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Default Reducing HV output voltage from Flyback/LOPT as used in arcademonitors

I'm looking for a safe and effective way to reduce the voltage output of
a replacement flyback that is not original for the circuit.

The initial problem - Electrohome 13" monitors used a specific flyback
transformer that is no longer produced.

The result - People are using the 19" Electrohome flyback as it fits
exactly the same, and is still in production overseas.

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is supposed to
be 18.5KV to 22.5KV. Thus the 13" tubes are running at up to 25KV which
is 10% over their original maximum rating and my concern is an increase
of soft X-Rays. My HV probes show somewhere around 25 to 30KV for the
19" flyback when used in a 13" chassis.

My original test was to use a 75R 5W dropping resistor to limit the B+
to 100VDC to the Flyback (and only the flyback/LOPT) vs. 120VDC for the
rest of the B+. The result was proper HV, however other voltages
developed by the flyback made the results somewhat less that optimum.
The image, while good, was clipped on the left side.

Then I removed the dropping resistor (returned jumper) and tried
removing resistor R516 - 180K from the B+ input side of the HV output.
No difference.

Tried changing the value of C519 0.047ufd/200V, however increasing the
value made no real difference in the HV output.

Does anyone have any ideas on how to reduce the HV, from near 30KV to
around 19KV, that is safe and reliable? The original circuits have an
X-Ray protection that kicks in when the B+ reached about 10% over the
nominal value and I need to retain that safety feature. I would prefer
something that is pretty idiot proof.

Schematics of Electrohome GO7-19-CBO & Electrohome GO7-13-FBO:

https://www.flippers.com/pdfs/Temp/E...-schematic.pdf

Thanks!

John :-#)#

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(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
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Default Reducing HV output voltage from Flyback/LOPT as used in arcademonitors

On Mon, 04 Jun 2018 15:30:40 -0700, John Robertson wrote:

I'm looking for a safe and effective way to reduce the voltage output of
a replacement flyback that is not original for the circuit.

The initial problem - Electrohome 13" monitors used a specific flyback
transformer that is no longer produced.

The result - People are using the 19" Electrohome flyback as it fits
exactly the same, and is still in production overseas.

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is supposed to
be 18.5KV to 22.5KV. Thus the 13" tubes are running at up to 25KV which
is 10% over their original maximum rating and my concern is an increase
of soft X-Rays. My HV probes show somewhere around 25 to 30KV for the
19" flyback when used in a 13" chassis.

My original test was to use a 75R 5W dropping resistor to limit the B+
to 100VDC to the Flyback (and only the flyback/LOPT) vs. 120VDC for the
rest of the B+. The result was proper HV, however other voltages
developed by the flyback made the results somewhat less that optimum.
The image, while good, was clipped on the left side.


Ugh! If they are getting other voltages off TAPS on the flyback, then it
is going to be real hard to ONLY turn down the UHV without affecting the
other voltages. This really requires different winding ratios. Now, if
the other voltages are just taken off the point where the transistor
drives the flyback, you could fix this by just adding a few turns to the
primary winding.

Jon
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Default Reducing HV output voltage from Flyback/LOPT as used in arcade monitors


"Jon Elson" wrote in message
...
On Mon, 04 Jun 2018 15:30:40 -0700, John Robertson wrote:

I'm looking for a safe and effective way to reduce the voltage output of
a replacement flyback that is not original for the circuit.

The initial problem - Electrohome 13" monitors used a specific flyback
transformer that is no longer produced.

The result - People are using the 19" Electrohome flyback as it fits
exactly the same, and is still in production overseas.

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is supposed to
be 18.5KV to 22.5KV. Thus the 13" tubes are running at up to 25KV which
is 10% over their original maximum rating and my concern is an increase
of soft X-Rays. My HV probes show somewhere around 25 to 30KV for the
19" flyback when used in a 13" chassis.

My original test was to use a 75R 5W dropping resistor to limit the B+
to 100VDC to the Flyback (and only the flyback/LOPT) vs. 120VDC for the
rest of the B+. The result was proper HV, however other voltages
developed by the flyback made the results somewhat less that optimum.
The image, while good, was clipped on the left side.


Ugh! If they are getting other voltages off TAPS on the flyback, then it
is going to be real hard to ONLY turn down the UHV without affecting the
other voltages. This really requires different winding ratios. Now, if
the other voltages are just taken off the point where the transistor
drives the flyback, you could fix this by just adding a few turns to the
primary winding.

Jon


That would also lower all the other voltages.

Since this is very low current, maybe some proper HV resistors to divide the
HVDC down to the proper level.

You can't do anything to the FB as it is most likely potted in epoxy.



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Default Reducing HV output voltage from Flyback/LOPT as used in arcademonitors

On 2018/06/04 3:48 PM, Jon Elson wrote:
On Mon, 04 Jun 2018 15:30:40 -0700, John Robertson wrote:

I'm looking for a safe and effective way to reduce the voltage output of
a replacement flyback that is not original for the circuit.

The initial problem - Electrohome 13" monitors used a specific flyback
transformer that is no longer produced.

The result - People are using the 19" Electrohome flyback as it fits
exactly the same, and is still in production overseas.

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is supposed to
be 18.5KV to 22.5KV. Thus the 13" tubes are running at up to 25KV which
is 10% over their original maximum rating and my concern is an increase
of soft X-Rays. My HV probes show somewhere around 25 to 30KV for the
19" flyback when used in a 13" chassis.

My original test was to use a 75R 5W dropping resistor to limit the B+
to 100VDC to the Flyback (and only the flyback/LOPT) vs. 120VDC for the
rest of the B+. The result was proper HV, however other voltages
developed by the flyback made the results somewhat less that optimum.
The image, while good, was clipped on the left side.


Ugh! If they are getting other voltages off TAPS on the flyback, then it
is going to be real hard to ONLY turn down the UHV without affecting the
other voltages. This really requires different winding ratios. Now, if
the other voltages are just taken off the point where the transistor
drives the flyback, you could fix this by just adding a few turns to the
primary winding.

Jon


Would that it was so easy! This is a sealed flyback in a plastic
housing. Late 70s design.

I have gotten a bit further - using a 75R to 100R in series with the
Flyback B+ in I can get the HV down to about 20KV, and the +12VDC supply
is fine with that. Now the problem is the image is shrunk on the left,
but that turns out to be blanking after all. It has to do with
transistor X304 and its base feed. Need to muck around with the
resistors and caps a bit I expect to try and reduce the horizontal
clipping. With X304 disconnected I do get a good, although narrower,
image. I will have to expand the width, hope adjusting the caps C513,513
or C515 will give me enough width.

John :-#)#

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MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
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Default Reducing HV output voltage from Flyback/LOPT as used in arcade monitors

On Monday, June 4, 2018 at 6:30:48 PM UTC-4, John Robertson wrote:
I'm looking for a safe and effective way to reduce the voltage output of
a replacement flyback that is not original for the circuit.

The initial problem - Electrohome 13" monitors used a specific flyback
transformer that is no longer produced.

The result - People are using the 19" Electrohome flyback as it fits
exactly the same, and is still in production overseas.

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is supposed to
be 18.5KV to 22.5KV. Thus the 13" tubes are running at up to 25KV which
is 10% over their original maximum rating and my concern is an increase
of soft X-Rays. My HV probes show somewhere around 25 to 30KV for the
19" flyback when used in a 13" chassis.

My original test was to use a 75R 5W dropping resistor to limit the B+
to 100VDC to the Flyback (and only the flyback/LOPT) vs. 120VDC for the
rest of the B+. The result was proper HV, however other voltages
developed by the flyback made the results somewhat less that optimum.
The image, while good, was clipped on the left side.

Then I removed the dropping resistor (returned jumper) and tried
removing resistor R516 - 180K from the B+ input side of the HV output.
No difference.

Tried changing the value of C519 0.047ufd/200V, however increasing the
value made no real difference in the HV output.

Does anyone have any ideas on how to reduce the HV, from near 30KV to
around 19KV, that is safe and reliable? The original circuits have an
X-Ray protection that kicks in when the B+ reached about 10% over the
nominal value and I need to retain that safety feature. I would prefer
something that is pretty idiot proof.

Schematics of Electrohome GO7-19-CBO & Electrohome GO7-13-FBO:

https://www.flippers.com/pdfs/Temp/E...-schematic.pdf

Thanks!

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."




I wouldn't worry so much about the HV as I would about the filament. If the filament voltage stays at or below 6.3, I wouldn't give it another thought. Most of those tubes have no trouble with a few extra KV. If the filament is high, drop that or the tube will have a life span emissions-wise in months.

Another way of lowering the global output of the fly is add some capacitance to the retrace cap. This will of course affect all the secondaries.

I'm not crazy about adding resistance to drop voltage on any load that's dynamic. If you scope the collector of the horiz output with and without a dropping resistor, you'll see the waveform will be different. You may have short horiz output transistor life. If the monitor uses some sort of series/pass regulator (most 70s regulators are) you can drop the voltage by playing with the regulator and keeping the supply tightly regulated to the fly.


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Default Reducing HV output voltage from Flyback/LOPT as used in arcade monitors

On Tuesday, 5 June 2018 01:53:49 UTC+1, John-Del wrote:
On Monday, June 4, 2018 at 6:30:48 PM UTC-4, John Robertson wrote:


I'm looking for a safe and effective way to reduce the voltage output of
a replacement flyback that is not original for the circuit.

The initial problem - Electrohome 13" monitors used a specific flyback
transformer that is no longer produced.

The result - People are using the 19" Electrohome flyback as it fits
exactly the same, and is still in production overseas.

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is supposed to
be 18.5KV to 22.5KV. Thus the 13" tubes are running at up to 25KV which
is 10% over their original maximum rating and my concern is an increase
of soft X-Rays. My HV probes show somewhere around 25 to 30KV for the
19" flyback when used in a 13" chassis.

My original test was to use a 75R 5W dropping resistor to limit the B+
to 100VDC to the Flyback (and only the flyback/LOPT) vs. 120VDC for the
rest of the B+. The result was proper HV, however other voltages
developed by the flyback made the results somewhat less that optimum.
The image, while good, was clipped on the left side.

Then I removed the dropping resistor (returned jumper) and tried
removing resistor R516 - 180K from the B+ input side of the HV output.
No difference.

Tried changing the value of C519 0.047ufd/200V, however increasing the
value made no real difference in the HV output.

Does anyone have any ideas on how to reduce the HV, from near 30KV to
around 19KV, that is safe and reliable? The original circuits have an
X-Ray protection that kicks in when the B+ reached about 10% over the
nominal value and I need to retain that safety feature. I would prefer
something that is pretty idiot proof.

Schematics of Electrohome GO7-19-CBO & Electrohome GO7-13-FBO:

https://www.flippers.com/pdfs/Temp/E...-schematic.pdf

Thanks!

John :-#)#


I wouldn't worry so much about the HV as I would about the filament. If the filament voltage stays at or below 6.3, I wouldn't give it another thought. Most of those tubes have no trouble with a few extra KV. If the filament is high, drop that or the tube will have a life span emissions-wise in months.


I used to boost tube heaters, and had a Sony with 66% heater voltage boost. It was an experiment on a totally dead tube. Years later it still worked just as well - emission ok, but tracking lousy.


Another way of lowering the global output of the fly is add some capacitance to the retrace cap. This will of course affect all the secondaries.

I'm not crazy about adding resistance to drop voltage on any load that's dynamic. If you scope the collector of the horiz output with and without a dropping resistor, you'll see the waveform will be different. You may have short horiz output transistor life. If the monitor uses some sort of series/pass regulator (most 70s regulators are) you can drop the voltage by playing with the regulator and keeping the supply tightly regulated to the fly.


I don't know whether you can add a new winding that goes in series with the EHT output, bucking its V_out. Wouldn't be trivial given its running voltage.

Series resistors may not work well, a string of MOVs might be better.

Have you checked the mfr specs of the tube? I doubt it's specced to 30kV but it's worth knowing exactly what you need to get it down to.


NT
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Default Reducing HV output voltage from Flyback/LOPT as used in arcademonitors

On 2018/06/04 5:53 PM, John-Del wrote:
On Monday, June 4, 2018 at 6:30:48 PM UTC-4, John Robertson wrote:
I'm looking for a safe and effective way to reduce the voltage output of
a replacement flyback that is not original for the circuit.

The initial problem - Electrohome 13" monitors used a specific flyback
transformer that is no longer produced.

The result - People are using the 19" Electrohome flyback as it fits
exactly the same, and is still in production overseas.

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is supposed to
be 18.5KV to 22.5KV. Thus the 13" tubes are running at up to 25KV which
is 10% over their original maximum rating and my concern is an increase
of soft X-Rays. My HV probes show somewhere around 25 to 30KV for the
19" flyback when used in a 13" chassis.

My original test was to use a 75R 5W dropping resistor to limit the B+
to 100VDC to the Flyback (and only the flyback/LOPT) vs. 120VDC for the
rest of the B+. The result was proper HV, however other voltages
developed by the flyback made the results somewhat less that optimum.
The image, while good, was clipped on the left side.

Then I removed the dropping resistor (returned jumper) and tried
removing resistor R516 - 180K from the B+ input side of the HV output.
No difference.

Tried changing the value of C519 0.047ufd/200V, however increasing the
value made no real difference in the HV output.

Does anyone have any ideas on how to reduce the HV, from near 30KV to
around 19KV, that is safe and reliable? The original circuits have an
X-Ray protection that kicks in when the B+ reached about 10% over the
nominal value and I need to retain that safety feature. I would prefer
something that is pretty idiot proof.

Schematics of Electrohome GO7-19-CBO & Electrohome GO7-13-FBO:

https://www.flippers.com/pdfs/Temp/E...-schematic.pdf

Thanks!

John :-#)#



I wouldn't worry so much about the HV as I would about the filament. If the filament voltage stays at or below 6.3, I wouldn't give it another thought. Most of those tubes have no trouble with a few extra KV. If the filament is high, drop that or the tube will have a life span emissions-wise in months.


I would disagree. These tubes were rated with a maximum HV at 22.5KV
(safety circuit would cut in), with the wrong flyback they are running
at close to 30KV, and I don't think that is a good idea from the X-Ray
risk perspective. A family friend of ours was an X-Ray specialist and
died of cancer relatively young...


Another way of lowering the global output of the fly is add some capacitance to the retrace cap. This will of course affect all the secondaries.


That may work, will try it. Thanks!


I'm not crazy about adding resistance to drop voltage on any load that's dynamic. If you scope the collector of the horiz output with and without a dropping resistor, you'll see the waveform will be different. You may have short horiz output transistor life. If the monitor uses some sort of series/pass regulator (most 70s regulators are) you can drop the voltage by playing with the regulator and keeping the supply tightly regulated to the fly.


Dropping the system B+ reduces the vertical deflection too much to be
useful.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
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Default Reducing HV output voltage from Flyback/LOPT as used in arcade monitors

On Tuesday, June 5, 2018 at 12:05:29 PM UTC-4, John Robertson wrote:
On 2018/06/04 5:53 PM, John-Del wrote:
On Monday, June 4, 2018 at 6:30:48 PM UTC-4, John Robertson wrote:
I'm looking for a safe and effective way to reduce the voltage output of
a replacement flyback that is not original for the circuit.

The initial problem - Electrohome 13" monitors used a specific flyback
transformer that is no longer produced.

The result - People are using the 19" Electrohome flyback as it fits
exactly the same, and is still in production overseas.

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is supposed to
be 18.5KV to 22.5KV. Thus the 13" tubes are running at up to 25KV which
is 10% over their original maximum rating and my concern is an increase
of soft X-Rays. My HV probes show somewhere around 25 to 30KV for the
19" flyback when used in a 13" chassis.

My original test was to use a 75R 5W dropping resistor to limit the B+
to 100VDC to the Flyback (and only the flyback/LOPT) vs. 120VDC for the
rest of the B+. The result was proper HV, however other voltages
developed by the flyback made the results somewhat less that optimum.
The image, while good, was clipped on the left side.

Then I removed the dropping resistor (returned jumper) and tried
removing resistor R516 - 180K from the B+ input side of the HV output.
No difference.

Tried changing the value of C519 0.047ufd/200V, however increasing the
value made no real difference in the HV output.

Does anyone have any ideas on how to reduce the HV, from near 30KV to
around 19KV, that is safe and reliable? The original circuits have an
X-Ray protection that kicks in when the B+ reached about 10% over the
nominal value and I need to retain that safety feature. I would prefer
something that is pretty idiot proof.

Schematics of Electrohome GO7-19-CBO & Electrohome GO7-13-FBO:

https://www.flippers.com/pdfs/Temp/E...-schematic.pdf

Thanks!

John :-#)#



I wouldn't worry so much about the HV as I would about the filament. If the filament voltage stays at or below 6.3, I wouldn't give it another thought. Most of those tubes have no trouble with a few extra KV. If the filament is high, drop that or the tube will have a life span emissions-wise in months.


I would disagree. These tubes were rated with a maximum HV at 22.5KV
(safety circuit would cut in), with the wrong flyback they are running
at close to 30KV, and I don't think that is a good idea from the X-Ray
risk perspective. A family friend of ours was an X-Ray specialist and
died of cancer relatively young...


Another way of lowering the global output of the fly is add some capacitance to the retrace cap. This will of course affect all the secondaries.


That may work, will try it. Thanks!


I'm not crazy about adding resistance to drop voltage on any load that's dynamic. If you scope the collector of the horiz output with and without a dropping resistor, you'll see the waveform will be different. You may have short horiz output transistor life. If the monitor uses some sort of series/pass regulator (most 70s regulators are) you can drop the voltage by playing with the regulator and keeping the supply tightly regulated to the fly.


Dropping the system B+ reduces the vertical deflection too much to be
useful.


Is the vert B+ sourced from the LV regulator?

If you have to use series resistance to lower B+ to the primary of the flyback, I might try adding capacitance on the far side of the resistor to stiffen it.

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Default Reducing HV output voltage from Flyback/LOPT as used in arcademonitors

On 2018/06/05 11:57 AM, John-Del wrote:
On Tuesday, June 5, 2018 at 12:05:29 PM UTC-4, John Robertson wrote:
On 2018/06/04 5:53 PM, John-Del wrote:
On Monday, June 4, 2018 at 6:30:48 PM UTC-4, John Robertson wrote:
I'm looking for a safe and effective way to reduce the voltage output of
a replacement flyback that is not original for the circuit.

The initial problem - Electrohome 13" monitors used a specific flyback
transformer that is no longer produced.

The result - People are using the 19" Electrohome flyback as it fits
exactly the same, and is still in production overseas.

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is supposed to
be 18.5KV to 22.5KV. Thus the 13" tubes are running at up to 25KV which
is 10% over their original maximum rating and my concern is an increase
of soft X-Rays. My HV probes show somewhere around 25 to 30KV for the
19" flyback when used in a 13" chassis.

My original test was to use a 75R 5W dropping resistor to limit the B+
to 100VDC to the Flyback (and only the flyback/LOPT) vs. 120VDC for the
rest of the B+. The result was proper HV, however other voltages
developed by the flyback made the results somewhat less that optimum.
The image, while good, was clipped on the left side.

Then I removed the dropping resistor (returned jumper) and tried
removing resistor R516 - 180K from the B+ input side of the HV output.
No difference.

Tried changing the value of C519 0.047ufd/200V, however increasing the
value made no real difference in the HV output.

Does anyone have any ideas on how to reduce the HV, from near 30KV to
around 19KV, that is safe and reliable? The original circuits have an
X-Ray protection that kicks in when the B+ reached about 10% over the
nominal value and I need to retain that safety feature. I would prefer
something that is pretty idiot proof.

Schematics of Electrohome GO7-19-CBO & Electrohome GO7-13-FBO:

https://www.flippers.com/pdfs/Temp/E...-schematic.pdf

Thanks!

John :-#)#



I wouldn't worry so much about the HV as I would about the filament. If the filament voltage stays at or below 6.3, I wouldn't give it another thought. Most of those tubes have no trouble with a few extra KV. If the filament is high, drop that or the tube will have a life span emissions-wise in months.


I would disagree. These tubes were rated with a maximum HV at 22.5KV
(safety circuit would cut in), with the wrong flyback they are running
at close to 30KV, and I don't think that is a good idea from the X-Ray
risk perspective. A family friend of ours was an X-Ray specialist and
died of cancer relatively young...


Another way of lowering the global output of the fly is add some capacitance to the retrace cap. This will of course affect all the secondaries.


That may work, will try it. Thanks!


I'm not crazy about adding resistance to drop voltage on any load that's dynamic. If you scope the collector of the horiz output with and without a dropping resistor, you'll see the waveform will be different. You may have short horiz output transistor life. If the monitor uses some sort of series/pass regulator (most 70s regulators are) you can drop the voltage by playing with the regulator and keeping the supply tightly regulated to the fly.


Dropping the system B+ reduces the vertical deflection too much to be
useful.


Is the vert B+ sourced from the LV regulator?


Schematics link is above. The vertical deflection is driven from the B+
(120VDC) directly.


If you have to use series resistance to lower B+ to the primary of the flyback, I might try adding capacitance on the far side of the resistor to stiffen it

That is probably a good idea, I will check that with my 'scope.

Need to adjust the Horizontal Blanking pulses to transistor X304 as the
picture is being clipped way too much on the left side. I'll post some
photos later.

Currently working on another project which is related to WPC pinball
games and their real-time clocks when using NVRAM. Then back to the GO7!

Thanks,

John :-#)#

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(Please post followups or tech inquiries to the USENET newsgroup)
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MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
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Default Reducing HV output voltage from Flyback/LOPT as used in arcademonitors

On 05.06.2018 00:30, John Robertson wrote:
I'm looking for a safe and effective way to reduce the voltage
output of a replacement flyback that is not original for the
circuit.

...

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is
supposed to be 18.5KV to 22.5KV. Thus the 13" tubes are running at up
to 25KV which is 10% over their original maximum rating and my
concern is an increase of soft X-Rays. My HV probes show somewhere
around 25 to 30KV for the 19" flyback when used in a 13" chassis.


Hi

According to the numbers you provided, the EHT needs to be reduced by
about 7 kV (while keeping other voltages derived from the transformer at
their usual levels).

The 7 kV difference is significant, but not insurmountable for a series
dropper approach. The current draw of a CRT anode is small, the power
dissipation should still be manageable: 7 W at 1 mA (if the CRT ever
takes that much current).

There are TVS diodes with voltages up to 600 V (nominal value at 1 mA
test current) available (Littelfuse P6KE600A). A series string of 12
such TVS diodes will have around 7 kV of voltage drop across them.

The continuous power handling capability should be enough (each TVS of
this size can dissipate over 1 W, with heatsinking even multiple W).

The TVS diodes are reasonably cheap (some 40 cents a piece at Mouser for
QTY 10), so the main difficulty would probably be the insulation
(potting) of the series string. Probably best to put the whole thing
into a long insulating tube and fill the tube with epoxy.

Regards
Dimitrij




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Default Reducing HV output voltage from Flyback/LOPT as used in arcademonitors

On 2018/06/05 3:06 PM, Dimitrij Klingbeil wrote:
On 05.06.2018 00:30, John Robertson wrote:
I'm looking for a safe and effective way to reduce the voltage
output of a replacement flyback that is not original for the
circuit.

...

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is
supposed to be 18.5KV to 22.5KV. Thus the 13" tubes are running at up
to 25KV which is 10% over their original maximum rating and my
concern is an increase of soft X-Rays. My HV probes show somewhere
around 25 to 30KV for the 19" flyback when used in a 13" chassis.


Hi

According to the numbers you provided, the EHT needs to be reduced by
about 7 kV (while keeping other voltages derived from the transformer at
their usual levels).

The 7 kV difference is significant, but not insurmountable for a series
dropper approach. The current draw of a CRT anode is small, the power
dissipation should still be manageable: 7 W at 1 mA (if the CRT ever
takes that much current).

There are TVS diodes with voltages up to 600 V (nominal value at 1 mA
test current) available (Littelfuse P6KE600A). A series string of 12
such TVS diodes will have around 7 kV of voltage drop across them.

The continuous power handling capability should be enough (each TVS of
this size can dissipate over 1 W, with heatsinking even multiple W).

The TVS diodes are reasonably cheap (some 40 cents a piece at Mouser for
QTY 10), so the main difficulty would probably be the insulation
(potting) of the series string. Probably best to put the whole thing
into a long insulating tube and fill the tube with epoxy.

Regards
Dimitrij



Interesting idea Dimitri, however I don't see it working out - 12 diodes
in series would make the anode wire ungainly at best. Then insulating,
etc. where I think the average tech probably won't have HV rated epoxy
or silicon glue. Appreciate the idea, and may use it elsewhere!

Another poster had suggested changing the capacitance at the Horizontal
Output transistor X01, and indeed that did work! I now have 19KV on the
HV output, screen looks normal and all is well.

Obviously I need to brush up on my Horizontal Output theory so I can
understand why this worked, but for anyone reading this I added 2 X
2200pf @ 1500V and one 1500pf @ 1500V caps. Took them off a dead GO7-CBO
- 19" chassis.

Thanks!

John :-#)#

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Default Reducing HV output voltage from Flyback/LOPT as used in arcademonitors - Solved!

On 2018/06/04 5:53 PM, John-Del wrote:
On Monday, June 4, 2018 at 6:30:48 PM UTC-4, John Robertson wrote:
I'm looking for a safe and effective way to reduce the voltage output of
a replacement flyback that is not original for the circuit.

The initial problem - Electrohome 13" monitors used a specific flyback
transformer that is no longer produced.

The result - People are using the 19" Electrohome flyback as it fits
exactly the same, and is still in production overseas.

The danger - However what they are not aware of is the HV for a 19"
picture tube is 22.5 to 25KV and for a 13" colour tube it is supposed to
be 18.5KV to 22.5KV. Thus the 13" tubes are running at up to 25KV which
is 10% over their original maximum rating and my concern is an increase
of soft X-Rays. My HV probes show somewhere around 25 to 30KV for the
19" flyback when used in a 13" chassis.

My original test was to use a 75R 5W dropping resistor to limit the B+
to 100VDC to the Flyback (and only the flyback/LOPT) vs. 120VDC for the
rest of the B+. The result was proper HV, however other voltages
developed by the flyback made the results somewhat less that optimum.
The image, while good, was clipped on the left side.

Then I removed the dropping resistor (returned jumper) and tried
removing resistor R516 - 180K from the B+ input side of the HV output.
No difference.

Tried changing the value of C519 0.047ufd/200V, however increasing the
value made no real difference in the HV output.

Does anyone have any ideas on how to reduce the HV, from near 30KV to
around 19KV, that is safe and reliable? The original circuits have an
X-Ray protection that kicks in when the B+ reached about 10% over the
nominal value and I need to retain that safety feature. I would prefer
something that is pretty idiot proof.

Schematics of Electrohome GO7-19-CBO & Electrohome GO7-13-FBO:

https://www.flippers.com/pdfs/Temp/E...-schematic.pdf

Thanks!

John :-#)#



I wouldn't worry so much about the HV as I would about the filament. If the filament voltage stays at or below 6.3, I wouldn't give it another thought. Most of those tubes have no trouble with a few extra KV. If the filament is high, drop that or the tube will have a life span emissions-wise in months.

Another way of lowering the global output of the fly is add some capacitance to the retrace cap. This will of course affect all the secondaries.


You (John-Del) suggested changing the capacitance at the Horizontal
Output transistor X01, and indeed that did work! I now have 19KV on the
HV output, screen looks normal and all is well. Voltages are all
nominal, but I will compare with a proper 13" chassis that is still
using the original flyback/LOPT.

Obviously I need to brush up on my Horizontal Output theory so I can
understand why this worked, but for anyone reading this I added 2 X
2200pf @ 1500V and one 1500pf @ 1500V caps. Took them off a dead GO7-CBO
- 19" chassis.


I'm not crazy about adding resistance to drop voltage on any load that's dynamic. If you scope the collector of the horiz output with and without a dropping resistor, you'll see the waveform will be different. You may have short horiz output transistor life. If the monitor uses some sort of series/pass regulator (most 70s regulators are) you can drop the voltage by playing with the regulator and keeping the supply tightly regulated to the fly.


Thanks!

John :-#)#

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Default Reducing HV output voltage from Flyback/LOPT as used in arcade monitors

Nice to find someone willing put put effort into **** like this. I commend it. And to use pretty high tech skills to do it, like about engineers level, modifications and KNOWING what works right and doesn't. Have any idea how hard it is to find people who CAN do that, let alone willing ? Keep it alive bro... (het, sounds like a good name for a company)

I'll put my suggestions first and commentary later to be sufferable...

The components around R 516, C 519 etc. have nothing to do with the HV level. They are for the ABL, they measure the actual HV current and cut the video gain down if it exceeds a certain level. There is not supposed to be voltage dropped there like in a CRO.

Notice the difference in the print around C 512 - 514. The 19" version has 2 extra caps there. They downed C 514 down to 2,ooo pF from 2,500. Then they added C 531 & 532. which slows down the retrace, makes all retrace rectified sources lower and trace rectified sources a little bit higher. You can tell which it is by scoping the input the the rectifier, if you see a large negative trace on a positive source it is trace rectified, if the pulse is positive on a positive source it is retrace rectified.

Question : this potted fly, CAN YOU GET TO THE CORE ? You do not have to get to the windings, if you can get to the core you can add bucking or boosting windings to any winding there. All that area that is encapsulated, can you see the ferrite thing around it ? If so, can you see a gap ? All we need is about 0.03 inches for good enough. That is big enough for # 24 AWG to get through and you can get it with like couple hundred volt insulation.

Increasing the capacitance alone might not do it, but a combination of changing the B+ and that might.

Comment :

This thing was built before internal pincusion correction in the CRTs. There is a saturable reactor and another one that is permanent magnet biased. there are also VDRs. This means that This indicated that voltage and current levels muct be at least close for good geometry. We are not talking moon shot accuracy here but we must remain within the "linear non-linearitiy" operating range of those devices.

It also seems that the B+ is lower in one than the other.; One says (somewhere) 120 regulated and the other says nothing, but both shutdown use the same resistors and Zeners, and that indicates that the B+ level is close if not the same.

If, after adding the capacitance I suggested you find that it is not enough then the next thing is to reduce the B+. but don't do it with a passive device. The best method would be to add a Zener diode of the voltage desired with the anode to ground and the cathode to to the junction of C 905 & R 914. You'll probably want to choose a standard value anyway so choose a lower one and put a pot in series. It might decrease the tightness of the regulation but bucking that we had the gain of the IC itself. Look at most of them, they try to operate in their linear range. That works to our advantage.

Keep this baby on the road !
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"Series resistors may not work well, a string of MOVs might be better. "

True, but MOVs dissipate power.
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"
Have you checked the mfr specs of the tube? I doubt it's speced to 30kV but it's worth knowing exactly what you need to get it down to. "

No 13" tube is speced that high, even in Zimbabwe.


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Given the thickness of the leaded glass on those CRTs, I doubt X-rays are a concern. But you could always have the gamers wear tin-foil hats.
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On 2018/06/06 8:12 AM, Terry Schwartz wrote:
Given the thickness of the leaded glass on those CRTs, I doubt X-rays are a concern. But you could always have the gamers wear tin-foil hats.


It is not just the face of the tube that emits X-Rays, the glass on the
bell housing can (I am pretty sure) leak as well. A common use for this
13" monitor was in cocktail tables. So the face of the tube is shown to
the players and the bell housing, well let us just say it is pretty much
inline with your waist on down...

Not wanting customer gonads to glow in the dark was my main impetus for
finding a simple, yet reliable solution that did not defeat the internal
over-voltage X-ray shutdown process.

John ;-#)#

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On Wednesday, June 6, 2018 at 10:12:14 AM UTC-5, Terry Schwartz wrote:
Given the thickness of the leaded glass on those CRTs, I doubt X-rays are a concern.


I would tend to agree, but radiation is not the only concern. There is the matter of spacing of the internal components as well as the thickness of the glass on the bell part. This does determine a limit as well and going much beyond it can cause a catastrophic failure likely to wreck the envelope so it cannot be rebuilt.

It also depends on the customer. If they are corporate and even give a thought to ISO compliance they won't like it. Even this modification if it brings it completely into specs is something ISO doesn't like. If they are informed of the excessive HV and go ahead and allow its use they become culpable for whatever happens due to that. If they are not notified then the servicer might just find out many new things about the legal system. I know it is not the US where we got more lawsuits than people, but they still have tort laws and there is still such a thing as ISO. Cheating the ISO can even result in criminal charges in some cases, though rare.

But you could always have the gamers wear tin-foil hats.


Tin is expensive. The **** you buy today is aluminum foil. While aluminum conducts electricity better than tin (Al 2.65*10^[10-8] v Sn 1.15*10^[10-7]) it has nothing to do with its admittance to "those" rays, or Xrays. Lead (Pb) would be better. The aluminum can create a reflection zone where the mind scrambling rays' effects are amplified. Lead however, fatigues too easily which makes it harder to fashion acceptable headwear using it. So it is no mystery why tin is so much more expensive. The damn conspirators are limiting production and buying up the supplies for their electronic contrivances to keep us in line, depriving us of the tin we need for those body suits. What else could it be ?

{for those humorically challenged - that last paragraph was a joke}
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"Not wanting customer gonads to glow in the dark..."

Simple, lead athletic cups. Like the ones you wear fro sports...

OK, joking aside, to find out if my plan will work you need some actual capacitors to pad that LOPT collector. Then along with the HV output, watch the duty cycle of the pulse on the collector, it should be somewhere around 20 %.

I just looked up the PAL line frequency and it is not lower than NTSC. We expect 12.5 uS retrace pulse so that is probably close to what you need.

HOWEVER, since it is a monitor and has no need for a back porch for a color sub burst, it may be shorter. The design seems like the engineers were conscientious, and shorter retrace is usually more energy efficient. Since these units were made to run continuously they may have made it their concern.

It is not easy to tell if the retrace is as intended. One way is to use the horizontal phase, as you said it was off. If you return the control to its original position and padding brings it back within spec then you are getting there. Another way is to temporarily reduce the B+ and turn up the G2 to reveal overscan hidden by blanking, and that is a bit subjective.

Modification is fun ain't it ?

And my question stands, the core. Can you see it and if so can you slip a piece of say, card stock between it and the molded part ?
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catastrophic failure likely to wreck the envelope so it cannot be rebuilt..

Rebuilt? Seriously? I think the last CRT rebuilder went out of business about a decade ago. Hawkeye. The only rebuilding operation left in the western world is in the Vintage TV museum, and that's only for show.

I think many arcade machines now are repaired by subbing in an LCD panel from a computer monitor. I've seen several, and they work great. Sometimes a small circuit board is required to invert polarities, etc., but there are a handful of guys selling those on line.

John, have you considered the LCD sub?

Terry


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It is not just the face of the tube that emits X-Rays, the glass on the
bell housing can (I am pretty sure) leak as well. A common use for this
13" monitor was in cocktail tables. So the face of the tube is shown to
the players and the bell housing, well let us just say it is pretty much
inline with your waist on down...

Not wanting customer gonads to glow in the dark was my main impetus for
finding a simple, yet reliable solution that did not defeat the internal
over-voltage X-ray shutdown process.


John, my DK JR cocktail is in a metal cabinet -- robust as all get-out. Are my gonads safe in the case of HV runaway? Not that I need them anymore, my breeding days are long past.

Actually I do believe that it's the accelerated electrons hitting the face of the tube that causes X-ray radiation. Any radiation out the sides is very low energy and likely stopped by the cabinet or maybe even the aquadag.

However -- excess high voltage used to cause CRT images to "bloom". Isn't that happening in your scenario?

Terry
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Default Reducing HV output voltage from Flyback/LOPT as used in arcademonitors

On 2018/06/06 12:14 PM, Terry Schwartz wrote:
catastrophic failure likely to wreck the envelope so it cannot be rebuilt.

Rebuilt? Seriously? I think the last CRT rebuilder went out of business about a decade ago. Hawkeye. The only rebuilding operation left in the western world is in the Vintage TV museum, and that's only for show.

I think many arcade machines now are repaired by subbing in an LCD panel from a computer monitor. I've seen several, and they work great. Sometimes a small circuit board is required to invert polarities, etc., but there are a handful of guys selling those on line.

John, have you considered the LCD sub?

Terry


We are trying to avoid going LCD, the original picture tube is just
fine, and gives a more realistic image on the customer's cabaret style
Pacman game. LCDs are flat, picture tubes were mostly curved.

We do do LCD conversions, but the reason I started this investigation is
other folks also like to repair monitors and when I realized a potential
risk I decided to do something about it.

FYI, we still have over 100 monitors in our shop in various states from
NOS to POS (Peace Of S...) that we plan to save as many as possible for
museums and collectors who are our customers.

John :-#)#

PS, there are people who are rebuilding picture tubes in their
garages...small tubes for early sets, but it is only a matter of time
before they progress to larger tubes - if there is a market!

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Default Reducing HV output voltage from Flyback/LOPT as used in arcade monitors

On Wednesday, June 6, 2018 at 4:21:50 PM UTC-4, John Robertson wrote:
On 2018/06/06 12:14 PM, Terry Schwartz wrote:
catastrophic failure likely to wreck the envelope so it cannot be rebuilt.

Rebuilt? Seriously? I think the last CRT rebuilder went out of business about a decade ago. Hawkeye. The only rebuilding operation left in the western world is in the Vintage TV museum, and that's only for show.

I think many arcade machines now are repaired by subbing in an LCD panel from a computer monitor. I've seen several, and they work great. Sometimes a small circuit board is required to invert polarities, etc., but there are a handful of guys selling those on line.

John, have you considered the LCD sub?

Terry


We are trying to avoid going LCD, the original picture tube is just
fine, and gives a more realistic image on the customer's cabaret style
Pacman game. LCDs are flat, picture tubes were mostly curved.

We do do LCD conversions, but the reason I started this investigation is
other folks also like to repair monitors and when I realized a potential
risk I decided to do something about it.

FYI, we still have over 100 monitors in our shop in various states from
NOS to POS (Peace Of S...) that we plan to save as many as possible for
museums and collectors who are our customers.

John :-#)#

PS, there are people who are rebuilding picture tubes in their
garages...small tubes for early sets, but it is only a matter of time
before they progress to larger tubes - if there is a market!

--
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John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."


Back in the 70s there were several companies that sold CRT rebuilding equipment out of the back of Radio Electronics and Electronic Servicing (and others). I came real close to buying one of those setups. I'm sure many others did and I'm sure some of the machines are still around, but the big problem would be sourcing the gun assy. For all we know, the Ruskies might still be making them.

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Default Reducing HV output voltage from Flyback/LOPT as used in arcademonitors

On 2018/06/06 2:11 PM, John-Del wrote:
On Wednesday, June 6, 2018 at 4:21:50 PM UTC-4, John Robertson wrote:
On 2018/06/06 12:14 PM, Terry Schwartz wrote:
catastrophic failure likely to wreck the envelope so it cannot be rebuilt.

Rebuilt? Seriously? I think the last CRT rebuilder went out of business about a decade ago. Hawkeye. The only rebuilding operation left in the western world is in the Vintage TV museum, and that's only for show.

I think many arcade machines now are repaired by subbing in an LCD panel from a computer monitor. I've seen several, and they work great. Sometimes a small circuit board is required to invert polarities, etc., but there are a handful of guys selling those on line.

John, have you considered the LCD sub?

Terry


We are trying to avoid going LCD, the original picture tube is just
fine, and gives a more realistic image on the customer's cabaret style
Pacman game. LCDs are flat, picture tubes were mostly curved.

We do do LCD conversions, but the reason I started this investigation is
other folks also like to repair monitors and when I realized a potential
risk I decided to do something about it.

FYI, we still have over 100 monitors in our shop in various states from
NOS to POS (Peace Of S...) that we plan to save as many as possible for
museums and collectors who are our customers.

John :-#)#

PS, there are people who are rebuilding picture tubes in their
garages...small tubes for early sets, but it is only a matter of time
before they progress to larger tubes - if there is a market!

--


Back in the 70s there were several companies that sold CRT rebuilding equipment out of the back of Radio Electronics and Electronic Servicing (and others). I came real close to buying one of those setups. I'm sure many others did and I'm sure some of the machines are still around, but the big problem would be sourcing the gun assy. For all we know, the Ruskies might still be making them.


People rebuild radio and other tubes, pretty sure a gun can be rebuilt -
if worth enough $$ to someone!

And here you go!

https://www.youtube.com/watch?v=W3G7b-DcOO4

John :-#)#

--
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Default Reducing HV output voltage from Flyback/LOPT as used in arcademonitors

On 2018/06/05 9:48 PM, wrote:
Nice to find someone willing put put effort into **** like this. I commend it. And to use pretty high tech skills to do it, like about engineers level, modifications and KNOWING what works right and doesn't. Have any idea how hard it is to find people who CAN do that, let alone willing ? Keep it alive bro... (het, sounds like a good name for a company)

I'll put my suggestions first and commentary later to be sufferable...

The components around R 516, C 519 etc. have nothing to do with the HV level. They are for the ABL, they measure the actual HV current and cut the video gain down if it exceeds a certain level. There is not supposed to be voltage dropped there like in a CRO.

Notice the difference in the print around C 512 - 514. The 19" version has 2 extra caps there. They downed C 514 down to 2,ooo pF from 2,500. Then they added C 531 & 532. which slows down the retrace, makes all retrace rectified sources lower and trace rectified sources a little bit higher. You can tell which it is by scoping the input the the rectifier, if you see a large negative trace on a positive source it is trace rectified, if the pulse is positive on a positive source it is retrace rectified.

Question : this potted fly, CAN YOU GET TO THE CORE ? You do not have to get to the windings, if you can get to the core you can add bucking or boosting windings to any winding there. All that area that is encapsulated, can you see the ferrite thing around it ? If so, can you see a gap ? All we need is about 0.03 inches for good enough. That is big enough for # 24 AWG to get through and you can get it with like couple hundred volt insulation.


The outside core is accessible, and there is a nice gap between it and
the potted windings.

ftp://flippers.com//usr/www/users/fl...BO_flyback.jpg


Increasing the capacitance alone might not do it, but a combination of changing the B+ and that might.

Comment :

This thing was built before internal pincusion correction in the CRTs. There is a saturable reactor and another one that is permanent magnet biased. there are also VDRs. This means that This indicated that voltage and current levels muct be at least close for good geometry. We are not talking moon shot accuracy here but we must remain within the "linear non-linearitiy" operating range of those devices.

It also seems that the B+ is lower in one than the other.; One says (somewhere) 120 regulated and the other says nothing, but both shutdown use the same resistors and Zeners, and that indicates that the B+ level is close if not the same.


Both 13 & 19" used 120VDC as their B+. The 19" regulator was simply
higher current.


If, after adding the capacitance I suggested you find that it is not enough then the next thing is to reduce the B+. but don't do it with a passive device. The best method would be to add a Zener diode of the voltage desired with the anode to ground and the cathode to to the junction of C 905 & R 914. You'll probably want to choose a standard value anyway so choose a lower one and put a pot in series. It might decrease the tightness of the regulation but bucking that we had the gain of the IC itself. Look at most of them, they try to operate in their linear range. That works to our advantage.


Capacitance of 6,000pf did work, the buck/boost idea is nice, but may
involve too much time, and it will be easy for someone to get wrong. A
single cap is nice and clean and almost fool-proof. I still have to
track down an original flyback driven 13" monitor to make sure the other
voltages (with the 6Kpf cap) are within reasonable limits, but the image
is good, so I assume all is well! The filament, screen, and focus
voltages all seem good, so I think we have a winner here. Will now try
doing a second monitor to see if this is not just a fluke...


Keep this baby on the road !


That is what we do at my shop!

Thanks for all your technical advice, that has clarified the schematic a
lot for me, obviously you have experience with either designing or
repairing monitors/TVs.

John :-#)#
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"The outside core is accessible, and there is a nice gap between it and the potted windings. "

It can be a chance getting the polarity right when you buck/boost, but with a fly (LOPT) like that it is easy to see on the scope. I wanted to buck the pulse to the yoke on this little 13" Sony I watch sometimes, I didn't buck the top end where the 1,000 volt pulse is, I bucked the bottom. Makes more sense.

"Both 13 & 19" used 120VDC as their B+. The 19" regulator was simply

higher current. "

Makes sense by backward reasoning. Shutdown is the same, there is a law or something that it must when the radiation hits a certain level and that is that. Thus, a unit with more nominal B+ will have a higher OV shutdown threshold.

"Capacitance of 6,000pf did work..."


It is possible it is perfect. For market share in the repair parts market they do occlude the fact that some of these parts are the same. Your average tech has no way of telling even with the best of equipment. And teachers can't teach what they do not know. they offered me a job, well one guy who worked at Case University. he said they can't find anyone to teach what I taught him to get the job there, and that was very basic. the traveling turned me off but I might take it now, however they must take me with absolutely zero accreditation, official anyway.

"I still have to

track down an original flyback driven 13" monitor to make sure the other voltages (with the 6Kpf cap) are within reasonable limits"

There appears to only be one scan derived source, 12 volts. They do not change the number of turns on one winding of a transformer for different screen sizes. It is almost for sure well within specs. think about it from the engineers' point of view.;

"That is what we do at my shop! "


Good. would you like some references to some music ? Judas Priest - Another Thing Comin', Queensryche - Best Man, there are more. I odn't give up. Well as a rule, sometimes I see no way to get er done and then I pull out faster than a (insert your own thaing here)

"Thanks for all your technical advice, that has clarified the schematic a lot for me, obviously you have experience with either designing or repairing monitors/TVs. "


Not designing so much, but I have made alot of money making things work that nobody else could. Part not available ? They called me. I was good. We had a bunch of countdown chips that were bad out of the box. No sync. With the addition of a generic PNP transistor I fixed it and the sets ran fine on the defective IC. I have modified more power supplies than they have designed. when I put a winding on a fly (LOPT) to isolate the filament of a CRT with an HK short I used a resistor of like 5K to make sure it was effectively shorted and not intermittent (which many were) and then boosted the high frequency response of the video amp to compensate for the stray capacitance introduced by the video being imposed on the line.

At one time, I considered a big shop. I have been in business but it only got to 2 locations and we got sick of it. But I considered a test for tech applicants. One of the first requirements is to be able to draw a block diagram of a color TV. And I don't mean 3 blocks, I mean with some detail.

From your posts I am pretty sure you can, but how many can ? Or could ? So many places had incompetent people it left a bad taste in the customers. Where I worked we were cheaper and better because we were more efficient, and ALSO MADE MORE MONEY. Competence pays off if you know how to use it.
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