Sony KV27S15 died

A shame those parts didn't fix it - I looked back at the prior posts and saw that we never did determine they were bad.

The raw DC for the turn-on relay is there, but what about the transistor Q604 which fires the turn-on relay? Do you get voltage to it's base? Or Q603? Looks like you should get a momentary 5 volts at it's collector at turn-on, then falling back to -7 volts, if I read it correctly.

Sometimes I will pull the whole chassis, put it on the bench, remove the horizontal output transistor, and troubleshoot that way, so that if the unit "wakes up" suddenly I won't have the HV anode flopping around when it does. I should mention however, I'm not the TV guy in our shop - I just help out where I can. Getting better on CRT sets though, just in time for them to be phased out...

Post back. I had one of these eat my lunch a while back - turned out it was a lightning struck unit and the customer didn't relay this information to me until the repair was well underway.

Mark Z.

Sorry - I did test them and they were bad, which made me wonder all the more what else happened because that should have fixed it.

If I remember correctly, I didn't see any activity at the base of Q604. Q603 I don't remember for sure now.

Was my assessment correct in that the switchers are not running, therefore manually closing the relay would have no effect?

I know this wasn't a lightning machine because my daughter was watching it at the time and she didn't say anything about there being a storm then. But I was away at SolidWorks World at the time so I can't say that from personal experience.

I'll check Q603 & Q604 better tonight. Thanks.

WT

Well, I hate to mention it at this point - but this is where I always go back and double - triple check my prior work. I've seen the switchers put in backwards, for example. It's easy to do.

I'm not the real expert on these but I have worked on a couple lately.

If you can read about 160 volts or so at the collector of switcher Q602, the the SMPS is running and we need to see why the relay isn't firing. If on the other hand that voltage is 300+ volts, or zero volts, then we can pursue that.

Mark Z.

I'll check those tonight.

Last night I did more measuring on some transistors.

Q603 5.7v at the emitter & base, no activity at the collector when the power button is pushed.

Q604 13.3v at the collector, no activity at the base. So then I went to Q614.

Q614 5.7 at the collector, no activity at the base.

Trying to follow the flow around into that one gets me lost.

WT

I worked on this a bit more tonight.

Checking at the collector of Q602 I have 27 vdc with no change on pushing the On button.

I also rechecked the installation of the two switchers to make sure I put them in correctly. I looked, measured, compared to the originals, checked the datasheet, measured again, checked about 10 times. They appear to be correct. I also pulled one out and checked it and it appears to still be good. I checked the other one in circuit and it appears to measure the same as the other one so I am assuming they are still good and not fried as were the old ones.

I haven't figured out how to check the output of the micro to see if it's even sending out a turn-on signal. Any clues there? I know it's getting a signal from the switch, though, so checking its output would be next logical step.

WT

You did replace R607, yes? That's the .1 ohm white resistor that feeds the switchers.

mz

Yup - part of the kit. The old resistor was open. I didn't recheck it last night, but I have rechecked it a couple times to make sure it didn't open.

Any thoughts as to which pin should change state coming out of the micro? That would tell me if it's working.

WT

Well the relay is controlled by the micro IC101 on the M board. The pin in question is pin 4.

I would look at it's 5 volt regulator first though, IC 103, also on the M board. Even if the 5 volt output on pin 5 is good, the reset output on pin 4 could be NG.

Mark Z.

This appears to be progress.

I checked the output on pin 4 of the micro and as I sort of expected, there is no change there. I checked again that the switch input was making it to the micro pin and it is. So then I checked the 5 volt regulator. I find

Anyway, with the 3.5 being low, I would assume that the regulator should be replaced. Thoughts?

WT

I do think I'd replace that regulator - but I'm not totally at ease with the progression of this repair. There's no reason the regulator or any other parts outside of the horizontal circuit should have gone bad if the horizontal parts died a "normal" death.

I'm concerned that if the regulator is replaced, then the set does try to fire up - the failure cycle may repeat, for example if the Y/C jungle chip IC301 is putting out a funky waveform.

Might be a good idea to pull the horizontal output transistor before trying to fire it up after replacing the regulator.

Mark Z.

Which brings up a question I have been deliberating. The original parts I replaced were a common "kit" based on people's experience. If those parts usually fix the problems with these sets, what causes them to go bad? Is it that the HOT goes first and kills the switchers and then opens the resistor? Or is it a switcher failing that takes out the others? Or, as I have also read, a bad solder joint on one of the transformers, whether the pair in the PS or the flyback that then takes out one of the above devices? I did resolder the transformers so if that caused the original problem, it's possible I already addressed it.

I'll replace the regulator, pull the HOT and see what I get. Thanks.

WT

It's hard to say with this sort of thing, there can be a lot of different events which can trigger a catastrophic chain reaction failure. In my own experience, most failures of this sort are triggered by either bad solder joints or failed electrolytic capacitors, often both are present. Sometimes parts just give out for no apparent reason, it happens, and some designs are better than others about keeping damage localized.

"Wayne Tiffany" wrote in message news:47c45a7c$0$1344$ snipped-for-privacy@reader.greatnowhere.com...

Here is the normal chain of events:

2) HOTransistor begins to heat up eventually leading to a short.

4) The fusible resistor opens and the set is dead.

If the original bad connection is not repaired, repeat steps

David

Ok, any ideas where to find the L78LR05D regulator? I checked Digikey, Mouser, and a Google search on "buy L78LR05D" and came up empty. Is there a suitable current replacement that you know of?

WT

That's just a standard 5V 3 terminal regulator. 78L05 should work, as will a

out

to

on

if u are equipt with voltohmmilliameter(vom) check first the presence of B+ on the collector of ur HOT.if it is normal Bet 100-135 v and assuming your PS works fine ,proceed to check the presence of hor. driving voltage on the Base of the driver transistor, using the lowest ac range of the tester but do not forget to insert the positive probe to the output terminal of the vom (Im talking of a analog test er , usually it has 3 terminals ) so that only the signal will be measured .because in the output terminal of the tester there is a coupling capacitor that blocks the dc potentials.connect the black probe to ground.locate the cold ground and not line ground of the PSupp. if u measured a driving voltage, atleast .05 or .09V put the probe this time at the collector of the driver , notice the driving voltage is much stronger .it will deflect the meter over its full scale.replace ur Hor output transistor, thats culprit also the flyback must be check . good luck

I'm certainly not the expert here, but the 78L05 is a 3 pin, 5 volt, 100 mA regulator. The L78LR05 that is on the board is a 5 pin, 5 volt, 150 mA regulator. The other two pins are for a reset output and a delay capacitor, and are most certainly connected.

I checked with our local Electronics Supply here in KC and they didn't find it listed at all. More thoughts?

WT

What we have been chasing is that the B+ is not there, and there appears to be no signal out of the micro. The why not is the current mystery. Thanks for the thoughts.

WT

Oh it's a 5 pin? Hmm that's odd, can you tell who made it? You might look at Fairchild or National Semi's website, both companies offer free samples of many parts.