontal lines are clear ands bright but the vertical lines are very feint & dim so its hard to see the box shapes. The intensity mainly seems to effect the vertical traces. This is the same on both of my scopes so I guess its normal but how do I adjust the brightness of these vertical traces so I can see a box shape not a series of hozizontal dashes. As soon as I can make out what I am seeing on the screen a bit easier the easier it will be to identify what I am seeing. Any suggestions?

[R_J]

Re: Viglen CRT monitor intermittent jumping

If you use the calibration test pulse it is likely 1 volt P/P, at 1Khz. if the timebase is set too fast it will display like you said, If you do not see a single or train of pulses it could be that the trigger source is set to the wrong input or the trigger polarity or level is wrong, try adjusting the trigger level should give a pulse.
If the square pulse itself is rounded or slopped and you are using a X10 probe, try adjusting the probe variable capacitor with a small screwdriver.
https://www.circuitspecialists.com/b...on-adjustment/

[roadrash]

Re: Viglen CRT monitor intermittent jumping

If you use the calibration test pulse it is likely 1 volt P/P, at 1Khz. if the timebase is set too fast it will display like you said, If you do not see a single or train of pulses it could be that the trigger source is set to the wrong input or the trigger polarity or level is wrong, try adjusting the trigger level should give a pulse.
If the square pulse itself is rounded or slopped and you are using a X10 probe, try adjusting the probe variable capacitor with a small screwdriver.
https://www.circuitspecialists.com/b...on-adjustment/

I tried what you said and the trigger settings are right. The biggest problem is most obvious on the Iwatsu SS-5802. The Iwatsu is the one ive been using and as it seemed the best because it hadnt had any problems. The Isotech scope had shown damp poblems inside after I bought it and I stripped, cleaned everything including all the switches on is ironically working the best and shows a display like it should be.
If you look at the pictures you can see the difference and see what I mean about the I Iwatsu scope having almost invisible vertical lines which makes the Calibration display look more like a series of hozizontal dashes. I would use the Isotech scope but I have no idea after it being so damp, whether it can be trusted. Is it possible to increase the brighness of these vertical lines on the Iwatsu and what do you think about the Isotech scope being any good.

[R_J]

Re: Viglen CRT monitor intermittent jumping

Both scopes seem to work so use either one, I woul'nt be too concerned about the one that showed signs of dampness, If it was going to cause a problem it would have when it was damp, not anymore.
The trace intensity cant be adjusted for part of the waveform (vert) its the trace speed going from the lower part to the upper part of the square wave that makes it look less bright.
It is a used scope, so the brightness is not like a new scope.
So go ahead and use the Isotech, you always have the other one as a spare.

[roadrash]

Re: Viglen CRT monitor intermittent jumping

OK thats great news. I just need a ilttle help here now RJ as to where I should start testing which I gather must be done with the monitorturned on. I can keep it opened up and connect it up to that old PC it goes with. Can you just point me to where I should start connecting that probe. I will try and see if I can get a better display of a video signal
on the scope now ive had more time to familiarise myself with its controls. I would guess we start at the video input (D sub) connector, but not sure which area to go to after that.

[R_J]

Re: Viglen CRT monitor intermittent jumping

When it comes to tracing the signal, Its hard for me as there is no schematic and only the picture of the circuit board, I would test where the sub-D connects to the board and look at the 3 rgb signals, they should be there.
I would then jump to the plug that feeds the signal to the crt neck board and check if the signal is also there (likely larger in amplitude) If it IS there then the circiuit on the main board is ok, If it is not there, the signal will need to be traced from the sub-d connector (pick a color) to the first component (ic or transistor).

[roadrash]

Re: Viglen CRT monitor intermittent jumping

I thought you might be interested I tried to see if I could see what area of the PCB that offcut got attracted to. Its always atracted and sticks to the same area. Its a strong magnetic field because it will even drag the offcut from one side of the pcb to the other.
Here are some pictures. The firat picture shows the pcb side and you can see me pointing to a offcut and where it stuck too when I dropped it on the pcb. Its just around the transformer in the area of a transistor D1397. Maybe its that what got zapped/shorted by that offcut. I will check it and any other parts around that area now I know where it is.
If no luck I will start tracing the video through the pcb. Is there any area to keep clear of when probing. Obviously the HT transformer etc i would think but anywhere else?

[R_J]

Re: Viglen CRT monitor intermittent jumping

That coil, L602, is the horizontal linarity coil, it is in series with the deflection yoke's horizontal winding, (I mentioned it before) If there was a fault with it or that circuit you would not get any high voltage or horizontal deflection.
However there is a large horizontal pulse on that coil and it may have fed that high voltage to an area and blew something?

They do supply some secondary voltages from the flyback transformer, I would look at where the pins from the flyback go and see if they feed any diodes, they usually have a low value resistor either between the flyback and diode or just after the diode.

Just stay away from the horizonal output/flyback transformer area and stay away from checking anything on the hot side of the power supply, you would just get a meaningless waveform as the ground would be wrong.

[roadrash]

Re: Viglen CRT monitor intermittent jumping

I have been removing and testing a few of the parts like diodes & transistors around that area to see if any are blown or faulty. So far all diodes are ok but this
D1397 transistor doesn't apear like a NPN transistor normaly does on my tester (like in the little schematic). Is it faulty maybe?

[R_J]

Re: Viglen CRT monitor intermittent jumping

That is the horizontal output transistor. It drives the horizontal deflection and also the high voltage transformer to light the crt. which you already proved is working by increasing the screen control and seeing a raster.
Pulling parts at random is only going to cause more problems.
As you can see there is a built in damper diode and base to emitter resistor, so that tester will not know that.
This is not the manual but is likely similar and does show how a the crt monitor works and where you should be looking fo a problem.
That transistor would be Q503 in THIS manual, the coil 602 has the same location number as your monitor. Most of the monitor is working (so far) you only have a loss of the video signal.

[roadrash]

Re: Viglen CRT monitor intermittent jumping

Wow thats excellent work RJ finding that manual. Sorry didnt think I was doing any harm taking bits out to test as thats what I was told is the best way. But after you suspect a part to be faulty of course not just randomly. Point taken and I will pop them back and this time wait to we find a possible suspect part to test.
I will get right onto looking through that manual.