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

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!

uilt. >

about a decade ago. Hawkeye. The only rebuilding operation left in the wes tern world is in the Vintage TV museum, and that's only for show.

l from a computer monitor. I've seen several, and they work great. Sometime s a small circuit board is required to invert polarities, etc., but there a re a handful of guys selling those on line.

Back in the 70s there were several companies that sold CRT rebuilding equip ment out of the back of Radio Electronics and Electronic Servicing (and oth ers). I came real close to buying one of those setups. I'm sure many othe rs did and I'm sure some of the machines are still around, but the big prob lem would be sourcing the gun assy. For all we know, the Ruskies might stil l 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!

John :-#)#

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

ftp://flippers.com//usr/www/users/flip/pdfs/Temp/Electrohome_GO-7_13inch_CBO_flyback.jpg

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

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...

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 :-#)#

e 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 th e pulse to the yoke on this little 13" Sony I watch sometimes, I didn't buc k the top end where the 1,000 volt pulse is, I bucked the bottom. Makes mor e sense.

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 thre shold.

It is possible it is perfect. For market share in the repair parts market t hey 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 c an't teach what they do not know. they offered me a job, well one guy who w orked at Case University. he said they can't find anyone to teach what I ta ught him to get the job there, and that was very basic. the traveling turne d me off but I might take it now, however they must take me with absolutely zero accreditation, official anyway.

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

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

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. Wel l as a rule, sometimes I see no way to get er done and then I pull out fast er than a (insert your own thaing here)

lot for me, obviously you have experience with either designing or repairin g monitors/TVs. "

Not designing so much, but I have made alot of money making things work tha t nobody else could. Part not available ? They called me. I was good. We ha d a bunch of countdown chips that were bad out of the box. No sync. With th e 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 design ed. when I put a winding on a fly (LOPT) to isolate the filament of a CRT w ith an HK short I used a resistor of like 5K to make sure it was effectivel y 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 g ot to 2 locations and we got sick of it. But I considered a test for tech a pplicants. One of the first requirements is to be able to draw a block diag ram 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. Wh ere 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.