AFT wont lock

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haklesup
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AFT wont lock

Post by haklesup » Mon Apr 19, 2004 3:45 pm

I've got this old Sony TV (circa 1993)and while using the AV inputs it works fine but when trying to tune any channels with the internal tuner it looks like someone has taken hold of the fine tuning knob and is twisting it back and forth (~0.5 Hz) so that the channel never locks in clearly. (i.e Automatic Fine Tuning is not locking in)<p>This TV has a cable ready tuner in a metal box type of arrangement inside. It's a module that connects with a limited number of wires and cables etc. My question is:<p>Is it worth trying to repair the tuner module itself or should I seek a replacement tuner module. Could it be something as simple as a connection to an external cap that went bad? or a well known failure mode.<p>I haven't opened the back yet, just peaked in the vent. I'm just looking for a level of effort estimate. I may just continue using it with a VCR but it is moving to a different room and it would be nice to have it 100%

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Edd
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Re: AFT wont lock

Post by Edd » Mon Apr 19, 2004 6:38 pm

Looks like you just might have lucked out. The unit is “seeking” and the redundant picture shift and the audio roar/hiccup should confirm that. Seems like that vintage Sony is at the pre- borderline before their going with synthesized tuner design .
Find your tuner and look just behind it or beside it and look for a video/aft module about 2in wide by 1 in thick by 2 in hi.. An alphanumerical string should give an integral component of “450” or 10-11-12 series as a secondary identifier mode. It has a hole in top for access for making a pot adj…but don’t touch that….that’s of no concern.
The unit needs about ~7..? pins unsoldered from the chassis main board bottom side that it is mounted to and it also seems like 2 maybe …4…? ground tabs for the shield can that the module is encased within also need to be floated. After pulling this subassembley and upon examination you will see that its internal PCB is in a slot cut in the shield on both of the side dimensions so wick/solder sucking is in order. Unsolder the PCB’s side foil interconnects to the shield/housing and slide out the PCB. You will find three miniature shielded RF coils on the board. Failure analysis under a 50x microscope should reveal micro cavitation and fracturing of the joint(s) of one or more of the coil terminals on those three xformers. MEK clean the area of the terminals and rosin flux and surgically reflow all of those transformer joints. De flux, reassemble, reinstall your IF/AFT subassembly and that should reinstate your Sony’s normal operation, with no alignment or adjustment being required.
RSVP.<p>73's de Edd
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;) ;)<p>[ April 19, 2004: Message edited by: Edd Whatley ]</p>

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haklesup
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Re: AFT wont lock

Post by haklesup » Wed Apr 21, 2004 12:14 pm

Thanks Edd, I had a feeling I would hear from you on this one. Peeked inside again last night and the description of the module you gave fits very well. Though I couldn't see markings, the size, location and presence of the pot on top all fit perfectly.<p>Lucked out would be right if I can effect a repair without the hastle of procuring replacement parts.<p>I plan to open it up in a week or two once I buy its replacement. I'll let you know what happens.

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Edd
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Re: AFT wont lock

Post by Edd » Thu Apr 22, 2004 12:36 pm

<<I plan to open it up in a week or two [[[[[ONCE I BUY ITS REPLACEMENT]]]]]. I'll let you know what happens. >>
SHAME, SHAME SHAME ……(a la Gomer Pyle)….most certainly you belittle yourself .
I certainly would not have expected YOU taking that approach…along with the extra $70 U.S. cushioning effect on your wallet.
Once you wick or suck the module out, you are already 75% home at that point. In reality just 2 xformer/coil joints inside on the module are causing your problem, the others are just for insurance since you are already in there. The grooves the PCB is slid into are cut into the housing so that a little lift up of each halve of the case is possible, letting one lift up and desolder each half individually, then a slide out of the PCB proper. Then squeeze together /reform the slits for PCB reinstallment.
Sony must have been sloppy in component lead pre prep prior to flow soldering with aged components with oxidized leads being in the mix. That would never have flown at NASA, in aerospace or in Mil Spec fabrication..<p><<Lucked out would be right if I can effect a repair without the hastle of procuring replacement parts.>><p>Its just the RF xformer/coils outside case wire leads to the PCB foil lands. Fresh solder reflow.……I’ll spot you the C and T in C_T ……heck….better yet…. I’ll even give you Ivory Soap odds of 99 86/100ths.<p>73's de Edd
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haklesup
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Re: AFT wont lock

Post by haklesup » Thu Apr 22, 2004 2:25 pm

The replacement was for the whole set not the part. My preference for waiting was not a safety position in case I screw up, I have confidence in my repair skills and in your authoritative answer. I just like to watch TV while I fix TV. I was planning to buy a new set all along and the amount of padding removed from my wallet will well exceed $70 by at least 10x.<p>However, your reply has gotten my Hakles Up and I may try to find time this weekend amongst my other projects (mostly home improvement).<p>Sony was a little sloppy around that time. I recall seeing many larger sets (>27") with bad HV diodes that caused the picture to dim to almost nothing.

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Re: AFT wont lock

Post by jollyrgr » Wed Apr 28, 2004 5:46 pm

I know several people that have had this exact same problem on Sony sets. I told them the fix and in every case I got it right the first time. Take Edd Whatley advice, he is exactly right. His explanation is very good. But I need to throw my two cents in.<p>Only try to do this repair if you know how to solder! I'm not talking about simple soldering of two wires together; you must know how to do PC board soldering. You will be working with RF circuits and sloppy soldering will only make things worse. You must have a solder vacuum (sucker) and/or solder wick. <p>The Sony tuners have cold solder joints inside the tuner. And, yes, the tuner is the metal box. Pull the connectors off the tuner and remove the tuner from the set. This may require unsoldering several connections from the main boad. Open the box. This may require unsoldering the shield from the box. Some sets have this but I do not recall if Sony does this or not. The circuit board will be soldered to the inside of the metal box. Depending on if this is a two sided shell or a single sided shell you may have to unsolder the board from the box to get at the under side of the board. Redo ALL the solder connections inside the tuner.<p>If you have gotten to the point of finding the tuner, you are almost there. The removal, resoldering, and replacment is straight forward. It might cost you an hour or two of work but is well worth the savings. But this is only true if you know how to solder. Messy solder jobs will only make things worse.
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!

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Edd
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Re: AFT wont lock

Post by Edd » Thu Apr 29, 2004 4:51 pm

The only thing that I might interject on the honorable Jolly Rogers post is that your exact problem item is the smaller /simpler IF/AF amp and AFT module…..NOT THE TUNER UNIT.
If ever against the tuner , its most common fallacies are its PCB peripheral ground plane foil to metal housing interconnects along with air core coil lead floating interconnects. Typically a sharp rapping on the tuner casing with a plastic tool handle on an operationing set tells all.
73's de Edd
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haklesup
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Re: AFT wont lock

Post by haklesup » Sun May 09, 2004 12:58 am

I bow to you Edd. You could not have been more correct. I found the cold solder joint on the exact component you described. See the picture<p>Image<p>Now the tuner locks in just fine.<p>On to the next problem with this set. The On Screen Display (OSD) does not turn off. Prior to the repair it just winked on and off randomly displaying a green "Video" in the upper right corner. Now ,after tinkering with the set, the OSD is on all the time (Video or channel #). Intermittant going to full failure after some handling. Sounds like another cold solder joint. Care to call this one too.

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