51MP391H/17 Project - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 2 Old 03-30-10, 10:54 PM Thread Starter
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51MP391H/17 Project

Hi Guys,

My son and I just started on one of these as a project.

A little background, my son is a poor college student. He's been getting by just fine on a 27" CRT but a few weeks ago he carted home a Toshiba 48" big screen. He lives in the country outside of a small town here in Nebraska and this unit had been in the tavern for 16 years running non-stop. One night while they were doing karoke the convergence went out. They called around and the TV shops told them it would be several hundred dollars to fix it, if they even could as it's so old it will be hard to get parts for. They actually asked my son to haul it to the dump and gave him gas and disposal fee money. He asked if they minded if he kept it and tried to fix it and they said no - as long as it was gone they didn't care where it went. We gave a shot at replaceing the convergence ICs and unfortunately it didn't work out so well. It ran just like it did before we started and then blew the pico fuses again. I rechecked everything, and replaced the fuses and still no go. We weren't attached to this unit andt he whole inside was covered in grease, dust, and smoke residue which I figured couldn't be good for it so I called it good, I just wasn't up to a ton of trouble shooting.

My son was a bit disappointed though as he'd been hoping to end up with a big screen. I kept an eye on Craigs List and found this Magnavox 51" 51MP392H/17 for $50. It had a convergence problem and no remote. I talked them down to $35 so we hopped up and picked it up the other day. It was built in 2004 so it's only six years old, but it's had a hard life - they had kids who banged it up pretty good and when we opened it up it was full of pencils, crayons, and -gulp- a bulletin board stick pin that was millimeters from shorting across the ac power input! The screen was replaced a couple years ago - one of the kids knocked it in. The screen is in fine shape but the mounts that hold the three pieces are boogered up so we need to get that repaired but it looks simple enough - I'm thinking some thin wood slats will work just fine. Actualy the screen sets in it fine, but it makes me nervous so it'll get fixed correctly.

We got it home and cleaned out and plugged it in. It fired up and yes, had a convergence problem. We took it apart and found four resistors burnt up - R3153, 3154, 3159, and 3160. I ordered two STK 392-120 convergence ics and 20 of the 6.8 1 watt resistors from Acme in Florida since they are so well reviewed here. We pulled the board the other night and replaced the convergence ICs, used Arctic Silver heat sink grease to reinstall them, and replaced all 12 of the 6.8 ohm resistors. Everything went well and I was feeling pretty good about this project (this board isn't hard to work on at all - plenty of room). We reassembled it and it would fire up, give three color bands across the screen with a snow back ground and that was it - we couldn't pull up a menu or anything. After a few seconds it would power down and blink the power button 9 times quickly, then pause, then blink 9 times, etc.. You couldn't get it to stop that unless you unplugged it and plugged it back in. Hmmmm, well that's annoying! Nothing annoys me more than going through a lot of work only to make the things worse than when I started! OK, I rechecked all the connectors we pulled and they were all in and tight. Tried again, no go. I pulled the service manual out and it said the nine blinks meant "HCS-GDE communication failure". I did a search here and then on the net to see if anyone else had seen this before. I ran across a posting where someone was having a similar problem (replaced the convergence ICs and then had a dead set). These boards have three cards that stand upright on them and one of the responders said that the metal one on the left is kind of the brains of the thing and it can be dislodged from it's connector during servicing and will sometimes cause this problem. I looked in the service manual and it said to remove that card you move it to the right and pull up. Well, I couldn't get that to work so we pulled the entire board out again so I could get a better look at it. That card has a connector kind of like pc memory chips and there are a couple catches you gotta release to pull it. I pulled it up slightly, used some canned air to blow the slot out, and reseated it. Then I got to looking closer . . . in the upper right corner on that card is a ribbon cable. It's not a standard ribbon cable, it's like mylar with the wires printed on it like they are printed on a pc board. That ribbon cable makes a loop in front of the card and it's mounted close to the metal can of the card so it's hard to see the connector since the front is hid by the cable and the back is hid by the can. I took a closer look and it was kind of pulled out and way crooked in the socket! I'm not sure if that happened orignally or when I pulled and reseated the card, but I think it was the original problem as I reinstalled the card tonight, hooked everything back up, and made double sure both ends of that cable were plugged in. That cable is really easy to bump around though - it's fairly rigid and it's right in the way of a connector that's in between that card and another one right above it. It's easy to pull the cable in between the cards during disassembly, but with big manly-man hands it's a booger to get hooked back up during re-asembly and as I was trying to wrangle it back in I was continually hitting that cable, so I really think that was the issue. I've included a couple pics showing the cable I'm talking about.

Anyway, once we got it all hooked back up we fired it up and this time we had a picture and we had menus and stuff! I forgot to mention, my son's Dish Network remote had a code to run the TV. We got to the manual convergence screen and were able to converge the unit!

Unfortunately it's a Phillips product . . . you guessed it, it's got the CRT contamination problem. It's not terrible yet, but you can definitely see it.

Sooooo, it looks like our project isn't over yet . . . Leonard, I hope you're up to walking us through this! I don't mind soldering and stuff, but I'm not overly comfortable with the thought of this task - it just looks kinda daunting. Still, I can do electrical and I'm good mechanically so I"m thinking we can pull this off. I just like to know exactly what I'm doing before we start, so if I take some pictures of the unit and list what I think we should do (such a post with pictures and arrows and a "I think we should pull this wire, this wire, undo these screws, etc.") would you mind waling us through this?

Sorry for the long post, I get kinda wordy sometimes!

So far it's been a pretty good project, we have $35 in the set, $30 in gas to go get it (my son's big 4wd truck gets really nasty gas mileage!), and $43 in parts so for a $108 we're pretty happy. I'm sure he could get by just fine for a while yet with the CRT coolant issue, but it's only going to get worse and it'll be better to tear into it now before he's used to having it rather than later when he is used to having it and will want to rush to get it back in service.

Project list:

*) Fix the convergence - Done!
*) Fix the CRT coolant - researching
*) Fix the screen mounts - this weekend's project
*) Repaint the case (the kids beat the snot out of it!) - will do after everything else.

Take Care,

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post #2 of 2 Old 03-31-10, 04:51 AM
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Re: 51MP391H/17 Project

I can provide general advice, but step b step help is really beyond the scope of the forum.

Looking for me, just google my username. I have used the same one for most sites for many years.
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