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jmetal88 06-03-2012 01:30 AM

Wanted: Flyback transformer
I've finished re-capping my Zenith 16C20 chassis (at least the papers and electrolytics), and I'm at a point where I'm starting to suspect my flyback transformer is bad. DC resistance on all pins seems to be spot-on, but I'm getting no output to the HV rectifier (not even from the 1v winding for the heater). Unfortunately, I don't have any equipment other than my multimeter to test the flyback, so I feel like I should just try to find a replacement at this point.

Compatible part numbers are Zenith S-45510 and Triad D-155, according to my Photofact. Please let me know if you have either of these that you'd be willing to give up! Thanks!

EDIT: I forgot, I e-mailed Moyer Electronics a while back and they said they could sell me a Merit HVO-176 as a replacement. In my opinion, they are charging way too much, so I won't be buying from them, but since they thought that one would work, I thought I'd mention the part number.

miniman82 06-03-2012 01:58 AM

With respect, you need more than a meter to diagnose this problem. How do you know if you have a drive waveform going to the output tube grid? I would not automatically suspect the flyback...

jmetal88 06-03-2012 02:07 AM

Well, I know that as I adjust the horizontal hold control, the frequency of the TV's 'squealing' changes. That's the best I can do in regards to detecting the horizontal drive waveform.

Believe me, I really wish I had better testing equipment, but I just don't have the money for it.

EDIT: By the way, if someone wants to sell me a cheap, working analog oscilloscope (like on the order of $40 shipped), I wouldn't refuse that, haha.

snelson903 06-03-2012 02:25 AM

where do you live ,i have good collection of scopes if you are in driving distance, i have some heathkit ones i could sell pretty cheap they need going over ,but i dont think they where used much, and have some other stuff too that could help you. i have always collected test equitment so got plenty ex stuff

jmetal88 06-03-2012 02:27 AM

I'm in Northeast Oklahoma.

snelson903 06-03-2012 03:24 AM

im in northern indiana the ship would probley cost to much ? i sometimes get some really good price on a scope off ebay you probley have to go threw it ,what i would do on anything off ebay you dont need to much of a fancy scope for older tv's. theres a mini scope on ebay right now 7.00 ship bid 10.00 see what you can find thats what i would do

jmetal88 06-03-2012 11:21 AM

I'd go for that scope, but I hate bidding on 'untested' test equipment. I'd like to at least see a dot or line on the screen in the picture before going for something. Right now, the cheapest one on eBay I would consider purchasing is about $70 shipped from Kansas. The reason I say that is because it's the cheapest one I can find that is shown powered up and includes test leads. It's still about $30 more than I want to consider paying for one though. Eh, maybe I can talk my dad into getting me a scope for my birthday in a couple of months...

jmetal88 06-03-2012 09:51 PM

Alright, I talked my parents into giving me $100 for an oscilloscope for my birthday a bit early. :)

I went for this one:

Hopefully, that'll let me test the circuits leading up to the flyback so I can determine if the flyback is indeed the real issue.

snelson903 06-03-2012 10:13 PM

looks good, just look it over good when you get it, the people that deliver things can be rough at times.

DavGoodlin 06-04-2012 10:49 AM

That's a nice dual trace scope. If you can, get two identical scope probes so you can compare signals such as a sync pulse to the horiz oscillator and drive signal to horiz out tube.

THE FLYBACK part of a resonant tank circuit that will make no high voltage unless the frequency is within a certain range.

jmetal88 06-05-2012 12:19 AM

I ordered these probes:

Probably not the best, considering how cheap they are, but I don't see why they wouldn't work for hobby purposes like this.

DavGoodlin 06-05-2012 10:50 AM

Those probes look better than anything I have, need to upgrade.

DaveWM 06-05-2012 01:20 PM

they will work but are cheaply made, fall apart on you, so handle with extreme care.

jmetal88 06-06-2012 02:45 AM

Well, the oscilloscope came in today (well, yesterday by now technically). I've been poking around the TV with an improvised probe made out of a length of wire. The horizontal oscillator circuit is definitely working, but the oscillation seems to be lost before it makes it to the horizontal output tube. Actually, I'm not seeing the oscillation anywhere except on pin 2 of the 6EA8 (and the other points directly connected to the horizontal hold control, but the amplitude is largest at this point). I wish I knew more about these circuits so I'd have some idea of what to try except going on with the trial-and-error approach I've been using. There's also no sync signals present, but I kind of expect that since I'm testing the set without the tuner attached.

miniman82 06-06-2012 10:22 AM

Bad coupling capacitor? You should have a sawtooth looking waveform at the grid of the horizontal output tube, if it's missing trace it back in the circuit to the place where it shows up and you will find the problem.

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