ADVENT Videobeam
 

Got a line on one.. non working but apparently good CRTs.

Anyone have experience with them? Looks very cool

Back in the 90's I did contract work for the cat that bough out all
the Advent parts & service stuff. It put him into a $1,000,000 house
in a rich Boston suburb.
All the chassis I saw were either Sylvania or Electrohomes. I think
there may have been one more. They were modified console chassis
so easy to fix. Most of the failures were CRT's. You will need the
OEM screen that is curved. Otherwise it doesnt register right.
BTW all the stuff is gone now & his shop closed.

73 Zeno:smoke:
LFOD !

We had a Advent 750 in the 70’s. It operated well all the time we owned it. It had a built in cross hatch generator which had to be tweaked a few times during warm up. It was fun.

The below photo was in 1978 in my home in Wisconsin. You can see the faint outlines of the console and on top the first Artari video game system. You can also see the first generation JVC VHS VTR on the right, an original Sony KV 7010UA, on the left, SAE components, Marantz SLT 12 turntable and a Sony TC 850.

I have the original sales brochures and paperwork for anybody interested. I can put it on line for download.

https://visions4netjournal.com/wp-co...D7DBE35D0.jpeg

This is interesting.

I would very much like to see the brochure and associated info. That's wss a very nice setup you had back then!

Zeno: could you get service info easily for these, or did you have to find the sylvania/electrohome data? I dont see any Sams for them.

I will post a link here when the materials are online.

I think the one I am going to get is also a 750. All I need to do is find the time to pick it up now, the arrangement to get it has been made. Look forward to troubleshooting it and getting it going - I hope it doesn't need all the capacitors changed! Also, have been unable to locate a schematic or service info so far.

Advent supplied manuals & IIRC they were a cross between there
own & the chassis OEM. The Sylvania was the common 3 module
Super-Set chassis. The Electrohome was there one & only Canada
built solid state set. Both were very well built & used straight forward
design so very easy to fix. Tons of manuals came in the lot & probably
paid for his kitchen & several baths ! Hundreds of CRT's of all
3 colors sold out 100%. Add to that all the small parts & complete chassii
& you can see the $$ made.

I think this one is a 750, but won't be sure until I actually get my hands on it.

Do they use one flyback for all three tube?

Also, can these tubes be tested with a normal CRT tester?

Yes & yes

Thank you!

Got it home - It's not an Advent, but a Canadian made ELECTROHOME/ADVENT. It looks just like the Advent 750, but everything is labeled made in Canada. The screen has ELECTROHOME molded into the plastic on the back.

My screen is missing a piece of cross bracing, so I couldn't get it to stand up. Projected on to my usual Stewart home theater screen, the image is very, very dim. It does converge though, and all the colours work. The controls are all dirty, it needs some contact cleaner. Going to get the screen set up and see how it looks on its proper screen - the one I have is full aluminum, hopefully it reflects well, because this projector has very weak light output!

Odds are the dim pix is all 3 CRT's are weak. You can test them with
a universal adapter on a Sencore etc. The G-2 setting may be different than the usual 50V. An adapter can be made up for any checker if you have the
schematic for the checker & pin out for the CRT.
Aside from that you can check the CRT voltages. educated guessing is cathodes 125-150V ( the higher the dimmer ), G-1 0-50V, G-2 400V. For focus the
controls should focus best apx mid range. I never measured HV so have no idea. A normal chassis with a tripler gives 25-32 KV but these may run less.

If nothing else you have a piece of TV history. These were the first big screen
projo's to sell VERY well & lead to all the ones to come.

73 Zeno:smoke:
LFOD !

When we got one of these for evaluation at Zenith, we set it up in a dark room. Then someone hooked up a video camera and we played with video feedback - we made a VHS tape with video feedback set to music - kind of a high tech abstract fireplace.

I connected the B&K 466, and neither of the socket adapters which fit would test a tube, but one of them would light it.

I baked each CRT at 8.4V for 9 minutes, and 9V for one minute (timing and voltage here my best guess for what might work based on filament glow and previous experience with normal CRTs)

I turned it on and got a much brighter, washed out, green picture. Then I set grayscale, and things started coming together.

Watched an episode of that new show Letterman has on Netflix, and also tested it with video games. Had to make an adapter to use the giant video input connector, but it works well.

For the screen stand, I cut a piece of 3/4 plywood to hold the supports together, since the original cross brace was missing.

There are some subtle geometry defects which to me suggest bad capacitors, namely a bit of an wave horizontally

Convergence is great though. Need to find a manual, do a recap, and dial it in. It sits right in front of the couch, where I can play with the controls.

Glad it’s working. The curved screen has a gain to it and focuses the brightness dead center, and falls off dramatically if you sit a tiny bit off center as you probably noticed.

BEWARE. The screen will scratch if you look at it wrong. Any kind of liquid will damage the screen. I’m a bit tardy on the brochures, but I will post them.

Advent 750 Owners Manual Link: https://visions4netjournal.com/wp-co...advent-750.pdf

Thank you very much!

Mine, being an Electrohome, is a little different from the instructions. The projector looks the same, but my screen has a white molded plastic back, with ELECTROHOME molded into it, and a tilt mount, with instructions how to set it to the correct angle by hanging a weight on a string off the top front, and measuring 7 5/8 inches from the bottom.

The screen is in decent shape - it appears to be some kind of aluminum film which is stuck directly to a plastic dish shaped background. The film is bubbling up in a couple places, but I'm just leaving it as is.

Your instruction book helped me to set up the position of the projector correctly. It doesn't completely fill the screen at the top left corner, and the bottom has a slight bow to it, so I think it will need some work.

One interesting thing I noticed, is the pattern generator only works when the unit has a video signal. If you switch to convergence when the unit is on but not connected to any source, it's just a blank screen.

show us some insides

I like that they suggest using it with an early U-matic deck (based in pictures).

Tonight turned it on, smelled smoke, then suddenly the picture looks horrible - washed out, no contrast, and blurry.
It looked ten times better yesterday. No idea what burned.

Now I can't set greyscale, even with brightness all the way down, in service mode I can't get the tubes to cut off.

To clarify the above post, the brightness is excessive, even with the brightness control all the way down. I am suspecting that the burning smell, was something related to the G2 voltage, since it seems to affect all three tubes equally. High G2 voltage should give this symptom, right? Another thing is, the power transformer gets very hot in this set.

Another thing I noticed, is the contrast control basically controls brightness, where previously it functioned normally as a contrast control.

G1 is just a bias control, and appears to be fine.brighness is set by the cathode, and the cathode DC voltage is about 200 or so, depending on the position of the brightness control.

Focus appears okay, the focus output of the voltage multiplier puts out about 6kV.

Checking the G2 has been so far impossible, theres no way to get the chassis out easily.

More exciting developments:
Screen voltage can be varied from 500-750V approx, and and the G1 Kine Bias is set to about 10V.

The focus take off point of the multiplier is about 6kV, and high voltage is about 23kV. My high voltage probe often reads low.

Good continuity though focus controls and focus voltage divider resistors.

The chassis can be very easily pulled, and really is just a console chassis. All wires have enough slack it can be operated while the bottom is accessible.Nothing under it appears damaged in any way.

The neck board has power supply voltages screened on to the board, and they measure as they should.

Not having service data, its impossible to know for sure, but after measuring voltages I think my theory that the tube are over biased is wrong, and I should instead be looking to the video amplifier.

Check the cathodes, they are probably low. Typical K volts on
a console is 125-175 ish depending on design & CRT.
They are run off a 200V supply from a FBT winding. Typ a fusable
resistor, rectifier then a 5-10 mfd filter. Sometimes the supply is
stacked on the main 130V B+ so the filter goes there instead of GND.
To find the 200V each jug has a hefty driver transistor. The collector
goes through a 2-3 watt resistor 18 K ohm plus. That is hooked to the
200V. Look at almost any SS color schematic & it will be near the same set up.
As for the G-2 the low end sounds to high. Typ 800V boost on the high
end & the low end 200-300 V. The wiper goes to G-2.

BTW if you can post some nudies for the group of the chassis.

73 Zeno:smoke:
LFOD !

Cathodes are actually high, at the top end of that range. About 175. The +200V terminal (marked on board) on the neck board is dead on 200V.

I will look into the bottom end G2 voltages being too high, by tracing out that part of the circuit.

Last night I tried the projector again - things have gone from bad, to worse - the picture now is totally losing contrast and brightness. It's an extremely dim, washed out and blurry picture, but if you turn up brightness the raster itself is quite bright.

I managed to track down a paper copy of the service manual, from www.stereomanuals.com - once it gets to me, I will be in a much better position to troubleshoot.

I'm starting to wonder if this is an AGC issue, but there's only an RF AGC control on this set, and I'm using the composite video input.

Will take some photos tonight for the forum - it's a very neat set, nice change from the usual.

I have to say that last night, the "audience" of the home theater was starting to lose patience :)

Another thing occured to me - why don't I just put on a test pattern and look at the CRT cathode waveforms with an oscilloscope?

They should look very similar to the cathode waveforms shown in the Sams for my Motorola Quasar works in a drawer set, no? I suppose I could pull the back off a known good TV, like said Motorola, and see how it compares.

Why not ! But usually a problem like this is voltage related. All 3 video
outputs are tied at the emitters to the B&W info. The colors come from the
demod to the bases. To simplify turn off the color & look at a stair case pattern.

BTW there is someone here & on AR selling Canadian service manuals. He may be able to supply you with the Electrohome manual for the normal console set......

LFOD !

I got notice the Advent service manual is in the mail - will be here within a week or so I'd assume.

I really look forward to getting it, so I can check what the voltages are supposed to be.

Either that or I can keep using it - it seems to get worse each time I use it, maybe it will fail altogether and become easier to fix

I've noticed that not all TVs are built this way. The Motorola I'm looking at mixes in the monochrome video signal earlier in the chain. Then there's tube sets which apply the monochrome signal to the cathode, and the colour info to the G1 of the CRT. If the Electrohome chassis does mix it in right at the emitter of the video outputs, then that's a good thing. Those three outputs are on a common heat sink, on a floating PC board suspended between the CRT tube sockets by stretched O rings.

The fact that the contrast control was directly controlling brightness, makes me wonder if the DC levels are correct in the video amplifier circuitry.

I hooked it up to a test pattern, and an oscilloscope. The brightness and contrast controls do their thing - the brightness shifts the video signal up and down, and the contrast controls its dynamic range. The amplitude is in all cases way too small, it is about a 70V peak to peak signal with brightness and contrast all the way up, with 175VDC on the cathodes. Changing the kine bias and screen controls does affect brightness, but I think the video signal is just too weak to turn the CRT on completely.

Here's some photos of the inner workings

So after removing the chassis to inspect the wiring, and poking around a bit, then re-seating socketed transistors in the video section, the problem magically went away. I let it run for a while, and the interference which preceded the problem popped in and out a couple of times.

I am now suspecting either a bad solder, or perhaps a shorted wire or component lead. I will let it run longer, and see if I can narrow it down more... I think the issue is somewhere in the video amplifier.

Thank goodness I didnt begin this work with a bulk recap!