Caution - do not use 19" flyback for 13" Electrohome chassis

JRR

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Caution - do not use 19" flyback for 13" Electrohome chassis

I have just run tests on a 13" chassis with the A29951-B flyback vs a second chassis with the original A19183-A flyback (called LOPT outside of North America).

My serious safety concerns are that the common 19" flyback (A29951-B) is NOT a suitable replacement for the 13" monitor. That size requires the A-19183-A flyback. The reason is the 19" flyback (A29951-x) runs with a higher HV circuitry for the 19" tube vs. the requirements of a 13" tube and this puts the monitor close to X-Ray emission with a HV of around 28KV on a 13" picture tube.

The design safety feature of the X-Ray protection circuit is bypassed when you put the wrong flyback in, so do NOT depend on the X-Ray protection circuit! That only cuts in when the B+ regulator shorts or the B+ is too high. The X-Ray protection circuit does not monitor the output of the Flyback/LOPT.

The Focus voltage go up to 11KV (19") instead of the 8KV (13") that the A19138-A produces. This is too high a voltage for these 13 inch picture tubes.

Also the Screen voltage minimum is 300VDC (19") instead of the 240VDC (13") that the 19183 generates, and this can cause people to think their picture tubes are shorted or bad when they are not.

I hope to have a cure for this - perhaps a dropping resistor in series with the HOT - but until someone comes up with a SAFE FIX do not use this flyback for 13" E-Home monitors.
 
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I've observed similar problems on some rebuilt G07 13" monitors, but have seen others that don't seem to suffer. On the rebuilds with high HV, I noticed that the HOT had been replaced with a 2SD870, which is the HOT for the 19" — the part for the 13" is 2SD869. I haven't revisited, but I believe that this is the source of the issue, rather than the flyback.

I'd certainly welcome more information on this.
 
I have just run tests on a 13" chassis with the A29951-B flyback vs a second chassis with the original A19183-A flyback (called LOPT outside of North America).

My serious safety concerns are that the common 19" flyback (A29951-B) is NOT a suitable replacement for the 13" monitor. That size requires the A-19183-A flyback. The reason is the 19" flyback (A29951-x) runs with a higher HV circuitry for the 19" tube vs. the requirements of a 13" tube and this puts the monitor close to X-Ray emission with a HV of around 28KV on a 13" picture tube.

The design safety feature of the X-Ray protection circuit is bypassed when you put the wrong flyback in, so do NOT depend on the X-Ray protection circuit! That only cuts in when the B+ regulator shorts or the B+ is too high. The X-Ray protection circuit does not monitor the output of the Flyback/LOPT.

The Focus voltage go up to 11KV (19") instead of the 8KV (13") that the A19138-A produces. This is too high a voltage for these 13 inch picture tubes.

Also the Screen voltage minimum is 300VDC (19") instead of the 240VDC (13") that the 19183 generates, and this can cause people to think their picture tubes are shorted or bad when they are not.

I hope to have a cure for this - perhaps a dropping resistor in series with the HOT - but until someone comes up with a SAFE FIX do not use this flyback for 13" E-Home monitors.

So who sells the one for the FBO?
 
Okay, I replaced the flyback in my 13" GO7 with a flyback for a 19" and had no problems. It works perfectly, and has ever since I replaced it. The GO7s have the same flyback.
 
Okay, I replaced the flyback in my 13" GO7 with a flyback for a 19" and had no problems. It works perfectly, and has ever since I replaced it. The GO7s have the same flyback.

There are different part numbers listed in the manual. Someone needs to compare a CBO fly to a FBO one, both electrically and physically.
 
Danger Will Robinson!

Okay, I replaced the flyback in my 13" GO7 with a flyback for a 19" and had no problems. It works perfectly, and has ever since I replaced it. The GO7s have the same flyback.
Yes, it will work, but it is NOT safe. You are close to generating X-rays on your 13" tube. My point is the flyback for the 19" IS NOT TO BE USED ON A 13" chassis. Why do you think that Electrohome MADE a separate flyback for the 13" monitor? For safety!
The X-Ray protection only kicks in if the B+ shorts, but your tube is already putting out more X-Rays that it was designed to. Why do you think there are standards and safety warnings on repair documents?
I hope you are past your reproductive age, the X-Rays from these 13" tubes radiate down and to the sides, the front is pretty safe as it is leaded glass, but not the rear or sides of the tube.
You are putting people at risk using the wrong flyback.
 
How much extra is unsafe though? I get what you're saying but is the extra being put out really unsafe?
 
There is no need to go off on me lol. There are no reproduction FBO flybacks, and I'd rather replace a bad flyback with a slightly different working one than have a game permanently down. Even if I MIGHT develop some problems later in life.
 
A different HOT is not the cause of overvoltage...

I've observed similar problems on some rebuilt G07 13" monitors, but have seen others that don't seem to suffer. On the rebuilds with high HV, I noticed that the HOT had been replaced with a 2SD870, which is the HOT for the 19" — the part for the 13" is 2SD869. I haven't revisited, but I believe that this is the source of the issue, rather than the flyback.

I'd certainly welcome more information on this.

Using a 2SD870 will not increase the output voltage of the flyback, it is simply a replacement for the original HOT (Horizontal Output Transistor). No replacement transistor could change the output voltage. The 2SD869 simply has a slightly lower breakdown voltage, which has no effect on the flyback, rather it was just s slight cost saving for Electrohome to use a part that was rated slightly lower breakdown.
The higher output voltages on the flyback are because it is in the wrong chassis.
 
How much extra is unsafe though? I get what you're saying but is the extra being put out really unsafe?

All I can say is if it didn't matter then Electrohome would have used the same flyback for both the 13 and 19" monitors.
 
There is no need to go off on me lol. There are no reproduction FBO flybacks, and I'd rather replace a bad flyback with a slightly different working one than have a game permanently down. Even if I MIGHT develop some problems later in life.

I agree that it is annoying that there is no replacement flyback at this time, but if enough people ask I'm sure it can be made.

This is a safety issue. Once done it is invisible to other users or potential owners down the line.

A bit more information - the X-Ray protection circuitry in the monitor is designed to cut in if the B+ goes about 8% overvoltage. In other words if the B+ voltage rose from 120VDC to 128VDC then the monitor would shut down for safety. The 19" flyback mounted in a 13" chassis has raised the output voltages for the HV from 21KV to around 28KV which is a rise of around 33% as measured on a 13" picture tube. In other words a rise of 4 times (8% vs 33%) what they considered maximum safe output percentage increase.
 
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There is little chance that a flyback will be made specifically for the 13"

Its hard enough getting one made for the k4600 and that's a far more common monitor, with no existing solution.


You could always try to reduce the b+ voltage and adjust some of the other passives to reduce the voltage or add some parasitics to the flyback to reduce the current through it, which would lower voltage.

lower B+ might screw with vertical deflection but I think you could adjust the resistance to correct for horizontal deflection.
 
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