Richtige Fernseher haben Röhren!

Richtige Fernseher haben Röhren!

In Brief: On this site you will find pictures and information about some of the electronic, electrical and electrotechnical Obsolete technology relics that the Frank Sharp Private museum has accumulated over the years .
Premise: There are lots of vintage electrical and electronic items that have not survived well or even completely disappeared and forgotten.

Or are not being collected nowadays in proportion to their significance or prevalence in their heyday, this is bad and the main part of the death land. The heavy, ugly sarcophagus; models with few endearing qualities, devices that have some over-riding disadvantage to ownership such as heavy weight,toxicity or inflated value when dismantled, tend to be under-represented by all but the most comprehensive collections and museums. They get relegated to the bottom of the wants list, derided as 'more trouble than they are worth', or just forgotten entirely. As a result, I started to notice gaps in the current representation of the history of electronic and electrical technology to the interested member of the public.

Following this idea around a bit, convinced me that a collection of the peculiar alone could not hope to survive on its own merits, but a museum that gave equal display space to the popular and the unpopular, would bring things to the attention of the average person that he has previously passed by or been shielded from. It's a matter of culture. From this, the Obsolete Technology Tellye Web Museum concept developed and all my other things too. It's an open platform for all electrical Electronic TV technology to have its few, but NOT last, moments of fame in a working, hand-on environment. We'll never own Colossus or Faraday's first transformer, but I can show things that you can't see at the Science Museum, and let you play with things that the Smithsonian can't allow people to touch, because my remit is different.

There was a society once that was the polar opposite of our disposable, junk society. A whole nation was built on the idea of placing quality before quantity in all things. The goal was not “more and newer,” but “better and higher" .This attitude was reflected not only in the manufacturing of material goods, but also in the realms of art and architecture, as well as in the social fabric of everyday life. The goal was for each new cohort of children to stand on a higher level than the preceding cohort: they were to be healthier, stronger, more intelligent, and more vibrant in every way.

The society that prioritized human, social and material quality is a Winner. Truly, it is the high point of all Western civilization. Consequently, its defeat meant the defeat of civilization itself.

Today, the West is headed for the abyss. For the ultimate fate of our disposable society is for that society itself to be disposed of. And this will happen sooner, rather than later.

OLD, but ORIGINAL, Well made, Funny, Not remotely controlled............. and not Made in CHINA.

How to use the site:
- If you landed here via any Search Engine, you will get what you searched for and you can search more using the search this blog feature provided by Google. You can visit more posts scrolling the left blog archive of all posts of the month/year,
or you can click on the main photo-page to start from the main page. Doing so it starts from the most recent post to the older post simple clicking on the Older Post button on the bottom of each page after reading , post after post.

You can even visit all posts, time to time, when reaching the bottom end of each page and click on the Older Post button.

- If you arrived here at the main page via bookmark you can visit all the site scrolling the left blog archive of all posts of the month/year pointing were you want , or more simple You can even visit all blog posts, from newer to older, clicking at the end of each bottom page on the Older Post button.
So you can see all the blog/site content surfing all pages in it.

- The search this blog feature provided by Google is a real search engine. If you're pointing particular things it will search IT for you; or you can place a brand name in the search query at your choice and visit all results page by page. It's useful since the content of the site is very large.

Note that if you don't find what you searched for, try it after a period of time; the site is a never ending job !

Every CRT Television saved let revive knowledge, thoughts, moments of the past life which will never return again.........

Many contemporary "televisions" (more correctly named as displays) would not have this level of staying power, many would ware out or require major services within just five years or less and of course, there is that perennial bug bear of planned obsolescence where components are deliberately designed to fail and, or manufactured with limited edition specificities..... and without considering........picture......sound........quality........
..............The bitterness of poor quality is remembered long after the sweetness of todays funny gadgets low price has faded from memory........ . . . . . .....
Don't forget the past, the end of the world is upon us! Pretty soon it will all turn to dust!

Have big FUN ! !
©2010, 2011, 2012, 2013, 2014 Frank Sharp - You do not have permission to copy photos and words from this blog, and any content may be never used it for auctions or commercial purposes, however feel free to post anything you see here with a courtesy link back, btw a link to the original post here , is mandatory.
All sets and apparates appearing here are property of Engineer Frank Sharp. NOTHING HERE IS FOR SALE !
All posts are presented here for informative, historical and educative purposes as applicable within Fair Use.

Tuesday, June 29, 2010


Here below a list of the original Flybacks LOPTS of many CRT TVs.
 Comparison list is organized with original code to the  HR DIEMEN corresponding Replacement part.
  These DC flybacks are found in every CRT computer monitor and are called the DST flybacks (diode-split transformers) because of the several high voltage diodes and secondaries inside. In addition to the high resistance resistor cascade (Bleeder) and focus/screen tuning potentiometers described above, these kinds may have an integrated high voltage filtering capacitor (few nanofarads at >=30 kV), or – optionally – a HV capacitor for dynamic focus.

The TV  DC flybacks are also diode-split (DST), however these are found in every modern CRT TV-set from mid-end 80s and onwards. These have just two screen-tuning potentiometers and no internal capacitors whatsoever !
ISTRUCTIONS: To search a specific item within this page use the search function of your browser.

Original Reference HR
D 001/37 HR 6009
D 002/37 HR 6062
D 003/37 HR 6003
D 004/37 HR 6005
D 005/37 HR 6045
D 012/37 HR 6032
D 014/37 HR 6180
D 016/37 HR 6145
D 022/37 HR 6062
D 023/37 HR 6158
D 026/37 HR 6179
D 030/37 HR 6182
D 032/37 HR 6154
D 036/37 HR 6089
D 041/37 HR 6058
D 046/37 HR 6113
D 047/37 HR 6144
D 049/37 HR 6150
D 050/37 HR 6057
D 052/37 HR 6060
D 053/37 HR 6181
D 056/37 HR 6182
D 059/37 HR 6157
D 060/37 HR 6388
D 061/37 HR 6284
D 063/37 HR 6293
D 064/37 HR 6284
D 066/37 HR 6149
D 067/37 HR 6388
D 069/37 HR 6182
D 070/37 HR 6160
D 071/37 HR 6160
D 076/37 HR 6175
D 081/37 HR 6159
D 102/37 HR 6043
D 108/37 HR 6100
D 118/37 HR 6100
D 171 HRT 225 BP
D 174 HR 1681 S
D 175 HR 1674 S
D 176 HR 1674 S
D 177 HRT 901
D 178 HRT 906
D 201/37 HR 6053
D 202/37 HR 6043
D 207/37 HR 6268
D 208/37 HR 6155
D 210/37 HR 6288
D 214/37 HR 6044
D 218/37 HR 6169
D 219/37 HR 6172
D 224/37 HR 6167
D 233/37 HR 6025
D 237/37 HR 6174
D 240/37 HR 6224
D 241/37 HR 6223
D 243/37 HR 6252
D 244/37 HR 6167
D 246/37 HR 6119
D 247/37 HR 6004
D 258/37 HR 6039
D 260/37 HR 6255
D 272/37 HR 6278
D 275/37 HR 6132
D 278/37 HR 6008
D 280/37 HR 6063
D 281/37 HR 6053
D 284/37 HR 6090
D 291/37 HR 6207
D 297/37 HR 6254
D 299/37 HR 6153
D 307/37 HR 6257
D 313/37 HR 6119
D 322/37 HR 6134
D 331/37 HR 6228
D 335/37 HR 6063
D 337/37 HR 6294
D 339/37 HR 6132
D 341/37 HR 6253
D 342/37 HR 6294
D 344/37 HR 6256
D 348/37 HR 6475
D 358/37 HR 6387
D 361/37 HR 7128
D 372/37 HR 6278
D 376/37 HR 6195
D 397/37 HR 6295
D 399/37 HR 6389
D-5 HRT 256
D-5 B HRT 257
D-6 HRT 262
DA 019 E HR 3533
DCF 1551 HR 6375
DCF 1551 A HR 6375
DCF 1551 M HR 6375
DCF 1551 M 7103 P HR 6375
DCF 1551 P HR 6375
DCF 1577 HR 7494
DCF 1577 A HR 7456
DCF 1577 N HR 7482
DCF 1580 HR 46045
DCF 1580 A HR 46045
DCF 1580 B HR 46025
DCF 1580 E HR 46045
DCF 2052 HR 6385
DCF 2052 A HR 6385
DCF 2052 P HR 6385
DCF 2077 HR 7481
DCF 2077 A HR 7455
DCF 2077 B HR 7916
DCF 2077 D HR 7916
DCF 2077 N HR 7481
DCF 2077 Y HR 7916
DCF 2077 Z HR 7468
DCF 2078 A HR 7458
DCF 2217 HR 7644
DCF 2217 A HR 8758
DCF 2217 J HR 7644
DCF 2217 L HR 7797
DCF 2217 Y HR 7797
DCS 2034 HR 6385
DCT 1470 HR 7456
DDF 9802 A HR 7455
DE 50 H 0000134 HR 7770
DE 50 H 0000155 HR 7770
DE 50 H 0000166 HR 7916
DE 50 H 0000177 HR 7880
DE 50 H 0000205 HR 8532
DFF 98020 HR 7455
DFF 98020 A HR 7455
DG 300000166 HR 42021
DG 300000174 HR 42023
DG 300000182 HR 42022
DG 300000191 HR 42042
DG 300000504 HR 42025
DG 300000512 HR 42026
DG 300000603 HR 42027
DG 300000709 HR 42101
DG 300001004 HR 42025
DG 300003009 HR 42049
DG 300004005 HR 46089
DG 300004005 M HR 46089
DG 300004005 N HR 46089
DG 300004048 HR 46089
DG 300005818 HR 46166
DG 300008507 HR 46184
DG 330000504 HR 42025
DG 330000512 HR 42026
DG 330000603 HR 42027
DG 330001004 HR 42025
DK 42010 B HR 7522
DM 3510-69428 HR 7898
DMQ 1445 HR 7456
DN-FA 2065 HR 8277
DNF-FA 1426 HR 7468
DNF-FA 2002 HR 7483
DNF-FA 2002 A HR 7483
DNF-FA 2002 B HR 7483
DNF-FA 2003 HR 7444
DNF-FA 2003 B HR 7483
DNF-FA 2014 HR 7736
DNF-FA 2017 HR 8303
DNF-FA 2019 HR 7468
DNF-FA 2040 HR 7605
DNF-FA 2041 HR 7736
DNF-FA 2044 HR 7731
DNF-FA 2044 A HR 7731
DNF-FA 2044 E HR 7731
DNF-FA 2065 HR 8277
DNF-FA 2066 HR 46038
DNF-FC 1401 HR 7452
DNF-FC 1404 B HR 7728
DNF-FC 1406 HR 7460
DNF-FC 1426 HR 7455
DNF-FC 1431 D HR 7834
DNF-FC 1432 HR 7742
DNF-FC 1434 HR 7729
DNF-FC 1445 HR 7608
DNF-FC 1452 HR 7472
DNF-FDA 0001 HR 8528
DNF-FE 2004 HR 8508
DNF-FL 2700 HR 7708
DNF-FL 2713 HR 7255
DNF-FL 2727 HR 46089
DNF-FL 2732 HR 8369
DNF-FL 2732 A HR 8369
DNF-FL 2732 B HR 8369
DNF-FMA 0002 HR 8402
DNF-FMA 01 HR 8689
DNF-FN 1407 HR 46167
DNF-FN 1419 HR 7695
DNF-FN 1419 A HR 7695
DNF-FN 1528 HR 46117
DNF-FN 1530 HR 46213
DNF-FN 1534 HR 46117
DNF-FT 0002 HR 46154
DNF-FXB 0012 HR 8440
DOK 8840 N HR 8218
DOK 8848 N HR 7464
DOK 8850 HR 7949
DR 1/TVK 72 HRT 205
DS 01 HR 7052
DS 011 HR 6257
DS 012 HR 6176
DS 014 HR 7546
DS 02 HR 7052
DS 03 HR 7037
DS 04 HR 7058
DS 07 HR 7088
DS 08 HR 7541
DS 09 HR 6053
DS 1 HR 7052
DS 10 HR 6219
DS 11 HR 6053
DS 12 HR 6257
DS 12-015601 HR 6268
DS 13 HR 6270
DS 14 HR 7546
DS 15 HR 7556
DS 16 HR 7575
DS 16 BLED HR 7581
DS 17 HR 7584
DS 17 BLED HR 7596
DS 18 HR 7599
DS 18 B HR 7286
DS 19 HR 8019
DS 19 X 14 HR 8019
DS 19 X 14 E 16 HR 8019
DS 2 HR 7052
DS 20 HR 8560
DS 3 HR 7037
DS 30 HR 6257
DS 31 HR 7338
DS 32 HR 8173
DS 34 HR 8279
DS 35 HR 8234
DS 4 HR 7053
DS 5 HR 7058
DS 50 HR 8840
DS 5021 B HR 7074
DS 53 HR 8839
DS 6 HR 7087
DS 60 HR 8849
DS 7 HR 7088
DS 8 HR 7168
DS 9 HR 6053
DS12/015.6.01 HR 6268
DS3/015.6.003 HR 7037
DS6/015.6.003 HR 7087
DT 2075/26 HR 2075
DT 2076/71 HR 6071
DT 2078/20 HR 7704
DT 2080 HR 1117
DT 2090/01 HR 2282 T1
DT 2094/42 HR 7962
DV 2076-20603 HR 8253
DV 2076-21161 HR 8630
DV 2076/20603 HR 8253
DV 2094-20411 HR 8026
DV 2094/01 HR 7963
DV 2094/09 HR 7811
DV 2094/20093 HR 7543
DV 2094/20410 HR 8026
DV 2094/20411 HR 8026
DV 2094/20633 HR 8019
DV 2094/20661 HR 8240
DV 2094/20662 HR 8240
DV 2094/2089.1 HR 8371
DV 2094/20891 HR 8371
DV 2094/21213 HR 7950
DV 2094/40 HR 7772
DV 2094/41 HR 7963
DV 2094/42-0 HR 7962
DV 2094/50 HR 8126
D92943-A7154-M211 HRT 228 BP

Line transformers generate the necessary deflection pulse and other many key voltages and the  high voltage for anode of the picture tube in tube televisions and computer monitors. Usually this is around 30 kV for a color device, but the current is  with approx. 0.5 to 4 mA.

The line transformer or horizontal output transformer (English: flyback transformer or line output transformer) is part of a television / monitor with picture tube. It is used to supply the line deflection coil of the deflection system and at the same time usually also to generate the high voltage of 20 to 30 kV required for the operation of the picture tube and other voltages necessary for the operation of the device.

Line transformers work with the line frequency, with European TV sets with 15.625 kHz. Line transformers of 100 Hz televisions work at twice the frequency, i.e. at 31.25 kHz. In monitors, the line transformer is operated at different frequencies, which depend on the resolution of the image sent by the computer. For example, the line frequency of a monitor with a resolution of 1024 × 768 pixels and 85 Hz vertical frequency is approximately 68.7 kHz. With these frequencies, the line output stage switches a switching tube or today a switching transistor, which are used to control the line transformer.
The whistling noise of some older monitors and most older, conventional TV sets arises from the fact that mainly the line transformer, but also other components such as coils and capacitors, are mechanically excited to vibrate by the occurring magnetic and electrostatic forces. Whistling has a frequency of 15.625 kHz due to the European television standard. TVs with 100 Hz technology and most high-resolution computer monitors whistle outside the listening area........

Line transformers are potted with resin and have a ferrite core and are therefore of course only suitable for high frequencies in the kHz range. Newer types, so-called diode split transformers, contain many individual diodes between the windings and thus supply a rectified high voltage (pulsating DC voltage). Older models made of black and white devices have an external cascade, the direct (high-frequency) output voltage is then only about 8 kV, but a little more current is available with such AC line transformers. Line transformers require an electronic control circuit which provides a square wave signal in the range of approx. 15 kHz.

Diode split transformer with permanently cast diodes and DC output The advantage of line transformers: They are easy and inexpensive (or free) and can be obtained in large numbers at radio / TV shops and in computer shops where devices are disposed of. Especially nowadays, in which tube monitors have to make room for flat screens, many old monitors and TVs are disposed of.

Removal and wiring of a line transformer:

Important when removing the line transformer from the TV or monitor: First discharge the picture tube, then remove the high-voltage connection, and draw out the pin assignment of the line transformer before unsoldering. Two connections are particularly important: supply supply (approx. 150V from the power supply unit) and connection that goes to the collector of the horizontal output transistor or on very older types to a tube or thyristor final stage.

The thick, well-insulated, red cable is the high-voltage output (approx. 30kV), while the somewhat thinner, black cable carries the focus voltage, which is only around 6kV. Finally, the orange cable brings the grid 2 voltage, which is only a few hundred volts. Television and monitor flyback transformer pinout have some common designed except that the monitor
flyback have a internal capacitor built in. The internal capacitor value have around 2.7 nanofarad to 4.5 nanofarad to improve the picture quality especially when the monitor which can go for a higher resolution compare to Tv. If without the internal capacitor in the monitor flyback the display will curve or slightly out of shape especially at both the right and left hand side of the picture and may present other imperfections not admitted for monitors. It acts as a filter. Internally they may have a high vealue resitor (600 to 900 mega ohm) in parallel to HV output. This to adapt the ouput impedance of the LOPT to the CRT Anode.

Mostly tv and monitor flyback transformers have about ten pins at the bottom of the flyback. Each of the pin have a purpose or function as part of a complete circuit. The common pins that you can find in monitor flyback are: B+ pin, Horizontal collector pulse, ABL (automatic blanking limiter), GROUND, G1, AFC (automatic frequency control), VCC, HEATER (to filament) and X-RAY protection.

The B+ and horizontal collector pulse pin forms one winding which we call it as flyback primary winding. It can  only can be test by using a flyback meter such as the  Lopt tester flyback transformer pinoutor sencore LC102 and LC103C.

Note that some monitors and TV design may have a separate HV and deflections circuits

Normal meters can't check this kind of fault. This is the most important winding compares to others and it can easily developed a short circuit when B+ voltage line or Horizontal output transistor (HOT) shorted. Sometimes a shorted internal capacitor in the flyback transformer may cause the primary winding to burn internally and the flyback became bulge and poured out the epoxy.

Other pins are the ground, G1, and AFC winding. AFC stand for automatic frequency control and it send signal (pulse) from the flyback transformer to the horizontal oscillator ic to lock or synchronize the frequency of the monitor. If this AFC line fails the picture will shift either to the far left or far right. There is no way that you can adjust the picture to the center even with the internal adjustment in the mainboard. The purpose of G1 voltage is to pull the electron generated from the cathode (after the heater or filament heat up) and passed it to G2 which is the screen voltage.

G1 normally is a negative voltage or positive from few volts to 32 volts in some most ancient designs . Most tv picture tube do not use G1 voltage. If the G1 voltage is missing or zero voltage to the picture tube the monitor display will becomes very bright with retrace lines (diagonal lines or flyback lines) across the screen and sometimes the monitor will goes into shutdown mode.
ABL stand for automatic beam limiter- I refer it as a limiter further circuit. Why? because whenever there is a contrast or bright problem i will search for this pin and begin to trace from there. Normally a resistor increased in resistance and a shorted ceramic capacitor caused the display to become dim and you may think it might be the fault of a bad CRT.

Heater or filament pin nowadays hardly found in monitor flyback because the crt heater voltage now is derived directly from the switch mode power supply. However heater pin is still can be found in television flyback transformer. If the anode voltage is too high (more than 30 kilovolt), the x-ray protect pin will send a signal to horizontal oscillator ic in order to disable the horizontal drive waveform THIS FOR SAFETY REASONS.

Without the horizontal drive pulse the high voltage generated by the flyback will collapsed and protect the user from excessive x-ray.

The flyback transformer pinout will also generate high pulse ac which later convert to dc through an ultra fast recovery diode. For your information, the ac pulse generated by the flyback transformer cannot be check with our normal analog or digital meter. the frequency is so high and you need a special meter to do the job. The dc voltages are then supply to various circuit such as the vertical output circuit. If you  understand all the functions of each flyback transformer pinout, repairing  monitor or tv will be much easier and save your precious time.

 TV / MONITOR  Fly-Back Transformer Replacement GUIDE:

All repairers with  experience, once made a replacement of a driver transformer with more or less fortune. All we did was to methodize the work and modify the circuit to work optimally.

But....... when it comes to a fly-back Transformer , practically all repairers think that if the replacement is not the exact fly-back  Transformer, absolutely nothing can be done. In principle we would like to clarify that manufacturers of replacement fly-backs do not manufacture all fly-back Transformer variants; they only manufacture some of them and then connect the bases according to the different models and mark them with a different code. ANYWAY SPECIFICITY IS OEM RELATED BY DESIGN.

EXAMPLE:Between different 20" fly-backs Transformer , for example, there are usually minimal differences except in the position of the legs. If there are notable differences, it is in the high voltage because this varies according to the size of the screen. The 14" tubes usually have extra high tensions of 18 to 20 KV; the 20" tubes between 23 and 25 KV and finally the 29 and 33" tubes have tensions higher than 28 KV / 36KV. In addition, the larger tubes have a different horizontal output circuit that has an east/west modulator to correct the pad effect plus other specific parts.

Let's limit our analysis to 14 and 20" TVs from which the fly-back Transformer is not achieved. The first step is to know a fly-back inside to understand the replacement work. Let's analyze the returns and live of the auxiliary windings.
CHECK schematic diagram and study it.

A modern fly-back Transformer is a hybrid of a high and low voltage transformer and a screen voltage and focus adjustment circuit. It can be divided for analysis into a transformer and a focus pack.


Transformer analysis:

The transformer is fundamental part of the horizontal output circuit because it connects the source to the collector of the horizontal output transistor through an inductance about 4 times greater than that of the yoke. In this way, only 1.5 to 1.7 A of the 6 or 7 A peak-to-peak current through the yoke flows through the fly-back and the horizontal source capacitor. Be aware that in older tvs which may  have greater deflection systems the currents are higher.

But the fly-back is not an inductor, it is a transformer and part of the energy existing in its primary is transformed into several low voltage windings, which feed different stages of the TV such as the jungle, the vertical output, the video stage , the sound, key voltages for chroma, sync, and many others services depending on design, and above all the tube filament (which is not rectified but applied as AC). These windings are strongly coupled to the primary because they are built above or below it.

The geometry of the fly-back core is very particular because it is a transformer that has a high voltage winding and the turns of that winding must be away from the core. Therefore, the classic shape of the core with an "E" and "I" shape is abandoned and a shape with two "U"'s is used where the HV winding enters loosely. The spool of that winding has a slotted shape, where only the diameter of a wire enters. In this way the winding is really a wire spiral and in reality it is not one single winding but 4 or many more , each one with its corresponding high voltage diode and its filtering capacitor, also of high voltage. This winding, because of its shape, is loosely coupled to the primary so that a fault in it, is not transferred as a short circuit but as a reduction of primary inductance but it will produce a malfunction.

As we know, the return of the high voltage winding is not connected to ground, but to the horizontal source. A 20" tube supports only a maximum current for each cathode of 330 uA; between the three cathodes they can consume a maximum of 1 mA and that current is directed from the cathodes to the aluminizing of the screen that is part of the final anode of the tube. This current returns through the winding and produces a voltage drop in a network
Synthetically, if the image is black there is no current and the voltage of ABL  When the brightness increases, the voltage increases  so that when 1 mA circulates, the voltage   is cancelled and there operates the jungle / luminance matrix stages limiting the brightness and contrast.

Analysis of the focus / G2 VOLT pack inside  DST Transformer

Flyback deflection systems are well known and widely used in television receivers. In such systems, a deflection voltage source drives an autotransformer with a ramp shaped current for deflecting an electron beam across the phosphor coated faceplate of a cathode ray tube (CRT). At the end of the ramp waveform, a relatively large retrace pulse is developed. This pulse is magnified by the turns of the flyback transformer winding and rectified to develop the high DC voltage required to operate the CRT. As is well known, although the high voltage system is tuned, the high DC voltage produced varies substantially with system loading that occurs due to increases in the electron beam current of the CRT. There have been numerous circuits in the art for "stiffening" the high voltage supply. In many applications, a separate, non-deflection-based high voltage system is used because of its tighter tolerance on regulation.

With the growing use of computer monitors, the need for precision CRT displays has increased. In these uses, high voltage regulation is critical and needs to be closely controlled to prevent unacceptable raster distortion and size changes. On the other hand, the needs of the marketplace are such that the cost of the monitor must be maintained as low as possible.

The focus pack has several functions: it is a double variable voltage attenuator also known as HV Bleeder. The highest voltage is for the focus and the lowest for the screen. The older tubes are low focus and the focus pack delivers voltages of approximately 8 KV. The newer and bigger ones are high focus and deliver about 9.5 KV. It is not possible to change a low-focus fly-back for a high-focus one, because it does not adjust the focus.

Generally, the conventional bleeder resistor is manufactured in the following manner. , there is prepared a ceramic substrate  made of Al2 O3 having a purity of about 96%. Its thickness is about 0.5-1.2 mm, and its area is 400-1500 mm2. Upon the ceramic substrate , there is printed PbAg, PtAg, Ag or their combination paste. Then the printed substrate is baked at a temperature of about 800° C., and thus, a printed circuit board is formed, and then lead wires are soldered. Then RuO2 is printed thereupon, and then the structure is baked at a temperature of about 850° C. Thus a resistor having a certain thickness is completed.

Meanwhile, in this resistor, electric current can flow only if the electrical resistance per unit length of the resistor is smaller than the air contact electrical resistivity. In the case where the voltage breakdown resistivity of air is 0.5 KV/mm, if a voltage of 20 KV is supplied across a resistor 12, there has to be secured a distance of 20 KV÷0.5 KV/mm=40 mm. Further, if the thermal degradation and the environmental factors are taken into account, then the safe distance must be 1.8 times as large as the above distance, that is, 40 mm×1.8=72 mm. Meanwhile, in the case where the resistor 12 is printed on the ceramic substrate 10 in a straight line, the length of the ceramic substrate has to be longer, with the result that the total bulk of the ceramic substrate becomes too large.

The screen voltage is approximately the same for all tubes (in the order of 250 to 350V or 500 to 800V). Both voltages are provided by voltage dividers and high value potentiometers because they are directed to grids in the tube that do not consume current. As you can see, the circuit is simply a series of two high voltage potentiometers and two high voltage resistors connected between the pacifier output and ground. In figure above I draw the focus pack circuit only with the characteristic voltages and resistances, which are practically the same (or at least proportional) for all the equipment.

The resistance values are high enough that it is impossible to measure them with a digital or analog tester. It is even impossible to measure the voltages at the focus and screen outputs without altering their value. And they're prone to defects such rising in values or dropping value.

Now that we know the circuit let's start with the replacement work. As the fly-back has two sections we must analyze the failures of both sections separately starting with the fly-backs that have problems in the focus pack.

The most common fault is a dark screen despite the existence of high voltage. A high voltage tip should really be used for the tester if we want to be sure of the existence of the 25KV of AT but generally the test of measuring the screen voltage with the potentiometer at maximum is usually enough to verify that there is high voltage.

The ideal is to use the focus pack of a disused fly-back  Transformer set on a 20" TV that works well to indicate 250V on the screen output by adjusting the potentiometer. Without much error you can interpret that this test TV is 25 KV and already has a high voltage attenuator set that you must connect to the pacifier of the TV under test with an alligator clip that will be covered by the pacifier so that no arcs are produced.

If there is good high voltage and the screen is dark the problem may not be in the fly-back  Transformer. The most basic thing is to see if the tube filament is on and measure the screen voltage if you have not already measured it. If both things are OK, you should measure the focus voltage, with a high voltage tip that has a resistance greater than 200 MOhms.

The measurement with instruments is not dangerous for the circuit, because the focus source is of high impedance. 

At the time when indicated to connect the three cathodes to earth briefly  with resistors of 150KOhms and to return to test if the screen illuminates the problem is in the video card or the jungle.

But if the problem is in the focus pack you don't need to change the whole fly back. Transformer In specialized stores they sell focus packs ready to be connected to the pacifier that generate the focus and screen voltage. Cut the cables of the damaged focus pack, connect the new ones and test. You can also use a fly-back that has a damaged winding. This case is specific with external HT bleeders where the focus voltage is obtained from.

  If the problem is in the winding section of the fly-back Transformer  the first thing to do is to check the operation of the stage with the simulated fly-back instrument. Connect it replacing the primary and measure the collector oscillogram with low source voltage (for example 10% of the nominal value); if you do not have an oscilloscope, try it with the horizontal output detector (a RF detector probe) which can be lowered free of charge from and if the delay voltage has a normal value of about 80V, pass gradually to higher source values until the nominal value is reached.
    If everything is normal, try connecting only the primary of the fly-back Transformer supposedly damaged. This means that you must disconnect all the auxiliary diodes, including the HV pacifier, and try again, starting with a source voltage of 10% of the nominal value, until you reach 100%. If everything is OK, the problem is not in the fly-back Transformer but in some of the auxiliary circuits. Connect the auxiliary diodes one by one and always perform the same test starting from 10% of the source voltage until the damaged auxiliary circuit is discovered. Note: Although unlikely, consider that there may be more than one damaged auxiliary circuit. 



In a typical switch mode power supply (SMPS) of a television receiver the AC mains supply voltage is coupled, for example, directly, and without using transformer coupling, to a bridge rectifier. An unregulated direct current (DC) input supply voltage is produced that is, for example, referenced to a common conductor, referred to as "hot" ground, and that is conductively isolated from the cold ground conductor. A pulse width modulator controls the duty cycle of a chopper transistor switch that applies the unregulated supply voltage across a primary winding of an isolating flyback transformer. A flyback voltage at a frequency that is determined by the modulator is developed at a secondary winding of the transformer and is rectified to produce a DC output supply voltage such as a voltage B+ that energizes a horizontal deflection circuit of the television receiver. The primary winding of the flyback transformer is, for example, conductively coupled to the hot ground conductor. The secondary winding of the flyback transformer and voltage B+ may be conductively isolated from the hot ground conductor by the hot-cold barrier formed by the transformer.

It may be desirable to synchronize the operation of the chopper transistor to horizontal scanning frequency for preventing the occurrence of an objectionable visual pattern in an image displayed in a display of the television receiver.

It may be further desirable to couple a horizontal synchronizing signal that is referenced to the cold ground to the pulse-width modulator that is referenced to the hot ground such that isolation is maintained.

A synchronized switch mode power supply, embodying an aspect of the invention, includes a transformer having first and second windings. A first switching arrangement is coupled to the first winding for generating a first switching current in the first winding to periodically energize the second winding. A source of a synchronizing input signal at a frequency that is related to a deflection frequency is provided. A second switching arrangement responsive to the input signal and coupled to the second winding periodically applies a low impedance across the energized second winding that by transformer action produces a substantial increase in the first switching current. A periodic first control signal is generated. The increase in the first switching current is sensed to synchronize the first control signal to the input signal. An output supply voltage is generated from an input supply voltage in accordance with the first control signal.

But if everything indicates that the problem is in the fly-back Transformer and the fly-back is not achieved, then we must find a fly-back Transformer as similar as possible (better original)  to ours and perform a very simple test. Make a 2 or 3 turns winding in any open place of the core by connecting one end of the winding to ground. If you have an oscilloscope, connect it over the added winding to raise the oscillogram; otherwise, connect the rewind pulse detector indicated above to a tip of the winding and then invert it to find both the positive and negative value of the signal. Connect only the primary of the new fly-back and run it at the nominal voltage.

 The oscillogram obtained will be similar to the one in figure: 

The oscillogram could appear inverted since we made our coil with any direction. If it appears inverted, change the ground connection to live. The most important thing is that you measure the peak pulse value of the signal, which in our case is 23.8V. If this voltage corresponds to three turns, calculate the value of voltage per turn as 23.8/3 = 7.9 V/turn.

If you don't have an oscilloscope, you can use the audio probe for the tester (A RF detector probe)  that will indicate directly the  value of the signal or make the double measurement with the delay detector.

Now we have to start modifying the auxiliary voltages of our substitute fly-back  Transformer if necessary. Let's start with the filament voltage. Observe the circuit of the substitute fly-back to find the ground leg and connect it to ground. Now measure the other auxiliary legs and note the peak to peak values. The filament should have a  peak pulse voltage of about 22 or 23 V. Do not try to measure the RMS voltage with a common tester or with the peak value probe. None of the classic instruments will show a peak pulse value of 6.3V. It is best to calculate the RMS value as a function of the peak-to-peak value for a delay time of 12 uS, which is what we did to indicate the correct peak value of 22.5V.

It is very likely that by changing the number of turns you will not be able to achieve the exact value. In that case you should calculate the excess turns and then adjust the resistor  value to get 22.5V on the filament. In our case you can test the voltage value of the filament winding and if it is close to the indicated one modify the value of resistor .

Is it very important that this voltage value is accurate? Yes, but a fluctuation of 1V cannot shorten the life of the tube but it's better avoided. The filament of a tube is far from the melting point, i.e. it is undervolted to increase the life to a value far above the cathode depletion but also better avoided.

Adjusting a Running Auxiliary Voltage

Let's suppose that the winding for the vertical voltage has to give 25V and gives 18. We measure that our fly-back has 7.9 V peaks per turn. For a delay time like the one indicated, the relationship between the positive semicircle and the peak value taken from the oscillogram in figure 30.4.3 is 3,07/23,8=0,13. This means that each turn adds a voltage of 3.67V to the rectified voltage and that to go from 18 to 25 you have to add approximately two turns (7.34V+18 = 25.34V). Without an oscilloscope, I have to add the two turns  and measure a voltage of 3.67/0.13= 28.2V with the peak probe. Now, I must cut the printed circuit and connect from the fly-back leg a wire that must pass twice inside the core and solder it to the cut track on the side of the diode.

Note: the direction of the winding is impossible to determine a priori, the most advisable thing to do is to choose any and measure if the voltage has the correct value. If not, the winding or connections must be reversed.

In this way all windings must be corrected, so that the fly-back is ready to perform a final test with everything connected.

But the auxiliary voltages are not all that differentiate one fly-back from another. In the next delivery we will explain how to perform the final test without burning anything in the attempt, and that should be changed if the width is not correct.

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