CF30E50, no filament. No voltage at the socket, or apparently at the CRT board. Resoldered CRT socket and flyback, no joy. Removed and put back CRT socket to eliminate socket pin corrosion. 30KV present.
4.9 ohms across heater pins with electronics attached. Tapping everything in reach has no effect.Original owner of the set gave it to me, saying the picture would fade in and out; my experience was that it faded out yesterday and hasn't come back since.
Where does the filament supply come from, a wind on the loptf? Wherever it is, just follow it back and see what bit's dead.
If you cant fix it, eg its an open wind on the loptf, there are 2 workarounds. One is to wrap usually 3 turns round the loptf to get the necessary voltage for filament supply. The other is to hook it up to some other supply rail that can supply the wanted V and has enough current delivery to cope with it. Last of all one can always fit a filament transformer.
All you need do is use your multimeter.
NT
If you are really only losing the filament and it is out completely, it is a simple matter to trace the filament pulses from the flyback, through the current limiting resistor, to the crt socket. You really need an o'scope as most meters do not accurately read the 15KHz pulses off the flyback to show the voltage.
You should have the G2 voltage ~300V on the crt socket which would in fact confirm the flyback is still running.
Not too bad for an 12 year old Toshiba that it still is worth taking the time to fix it.
I'll try that. Usually my Fluke 77 comes through, but it's worth checking. Oddly enough I can't see the heaters lighting inside the tube neck when it's operating.
Will do, but the HV disappears so fast when the set is shut off that I'd expect it to disappear fast if the drive stops. I did in fact see the picture fade in and out a few times since my original post, and it's gradual.
I have a 22 year old Toshiba whose only problem is intermittent full volume. I plan to troubleshoot it. Picture is still near perfect. I have another 22 year old 13" Toshiba that I just gave away, and the recipient is blissfully happy with it. If only they hadn't stopped making their own sets...
I've always found a multimeter fine. Yes it reads a bit wrong cos of the waveshape, but you only need to know roughly whats there to see if its ok or not.
NT
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