Help needed to repair a Sony Trinitron KV-2165MT power failure

[E-design]

I don't think that transistor is very critical. Something like a common 2N3904 should work just fine.

 

[e-music]

Thank you. I will give it a try if I couldn't find the alternatives suggested by Relayer nearby. It's a thru-hole package, but I believe I can mount it on the SMD pads.

 

[E-design]

You can get it in SM as well.
https://www.mouser.com/ds/2/149/2N3904-82270.pdf

 

[e-music]

I didn't notice it's available in SOT23 package but I was able to find the BC846 from the same supplier and the order is underway now. I would rather start off by replacing the bulged capacitor for the older set and see whether I can get it back to life so I can enjoy the news again in my workshop while trying to repair the KV-2165MT, which might be a little bit trickier!

 

[e-music]

Hello Relayer,

I have ordered the following:
- PC111
- BC846
- 2SA1162
- SE115N

And some electrolytic capacitors to replace those in the PSU, as suggested by Brian.

Now, to be honest with you, I was a little bit scared to open these sets as I have never been exposed to a CRT TV before and I know that they utilize some potentially lethal parts/sections that I do not come across on a daily basis when dealing with digital electronics and embedded design. I spent almost a week watching videos and educating myself about the inner workings of CRTs.

All of the tests I've done before (live ones) were with the main board connected to the mains only. All cables, CRT neck board, suction cup, and all others are disconnected while I was taking measurements. I remember testing only once with all the cables in place, and as far as I remember, I had a spark around the posistor area. The HOT was shorted out so I replaced it with a new one, but from what I remember, I didn't read any voltage around the Flyback Transformer.

With that being said, is there any precautions that I have to take in mind in order to protect myself from a deadly shock? Do I have to connect all cables when taking the measurements or when performing the tests? And by the way, I've seen some crazy videos for some guys making sparks with the suction cup removed as they approach the back of the CRT while the set is on. Is this one of the possible ways to verify the flyback is working? Can I do something similar to test my FBT?

Thank you again for your time, and I look forward to get your advice so I can feel more comfortable when attempting the repair!

Best regards,

e-music

 

[betwixt]

First rule of working with CRT TV's - never remove the connections to the CRT! Connect them back up again, it's far safer than having several KV of wiring lying around and the EHT to the suction cap can go well above flash-over voltage if it isn't loaded properly. You are far more likely to damage the flyback transformer with the CRT disconnected.

The CRT base will have both ground and up to about 5KV on it for the focus control so treat it with care. Remember that the CRT is the load for those voltages, not the source of them!

Brian.

 

[Relayer]

Hello e-music,

I know that they utilize some potentially lethal parts/sections that I do not come across on a daily basis

When ever servicing any electronic devices employing a Switch-Mode Power Supply design, precautions MUST always be
observed.

The Hot side of any SMPS is in effect connected directly at mains potential. Due to no isolation between the 240V or 120V
mains power and the Hot side of the power supply, it has the potential to kill. The current that could possibly pass through
your body would only be dictated by the current rating of the PSU's main fuse.
The chopper transformer, opto-couplers and high voltage caps and/or high value resistors are virtually the only components
that are providing any isolation between the Hot and Cold side of any appliance.
You work on the Hot side as little as possible when having the appliance turned on.
There are instances where you need to take Hot side voltage measurements, but you need to be extremely careful.

When ever servicing, say a CRT Television, you need to switch it on prior to any disassembly to observe any symptoms
while powered. Any ticking noises, hiccuping (PSU trying to start, senses a short and shuts down, then repeats), sparks etc.
Next, remove the rear cover, then take a look at virtually anything on the main board, the CRT and the ultor cap (suction cap),
and any other items connected to the main board. eg. speakers, deflection yoke and CRT board.

If nothing amiss, then blow the insides out with compressed air. A vacuum cleaner isn't the best to use, as it doesn't get the
dust up sufficiently, plus you risk damaging components.
Best way is just to remove the main board and dust it down with a clean paint brush. But before doing that, read the next step.

Turn the TV on again and observe to see if there is any distress such as arching, components giving off smoke etc.
If all good, turn off the set. Turn it off at the mains and remove the plug.

Next thing you need to do is to discharge the ultor cap connection to the bell of the tube.
You just need a jumper cable, preferably with crocodile clips on each end, then connect one end to the shaft of a flat bladed
screwdriver with a plastic or rubber handle. The other end of your cable should go to any good earth point, preferably to the
braided wire that partially surrounds the bell of the picture tube.

Next, gently push the blade of the screwdriver under the ultor cap until you hit one of the solid wires or metal plug underneath
or you actually hear a discharge. Gently jiggle the screwdriver to make sure its completely discharged.
You can now remove the ultor cap.

Next, you remove the main board, which ever way it needs to come out, but only hold the board by the edges. Try not touching
the solder side of the board with your fingers, especially near the mains connector to the PCB.
Once removed, take note of where the main filter capacitor/s are located.
Now, flip it over and place it on a bench with the solder side up.
Use the crocodile clip cable, and place it across the main filter cap/s and discharge it/them. But expect a mild c.r.a.c.k.i.n.g sound and
possible sparks when doing it.
Its preferably better to make up a cable system using crocodile clips and inserting a 100 ohm 5 Watt resistor in the middle of the
cable. This will prevent the sparks and/or c.r.a.c.k.s you'll hear, as it will discharge it at a slower pace. Though this is a great cable if
you do a fair bit of SMPS repairs, but otherwise wasted.
The main board will now be safe to handle without copping any nasty shocks.

Take note: Every time you need to energize the TV, the procedure above will have to be repeated.

Next you should give the whole main board a close inspection on both sides of it.
Solder side: Check for any dry or cracked joints, especially around heavy current areas, as well as the flyback and chopper
transformers, as well as heavily heat-sinked components.
Component side: Check for any parts cracked, burned or deformed, including coils and connectors. Check for hot spots on
the PCB itself for any overheating.

Now to actually answer your question, and I'm sorry it took so long, but the biggest risk is, as I've said already, the Hot side
of the PSU is the most dangerous section of any CRT TV, as well as any other appliance that uses SMPS technology.
You can be zapped by a multitude of other sections on the TV, even the ultor cap, but unless you have a heart condition, the
worst you'll ever get is get thrown across the room.
Large screen TV's usually pack 30kv at the ultor, but due to the very small currents involved, it would rarely kill anyone.
Though being thrown across the room isn't pleasant, and even the blase attitude I seem to have with the above, caution
is still the key. No one likes to be zapped, weather its a large one or a very mild one.

Once in my servicing days, I got a fair jolt from something, can't remember exactly, and my reaction was to jerk my hand up.
I ended up hitting the CRT board and cracking it. Thankfully I didn't break the neck of the tube.

If ever you need to take voltage measurements on the Hot side of the PSU, you need to plan it out before you do so.
Make sure yo know what component leg you need to target, weather you have the board with component or solder side
up. Keep your hands on the probes and try not touching any other components or heat-sinks in the process.
When doing Hot side measurement, you can only use a grounding point on the Hot side. NEVER use one on the Cold side.
Same goes with cold side measurements: only Cold side ground points.
This is what I mean in regards to planning what you need to do on a live set.
Most important is wearing good shoes, preferably with a rubber sole. NEVER barefoot or in socks only and definitely no
water on the floor.

I hope the above helps relieve any doubts you have with CRT tellys, even though it was all a bit long winded.
If you still have any reservations, please let me know.
Regards,
Relayer

 

[e-music]

Hello Relayer,

Thank you very much for all the info. I got the parts yesterday and I just started few hours ago. I thought I would first try to replace that bulged cap for the old set that was running recently perhaps I can get it back to life easily, but unfortunately, it seems there's something else that still prevents the set from starting up. After replacing the cap and turning the power on, there's a loud clicking sound but nothing else happens. I'm not sure whether this was a relay or not, but I was very afraid to keep it on for more than few seconds, so I switched it off immediately. No smoke, sparks, overheating, or anything else observed.

By the way, I used a cap with a higher rating, but same uF value. The original one was 160v/330uF, but the one I have used is 250v/330uF. I don't know if that ticking sound had anything to do with that cap.

In getting back to the newer set, the KV-2165MT, I have replaced the STR, the Q603 transistor, and have got IC602 and IC603, but I thought I would first continue testing before replacing them blindly.

I have everything around me now and I'm ready to follow your steps, but believe it or not, I spent two hours trying to find that R014 thing, but couldn't find it on the board. Following the traces of the D604 and D608 cathodes didn't help me get it either. On the schematic, it seems it's sharing one leg with Pin#1 of IC004 and C033, and Q002 is located somewhere nearby, but on the board, there's a huge distance between Q002 and IC004. This is really driving me nuts. Any ideas?

Thanks again for your awesome follow up!

 

[Relayer]

Hello e-music,

there's a loud clicking sound but nothing else happens

You need to try and isolate that sound if you can. Try and determine if it is a relay clicking
or something else.
If it isn't the relay clicking, then check the horizontal output transistor (Q802) for shorts.
If no short is found, then you need to short the base and emitter of Q802 together.
If it still ticks, then there's a good chance the horizontal flyback transformer has a shorted
turn and would need to be replaced.

The original one was 160v/330uF, but the one I have used is 250v/330uF. I don't know if that ticking sound had anything to do with that cap.

A higher voltage rated cap is always preferable, so no dramas there. I doubt it would have any relation to the ticking sound, though its possible that you have partially
repaired the set and new symptoms have emerged, thus it ticked, where-as it didn't tick prior to replacing the cap.

I have everything around me now and I'm ready to follow your steps, but believe it or not, I spent two hours trying to find that R014 thing, but couldn't find it on the board. Following the traces of the D604 and D608 cathodes didn't help me get it either. On the schematic, it seems it's sharing one leg with Pin#1 of IC004 and C033, and Q002 is located somewhere nearby, but on the board, there's a huge distance between Q002 and IC004. This is really driving me nuts. Any ideas?

I've been there, and done that in regards to trying to find a component through the mess of others, and it can be extremely frustrating.
Worse on double-sided PCB's. :bang:

The resistor in question is a 2 Watt device, therefore it should stand out from many other components. Safety (fusible) resistors usually
have the body of the resistor colored gray. You should see several in the power supply alone.

This resistors (R014) function is to fail due to excessive currents drawn by IC004, which is just a glorified zener diode.

Its not overly critical that you can't find the part, as isolating the horizontal stage is more important, to which I'm sure your problem lies.
Though there's a good chance its your PSU instead, or both.
Doing the light bulb test will determine, (in most cases) what part of the set is the guilty party.

Prior to doing the light bulb test, install the new components first, but don't turn the TV on. Place your light bulb onto the 115V rail and
isolate the chip fuse (PS801). Its ready for the test.

If the light bulb lights up fairly well, then that's a good indication that your PSU is repaired. So the components you got for it was worthwhile.
There is a possibility that the same components may destroy themselves again. I don't mean to sound dire, but I need to prepare you just in case.
Though I am confident the PSU should work.

If there are sparks or smoke when turning it on, then switch off immediately.

If the light bulb lights up with no distress, make sure you measure the voltage of the 115V rail. If its close to the mark, then switch off.

Next you need to remove the bulb, install the fuse (PS801), then turn it on.
If nothing untoward happens and there's silence, you need to measure the 115V and 15V rails on your PSU.

If you get sparks or smoke, turn off immediately.
Once again, I need to warn you that there is a possibility your new components may sacrifice themselves again, but lets hope not.

I'll leave it there for now. Let me know how you get on, and hopefully all will go well. :smile:
GOOD LUCK!!! :thumbsup:
Regards,
Relayer

 

[e-music]

Hello Relayer,

Thank you very much. A great reply, as usual!

Well, I almost gave up finding R014. I will move to the next step, removing the PS801 fuse, and will continue from there. Will report the results back.

Regards

P.S. IC602, IC603, Q603, IC601 all have been replaced by new ones already!

- - - Updated - - -

If it isn't the relay clicking, then check the horizontal output transistor (Q802) for shorts.

By the way, this was for the KV-2162M9, the older set. I don't have a schematic for that one.

 

[e-music]

Hello Relayer,

By removing the PS801 fuse, I believe I will also isolate the flyback, as well as the HOT. By then, is there any problem if I continue testing and taking measurements with all connectors, suction cap, CRT board, and everything else is disconnected? I just don't see how to flip the board and take measurements on the solder side with only few inches of cables connected to each other.

Thanks

- - - Updated - - -

I just managed to remove PS801 and to my astonishment, it was totally OPEN!:lol: I can see now why I couldn't trace the 115v down the rail from the cathodes of D604 and D608. The fuse was totally open. I don't know if you still remember from my earlier replies that the first thing I had to replace after the first couple of hours troubleshooting the set was the HOT, as it was all shorted out. I believe we're pretty close now. What do you think?

Thanks

 

[e-music]

R620, 470Ω/3W resistor @ degauss circuit is open, too! I have a 560Ω resistor at home, but not sure of its power rating or if I can use it there. It say 560Ω J/RSU2/M1D4.

- - - Updated - - -

OK, I'm done testing with the light bulb. The bulb was very dim. Voltage reading from D604/D608 cathodes was 82V. I don't get any voltage around the STR pins. Pins 1 and 2 of IC603 read 15V/14.8V respectively. R620 is still removed. I still have 5V coming to the MCU, and I could read 15V and 9V around the RF section, but almost 70% of the circuit is shut down. Any ideas where to look next?

Thanks again.

 

[E-design]

Voltages on pins 1/2 are very low. Make sure C604 charges up to the full rectified mains voltage (170 or 320 VDC) depending on your mains input. If R601 went high in value, it could be causing this low-voltage readings.

 

[e-music]

Hello e-design,

Thanks for your input. Yes, I believe it does. The reading across C604 pins was around 320 VDC. I didn't check R601 yet, but I will check it and see if there's anything wrong.

- - - Updated - - -

R601 and R621 are both giving correct readings, 1.8Ω.

 

[E-design]

Well, the only thing in between is the switching transformer windings. Check for dry joints around the winding pins 2/3/4/5 on the pcb. What is the resistance between pin 1 of STR and the C604? First discharge C604 of course.

 

[e-music]

I don't think I have dry joints anymore as I have already removed the transformer then returned it back to the PCB. Resistance between Pin#1 of STR and C604 is 0.1Ω

 

[E-design]

I don't get any voltage around the STR pins

Surely you should have some voltage on pin 1 of the STR?

 

[e-music]

Yes, that's pretty weird as I remember I had a voltage reading on that pin before doing the last replacements, but not sure how much it was. I believe it was -110V or something. Not sure though. What/where is the voltage reference for the STR? I don't know if I missed something here? On the datasheet, there's 81.7 marking on the first pin, 76.7 on the second, and so on. Are these the actual voltages when the STR is working normally?

 

[Relayer]

Hello e-music,
Sorry to hear not everything went well. :sad:

OK. I had a good look at the schematic today and realized I'd made a mistake in my interpretation of grounding
on the Hot side of the PSU.

Could I get you to do something for me please.
Can you please set your multi-meter to its lowest ohms setting and measure any ground point on the Hot side
of the PSU and a ground point on the Cold side.
If its virtually zero ohms, then the PSU is basically floating as shown in the picture below:

Therefore you need to place your negative probe, not on any ground points shown on the schematic, but placing
it anywhere which is highlighted on the next picture:

I deeply apologize for this error on my part, but hopefully now you may get some sensible readings when measuring
anything within the shaded areas in the first picture.

You can now measure between Pins 1 and 2 of IC601.
Negative probe to Pin 2 and positive to Pin 1.
Use Pin 2 as your ground reference to measure other areas within the floating field.

See if you get a reading of 81.7 volts between Pins 1 and 2.
Also measure between the Base of Q601 and Pin 2 of IC601 and see if you get the correct reading as indicated on the
schematic.
If any of the above shows a close measurement of the indicated voltages, then there's a good chance the PSU is OK.

You still need to maintain the light bulb trick and ensure that PS801 is out of circuit.
If the PSU is giving you 115 volts on its main rail, then the light bulb will no longer be needed and we'll need to look
at the horizontal stage next.

If you're still getting only around 82 volts at the cathode of say D604, then the PSU is faulty.

As for the degaussing thermistor:
Firstly, you need to remove the degaussing thermistor entirely and give it a good shake. If you hear
it rattling, then it will need to be replaced.
If R620 has a gray body color, then it should be replaced by an equivalent type. It can be replaced with
a 470Ω 5 Watt wire-wound resistor, but the original is there for safety reasons, to prevent the resistor from
burning up due to an overload. Though a 5 watt resistor should only go open circuit and not burn up.
R620's purpose is to share the current with the thermistor, until idle current is achieved when the coils
settle down.
I personally wouldn't use a 560Ω resistor, even if the wattage rating is adequate. Most CRT tellys
use a 470Ω 5 Watter, so it should be OK to use one of those if you find it difficult to find a 3 Watt fusible.
If you do decide to go the wire-wound type, make sure the resistors leads are the thin bendable type, and
NOT the solid leg types that are out there.
I doubt you'll be able to fit the wire-wound horizontally, but make sure you fit it with at least 5mm spacing
from the body of the resistor and the PCB.
If you do manage to bend the resistor legs to mount it horizontally, then still ensure a minimum spacing of 5mm
or more.

By then, is there any problem if I continue testing and taking measurements with all connectors, suction cap, CRT board, and everything else is disconnected? I just don't see how to flip the board and take measurements on the solder side with only few inches of cables connected to each other.

No. All connectors, ultor cap, and everything MUST be connected when taking voltage measurements.
But ALL can be disconnected when making static tests, such as ohm, diode, cap etc readings, or when you
need to solder and de-solder components or joints.
I have to admit that having to disconnect everything, then reconnecting just to get access to the solder side
of the main board is painful, but that's the way it can only be done.

Please let us know how you get on, then we can go from there.
Regards,
Relayer

 

[e-music]

Hello Relayer,

Thank you very much. I'm reading through your reply now, but again, non of the photos opened. By the way, previous photos you uploaded few days ago are loading now. I guess you changed from that external host to the forum upload. You may do it again for these new photos.

No problem, we were created to fail, too! )

- - - Updated - - -

I did the GND to GND measurement and it was like you said, 0Ω. I had an old mark I wrote earlier around D602 as it was shorted out both ways, but I believe that's normal because I was reading windings 7/8. I will continue through the other tests, as soon as the photos are loading. Thank you again for your excellent follow up. I really appreciate it!

- - - Updated - - -

I have made the measurements as suggested, and here are the readings I've got:

Pins 1/2 of STR: 0 VDC. When switching my multimeter to AC mode, I get 4.5 VAC and everytime I touch the probe with the pins, I could hear a faint hissing sound. If I remove the probes few seconds then take another measurement, I get something around 15 VAC. Repeating this for the third time, the reading now is around 35 VAC. Doing it for the fourth time, the reading is again 4.5 VAC.

The reading for pins 2 of STR and base of Q601 is giving me around 1.5VDC. Also, same hissing sound when touching the probe with the base.

If I turn the set off then on immediately, the power LED doesn't come on. If I allow few seconds for the capacitor to discharge, the power LED now come on then goes off after almost 4 seconds and stays off. I didn't order a new cap for C604, but I remember once I discharged it with an isolated clamp while STR was removed, which gave a huge spark in front of my face and everybody around here was frightened due to the loud explosion. They thought I was already dead as I already warned them before I attempt to play around this potentially deadly thing. I believe the charge C604 holds was dissipated by STR when it was mounted, therefore it didn't hold the charge more than few seconds after turning the power off, that's if not a short in the PSU causing it to discharge immediately as power goes off.

Troubleshooting this things has proved to be much more complicated than anticipated. Not sure what to do next! :bang:

Thanks again for all of your contributions.