Need Help with Finding an Amdek V220A Flyback (FMC-1245NL) Replacement

[awewsomegamer]

Hello, I've had this monitor for nearly two years now, over that time the image has severely degraded to the point where now nothing is displayed.

The problem, randomly varying brightness/contrast, was barely noticeable at first, and the picture looked completely fine asides from geometric issues (see Picture_in_June_2024.mp4).
I began looking for information on how I could fix this problem, ending up opening the CRT (whilst off and discharged) and replacing a nasty looking capacitor (C525).
However, I found no useful information about this monitor, nor any of its major components (tube, flyback, vertical oscillator), online.
Over the course of one year the picture degraded so much that at maximum brightness and contrast it was still very dim and low contrast (see Picture_in_July_2025.mp4).
At this point I opened up the CRT again and had another look around. I cleaned all potentiometers, which did not fix the issue, and recapped the video circuitry and neckboard, again this did not fix the issue.

I decided to look into replacing the flyback. Upon searching it up, I found a page from Samsung, https://samsungparts.com/products/2859-116-010, listing it as sold out. I sent them an email asking about if they had specifications for it, but they did not respond.

After a while, I decided to digitize the board so that it would be easier to unravel, which revealed another potential problem area: the trimmer resistors near the brightness knob (VR501 and VR503).
From VR501 I could get a stable reading between pins 1 and 2 (~128 kOhm), turning it all the way towards pin 3 gave a reading of 200 kOhm.
However, VR503 was very different, from the only text on it "B2M", I figured its range was likely 2 MOhm, but I could never get a clear reading from it with the multimeter.
Out of circuit, I hooked my oscilloscope's signal generator to pin 2 (in circuit goes to G4) and a probe to pin 3 (in circuit goes to GND) **.
A very similar pattern emerged to how the picture was behaving: there were long periods of low resistance and intermittent bursts of high resistance to ground.
This was the last possible problem I could diagnose and attempt to fix, otherwise it would probably be an issue with the flyback, or something supplying it.
Since I do not have the skill-set to test if it was an issue with the flyback, if replacing VR503 did not work then I would bring the monitor to a repair shop.
**: In circuit, pin 1 of VR503 goes to G2.

Replacing VR503 with a modern alternative, did not fix the issue. Infact, the monitor displayed no picture - even if using the original VR503.
I proceeded to drop it off at a local repair shop, with all original parts in circuit (except for the capacitors I replaced earlier; however, I did provide them labelled in a ziplock bag) and an explanation of what I had done.

A couple days ago I picked the monitor up from the repair shop, and was told that the issue was most likely with the flyback, as everything else looked good.

Would anyone happen to know, or has worked with, this monitor, or know of an equivalent flyback transformer?

--------------------------------------------------------------------------------------------
IMG_1725.jpg: A picture of the front of the monitor
IMG_1727.jpg: A picture of the back of the monitor
IMG_1731.jpg: A picture of the left side of the monitor
IMG_5008.jpg: A picture of the flyback transformer (T502) with the heatsink of the HOT (Q503) to the bottom and the H-width coil to the right (L502)

Picture_in_June_2024.mp4:

Picture_in_July_2025.mp4:

Notice how contrast and brightness appear to change over time. Most prominently with the clouds behind the statues in the middle of the screen.

*Board: Samsung (?) Chassis NO. GCB, 3003-703-910, 94V-0, KC-16
Flyback: Samsung FMC-1245NL (#2859-116-010)
Tube: Samsung 12NBYLAN
Vertical Oscilliator: Samsung KA2130A (2E2)
*: These are all markings on the board, the first one is toward the top of the circuit by the power switch and the rest are all bunched around T502.

Here is a link to a repository with my attempts to reverse engineer the board: https://github.com/awewsomegamer/Amdek-V220A, revision three is the latest. Please note I am very much a beginner so there may be some nonsense in these schematics.

 

[Hugo Holden]

I decided to look into replacing the flyback

I cannot understand from the limited data that you have presented here, that there is likely anything at all wrong with the flyback transformer in your VDU.

Do you understand H. scan efficiency output stages and EHT generation from those and how these work? And understand the effects of any EHT variations on the raster scan, if they are indeed even there ?

Do you understand how to diagnose troubles when you see an abnormality in either the raster scan, or the picture content within the raster. Can you distinguish between these two different things so as to be able to formulate a proper diagnosis as to what is wrong with your VDU ?

Your video image shows an H. synchronisation defect, assuming it is a synchronised H scan oscillator arrangement and not direct drive, you could confirm that, if it is the former there will be an H. hold control, if the latter not. It is not a defect in the flyback transformer unless there is frank obvious arcing going on upsetting the H scan, even then that would be highly unlikey over only half of the vertical scan time . The video image shows that something is causing severe phase error noise affecting the H scan/osc stage but only in the upper half of the raster's vertical scan time.

But you see, every inexperienced you-tuber and blogger cannot help themselves blaming the flyback transformer as a knee jerk reaction for a defect in a CRT based VDU, it is a lot like the inexperienced computer repairer blames the CPU first and replaces that, then oddly they are surprised when the fault remains.

Probably, at the rate things are going, there will likely be few experienced CRT based TV and VDU repair technicians around in the next 20 years, we will all die off, leaving the inexperienced and clueless to post all sorts of misinformation and nonsence about flyback transformers on youtube.

You see the thing is, most now do not understand the operating theory of the H scan stages in magnetic deflection systems for CRT's because they think Ampere's theory of magnetism is obsolete and nothing like the H scan output stage is studied in modern microelectronic courses, sans the Flyback supply, but these in most SMPS's are stepdown systems now, yet alone the many other of the more subtle aspects of the vintage circuitry in CRT based VDUs. It has become obsolete and ill understood technology now, along with the technicians that once understood it. I count myself in that group.

Obviously this problem would be dead easy to diagnose and fix with the VDU's schematic and a scope. Rather than the github link if you posted the schematic here as a .jpg image or similar I could make more suggestions of how to diagnose and fix it, before I "age out". For example I could draw on the schematic, where to make tests and re-post it. For this you will need a scope.

 

[Hugo Holden]

There is a fault mode that could explain what appears to be interaction between the horizontal and vertical timing, the random like nature of the disturbance in the scan and the progresive nature of it degrading over time. Though this problem is more common in color VDU's because the voltages are higher. Unfortunately some of the glues used in the deflection yokes, erroded through the enamel copper wire's insulation. If there was a failure like that and some arcing in the deflection yoke, a pattern like this could occur. Though we have not commonly seen this in mochrome VDU's.

One way to help tell is to find out if the disturbance is primarily in the raster scan or in the video. If the width control (normally an inductor that has a ferrite slug is adjusted with a plastic tool) to reduce the raster width so that the raster scan edges are visible down each side, the raster scan can be inspected for horizontal width stability.

Some arcing in the phenolic pcb between part of the H & V scan circuitry could also do it, or be more probable in a monochrome VDU with a phenolic pcb, so switch out the room lights and have a good look around on the pcb in the dark and see if you can identify anything in that area.

If the fault was confined to the H scan and EHT generation circuitry alone, and there was arcing or a component in the evolution of failure there, for example in the flyback transformer, it is far more likely that the defect you are seeing would appear over the whole screen, not just the top half of the vertical scan timing.

 

[awewsomegamer]

Thank you for your response, Hugo.

I do not understand the things you have listed. I am not an experienced electrical engineer nor technician of any sorts.

I think you are referring to the artifacting in the July 2025 video. This is normal as I paused the VCR there and it does that no matter what display I hook it to. I should have shown the same VIC 20 output instead.

If you look towards the middle of the screen in that video you can see brightness and contrast change over time.

During the few tests I did with the back of the CRT off, I did not hear nor see any arcing on the board.

The repair shop I took the CRT to claims to have experience with retro CRT TV's (particularly Samsung ones) and claims to have been doing so for decades.

Here are pictures of the board's schematic. Do note, this is my best attempt at reverse engineering it. This is not anything official from Samsung nor Amdek.



This is the neckboard, I have moved things slightly over in this photo to make things a little bit more clear.

 

[andy]

I think you are referring to the artifacting in the July 2025 video. This is normal as I paused the VCR there and it does that no matter what display I hook it to. I should have shown the same VIC 20 output instead.

If you look towards the middle of the screen in that video you can see brightness and contrast change over time.

That changes everything. You should have mentioned that it was a poorly synchronized video source...

When flybacks fail, they usually fail quickly or instantly. A bad flyback wouldn't affect the contrast. This is all good news since it means you probably don't need a new flyback.

All repair shops claim to be highly experienced in everything. They never say "I don't know". If they can't figure out the problem they just blame an expensive or unavailable part.

 

[awewsomegamer]

That changes everything. You should have mentioned that it was a poorly synchronized video source...

When flybacks fail, they usually fail quickly or instantly. A bad flyback wouldn't affect the contrast. This is all good news since it means you probably don't need a new flyback.

All repair shops claim to be highly experienced in everything. They never say "I don't know". If they can't figure out the problem they just blame an expensive or unavailable part.

Hello Andy,

Did not know flybacks were quick to die, so this is very good to know now.

I am thinking of testing some components out of circuit in the "brightness" (everything on the negative end of C518) circuitry tomorrow.

Do you have any recommendations of where else I should look?

Thank you.

 

[Hugo Holden]

With that video source that much error in the video signal, it can change the background contrast & brightness, because it confuses the video's DC axis. It is no use for any diagnostic application, we need to see a perfect signal.

I wonder, so we can see better what is worrying you can you make a better video of what you are seeing wrong on the screen, maybe a grey scale test pattern, known to come from a stable video source.

 

[Hugo Holden]

Also, if it is just a fluctuating brightness or contrast issue, one test you can do is to not feed it with a video signal at all, and turn up the brightness control (and any sub brightness control presets) to illuminate the screen and inspect it to see if the brightness level is fluctuating or not?

 

[Hugo Holden]

PS: that reverse engineered schematic looks like it was done by someone with no knowledge of how to draw a proper schematic, its hopeless. A schematic is supposed to assist in explaining the signal flow and the circuit operations.

I reverse engineered an entire VDU that had no documentation, a more complex one than the Amdek, have a look at the way the schematics are drawn.

But that is not really enough, either, if anyone wants to help anyone else with reverse engineering, it also requires that the circuit's operating theory is described too, that is if you want to make a document that will act like a service manual, which will be able to help others repair things. This is the kind of thing that is required for the Amdek VDU or any VDU with unavailable documentation:

https://www.worldphaco.com/uploads/The_1987_Vintage_Avionics_Conrac_Video_monitor..pdf

 

[awewsomegamer]

With that video source that much error in the video signal, it can change the background contrast & brightness, because it confuses the video's DC axis. It is no use for any diagnostic application, we need to see a perfect signal.

I wonder, so we can see better what is worrying you can you make a better video of what you are seeing wrong on the screen, maybe a grey scale test pattern, known to come from a stable video source.

The monitor currently displays no picture no matter what source I give it.

Unfortunately, I did not take any video of it with a test pattern, so I am unable to provide a real video.

I can, however, provide this recreation of what it would have looked like:

 

[awewsomegamer]

Also, if it is just a fluctuating brightness or contrast issue, one test you can do is to not feed it with a video signal at all, and turn up the brightness control (and any sub brightness control presets) to illuminate the screen and inspect it to see if the brightness level is fluctuating or not?

Without a video input, the monitor refuses to turn on.

I once gave it a plain white screen, and it did exactly what is shown in the video in my last post.

I have tested it with multiple video sources too, and it always had this same issue.

 

[Hugo Holden]

Without a video input, the monitor refuses to turn on.

I once gave it a plain white screen, and it did exactly what is shown in the video in my last post.

I have tested it with multiple video sources too, and it always had this same issue.

Maybe good that the intermittent fault has now progressed to a frank failure.

There is likely an issue with the relative grid to cathode voltage of the CRT, this controls the CRT's beam current. Though there is a low voltage anode connection to the CRT that could also cause this effect, if it was intermittently going open or acring over, by that I mean many CRT sockets themselves or neck board have spark gaps, if contaminated they can arc over at too low a voltage.

In any case, more than likel,y there is an intermittent issue in either the CRT's grid or standing cathode voltage.

In most computer VDU's the video output stage drives the cathode directly, this normally suspends the cathode at a positive voltage of more than 50 to 70V. The brightness control is usually connected to the CRT's grid circuit. If that supply is near zero volt thens the beam current of the CRT is cut off, because the grid is significantly more negative than the cathode (it is all about relative voltage between these two electrodes).

If either the grid value is made more positive, or the cathode made more negative, the relative voltage drops and the CRT's beam current and brightness increases. When the grid and cathode voltages are equal the CRT is at max brightness. Since the cathode voltage is provided (normally) by the video amplifier, there could be a fault there.

Now if the beam is blacked out (assuming its not another issue) it implies that either the cathode is stuck at a high positive potential with respect to the brightness control & grid potential, or if that is not the case, the grid is at too high a negative potential. Some circuits do provide the the grid & brightness control circuit with a negative potential, especially of the cathode potential is relatively low, as it is say in the PET VDU.

In any case, we should be able to figure out which of the two circuits has the poroblem because it is normally easy to identify the wires leading to the CRT and you can measure the three voltages, the grid, cathode and anode voltage at the CRT base and we can work out why the CRT is cutt off.

If you could take some detailed photos of the main board top, and botom and the CRT socket/neck board of present, we can work out where to test it.

 

[awewsomegamer]

Maybe good that the intermittent fault has now progressed to a frank failure.

There is likely an issue with the relative grid to cathode voltage of the CRT, this controls the CRT's beam current. Though there is a low voltage anode connection to the CRT that could also cause this effect, if it was intermittently going open or acring over, by that I mean many CRT sockets themselves or neck board have spark gaps, if contaminated they can arc over at too low a voltage.

In any case, more than likel,y there is an intermittent issue in either the CRT's grid or standing cathode voltage.

In most computer VDU's the video output stage drives the cathode directly, this normally suspends the cathode at a positive voltage of more than 50 to 70V. The brightness control is usually connected to the CRT's grid circuit. If that supply is near zero volt thens the beam current of the CRT is cut off, because the grid is significantly more negative than the cathode (it is all about relative voltage between these two electrodes).

If either the grid value is made more positive, or the cathode made more negative, the relative voltage drops and the CRT's beam current and brightness increases. When the grid and cathode voltages are equal the CRT is at max brightness. Since the cathode voltage is provided (normally) by the video amplifier, there could be a fault there.

Now if the beam is blacked out (assuming its not another issue) it implies that either the cathode is stuck at a high positive potential with respect to the brightness control & grid potential, or if that is not the case, the grid is at too high a negative potential. Some circuits do provide the the grid & brightness control circuit with a negative potential, especially of the cathode potential is relatively low, as it is say in the PET VDU.

In any case, we should be able to figure out which of the two circuits has the poroblem because it is normally easy to identify the wires leading to the CRT and you can measure the three voltages, the grid, cathode and anode voltage at the CRT base and we can work out why the CRT is cutt off.

If you could take some detailed photos of the main board top, and botom and the CRT socket/neck board of present, we can work out where to test it.

I took some higher quality pictures of the main and neck boards and the tube itself. Let me know if you need any other angles or if a picture should be retook.

There were the suspicious trimmer resistors in the brightness circuitry (VR503, VR501).

 

[Hugo Holden]

I'm sorry but those imgur images. whatever they are, cannot help me one iota, I cannot view any of them. It wants me to "Sign in".

Do me a favor and just post .jpg images here. If you can see "imgur hosted images" on your screen just use ALT-Printscreen to send them to the clipboard, then paste them into any photo editor and post them here on this thread as a .jpg, where I can actually view them without relying on a third party image hosting service cluttered with nonsence and advertising.

I have attached what I get on going to your link and clicking on it anywhere is of no help.

If people are helping you, you have to do a better job helping them and post clear and concise information on a thread, not on a link to another service.

 

[Plasma]

I'm sorry but those imgur images. whatever they are, cannot help me one iota, I cannot view any of them. It wants me to "Sign in".

You do not need to sign in to view imgur. It looks like you just have your browser zoomed in 1000% or something. Reset the zoom level and you should see the photos.

 

[andy]

Without some basic diagnostic information it will be impossible for anyone to help you remotely. To start with: Is there any EHT/high voltage? Is the CRT heater glowing? What are the voltages on the cathode, G1, and G2?

 

[awewsomegamer]

Without some basic diagnostic information it will be impossible for anyone to help you remotely. To start with: Is there any EHT/high voltage? Is the CRT heater glowing? What are the voltages on the cathode, G1, and G2?

I understand, I will measure those voltages and get back to you. Currently I have everything disassembled for pictures, and I am waiting to see if any different pictures need be taken.

From the last time I turned it on, the heater does glow.

 

[awewsomegamer]

I'm sorry but those imgur images. whatever they are, cannot help me one iota, I cannot view any of them. It wants me to "Sign in".

Do me a favor and just post .jpg images here. If you can see "imgur hosted images" on your screen just use ALT-Printscreen to send them to the clipboard, then paste them into any photo editor and post them here on this thread as a .jpg, where I can actually view them without relying on a third party image hosting service cluttered with nonsence and advertising.

I have attached what I get on going to your link and clicking on it anywhere is of no help.

If people are helping you, you have to do a better job helping them and post clear and concise information on a thread, not on a link to another service.

I have compressed the images to post them here.

I have attached the images in this order:

DSC_4636, DSC_4638, DSC_4639:
Back of the main board in full, top half only, and bottom half only. The red capacitor is UC1

DSC_4640, DSC_4641:
Back of the main board in full and bottom half only. UC1 is folded out of the way.

DSC_4642, DSC_4644, DSC_4645:
Front of the main board in full, top half only, and bottom half only.
White=G1, Brown=G2, Green=G4, Blue=A, Thin Black (Hugging Yellow)=G,
Thick Black (Begins Top Left, on Power Switch)=S, Orange=B, Yellow=K,
Green (Jumping Over Heatsink)=Video In, Red (Jumping Power Switch to Fuse)=P4

DSC_4651, DSC_4652:
Front of the main board in full and bottom half only. Q702 and its heatsink removed.

DSC_4647, DSC_4650:
The back and front of the neck board.
White=G1, Brown=G2, Green=G4, Blue=A, Thin Black (Bottom Right)=G,
Thick Black (Top Left)=GND Orange=B, Yellow=K

DSC_4630, DSC_4633:
The right and left of the CRT.

DSC_4626:
The back of the CRT in full. Blue=H2, Brown=V2, Yellow=V1, Red=H1

 

[Hugo Holden]

Ok. decent photos posted, that is the way to do it, well done.

I have reverse engineered and studied the CRT neck board. It is a fairly classic arrangement with a Cascode video output stage driving the CRT's cathode. It will be fairly straightforward with this data to find your problem. I'm actually pretty sure I know where it probably is already. I'm sure @andy will see it too.

However, it took about 1 hour to do this, I will have to write again tomorrow to conclude the information and explain what to do.

Of course if I had this in front of me on the desk, I could have done it in 10 minutes, it is much more difficult with photos (even when they are good)

 

[Hugo Holden]

As mentioned on post #12 we are looking for a disturnbance in the voltage levels of three of the CRT elements which can alter the CRT's average beam current, the cathode (fed by the video amplifier), the G1 grid, that will be connected to the Brightness control circuit on the main board and the G2 grid.

The G2 grid is not aptly named, it is really an Anode, it has a positive voltage applied to it, typically around 150V to 300V, its job, much like the anode voltage in a triode Tube, is to initially accelerate electrons away from the cathode. If its voltage was fluctuating, so would the CRT's beam current. After the electrons stream passes throug that electrode, they then are accelerated by the the man EHT voltage and pass through the focus lens, which is another gun electrode shaped like a cylinder. The G1 grid's job is to repel electrons back toward the cathode which is why it has a potential that is generally negative with respect to the cathode. If the G1 grid voltage is equal to the cathode voltage, then that is the maximum brightness or beam current the gun can provide. It can take a realtive voltage between the grid and cathode of around 40 to 70V to cut off the beam depending on the CRT.

So logically now we have the three important points, K(cathode), G1, and G2 that can be checked with a scope (using a x 10 or better x100 probe on DC coupling, or a meter) to look for voltage fluctations and find out where they are coming from.

However, you may not need to because the cause is possibly found already:

In post #12 I mentioned spark gaps. These are closely spaced gaps between two metal electrodes that are designed to flash over if the voltage exceeds a certain value, often in the 1000V vicinity depending on the design. They are sometimes built into a CRT's socket assembly, inside the socket or are discrete devices on the CRT's neck board that look somewhat like a brown ceramic capacitor with a saw cut halfway through it. This creates a controlled gap. Really good types are "spark gap tubes" that are sealed from atmospheric contaminants. Spark gaps are not an absolute requirement for any VDU, many never had them at all.

Unfortunately on your neck board the spark gaps have been created by Heath Robinson. They made them out of gaps in the pcb tracks (see attached one of your photos modified). While they might have gotten away with that a tad better on a Fiberglass pcb, on a Phenolic one it is a disaster, because with each discharge the phenolic surface (even around a punched out edge) gets carbonised and utimately they become irregularly conductive, like an erratic resistor, until the point they start arcing continuously. It would actually explain the progressive worsening of the symptoms. It looks like SG4 and SG6 have been arcing or are at least contaminated.

In any case what you need to do here is scrape into the phenolic surface of the pcb between the spark gaps. Itis hard to tell from the photo, but if the rectangular areas there are actually full thickness punchings in the pcb, the same process happens on the inner edges of the material. If they are like that you can run a drill through the holes to clear out any carbonization that way. If that solved the problem I'd be inclined to get rid of them, remove some copper from the fingers, about a 1mm or so and or remove the copper fingers and after the board was thoroughly cleaned apply some varnish to prevent arcing any future arcing. This does not put the CRT at any significant risk.

If it turns out the spark gaps are not the cause, then we move to testing the voltages as planned. One of the most likely places that you can end up with fluctuating voltages is in circuits where the voltage is determined by open frame potentiometers or preset pots. The reason is these are not protected from contamination and they can go intermittent. It would happen less likely with the user brightness control, as it gets manipulated and tends to self clean, but it can readily happen with the preset brightness pot in series with the user control. So one move would be to clean and excercise that preset(see attached photo) Any fluctuations in the focus voltagewon't be the cause because with those you would just see the beam focus changing, not brightness levels shifts.

In case you are wondering about the Heath Robinson reference, from Google:

"When someone says Heath Robinson made a machine, they are describing an absurdly complex, rickety, or impractical contraption designed to perform a very simple task. The phrase often implies the machine was cobbled together from odd bits, string, or tape"