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TV flyback transformer replacement without RC snubber?

Thread starter #1
I need to replace the flyback transformer on my Atari SC1224 CRT monitor. The flyback I removed from this monitor has a model number of Kf4825G, and has an RC snubber attached to it, which does not seem to be easily removable. The high voltage cable goes through this to the CRT. Here is a picture of the bad flyback:
IMG_1507-min.JPG

The only replacement flyback I've found, which according to the eBay listing it's a replacement Kf4825G flybacks, does not come with the RC snubber. This is the eBay listing for it. And here's a picture:
s-l500.jpg

Is it possible that with this replacement flyback, the RC snubber is not needed? Or, should I attach the existing RC snubber to the new flyback? It does not seem to be easily disconnected from the flyback. Looks like I would have to cut the thick red HV cable? (I don't think that's a good idea)

I already messaged the seller asking this, but he has no idea.

Here is the Service Manual, if anybody wants to see it.

Thanks for your help.
 

ronsimpson

Well-Known Member
Most Helpful Member
#2
Not a snubber.
I marked in red the high voltage wire. From the flyback to the CRT. The bleader resistor is to discharge the high voltage before you can get shocked. And it helps regulate the high voltage supply by placing a minimum load on it. The capacitor is like the capacitor on any power supply after the diode-transformer. (There is more capacitance inside the CRT but the external one adds to the regulation)
1551915041488.png
It is possible you can get a transformer with the R & C inside the transformer.
From the ebay picture I can not tell if the transformer has the RC inside but I think it does. Does it have the F and C pots. I can not see and there is no data. From every where I checked there is no data on the new transformer and that is not good. "Flyback for China TV" That is not enough information.
 
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
#3
Basically all you can do is try it and see if it works - and as already mentioned, it's not a snubber.

Performance wise the only differences if those components are not inside the transformer are:

1 - the CRT will stayed charged up - this is extremely common anyway.

2 - without the capacitor the picture may experience more 'blooming' (picture size varying with brightness).

Most CRT sets didn't include either of those two components, relying on the CRT capacitance (between aquadag and final anode) to provide enough.
 

unclejed613

Well-Known Member
Most Helpful Member
#4
if it's any help, the original part is a Panasonic flyback. it's likely (if the replacement flyback works) you will notice nothing different. you will need to adjust the focus and screen controls. the screen control adjusts the background. with a raster with no video (black background) you should adjust Screen until the background just barely disappears. for focus, you need a test pattern, or a screen full of text, and adjust for the sharpest overall image. since the flyback provides power supplies for other circuits in the monitor, you may need to readjust a few things like H size, H linearity (since the FBT is the horizontal output transformer it's very likely these will need adjustment). V size and V lin may need some adjustment, but probably not much as long as the power supply rail voltage doesn't change much. some
Here is the Service Manual, if anybody wants to see it.
something is wrong with that service manual. the schematic is for a small (7 to 10 inch) monochrome monitor. notice there's only one cathode in a CRT that should have three, and the horizontal output is a BU406 which is a TO-220 device, while H out transistors for color monitors are usually TO-3P or similar larger case style devices.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#5
something is wrong with that service manual. the schematic is for a small (7 to 10 inch) monochrome monitor. notice there's only one cathode in a CRT that should have three, and the horizontal output is a BU406 which is a TO-220 device, while H out transistors for color monitors are usually TO-3P or similar larger case style devices.
As far as I can tell there's nothing wrong with the service manual?, it's probably a small monochrome monitor, and plenty of line output devices have been TO-220 in smaller sets, both colour and monochrome.
 

unclejed613

Well-Known Member
Most Helpful Member
#6
if you look at the service manual posted in #1, page 3 is the schematic of a monochrome monitor. my bad, i scrolled down to page 3, but the schematic is actually on page 10.
to OP: if you are replacing the flyback because the horizontal output transistor keeps shorting, try replacing C713 (electrolytic cap connected to the driver transformer T701) first. that cap dries out and the waveform driving the horizontal output transistor changes, and causes overheating of the output transistor. depending on how badly the cap is dried out, the output transistor failure could be almost instantly, to several minutes, to several hours. if it doesn't fail instantly, you may see that the raster doesn't fill the screen on the sides, or even the picture being compressed on one side (usually on the left. the hotter the output transistor gets, the worse the picture gets.
 

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