Sony KV-13M!0 shuts down about 1 second after turned on

[rfranzk]

Hello All,

I have a Sony KV-13M10 that shuts down about 1 second after turned on. The board shows a couple of components that show evidence of being hot. Q606 which is a voltage regulator (found on schematic page 28 location J-6) and (Q602 & Q603 found at J-2 on page 28)which both have heat sinks and I would expect some discoloration of the board. I don't know whether it is a power supply problem, or an over current shut down problem. I am unsure where to start as it won't stay powered up long enough to measure voltages anywhere.

Any help would be appreciated.

Thanks in advance. rfranzk.

 

[Nigel Goodwin]

Most common cause would be the LOTP transistor S/C or leaky, most probably caused by the LOPTX arcing over inside.

Remove Q551 and check it (the set shouldn't trip off with Q551 removed), if it's faulty check for dry joints on the line driver transformer - IF there are obvious dry joints, then resolder them and fit a new transistor.

If there aren't any dry joints, then there's a high probability the LOPTX is duff, and replacing the transistor will simply blow it again instantly.

 

[rfranzk]

Thanks for your reply Nigel,

I removed Q551 and set still powers down. It appears the Base to Emitter junction is shorted on the transistor. The solder joints on the flyback all look ok but I will touch them up just to be sure. Since the unit still powers down with the transistor removed I suspect more issues. What do you suggest as next step?

Thanks.
rfranzk.

 

[Nigel Goodwin]

Thanks for your reply Nigel,

I removed Q551 and set still powers down. It appears the Base to Emitter junction is shorted on the transistor. The solder joints on the flyback all look ok but I will touch them up just to be sure. Since the unit still powers down with the transistor removed I suspect more issues. What do you suggest as next step?

LOPT transistors commonly have a low value resistor between base and emitter, so if it's not short or leaky collector to emitter it's probably fine.

Check the voltage on pin 7 of IC502, this is the output from the comparator, and feeds the latching trip circuit - it should be -12V odd, if it goes positive it will set the trip.

 

[rfranzk]

Thanks Nigel,
I tested voltages at IC502 and not what It should have. Pin(1) 150mV, (2) 1.5V (3) 1.5V (4) 190mV (5) -1mV (6) 10.28V (7) -140mV (8) 320mV. I couldn't find a test point ground on the board so I took ground off of jumper wire 159. There is also a test point 90 that says it should have 13V where I measured 100 mV. I did all these with the LOPT removed. I hope this doesn't affect these lower voltages. I will take a closer look at the schematic tonight to see where tp90 gets its voltage. Let me know what you think the next move is.

Thanks again.
rfranzk.

 

[Nigel Goodwin]

Use the metal body of the tuner for the ground point.

 

[rfranzk]

Thanks for the tip on tuner body for grounding, Rechecked and all measurements basically the same. No voltage (Or millivolts) at TP 90 should be 13V and TP99 should be -13V. On the LOHT I have 11.2M ohm collector to emitter. Is this a problem? A local supplier has one in stock and I think I will get one to compare.

I won;t be able to look at this again until later this p.m.

Thanks for your help!!

rfranzk

 

[rfranzk]

Update!! I got a new transistor and it measured different enough to try. Also looking at the schematic the voltages that were missing come from the flyback. After replacing the transistor I have some improvements but not complete solution yet. Voltage at pin 7 is now -11.2 volts, voltages at the test points 90 & 99 are 12.5 Vand -12.5V. There is audio now and parts of the board stay powered on with switch. The relay shuts down in 1.5 seconds and no video display. Back to the schematic.

Thanks. rfranzk.

 

[Nigel Goodwin]

Update!! I got a new transistor and it measured different enough to try. Also looking at the schematic the voltages that were missing come from the flyback. After replacing the transistor I have some improvements but not complete solution yet. Voltage at pin 7 is now -11.2 volts, voltages at the test points 90 & 99 are 12.5 Vand -12.5V. There is audio now and parts of the board stay powered on with switch. The relay shuts down in 1.5 seconds and no video display. Back to the schematic.

Thanks. rfranzk.

Does pin 7 go high as it shuts down?.

If you have a suitable scope you might scope the collector of the LOPT (you need a x10 probe and a scope with a suitably high range - 10V/cm or better, timebase at 20uS/div). If it's working you get a more than full screen nice clean rounded pulse, if the LOPTX is shorted turns you get a much smaller and ragged, repeated, series of pulses.

 

[rfranzk]

Does pin 7 go high as it shuts down?.

If you have a suitable scope you might scope the collector of the LOPT (you need a x10 probe and a scope with a suitably high range - 10V/cm or better, timebase at 20uS/div). If it's working you get a more than full screen nice clean rounded pulse, if the LOPTX is shorted turns you get a much smaller and ragged, repeated, series of pulses.

Pin 7 stays at -11.2 volts after relay shuts down. I do have a scope but not at this location. (I am a newbie and never used a scope, will need some tutoring) I do have a KV probe and measured 24KV at the LOPTX output at the CRT. I can see the heaters at the CRT warm up also. Test point 96 calls for 900V and I measured 885V. If I need to I will get the scope here to scope the LOPT.

I was looking at the driver circuit for the relay and the Q is smd beneath the relay. Unsure about testing it. The thermistor THP601 gets pretty warm. I don't know if this indicates overcurrent or is normal. I thought i would measure volt drop across it.

Thanks. rfranzk.

 

[Nigel Goodwin]

If the heaters are coming on, presumably they go off once it trips?.

Check the voltage rails on the frame chip.

 

[rfranzk]

If the heaters are coming on, presumably they go off once it trips?.

Check the voltage rails on the frame chip.

I can see the heaters on at CRT all the time unit is powered up. (They seem dim but are on) I measured voltages at the C board on the Picture tube and got I think what is expected. Pin (1) 472V (8,9,10) 186V (12) 592V At CN702 I got Pin(1) 895V (2) 180) (3) 0V ground and just millivolts at H1 and H2 which I assume are heater connectors.



I don't know what you mean by the "frame chip"

Thanks. rfranzk

 

[Nigel Goodwin]

It's IC501, check the voltages on pins 1 and 6, a common fault is dry joints on the chip, but this often kills the chip as well, and blows the resistors feeding the chip R531 and R533.

 

[tvtech]

It's IC501, check the voltages on pins 1 and 6, a common fault is dry joints on the chip, but this often kills the chip as well, and blows the resistors feeding the chip R531 and R533.

Compliments to you Nigel. You have not forgotten your CRT stuff even after years of not fixing them

Accurate advise all the way. I am impressed

You must be a brilliant guy to work with in a Service Department environment.

Regards,
tvtech

 

[Nigel Goodwin]

Compliments to you Nigel. You have not forgotten your CRT stuff even after years of not fixing them

Accurate advise all the way. I am impressed

You must be a brilliant guy to work with in a Service Department environment.

I work for a Sony main dealer, so I've repaired a LOT of Sony CRT sets over the years

 

[rfranzk]

It's IC501, check the voltages on pins 1 and 6, a common fault is dry joints on the chip, but this often kills the chip as well, and blows the resistors feeding the chip R531 and R533.

Voltage on pin (1) -12.6V pin (6) 12.6V R531 and R533 both measured 6.9 ohm R533 had oxide or ceramic flaking off. I replaced it with no change in values.

Thanks again Nigel, I am lucky to have suck knowledgable assistance.

 

[Nigel Goodwin]

OK, EHT is there, heaters are there - but you have no picture?.

I would imagine the frame is OK, as the HT supplies are there.

For a simple (crude and nasty) test get a 1K resistor (or similar) and connect it via a piece of wire (croc clip lead?) to the tuner and then briefly touch the other end to one of the video output transistor collectors (the metal tabs) Q711, Q731, or Q751. This should give you a VERY over bright full size picture - if it gives you a bright line, then there's obviously a fault in that circuit.

 

[rfranzk]

OK, EHT is there, heaters are there - but you have no picture?.

I would imagine the frame is OK, as the HT supplies are there.

For a simple (crude and nasty) test get a 1K resistor (or similar) and connect it via a piece of wire (croc clip lead?) to the tuner and then briefly touch the other end to one of the video output transistor collectors (the metal tabs) Q711, Q731, or Q751. This should give you a VERY over bright full size picture - if it gives you a bright line, then there's obviously a fault in that circuit.

Crude but effective. Full screen comes on in different color with 1k to collector of each transistor. If left for any length of time the set shuts down when ground through 1k applied to either transistor The display is full and bright (Does have horizontal lines across) This looks promising to me.

Thanks. rfranzk.

 

[Nigel Goodwin]

So all the high power bits are working (you get flyback lines because you're directly setting the tube).

Personally I've never used a resistor - just stuck the meter on amps, and shorted the cathodes to ground (VERY briefly)

Try checking round IC301 now, with a scope if you can to check for any signals going in and coming out.

 

[tvtech]

Very, very strong post and totally off topic that I posted.

So I deleted it.

I must stay sane. I must not let the beings I work with get to me. Not doing me any good.

I must not fall to their levels/standards of anything.

Otherwise, I become useless too. And that I could not handle.

Chin up. That's what I keep telling myself.

Regards,
tvtech