H9 Terminal - Flyback noise

[Darko Mesaroš]

Hello folks at SEBHC,

I just recently got a gorgeous looking H9. However it seems to be having some issues with its flyback transformer (among other issues).

Looking at the pictures attached, you can see that the screen is garbled, but more than that the flyback transformer is producing a lot of high pitched noises. And, at times, it stops wit the noise and the screen is normal. It tends to go in an out of being good and not. 

I've done a cursory look around the flyback to see if there are any obvious issues, but nothing seems to stand out. (I attached an image of the uncovered flyback. 

Do you have any troubleshooting steps for me? If the flyback is completely gone, is there a possibility of finding a replacement? 

Thank you,

Darko

[Dave McGuire]

That sounds like corona discharge to me. Try (carefully!) looking at
the flyback transformer and cable area in a darkened room, see if you
see any discharges.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

[glenn.f...@gmail.com]

Looks amazingly clean inside. With patience you should be able to get this working like new.

 

Just a guess but it sounds like there could be some arcing from the CRT anode lead to a ground somewhere? Does the anode lead cable look to be in good shape? If you observe in the dark do you see any arcing?  Make sure the cable is not in close proximity to ground or other circuitry. My gut feeling is there’s not an issue with the flyback transformer itself. Possibly a problem elsewhere in the horizontal circuitry…?

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[Darko Mesaros]

I just realized that the pictures I took are not as good. But okay! So, I've done a few tests:

1: In a dark room I looked for arcing or light from the flyback transformer side. Nothing, everything seems to looking fine. 

2: I did a very irresponsible thing: while the H9 was running I approached the flyback transformer with a screwdriver. I got arcing from the transformer to the screwdriver. 

Now the red coating on the flyback looks intact, and i see no cracks or holes on it. 

I'll have a look at the cable Glenn, and see if there are some other potential issues. Do the electrolytic caps usually go bad on these? 

Darko

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--

Darko Mesaroš
System/Network Administrator
MCTS, MCITP: Server Administator, MCITP: Enterprise Administrator
mailto: darko.s...@gmail.com
Follow me on Twitter: http://twitter.com/darkosubotica
sent from Webmail

[Glenn Roberts]

All electrolytics of this age can go bad and are worth testing. In my own experience with Heath computing gear I would say the electrolytic capacitors have rarely been an issue. I also don’t see how that could explain your symptoms.

Sent from my iPad

On Jul 23, 2026, at 11:07 AM, Darko Mesaros <darko.s...@gmail.com> wrote:



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[Darko Mesaroš]

That is fair! 
I'll do a CRT discharge today and check the anode to see if it is clean. Will inspect rest of the circuitry and report back.

[Darko Mesaroš]

After some more tinkering, the noise / broken image seems to be gone (for now). I cleaned the anode suction cup as well as the tube, and added some dielectric grease. Poked around the little NPN next to the flyback and it seems to okay now.

It went from this:

To this:

Still not fixed fully. Ie the keyboard stopped sending characters to the screen and I have some repeating dots on the screen. I will check on a bunch of ICs tomorrow. 

Any recommendation on what should I replace on the H9 no matter what the case?

[Glenn Roberts]

It appears to be in PLOT mode. Cant tell but it doesn’t look like the PLOT key is depressed?

Sent from my iPad

On Jul 24, 2026, at 1:13 AM, Darko Mesaroš <darko.s...@gmail.com> wrote:

After some more tinkering, the noise / broken image seems to be gone (for now). I cleaned the anode suction cup as well as the tube, and added some dielectric grease. Poked around the little NPN next to the flyback and it seems to okay now.

It went from this:

<IMG_4755 Large.jpeg>

To this:

<IMG_4760 Large.jpeg>

<IMG_4759 Large.jpeg>

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<IMG_4755 Large.jpeg>

<IMG_4760 Large.jpeg>

<IMG_4759 Large.jpeg>

[Tim R]

Darko,

I think Glenn is right. Plot mode does leave a dash on screen that corresponds with the key pressed.  If you press keys in alphabetical order, the dash will appear higher on the screen as you go. I put together a few YouTubes on my H9, including a segment on this one starting at the 6:08 minute point that shows the final proper operation of the unit and all of its different features (following the tests fro the assembly manual). It's not the best video, but it might help as a point of comparison. https://youtu.be/eji6SvhWO7k?si=lzL62FxmtiMRwj5J

Also, I have encountered a high-pitched noise like you describe on a CRT monitor in the past. In my case, the cause was a bad/cracked solder joint. I would get the whine, and if i gave the case a light tap, the monitor would work fine for awhile. I did a general reflow of the video board and the problem was permanently solved. Thermal contraction and expansion over years of operation can end up eventually causing this issue. It used to happen in old CRT televisions fairly often.

Tim

[Darko Mesaroš]

You are both right. The Plot mode is on, as I hit the key to try it. But even without the plot mode, I get no keyboard input. But as I said, that is a problem for a future Darko!

What I will do now, I reflow the video board (actually all the boards). I'll report back!