Sony KV27S15 died

Well, that's the inexperience showing through. I didn't think to chase the Sony part number. Thanks.

WT

Found one and ordered. Next week when it arrives we'll see if it makes any difference.

Something that keeps coming to mind is that the family has complained for some time that if they hit the volume up or down button, the channel would also change. I had thought it was maybe related to dirty switch contacts, but now I'm not so sure. We also have another Sony set that is doing it now. In both cases the remote would operate it just fine. So I'm sitting here thinking that if this 5v regulator had been failing for some time, could that affect that? And if so, is it failing on the other set??

WT

Front panel buttons are usually multiplexed, a bad connection on or to the panel will cause weird things like this to happen. Glass cleaner dripped down into the switches can cause it too.

Page 50 of the PDF (showing page 77 of the paper manual) shows that the switches involved are part of a resistive ladder arrangement. Obviously, a problem with the switches here will cause the stated symptom. I would look no further than this, except perhaps for some contamination on the board or switches themselves. We sometimes see this type of thing from people squirting cleaner directly on the screen - it runs down into the switches.

Mark Z.

Did a little investigating this weekend and I think the problem with these switches is in the switches. I measured the resistance to ground as I pressed the switches and they all wander all over the place depending on how you press them. I'm surprised they work at all! My guess is oxidation on the contacts and they don't appear to be disassembleable. I may live with that one rather than replace all the switches.

WT

Sometimes you can improve the action of the switches considerably by flushing them with DeOxit.

Mark Z.

I'm not sure I could get any into them - they appear to be pretty tight with no holes in the corners, etc. Thanks.

WT

Naw, just use the pinpoint applicator and force the spray into the switch where the black little moving button meets the main body of the switch. After you force some cleaner in there, press the switch maybe 40 or 50 times. It may be easier to remove each switch to work with it, then re-install after.

Mark Z.

Next frustrating setback. Got the 5v regulator, installed it, not a good result.

I measured for the 5v and was only getting 4.35. Not a good sign for a new regulator, and the Sony part to boot. I turned around to look at the schematic, and heard some soft sound. Didn't see any smoke, but that regulator was too hot to touch. Quickly pulled the plug and said Hmmm. I never did try turning the set on because I wanted to make sure I had a good

5v to the micro before I tried anything else. Obviously I didn't get that far. The fact that I never got to 5v leads me to think that something was drawing way too much current and the regulator couldn't keep up. One obvious possibility is the micro on that board.

I might be to the end of my ability to test here not due to lack of good help, but due to lack of experience and parts. Any other thoughts at this point?

WT

"Wayne Tiffany" wrote in news:47d52b55$0$1345$ snipped-for-privacy@reader.greatnowhere.com:

Some regulators have overtemp protection built in. Those can survive an overload like you saw.

The fact that you have a non zero voltage says you don't have a dead short.

You might be able to trace down the overload by measuring resistance. It would have been better if you had a dead short, however, because then you could use an ESR meter or low ohm meter to track it down. You may need to start removing parts, jumpers, and/or cutting traces.

Pick a nice clear run of a trace and cut it with a sharp razor knife. To patch it later, scrape off the solder resist, tin and solder a bridge across the cut with a short piece of wire that will handle the current.

Try to isolate various sections in a logical manner.

Don't forget to bridge ALL the cuts!

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bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an 
infinite set.

bz+spr@ch100-5.chem.lsu.edu   remove ch100-5 to avoid spam trap

That was exactly what I was about to suggest. Done well, it really works. Start by cutting traces that isolate large sections, then when you find the short, narrow down.

Good thought - I'll take a look like that when I get a chance. Thanks.

WT

I will often sub in an external power supply and just see what gets hot. No need to cut any foil runs at this point.

Mark Z.

"Mark D. Zacharias" wrote in news:4auBj.25648$ snipped-for-privacy@newssvr14.news.prodigy.net:

You need to be a bit careful to isolate the original supply because back feeding some supplies can give misleading indications or damage the supply. For example, I have been told that some 3 terminal regulators are damaged by back feeding.

Also, you need to make sure you provide ALL + and - voltages in the right order as some ICs do NOT like it when one or more supply voltages is missing.

Cutting out the 5 volts is unlikely to do MORE damage than has already occurred but feeding +5 without the -5, +12, -12 [or whatever] could take out good ICs.

My FAVORITE tool is the 'Curve Tracer' that I build from a 1970's article in Radio/Television magazine. It can spot 'sick' gates on an IC, and a lot of other problems 'in circuit'.

It is similar to this one:

Mine is like the single range model. It is all built into a wall wart except for the test leads. I clip my scope to resistor leads that come out through holes in the case.

Anyway, I find it very useful for locating bad transistors and bad gates on IC because the 'knee' gets rounded or is absent on bad junctions.

Often, you can test 'in circuit', but sometimes you will have to cut some traces to isolate the junction from caps or resistors that are in parallel with it.

A little practice with one of these, and a few 'reference junctions' to compare with the curves you see, and you may love your curve tracer too.

Here is a modern version using your computer's sound card:

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bz    	73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an 
infinite set.

bz+ser@ch100-5.chem.lsu.edu   remove ch100-5 to avoid spam trap

Never had a problem doing this - and in this case it's a single-ended 5 volt supply. I've even added in a variable supply at the output of a regulator to supplant the existing regulator while a unit is running. Just reduces the current requirement on the existing regulator.

Found lots of shorted IC's and the like this way without having to trace a power supply line all over a complex unit. About the only time this technique hasn't worked in my experience is when there is a ZERO ohm short, since some resistance is necessary in order for heat to be generated.

Mark Z.

"M0 D. Zacharias" wrote in news:NqPBj.13870$ snipped-for-privacy@newssvr12.news.prodigy.net:

Your method could work on zero ohm shorts, also, IF you happened to have an IR sensitive camera available. The trace leading to the short should 'stand out' in an IR view of the board.

Some CCD cameras are sensitive to IR radiation, so looking at the board through your camera viewfinder, may show the way to the short.

--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an 
infinite set.

bz+spr@ch100-5.chem.lsu.edu   remove ch100-5 to avoid spam trap