What's This Thing Attached to My Flyback? (& Other Questions)

Hi, everyone. New poster here.

I'm aiming to build a high-voltage power supply for an electrostatic precipitator cheaply using a salvage flyback transformer. Fortunately for me, my in-laws had an old TV they wanted to discard. Unfortunately, I'm kinda puzzled by what I'm seeing.

The biggest puzzler for me is: What's that thing between the flyback and the suction cup?
Picture:


As you can see, it's got two high-voltage connections on the top (they're labeled "in" and "out") and 4 pins on the base.

My Google-Fu has failed me here: I'd think it was a splitter, but there's only one output. My next guess would be a rectifier/voltage multiplier, but aren't those supposed to be incorporated into the flyback casing? Anyway, I'm stumped.

Does anyone know what this thing is? Should I remove it from the line or keep it? If I keep it, what (if anything) to I do with the pins on the base?

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Second issue: I'm having trouble locating the pins for the primary winding.
Searching the internet has turned up conflicting explanations:

• The pair of pins with the highest resistance is the primary.
• The pair of pins with the lowest resistance is the primary.
• The pair of pins with ~1 Ohm resistance is the primary. (No explanation of which to choose if two pairs are ~1 Ohm...)
• The pair of pins with resistance ~0.5-2.0 Ohm is the primary. (Again, no explanation of which to choose if two pairs fall in that range.)

Who's right?

This flyback has 11 pins (not counting the pin for the "focus" and "screen" knobs). (Not sure if it matters, but pin 11 is shorter than the others.) I've measured the following:
(Note: Touching the probes on my multimeter to each other = fluctuates ~1.0-1.5 Ohm (I think this means my multimeter stinks...))


Any thoughts on which pair is the primary?

(The label is very faded, but I think it says "TFB4132BD." I haven't been able to find a pinout for this model online.)

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Third issue: What (if anything) should be done with the "focus" and "screen" knobs and their pin?

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Fourth issue: Thanks to the folks at Toshiba applying copious solder to both sides of the joints, I had to apply a lot of heat and violence to separate the flyback from the board. What are the odds that I've already fried this transformer? In general, how much abuse can these take, particularly in the form of a hot soldering iron against their pins?

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Thanks for taking the time to read this!

The primary on mine was 1 to 2 ohms.
When you get it working, hold the HV wire near the other terminals.
It will tell you which one is the HV negative.

What's This Thing Attached to My Flyback?

Click to expand...

There is most likely a Resistor(s) and a Capacitor from the high voltage to pins on the bottom of the "Thing".
Many small Flyback Transformers do not have the RC. The transformer from post #2 does have the RC in side the transformer.
The capacitor reduces the ripple voltage.
The resistor is there for two reasons, 1--is to supply a minimum load. 2--is part of a voltage divider to take the high voltage down to 5 volts for feedback. (used to measure the HV)

Resistor: I can not see but there might be only one resistor to a single pin. Or there might be a 2 to 5 watt resistor to a pin and a second resistor from that pin to another pin. (so both resistors of the voltage divider are in the "thing".

If you can find the ground end of the focus pots....connect to ground.

At one time I had filing cabinets full of data sheets for flyback transformers. All gone now. I have engineering books of hand drawn data on prototypes. Not much help to you now.

Thank you ClydeCrashKop and ronsimpson.

ClydeCrashKop: The pins you circled correspond to pins 1 & 2 in my chart (1.8 Ohms, tied for highest resistance with 1 & 3). Does that sound right?

ronsimpson: What should I do with the "thing"? Connect some or all of the pins to "third rail" earth ground? Back to the negative pin on the secondary (once I find it)? Leave the pins disconnected? Remove it entirely? (Aside: On closer inspection, "C", "NC," "NC," "NC" is stamped in the plastic near each pin on the bottom of the "thing." No idea what that means...)

Thanks again!

Go back to the donor television and sketch an schematic looking at the board traces. Primary terminals should have power rail and a biggie mosfet/transistor, if you have no servicing schematic.

Externet said:

Primary terminals should have power rail and a biggie mosfet/transistor.

Click to expand...

Unlikely to be a MOSFET, I've never seen one used for LOPT in all my years of repairing TV's - you VERY occasionally got them in SMPSU's, but it was fairly rare as they were more expensive and less reliable.

If he knows the model of the TV the TX came from, he could google for a service manual, which should sort him out.

UnskilledOne said:

What should I do with the "thing"?

Click to expand...

Could cut the wire and remove it.
Could connect all the pins to ground.

Could the "thing" simply be a voltage multiplier, x3 or x5 ??

JimB

JimB said:

Could the "thing" simply be a voltage multiplier, x3 or x5 ??

JimB

Click to expand...

No, it's a capacitor (to regulate the voltage to the CRT, basically a reservoir capacitor), it will also include a discharge resistor, which 'might' be used for voltage feedback as mentioned previously (but that would be unusual).

I suspect such additions, which were pretty rare, were to compensate for poor design? - with a decent designed LOPT stage the CRT capacitance is plenty.

Nigel Goodwin said:

No, it's a capacitor

Click to expand...

OK, shows how au fait I am with TV technology.

The last thing that I worked on which was any where near to that was my old Telequipment D75 'scope.
The multiplier was dead, so I had to build a new one from scratch.
The maintenance manual had a schematic of the multiplier, but did not show any values as it was a potted module, so I made an inspired guess and it is still working 25 years later.

JimB

Nigel Goodwin said:

I suspect such additions, which were pretty rare, were to compensate for poor design? - with a decent designed LOPT stage the CRT capacitance is plenty.

Click to expand...

It was not common for old TVs to have a bleeder resistor on the HV. I used them to save TV repairmen and to help regulate the High Voltage.
The picture size is related to the high voltage. On most TV sets a picture that is 99.9% black is smaller than a picture that is 99% white. I have seen 10% change in size.
Watching TV with Cowboys and Indians running through the trees .... no one notices that the size of the trees changes depending on how bright/dark a tree is.
The reason we hate to see computer text on a TV is that the size of the picture changes with the video. It was a real problem to have a line of black text on white background followed by 10 lines of white text on a black background. These "text boxes" changed size from top to bottom.
CRT monitors used for computers or medical imaging can not have the size change with brightness. Low end monitors used bleader resistors to help with regulation. Capacitors limit how fast the HV can change. A large capacitor does not hold the HV constant but it might take 100s of lines for the voltage to change. This looks better.
In good CRT monitors there is HV feedback and some times horizontal size feed back. For many years we made monitors that held 30,000 volts to with in 10 volts from full load to no load. We bragged we held the horizontal and vertical size to 1/2000 under any condition.

HV Negative connection.