Toshiba CRT A80ERF031X13 Shorted, appreciate advice

They used to, when CRTs were run from 6.3 V AC on a transformer winding from the 120V power mains, have a special 6.3V transformer 1:1 turns ratio, but with very good high-frequency isolation, that you used to isolate the heater-cathode from the low impedance of the regular transformer windings. The smear you describe is due to poor low-frequcny isolation. You could run the tube with an ordinary 6.3V power transformer if you could put inductors in each of the secondary windings and also maintain low capacitive coupling across the windings.

Now that CRTs are run from a high-frequency source, either the pwer supply or the horizontal output circuit, things are not so easy beacause they are running on pulsesthat have the equivalent heating power, but which are nothing close to sinusoidal and thus impossible to use an isolation transformer.

H. R. Hofmann

I just posted a TV with the same "common" Phillips CRT. I'm going to try the "focus, & G2 arc trick"! Here's a technique I have been using, with good results. I hope it helps you. Dani.

I would like to share this great tip with all you great helpfull Tech's out there! This is only for Technicians who really know there way around the inside of a T.V.! Please don't just anyone try this!! If you don't have a proper CRT rejuvinating set, this will be a great fix, for an otherwise lost cause.

Sony 1 K problems, that is T.V.'s with the red, or green, or blue having too low, or high of an emission to get a raster due to the "blanking circuit", can be solved with an odd, & somewhat dangerous technique! With the set off, unsolder each cathode on the CRT board, then momentarily bridge the gap of each gun, one at a time, to see how much emission there is. You will have to raise the G 2 pot to get a bit of raster in a darkened room! Next solder the two good cathodes (usually only one is out of gain specs), back, leaving the bad one. Now this is where it gets dangerous!!! While the set is off remove the focus line from the CRT socket ( 5000 volts), & while the set is running, momentarily make contact with the unsoldered leg of the bad gun. Do this with caution, & at least five times. It will try to arc, but just keep a steady hand, & keep the wire with a good insulated tool at the unsoldered leg only. Now, while the set is off, unhook the G 2 wire, & set it to about 200 volts DC unloaded, & charge a 100 uf capacitor @ 250 volts. Do this two, or three times, then discharge it to the unsoldered gun, while the set is runing. Do this charging, & discharging to the gun at least five times! At this point, you should see the bad gun get brighter, & brighter. I have done quite a lot of experimenting, & this will save a lot of those Sony CRT's, that would otherwise be toast. Grey scale comes back to within a close enough spec, to make the customer happy. Just don't give a long warranty. Hope this helps you all out. Take care, Dani.

Len, I can't believe you don't know this.

You fix the set with a piece of wire. Cut the traces going to the filament pins and wrap the wire through the flyback. Two turns does it alot. You need either a true RMS meter to read the 6.3 volts or on a scope on an NTSC set you are looking for 23 volts peak to peak.

Make sure you isolate those pins completely, that there are no compenents felt from the original filament supply. One might be grounded on quite a large foil, in this case some type of small grinder is useful, because you need to grind all the way around the solder pad in some cases.

You never know what you are going to get, you might not want to completely on the hot side because you might want to use the resistor. If emission is strong, you do not want to feed it any more than about

26 peak to peak, that is like already having a brightwener on it and will kill these new CRTs.

And when you wire this contraption up, don't be too neat. Don't strap the wires all up nice and neat, that causes capacitance and that is what will smear that color.

Keep them loose, or go the other route, tighten them up and apply equalization to that particular output stage.

To do that you must locate some resistor, most likely in the emitter circuit of the video output for the affected color. Then you need to find a small capacitor to put across that resistor. The resistor must be high enough in value to allow for the changed frequency response desired. What's more, put a 10K resistor between the cathode and the heater, that simulates the short, and will keep the short from shorting if it were intermittent.

Last time I did this it was on Panasonics. I had to because it seems their video outputs were more of a current drive than a voltage drive. They did niot brute force it like alot of manufacturers, they actually matched the impedance and equalization to the CRT. As such, when you start transmitting the red video from the wire wrapped around the flyback, it causes a capacitive load.

If you do not want to deal with putting in some pre eq on the video output, you can just reconverge the set, with the 10K resistor in place.

You DC supply loaded it down alot more because of mass as well as it's HF coupling to the power source. It will not be as bad with a piece of wire and even just reconverging it, you have a usable set.

I actually did not invent this process, but I damn well reinvented it. If you want to know more just RSVP.

JURB

I do know about the flyback trick and have used it many times in the past, but more successfully on B&W's than on color sets. Its sort of like winding a filament for a 1B3. On color though I almost always had smearing. Now I know why. Your explanation was really good. I'll save this post and try some of what you mentioned next time. On this

32 with the Red cathode to filament short I already did part of what you suggessted. I wound three turns of wire around the flyback core and connected this to the CRT filament after isolating it from the chassis. On startup, the filament lit up like a christmas tree bulb for the period it took for me to see this and pull the plug. Dunno...I was certain three turns wouldn't be too much and just as certain that the tube was history, but I was wrong on both accounts. The short is gone and the pix is great. Go figure! Must have been some thermal expansion at work there. Anyway, you can't argue with success. Some times we actually win a few. I'll run it for a few days and then call the customer and tell him its fixed, but with no guarantee of course. This was obviously an accident but I might try it again sometime on an otherwise dead issue. Thanks for all the great advice guys, Lenny.