1978 Magnavox 25" Star System, Lost my Video

I bought a really beautiful brand new Magnavox 25" Star System console TV in June of 1978, and with only two visits from the repairman (one was a close lightning strike), it has always worked great. A few months ago, I turned it on and no video. The tuning and audio work fine, just no picture. Thinking back, the picture lately had some lines at the bottom and top of the screen (I think) and looked like it was a little smaller vertically. Bummer.

I can't give this great old TV up without a fight. The last service was in March of 1998 and needed a transistor for the green drive. The tech said it was a T995 chassis and the CRT was in fanfastic shape with no leakage at all (it had a good vacuum). In fact, up till the time the picture went out, the color was real good. And then it just quit.

The first thing I think I need is a service manual. My guess is that some of the electrolytic caps have dried out and/or a transistor has given it up. Although I have a good deal of experience working on circuit boards and replacing components, TVs are a whole new bag for me. I'd bring someone in but everyone I call says it's not worth it. Yea? Like hell.

Any help is greatly appreciated, but remember, Flyback? What's a Flyback?

[site123a]

The TV's made during the 70s would display a blank picture if the x-ray protection circuit was on. You may want to start looking in the power supply first.

[radiotvnut]

I believe I have some modules for that chassis if you need one. Can you tell if the set has high voltage? If there is no HV; it could be a power supply problem, a problem with the horizontal oscillator or drive circuits, or horizontal output circuit (tripler, flyback, etc). If you have HV, try pulling the service switch on the back of the set to see if you can get a line on the screen. Cleaning the service switch with control cleaner may help. You could also have a defective vertical module or video module. I'll see if I have a Sams Photofact for that chassis.

[Bill R]

If the on screen channel display works then there is no high voltage or xray protection problem. Don't overlook the possibility of oxidized connectors where the modules plug into the mother board. I seem to recall there was a low level video module that would cause no pic. Be sure you get a manual that covers the Star system since the t995 chassis was also used on a non star set. The non star system set did not have the on screen display and such.

Bill R

Thanks guys for the response. I'm not getting anything on the screen, no picture, no channels, no clock. That's a great point Bill, thanks. This project will sure be a great learning experience for me. Before I do anything, I'd like to get a good book on basic TV repair so I don't drive you guys nuts with a bunch of obvious (to you) questions. I'll check out amazon. Any suggestions? Radiotvnut, I'd be interested in any modules you may have. Thanks again.

[zenith2134]

Everyone's giving you good suggestions here - Since you say you aren't very expereinced with tv repair, try cleaning all connectors, potentiometers, and switches. Keeping it simple pays off sometimes.

However, it does sound like you have a dead deflection amplifier, video amp, or bad solder joints somewhere. Many times the solder points weaken around where the modules plug-in, and more often than not, around high-heat areas.

Since you have no video and possibly no HV, try reflowing solder around the Horizontal output transistor (on a large heatsink), and around the HV section, but ONLY IF YOU ARE COMFORTABLE WORKING NEAR HIGH VOLTAGES.

These voltages remain even when the set has been unplugged.

Hey, I'm not the greatest tech, but I have revived many, many tv sets, so shoot me a private msg. If you have some questions. Take care and good luck/ Tom

[Bill R]

No video, or on screen display. Problem is likely in the sweep section. I would resolder all the connections to the Horizontal sweep modules connectors, and around the flyback. Next I would check and or replace the Horiz. output transistor. I do not recall a lot of flyback problems with these.

Bill R

Thanks for your posts guys. The biggest question I have right now is whether I have HV. I think I do, because when the set goes on, the front of the picture tube will pull the hair right off your arm with the static that's there. Also, there is a thin flash of white light at the very top of the screen when first turned on, and then all darkness. I have a ticking that comes from the back of the tube that goes away when the service switch is moved from normal to service. I did measure some voltages on the main board at the TP's and everything was normal (80v, 125v, 24v, etc). I stayed away from any high voltage for now.

Some more info, this is chassis number T995-02 DC. The final unit number is RH4847PE01 and was made in Jan of 1978.

I ran across a web site (www.euras.com/english) that listed this tv in thier database of common problems. They say that vertical deflection is a common problem with this set. Sounds like what I might have (or as Bill says, horizontal sweep problems). I will have to join them to see what thier fix for the problem is. Anybody ever heard of them? Does this make sense? Thanks for your time guys.

[radiotvnut]

From what you say, there is HV present. That ticking you hear is probably the Vertical windings of the deflection yoke singing for you. When you pull the service switch; that will kill vertical drive to the yoke, thus, eliminating the fast ticking sound. I suspect the vertical and horizontal / HV circuits are functioning. That low level video module would probably be my next place to look for trouble. Give me the number of that module and I'll see if I've got it. Also, make sure the filament is lit in the neck of the CRT. No filament voltage will give you a black screen. I do hope you can get that set up and running again. That set is 1000 times better than most garbage currently available.

No doubt about it, the vertical adjust will speed up or slow down the ticking that comes from the back of the tube. The low level video module number is 703640-5. However the neck of the tube is dark, I don't see anything glowing inside it. With the set on or off, it looks the same. Could this mean the picture tube is shot? I hope it's just not getting any voltage because that could be fixed.

I'd really like to save this TV, it has so much more class and style than the black boxes of today. Thanks for your comments.

[jpdylon]

If the CRT is dark at the neck, there are two possible causes:

1. CRT filament is open (bye bye CRT)
2. filament supply voltage is not present.

If its the supply voltage, then go to the power supply. If this set has a filament transformer it may be bad. If this set has a filament winding in the flyback, you will either need to purchase a new flyback or add a filament transformer .

Another thing that may cause the filament to be dark is a poor connection at the neck of the CRT. If possible, remove the connector from the CRT neck. Whether its just a connector, or a circuit board is attached to it, make sure nothing is securing it to the neck before removing it.

What you are looking for is corrosion or carbon on the pins of the tube and the socket it fits in . It will be green and powdery looking or black if its carbon. If any exists, use a pipe cleaner with a good contact cleaner (I like caig De-oxit) in the socket. Use very fine sandpaper (1000 - 2000 grit) to burnish the pins of the tube.

Also, if this has a circuit board attached to the CRT connector, check to make sure there are no bad solder connections. The solder connections are the silvery dots that have a pin or wire attached to. if there are any cracks in the solder around where the CRT socket is it may be the cause of your dead tube.

I hope this of some help. I'm more of a techy guy, and not that good at explaining these sorts of things. Good luck on getting your vintage set running. Sounds like it has served you well up until this point.

[radiotvnut]

I pulled the Sams (1815-1) on this set, and, there is a two amp fuse in the CRT filament circuit. It's very possible that this fuse is open. The CRT gets it's filament voltage from the main power transformer. It's either going to be a blown fuse, an open filament winding, or an open CRT filament. Even if the CRT is bad; don't scrap the set just yet because I'm sure a good used tube can be found.

Thanks radiotvnut, I found the 1815-1 on sams last night. Would it be worth my buying it from them? I've seen the fuse you mentioned on the circuit board but it looked good, not dark and all. I'll pull it and put the ohm meter to it. I want to test the voltage at the 2 wire connector that goes up to the tube. What kind of voltage should I get if the power supply is OK?

I think the lack of the filament firing up is my basic problem. Whether it can be fixed or not, we'll see. Thanks for your comments.

Wow! Here's a surprise. That 2A 250V fuse for the CRT fiament that looks like new when taken out of the circuit and cleaned up had failed. Not blown mind you, just failed. This is one of those fuses that has a spring in it for slow blo action. In the circuit it looked just fine, knowing what a blown fuse looks like and all. But upon close inspection, the spring had just pulled away from the other internal part of the fuse. The glass is crystal clear. I think this means that no other TV part pulled to much current causing the fuse to fail. If that's right, a new fuse should put me back in business. I've never seen this before. I'll report back when a new fuse is in place.

[Randy Bassham]

That style of fuse is prone to fail that way, The spring gives a pull on the solder connection all the time and sometimes they just separate on their own with no fault in the circuit. Back when I worked for a Magnavox dealer we'd also see the solder connections of the crt socket to the PC board become faulty, look close and see if any seem to have a circular crack in the solder. IMHO the T995 was the best color chassis Magnavox ever built.