Schematic Questions - Videokarma.org TV - Video

cdmarion · #1 01-04-2009, 09:01 AM

Hi everyone, I'm working on a Stewart Warner Model 9104B, Sams #Set 105-Folder 10.

I've got three tubes, V9-6au6- AGC Keying, V16-12au7-Sync Clipper and V18-6al5- H AFC- All three tubes are not getting hot, the heaters do not apear to be working.

When I look at the schematic, at the tube heaters it shows one pin grounded and the other has a arrow pointing to an X. This is my first question, what does the X refer to and how do I trace the heater circuit when it's not traced out on the schematic? I know I'm missing something really simple here.

Any thoughts?

jonboy55 · #2 01-04-2009, 09:43 AM

While I don't have Sams #105, I do have the Rider TV books and this TV is in Volume #4 pages 22-44.

According to the schematic, all the tube filaments run in parallel. As you said, one side goes to ground. In all the tubes the other side goes straight to the "green" wire on the power transformer.

In your schematic the "x" may simply refer to this "green" wire on the transformer. Check the schematic and see if there is a wire labeled "x" coming from the transformer. Sometimes they use this short cut to reduce the number of lines on the schematic.

If there is no voltage at the filament pins, check for a cold solder joint or a broken wire. Thought not probable, make sure the tubes are good.

Good luck.

Old1625 · #3 01-04-2009, 11:51 AM

Yeah, the other end of that "x" will be found at the power transformer on one of its secondary windings. This cuts confusion, as actually drawing in all these filament supply lines would make for a very busy and confusing schematic.

Some sets of that era have fusible links for filament feeds. The bottom line is that you need to actually measure the AC voltage between pins 3&4 of the seven-pin tubes to verify filament supply. On the 12AU7 measure the filament voltage between pin 9 and the tied-together pins 4&5 as is usually found.

Both the 6AU6 and 12AU7 can be deceiving, as their construction and cathode characteristics are such that sometimes it's not easy to see the glow. This also may be true of some 6AL5s. And the duties each of those tubes has are all relatively low power. A 6AL5 seldom gives off any significant warmth, and an AGC keyer is not likely to get all that warm either.

cdmarion · #4 01-04-2009, 04:53 PM

Thanks guys for clearing the X thing up, it make perfect sense now.

Now for the next question, in the Voltage measurement chart I keep seeing "OV". What exactly does this mean?

As far as the TV's concerned, I have the proper heater Voltage at all three tubes. I can't see any indication there is anything happening though. I'm used to seeing things glowing. I agree, I think it's just the nature of the tubes in this instance.

Now for the big question, I fired this thing up today and I have no raster. I got the flouresent bulb to glow at the Flyback, HV Rectifier tube 1B3GT and the Horizontal Output Tube 6BG6G. But have no Voltage at the second anode at the CRT.

Any suggestions on where to go next?

Einar72 · #5 01-04-2009, 05:17 PM

Conventionally, it means "zero volts" with reference to chassis ground, unless a specific B- node is specified. The latter is found on "hot-chassis models" lacking a power transformer.

nasadowsk · #6 01-04-2009, 05:55 PM

I'd look to see if the 1B3's lit up, assuming you can see the underside safely while the set's on. You might need a dim room. Be very careful. You'll see the filament's slight dull red glow, which might be brighter than that, sometimes dull orange.

I like to use an HV probe, though - it's far safer.

If there's HV, then you might need to adjust the ion trap.

Realistically, if the set hasn't been recaped, I wouldn't even expect a raster...

cdmarion · #7 01-04-2009, 06:31 PM

I guess I should have mentioned that I just recapped the set. Sorry.

I've checked the voltage at the CRT anode with a HV probe and it was zero.

I've also replaced the 1B3 with a replacement, both test good on the tester.

jonboy55 · #8 01-04-2009, 06:51 PM

Have you checked the voltage coming from the power supply section? Many times you will need to replace the electrolytics in the power supply section to obtain the correct voltage. Also check the flyback transformer.

nasadowsk · #9 01-04-2009, 06:57 PM

I'd trace the wiring out from the 1B3 socket to the HV connector on the CRT. You might have a break or short. Beyond that, assuming the flyback's not toast, you're either off frequency, or not getting enough drive, or the yoke's bad.

If there's an HV filter cap, it might be shorted, too. You can disconnect it as a test...

jonboy55 · #10 01-04-2009, 06:59 PM

Also, check the "door knob" cap from pin 2 of the 1B3. That's the 10,000 volt cap.

cdmarion · #11 01-04-2009, 07:59 PM

Ok, thanks for the ideas, I'll hit it again tomorrow evening and let you guys know what I find.

jetblack · #12 01-05-2009, 04:09 AM

Some people use "x" in place of "trans" (xformer in place of transformer).

cdmarion · #13 01-06-2009, 03:54 PM

Ok, I got back at it and noticed the high pitch noise of the Horizontal Oscillator is missing. I played with the horizontal hold control and still no noise. This set has no Horizontal Oscillator tube marked as such. Does anyone know which tube would be my Oscillator tube?

If I remember rite the Hor Osc. tube plays a part in producing High Voltage. So If theres a problem in that circuit then there may be no HV. I'm thinking out loud here so please correct me if I'm wrong.

I know I've got AC at the top of the 1B3 and the Hor Output but I'm not sure how much I'm supposed to have. Under the 1B3 in the Measurements chart it say "Do Not Measure" and gives no voltage specs. What is the preferred method of measuring the 1B3 top and bottom?

Thanks for the help

nasadowsk · #14 01-06-2009, 05:25 PM

Don't measure the horizontal plate, ever. It's got a multi-kv pulse riding on it.

Ditto for the 1B3, which has AC on it.

The bottom, there's no easy/safe way to measure the filament voltage, but the HV out can be hit with a probe capable of reading up to 20,000 volts.

Without horizontal that's strong enough and close enough on-frequency, you don't get HV.

You need a scope to see if you've got the drive and frequency required.

jonboy55 · #15 01-06-2009, 05:44 PM

As far as the horizontal circuit the tubes are as follows:

6BG6G - horizontal scanning output
12AU7 - horizontal scanning multivibrator
6AL5 - horizontal AFC phase detector
6W4 - horizontal damping

I'm sure you've checked all the tubes and their voltages. The 6BG6 is very important. In some sets I've found that one 6BG6 will work and another one won't work. Same for the 1B3.

Again, don't forget to check the 10K volt capacitor.

I hope this helps.