Magnavox FP5230 repair

Well here I am, replying to myself like usual. I talked to the original owners, and they said it was the power supply board. Their story likes to change. Would anybody know if the flyback transformer would cause this? I'm assuming not, because the audio works fine. However, it's a rear projection TV and I assume all bets are off there; audio could be getting its juice elsewhere.

I thought I'd add stuff from the FAQ -- I didn't realize it was part of the group's FAQ until I checked it again. Specifically:

I have sound, but no raster. I can hear the horizontal deflection, but I don't get any static or any hint of the display trying to display anything--even black.

The flyback transform buzzes, but not very loudly. I wouldn't hear it from across the room. My assumption there is that it is actually working.

Don't make any assumptions based on what the original owners said. It's secondhand information from people who don't understand the technical details. And it wasn't repaired, so it was only a guess anyway.

Make your own tests and measurements.

Adam Preble wrote:

Sounds like "module jockeys". I wouldn't put much faith in that information.

If you get sound, the "regulator" is probably fine.

More likely the large signal board (LSB), which has the power and deflection circuits.

Unlike small TV's that most of us are accustomed to, the horizontal deflection and high voltage circuits are separate. These sets also have protection circuits that shut down high voltage or blank video if they sense any number of error conditions like loss of scan, excessive beam current, etc.

Having said that: If the tube filaments light, you have horizontal deflection. The buzzing you hear is probably vertical deflection.

A bad thing happened on some of these sets if connected to, say, a VCR that goes to blue screen due to loss of signal. Blue tube after being driven 100% for awhile gets so hot that it will actually crack and lose vacuum. Sometimes you can see the crack through the lens, sometimes it drips onto the LSB, which burns things up, but in either case the blue tube now draws excessive beam current which shuts down high voltage. Usually throw away when this happens.

If that hasn't happened, a common electrical failure is for the high voltage transformer T900 to break down, which causes the HVOT transistor Q906 to overheat and short out, which blows open 0.33 Ohm fusible resistor R934. R934 is hidden in front of the heat sink on the right front of the board. It's not easy to get at, but easy to test once you do. If open, it usually means T900 and Q906 are both bad. Couple hun to fix, but usually worth it.

If not one of the above, check back for more ideas.

I'm assuming they were talking about the flyback transformer.

Is that the large board dead-center in the rear the TV?

I don't see any activity in the tubes. Is it very subtle?

I'm assuming I'd be able to tell this right away. I don't see anything amongst all the dust in there television.

That's some good tips. I got my gloves on and started playing around with that resistor. It was exactly where you said. My multimeter isn't the best, so I don't know if it would detect that as a short. It certainly didn't. I know I wouldn't get the specified resistance if I tried plugging in straight, but I figured the equivalent power-off resistance (assuming a day unplugged) showed 60k kOhms for that resistor. What is most telling is it looks like a chunk on the right side of it has burnt out. It's rough right there, so I suspect it has blown.

If that's a sign that it's blown, I'll clip it off at one end so I can measure current through that path. Do you know how much current should go through that when powered up? I just wanted to check before I did that. I don't have a soldering iron on hand right now. But if it comes down to that, I can get a Weller in a hurry.

To see the tube filaments glow, you probably need to be looking through the convergence board access hole in the front of the set.

Most multimeters will show a couple tenths of an Ohm with the leads shorted. If the 0.33 Ohm resistor doesn't show in the same neighborhood, it's bad. The actual value is not critical in this application, it's there to be a fuse. And yours certainly sounds like it's blown.

I wouldn't recommend trying to measure the current. You may damage your meter or other parts of the board, or more likely the power supply will current-limit and you won't get useful data anyway. Instead measure collector to emitter resistance of Q906 (use low Ohms range). I bet it's shorted, and if so it's almost always caused by T900 being bad.

Not the best tool for the job, but can be used in a pinch. If you are not practiced in the art of desoldering, you might want to experiment with some unimportant throwaway pc board until you can remove large parts without peeling off traces. The flyback can be especially frustrating, as it has a lot of large pins. You'll need some solderwick or one of those solder-pullit things.

And let us know when you get to removing the HV wire from the old flyback, it's a bit tricky too.

It's nice of them to label that one on the board. I measured a low resistance between the collector and the emitter, and my multimeter actually chirped when I tested for a short. It is hard to get the probes in that space, since a capacitor is in the way, but I tried it twice and got a short each time.

I was told flyback transformers are the common thing to go on televisions in general. Are you saying this transistor, that fuse resistor, and the transformer are likely the things to change?

I know it goes OT, but what kind of iron do you recommend then? I've done some desoldering, but my worst experience with it was desoldering on perfboard, but I'd take out the rings sometimes. You'd bet I'd practice before trying to pull off a big blob. That and the flyback would kill me in the process of playing with it.

I see some stuff in the FAQ about it. I have to get myself a few high watt, mega ohm resistors. I'm hoping if I leave it unplugged a few days, it will only mildly kill me as oppose to completely free me.

Second response since I've looked into replacing these parts. I can get a replacement flyback transformer supposedly for $81.70 at PartseStore.com

It fits my television model perfectly, but I don't know if that's T900. There's one for $74 also; what do I use?

Q906 is a D1556, with "4E" printed on it in smaller letters. Discarding the 4E, I can get a replacement NTE2331 for ~$6. The fuseable resistor should be easy enough to find locally. Maybe I can get this all locally--anybody know good parts places in Austin, TX? Just thought I'd ask.

I see the transistor is used for horizontal deflection. So would that explain the lack of display right there? What about vertical?

Given that fuseable resistor and that transistor are burnt, what else should I consider replacing?

Just happen to have seen a few of these in my employment at a (former) Magnavox dealer.

Twenty KV plus is rough service even for parts designed for it.

High probability, yes.

Probably not what you want to hear, but I use a dedicated desoldering tool, Pace MP-1 that cost several hundred. It has hollow tips and built-in vacuum pump. Hard to justify the cost for occaisional jobs like you're doing, but well worth it when you do this sort of thing nearly every day. I think Ungar made a lower-cost squeeze bulb type of tool, which I haven't tried, think maybe Weller owns this design now.

The focus/screen control block has a built-in bleeder resistor, so if it has been off for a few minutes the HV is already bled away. I've never had one of these bite me (unlike normal TV's). I was referring to the mechanics of the clip that holds the HV wire into the flyback. I think maybe the replacement flybacks come with a new clip nowadays.

Should work. 4E is probably a date or batch code.

No, actually Q802/T801 does horizontal deflection, tube filaments,

Usually T900, Q906, R934 are all that is needed, unless there is something else wrong with the set. I'd give the solder joints a good visual inspection while the board is out and re-do any that look bad. Barring elctrical problems, it's likely to need fluid change/optical cleaning, minor convergence and color balance tweaking.

I managed to find a 67104 for about $74. It came to $90 with shipping and tax. I'll see when it shows up--God bless the Internet . . .

That's odd; I thought the datasheet stated it was horizontal deflection. As long as it works . . .

I've read some stuff in the FAQ and convergence and color balance. I guess I have to get myself a test pattern. It has an S-Video in so I figured my laptop could provide that signal. This is the first I've heard that there's fluid to change in a television. I see on google what it's roughly about. Does it come down to scooping stuff out with a turkey baster?

As for optical cleaning, I assume rubbing it with Q-tips of some solution would be ideal; perhaps using one of those towelletes that come with glasses. I'm not going to guess what exactly, but it seems like there's good information online about it.

I'll update with a new thread when I get the parts and my tools ready. It'll be fun taking off that board so I can mess with the parts easily.

I haven't tried a turkey baster, sounds like it could be messy. I use an ordinary vacuum cleaner plus a collection chamber made with an oxygen bubbler (medical supply house will probably call it a humidifier) and associated vinyl tubing plus a certain type of toilet tank flush flapper that adapts the vacuum hose to smaller tubing nicely. The collection chamber avoids sucking fluid directly into the vacuum's hose, which would pretty much ruin it for any other use.

Depending on the way the set is constructed, you sometimes have to tilt it forward or backward so that the fill hole is uphill, but this is a lot less work than what the factory expects you to do, which is to remove all the CRT's from the set.

Whatever you do, don't dribble it on the circuit board or wiring, because it is somewhat conductive.

Plain toilet paper, kleenex (not the stuff with lotion), or kitchen towels work good for the majority of the work, finish up with something lint-free. Sometimes have to make a pass with methanol or isopropyl to cut nicotine or grease film, then follow on with Windex.

Obviously, don't worry about the optics until you have the electrical working.

I strongly suggest doing it right, pulling the tubes out, taking them apart, cleaning all of the contaminated material out, resealing, refilling and re-installing.

Leonard

Would you remove the engine from your car to change oil and filter? Pulling the tubes is a *lot* more work, exposes them to an increased risk of damage, and is normally unnecessary, as you can clean all the optics just as well in situ. If you feel the need to clean the anode leads, then removing the tubes would make that a bit easier. And I guess if you are sloppy about draining/filling, pulling the tubes moves your mess somewhere else. I've been putting down a towel as a safety measure. The vacuum collection chamber idea sounds interesting. If it works well, it could make for a pretty slick operation. I guess it's a matter of choice, but I usually leave the tubes in place unless there's a compelling reason to move them, and I tend to discount your implication that Bill is somehow doing it wrong. It sounds to me like he might know what he's doing.

How can you possibly get all of the contaminated coolant out? How can you possibly clean the encrusted residue from the lens without dissassembly. I guess if you never took one apart you would not realize what it takes to really clean these things. Actually, removing the crts is not that much trouble, and there is no risk of getting coolant on the boards or anode leads.

I have gone behind techs who have changed coolant in the home without removing the tubes and the results were not very impressive.

If I needed to clean encrusted matter and contaminants that affected the performance of my car I would certainly remove the engine and take it apart. Fortunately, this is not the case, so your analogy is meaningless.

Leonard

Well, duh! Of course you take the lens off. Don't have to pull the tube to do that.

You can do that even if there is an easier way that costs less and works just as well. Your money, your choice.

He probably takes it to Jiffy Lube to get it "done right". That probably was unfair, but I couldn't resist.

But really, there's more than one way to skin a cat. A good tech can do miracles with chewing gum and tape, while a poor one will screw up in spite of the best parts, tools, and procedures.

The factory folks rarely have to deal with the tubes in any condition except filled and ready to install, and they would rather sell a new set anyway, so there's no incentive for them to figure out a more efficient cleaning method.

Aftermarket repair, on the other hand, is highly competitive. Compare taking all day and charging $400 (which is what most shops do) with making it look easy and being out before lunch with just as good a picture for $150. Which do you think the customer is going to be happier with, and more likely to call for the next job?

I can't take credit for the vacuum collection chamber, by the way, a co-worker turned me on to that, but I like it.

I've gone behind a tech who somehow managed to switch the blue and green tubes, and that wasn't impressive.

Most cleaning and repairs are done with the engine in the car. Usually doesn't come out unless machining is needed. There are exceptions, of course, where poor design makes routine maintenance impossible. And even then, they often come up with a workaround. I am reminded of the Chevy Monza, where it was impossible to change one of the spark plugs. The repair kit consisted of a hole saw, a template to show where to put the hole in the inner fender, and a rubber plug to fill the hole when done.

My opinion is that doing the job with the CRTs in the set is not easier enough to justify the risk of not getting all of the contaminants out and getting coolant on the anode lead or circuit boards. I know lots of techs do it another way, but I have seen a number of them that had to be redone and that ended up with problems from coolant getting in places that it should not. Just my opinion, but when a technique risks creating problems, it seems the safer, more thorough way of doing it is the more professional way to go.

Leonard