philco-ford roundie score - pics - Page 3 - Videokarma.org TV - Video

DaveWM · #31 10-25-2011, 08:48 AM

one last thing, depending on the set, you may be able to just connect the composite video directly to were the video detector diode out is. there should be a test point there (used for scoping the video out for test purposes).

this will give you a pic, you would also need to connect the audio to the correct place (on the audio pot). this bypasses the tuner and IF completly.

the only issue may be the the direction and power of the composite video.

if its too weak you may get a weak snowy pic, and if its reversed from what the tv wants you get a negative pic.

Before trying it I would check the voltage at the test point (to ground) just to make sure its at 0 potential, it prob is, but would not hurt to check before putting the composite video there.

I just checked my philco, it looks like you want test point B and it 1.5v pp which may be more than what your DVD comp video puts out (think they are about .5v pp IIRC).

the test point is on the sweep/sound board at looking at the 6MG8 chroma amp/video cathode follower sync amp tube, right by the tube at the 4 o:clock posistion, near the side of the board.

this is where a nice adjustable video amp (with a phase invert option) would come in handy.

fujifrontier · #32 10-25-2011, 12:28 PM

The ant balun was brand new.

At this point, because of my zero expertise with actually working on the electronics part, doing tests, etc (I don't have a VM or any schematics or repair books; this TV apparently seems to be rare because I can't find any info) I want to be rid of the tuner and just use the tuner sub box, I'm a little frustrated with it at this point.

The channel quality did NOT improve with slight twists of the knob or going back and forth quickly. The audio was always solid, and it would occasionally tune in an unwatchable picture if you kept twisting the fine tuning in either direction for awhile. I'll try taking it apart and cleaning it when I get the set back. I use external speakers so no audio would be fine if I went that route of injecting composite.

I suppose right now I kind of feel like the blonde pointing at the car with a blown radiator hose and saying "but it doesn't goooooo!!" and I have the you guys the mechanics telling me "well it has a blown radiator hose" and what I need to do to fix it. I really do appreciate the shared expertise, I'm more of a visual learner and apologise for not comprehending immediately what needs to be done. If I had a diagramme or something that actually illustrated these points where to measure/test, etc I'd be a lot more at ease.

DaveWM · #33 10-25-2011, 01:10 PM

the tuner subber is prob the easiest solution, they are on ebay all the time, however worst case is you get a bad one, so dont spend more that 15-20$

I think most are battery operated (to allow use on hot chassis sets). but still not a huge deal.

Charlie · #34 10-25-2011, 03:39 PM

Fuji: I checked further into that site. If you click the color banner at the top of the page, it goes into more detail. Sounds like he does a tuner exchange (if he has yours already) for 25 dollars. That sounds like an awesome deal to me. Look on your tuner and get the part number and see what he has in stock.

If you send me your email, I can give you a copy of the diagram for my set. Mine is the 19MT79 and will be damn close to the one you have. My set is just a little newer and uses the tuning eye... most of what's on the chassis will be the same.

DaveWM · #35 10-25-2011, 04:21 PM

that sounds like a great solution. You would still have to install it but there is not much to that.

Electronic M · #36 10-25-2011, 05:17 PM

Many tuners only have three wires asside from the coaxial one with the RCA jack. the wires usually are B+, AGC, and a 6.3 source for the tube heater and any indicator bulbs.
The outer lead of the coax serves as a common ground for the entire tuner, and it's center lead caries the IF a/v carier signal to the IF amps that feed the signal on to subsequent stages.

zenith2134 · #37 10-25-2011, 05:49 PM

^that was a great, accurate explanation

sampson159 · #38 10-26-2011, 07:01 AM

united tuner service is still in business here in columbus,ohio.martin is fully operational at his facility.not sure of pricing but he did a tuner for my sylvania gt matic a couple of years ago for 25.00.it might be worth it to ship the tuner here.we have all dealt with him for years and his work is top notch.

Ralph S · #39 10-26-2011, 12:00 PM

Does United Tuner service also do Mallory Inductuners?

fujifrontier · #40 10-26-2011, 06:47 PM

Well I'm feeling a bit more confident today. Got the set back, and unmounted the tuner without the set killing me :p Took some pics!

And you guys are right-on with that solution of the guy that charges $25 for a tuner exchange. I'll first see how satisfied I am with the tuner subber, if I ever overcome my morbid fear of soldering (I've never been able to successfully solder a connection in my life) then I'll totally disconnect it and send it in to the guy. It looks like I might have to, to get the set working on its own without the subber, because one of the wires broke off (I suspect it's the one that provides the 6,3v to it [it's mounted with 2 other wires on a board with a small cap on it]). It's chassis 17MT80. It also has an interesting logo underneath the glued-on metal plate, says "S[]S COLOR" on it.
So, what kind of signal is output exactly from the tuner to the RCA-connection that goes into the IF? How does it differ from the composite connection output by, let's say, a DVD player?

DaveWM · #41 10-26-2011, 07:02 PM

the IF is an intermediate freqency signal 44mhz. All the tuner does is takes the entire old TV broadcast band and selects a channel within that band and converts it to a single freqency, allowing for a better amp (only has to deal with one freq) to work. From there the AM modulated video signal is detected by a diode and the result is the composite signal. this is the same signal you get from the yellow rca lead on the DVD or converter box. the only difference will prob be the amplitude which is prob greater from the IF amp/detector diode vs. the DVD video out.

fujifrontier · #42 10-26-2011, 07:25 PM

Ahhhh. For giggles I fired the set up and connected the tuner-out RCA line to the DVD player. No dice. I can't wait for my subber to get here.

I also thought it was rather convenient that the old man restored the tamper-proof metal thing that retains the cord in the set's particleboard back cover. It was loose when I brought it in and I mentioned offhand when I went to see it running with the subber that I could handle the convergence myself when he was backing away saying "nooo noo it's got plastic knobs and those things can break."

I'm a little annoyed I let the set sit with him so long. he apparently has moved on to bigger and better things as the shop is FILLED with flatscreens. He probably makes a killing replacing inverters, ccfl backlights etc. I feel a little cheated and let down that having all the old remnants of a 50s TV shop like carts that say "It Pays to Say RCA," a forgotten tube caddy just sitting there and a large file cabinet labeled SAMS PHOTOFACT, none of the original talent or expertise would be around to consult.

Electronic M · #43 10-26-2011, 07:35 PM

fujifrontier --->"How does it differ from the composite connection output by, let's say, a DVD player? "

The IF out is greatly different from Composite video. The tuner takes the carier radio frequency that has been amplitude modualted by the video signal, and frequency modulated by the sound at the transmiter, and filters out all but the carier frequency of the channel of your choice then mixes the signal with an oscilator whose frequency when subtracted from the frequency of the transmitter is is the IF frequency (there is also some amplification that happens in most tuners). To sum it up the tuner takes a station and lowers it's carier frequency to the fixed frequency of the IFs.

The signal then goes down the RCA cord to the IF amps which greatly amplify the fixed IF frequency that the tuner puts out(here the IF is still modualted in the same way as the transmitter signal at this point).

Then after passing through all the video IF amps the signal(containing both modulated audio and modualted video) is sent to the video detector. The video detector DEmodulates the video part of the IF and outputs composite video (but in most sets this signal also contains modulated sound that is split off and sent to the sound IF at this point) the remaining audio carier is filtered out here and the cleaned composite video is sent off to be split into Synch, color video, and monochrome video which after being processed by their respective circuits form the image you see on the screen.

You would see nothing resembling a picture if you connected that RCA IF cable to your DVD players composite out. So don't try it.

If any of this is confusing I can clarify (I could also deccribe the video circuits after the detector if your curious). The tuner IF and detector of a TV are a specalized type of "superhetrodyne reciever" circuit (google what is in the "" to learn more) with the tuner doing the job of all stages between the antenna and the IF(IF is short for intermediate frequency by the way).

Hope you found this enlightening.

DaveWM · #44 10-26-2011, 07:42 PM

again, if you want you can connect the composite video out to the test point I mentioned before, the inner part of the cable there, the outer part to the chassis ground. Its the stake that is at 4 o clock from the top of the cathode follower tube I mentioned before. It may work, will depend on the PP requirements of that tube. If you have a sams it shows you the test point. this will only give you video, for audio you would need to connect the audio out to the volume pot.

before connecting anything its best to test with a multimeter to test for DC potential.

bluenorm · #45 10-26-2011, 07:53 PM

there is another tuner repair guy in texas. his name is Louis Stangle from Quality Tuner repair services in Longview texas his phone is 877 753-3204 or 903 753-3204. I have use him in the past. request to talk to him Personally.
quality work!

is there a phone number for United tuner service?