Viglen CRT monitor intermittent jumping

[R_J]

Re: Viglen CRT monitor intermittent jumping

Ok thats good, now whats the voltage on the other RED wire I asked about? It supples a lower voltage to the video circuit on the main baord and also up to the crt neck board
On one of your pictures that regulator ic looks like it could be a 7812, so the red wire should have 12 volts on it

[roadrash]

Re: Viglen CRT monitor intermittent jumping

That was one of the first voltages I asked about (back in post #26), you said there WAS 115 volts on that red wire

Using "the picture", point to the wire you unsoldered during cap removal.


But that is still not the voltage I asked you to measure. but that 115v needs to be there because it is the supply voltage for the R,G.B driver transistors (the big to220's on the neck board)

I forgot to change the scale on the meter to 200v, I am measuring 125v now on this wire.

[R_J]

Re: Viglen CRT monitor intermittent jumping

but I can ony measure 1.0v DC on the red wire (next to orange wire) on the neck board

That was one of the first voltages I asked about (back in post #26), you said there WAS 115 volts on that red wire

Quote:
Check if you have the 115 volt screen supply on the neck board (it is marked)

Yes it is. It did get detached and unsoldered during removing a cap but i resoldered it back.

Using "the picture", point to the wire you unsoldered during cap removal.


But that is still not the voltage I asked you to measure. but that 115v needs to be there because it is the supply voltage for the R,G.B driver transistors (the big to220's on the neck board)

[roadrash]

Re: Viglen CRT monitor intermittent jumping

So you are getting the video signal to the crt neck board (the board that plugs onto the crt). Now see if you are getting it to the transistors on that board.
On the plug that goes to the neck board that has the 3 video signals, there is also a red wire, what is the voltage on it?

That picture you provided is the side of the deflection yoke, you don't need to check anything on it.

Oh sorry that is called the deflection yolk. There is video signal on the power transistors but I can ony measure 1.0v DC on the red wire (next to orange wire) on the neck board. The tube heater light is a orange glow shouldnt it be a bit brighter than that?

[petehall347]

Re: Viglen CRT monitor intermittent jumping

all i was thinking in the past i have seen a lost colour because of bad transistor . on that board . its been a long time since i played around with crt though .

[R_J]

Re: Viglen CRT monitor intermittent jumping

I had him check the +115 and he said it was there, I also asked about Q807 "Q807 has between 2.4 & 3.6v on all pins" which seems low?
So now I am asking about a lead (red wire)that goes from the main to the neck board as I think it could be a supply for the board.

Its hard to trace based on the pictures that are obscured by wires, and no schematic.

[petehall347]

Re: Viglen CRT monitor intermittent jumping

wondering if the power has been knocked out for the neck board . wouldn't think it was all dead otherwise .

[R_J]

Re: Viglen CRT monitor intermittent jumping

So you are getting the video signal to the crt neck board (the board that plugs onto the crt). Now see if you are getting it to the transistors on that board.
On the plug that goes to the neck board that has the 3 video signals, there is also a red wire, what is the voltage on it?

That picture you provided is the side of the deflection yoke, you don't need to check anything on it.

[roadrash]

Re: Viglen CRT monitor intermittent jumping

You say the scope screen goes blank when checking for a signal on these 3 points? What is the input voltage range on the scope set to and is it also set to AC and NOT DC.
You should have a similar signal on the neck board as you measured where the DB9 connector connects to the mainboard, only the amplitude would likely be larger.

I am starting to suspect there are no or low voltages to the area that does the signal processing on the main board.

I also don't see any yellow wire going to the neck board, The r,g,b wires between the neck board and main board are thin coax cables.
There are no sync signals that go to the crt board.

Looks like a misunderstanding, I was thinking when you said neck you meant around the base of the tube where where are 4 wires RGBY solderd on. These come up from the 4 pin connector on the pcb. Sorry about that I ested the right 3 coax wires on the tube pcb and they do have the same signal as that on the 9 pin D connector.

[R_J]

Re: Viglen CRT monitor intermittent jumping

You say the scope screen goes blank when checking for a signal on these 3 points? What is the input voltage range on the scope set to and is it also set to AC and NOT DC.
You should have a similar signal on the neck board as you measured where the DB9 connector connects to the mainboard, only the amplitude would likely be larger.

I am starting to suspect there are no or low voltages to the area that does the signal processing on the main board.

I also don't see any yellow wire going to the neck board, The r,g,b wires between the neck board and main board are thin coax cables.
There are no sync signals that go to the crt board.

[roadrash]

Re: Viglen CRT monitor intermittent jumping

Check if there is any video on the neck board, R in, G in, and B in. also check if you have voltages on Q807 e-b-c.

Q807 has between 2.4 & 3.6v on all pins
The RGB wires conected around the tube dont show any signal. The scope screen goes blank. (There is a Red, Green, Blue, & Yellow on that group of wires, is the yellow a sync or something?

That could be good video? what is the pc outputing? a single c:> prompt a bios menu?

The PC boots straight to a graphical type desktop call GEM (graphical environment manager)

[R_J]

Re: Viglen CRT monitor intermittent jumping

Check if there is any video on the neck board, R in, G in, and B in. also check if you have voltages on Q807 e-b-c.

[R_J]

Re: Viglen CRT monitor intermittent jumping

If you really want the video to be stable and triggered you are just looking to see where it is being lost.
If you really want a stable video signal for one video frame or one line, feed the vertcal sync pulse from the pc into channel 2 of the scope and have the scope set to trigger on channel 2
That could be good video? what is the pc outputing? a single c:> prompt a bios menu?
Adjust the variable on the trigger control should provide a single frame of video.

Type stuff on the keyboard and you should see the waveform change

Remember this is a video signal that has NO sync pulses within it so it is hard to display a steady pattern. It is NOT like a regular broadcast composite video signal, that has the sync as part of the video waveform.
On the computer the vertical and horizontal sync pulses are on seperate pins.

I will take a guess at the video displayed on the scope and also guess that the scope trace did not start at the start of the scan (likely triggerd by some part of the video)

[roadrash]

Re: Viglen CRT monitor intermittent jumping

Ive got it all back together and powered up and it seems quite happy and tube lit up. Still no picture when connected to PC though. I had a another go at testing for a video signal on the pins that carry the RGB signals. I used the Isotech scope this time and I got this display that does look different to what I get from the pins on the dsub connector. I read a article online that covered measuring video signals on a anolouigue and digital scop[e and it says its very hard to get a decent display with out something call a video trigger which I dont think this scope has. Anyway does this picture look anything even remotely useabe?

[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.

[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

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 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 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

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).