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

Hello guys,

I have got two old Sony CRT TV sets. KV-2165MT and KV-2162M9. They were both left off for so long in a relatively humid area (home is only 2 miles from beach). It seems the older one (KV-2162M9) was the last one standing before we move here.

Since we moved here, it's been working flawlessly for about few weeks, and its picture was really nice. Later, the TV started to take 5~10 mins to start up, and some times more. Few days later, it refused to work. I removed the power cord and kept it unplugged for about two days and when tested it later on, the TV started up normally. However, the following day, the TV refused to work at all. I tried to remove the cable for few days again, but that didn't work. The hair dryer trick didn't help either.

The TV is completely dead now. No picture, no audio, only the red power LED turns on for couple of seconds then goes off everytime I turn it on, with a faint hissing or clicking sound coming out of its speakers as it turns off. Red LED blinks as I press any button in the front panel, and it gives an indication when the max/min volume reached when I play with volume buttons. Now, the funny thing is, when we tested the other set (KV-2165MT) which looks much better, it has exactly the same symptom. Just like if it was an infection affected both sets somehow??!! :-D

Because they both had the same issue, and the KV-2165MT looks much better, I decided to start with that one first. The schematics file (scan) is attached, and here is a link for a service manual for a similar model, but this one is the original PDF so it's much clearer than the first one:
http://monitor.espec.ws/files/kv-2185_sony_chassis_g3e_110.pdf

I started off by cleaning the entire set with a hoover and all circuit boards with a special spray so I can see what's going on under all that dust. I tested the set after cleaning, of course, it's still dead. Well, the main board has turned very dark under the large resistors at the power supply area, but the fuse is still intact. No capacitor is found to be bulged, checked almost all diodes/caps for short or leakage, but nothing yet. Some were tested in circuit, and others were removed from circuit for test.

When I got to the horizontal deflection area, I found the whole part shorted out (2SD1878). I removed it from circuit and, yep it was shorted out. Replaced it with a new one, but the TV still refuses to work. But as far as I remember, when tested with all cables connected, I spotted some sparks around the posistor area, between the posistor and the big square white resistor. I removed the power cord, disconnected all cables, removed the flyback suction cup from the tube and covered it and continued testing with only the power cable connected to the main board.

At this stage, the main 300v capacitor was not holding any charge after turning the power off, and it is the case for the 160v cap in the secondary section. After keeping the power on for few minutes, the STRS6307 has become very hot. The posistor gets very hot, too, but I believe it's normal.

After spending several hours, I found a short across the C628 cap. Removed the cap but the short still there. Voltages around the photocoupler, regulator, and Q601, Q603 are not the correct ones as it seems in the schematic. Even removing the whole 9-pin regulator didn't help, until I removed the transformer, T601. Now the short has gone, the STRS6307 doesn't get hot after several minutes. Could it be the transformer?

By the way, there's a 5v around the uC and the IR-Sensor, but there's a whole section that has no voltage whatsoever, of course when the transformer was mounted on board. The transformer is removed now, but don't know what to do next? I have a new STRS6307 that I can try out, but it seems fine when the transistor was removed, though the voltages I read across its pins were around -50, not -76 as the schematic says.

Any ideas?

Could be a lot of things but my first guess would be one or more of:
R615 (use one rated at > 300V)
C604, C619, and less likely C609 or C610.

None are particularly expensive, in view of the TVs age it would be wise to replace them all.

Brian.

Hi Brian,

Thanks for your reply. So, it's more likely one of those passive parts at the high voltage section? What about the transformer? Why you think the short has gone when I removed it? Or maybe when the transformer is removed, the circuit is open for that shorted part beyond the transformer? Anyways, of course those are not expensive at all and I'm gonna replace them all and report the outcome.

You will read a low resistance over C628 because you're reading the resistance of the winding 7/8 as shown.

I suggest verifying and getting the main PSU to work correctly before looking for other problems.

You can try to disconnect the 115 V line after C609 and connect a low wattage 10-20 W incandescent mains bulb as a load. There is a good chance that IC602/IC603 may be faulty that caused the 115 V line to rise and damaged Q802. You have the protection diode D608 that should have clamped any over-voltage, so make sure you check D608 for any leakage.

IC602 is discontinued, so you may have to cannibalize that out of another set if that is faulty.

Alternatively, it could be replaced by making the circuit using a TL431 shunt regulator.

Thank you very much for all the info. That was very helpful. I will first get an incandescent bulb as I had this in mind for so long now, then I will try all the other things you suggested. I believe I can still find IC602, it's not a big deal for me finding an obsolete chip. By the way, is it normal for the STRS6307 to become very hot after couple of minutes?

Ah, yes, I will return that transformer. It looks pretty good and like you said, I was reading one of its windings. That's why I had short across that C628.

I will report any updates once I'm done testing the above...

Thank you again for your help!

The STR chip will heat up when operating normally, as it is after all just a power transistor with some supporting circuitry. One of the internal functions is peak current limiting, which is sensed over R609 and used to turn on another internal transistor to reduce base-drive to the main switching transistor. The limiting will activate once the peak switching current in the emitter of the main transistor exceeds about 4 A. So, the STR chip may heat up more when it is trying to operate at maximum power due to a heavy load caused by a failed component.

Winding 7/8 provides the base drive to the switching power transistor once the switching start after power on. Initial start is performed by R602/17 and R615. Terminal 8 is connected to the emitter of the internal power transistor and terminal 7, connects to the base input via R623 and C607. It looks like the pulse out of winding 7/8 is rectified and filtered, then sensed via terminal 4/5 to provide some feedback to control/limit the power of the main switching transistor.

You should carefully check all the diodes around the STR for possible leakage as well.

Hello e-music,

By the way, there's a 5v around the uC and the IR-Sensor

Click to expand...

Does that 5V stay there constantly while the set is on, or does it eventually fade away?

By the way, if need be and you need to replace IC601 (STRS-6307), you can obtain it from
WES Components here in Australia. The price is: $12.05 AUD
Here's their link: WES Components
You'll have to register before they'll let you download their pdf price lists. But its definitely
worth it, as they stock quite a bit of obsolete parts.
Regards,
Relayer

As with any troubleshooting procedures, isolation is the way to get a direction. Start first to establish the presence of the 155v near the flyback pin2. If no have, check inward there is a fuse 600ma via 1.2ohm 2w resistor. Deload this line by desoldering and hanging flyback pin2 then measure again. If you found anomalous then move further inward to the source of this 115v whivh is then your STR chip via T601. Verify if have input volatges in T601. likewise deload the output of T601 and make measurements in the input side of it. Also complete dead set almost always are caused by either Horizout transistor and flyback.

Hello Relayer,

Thank you for your reply. Yes, as far as I remember, the 5V is a steady one and doesn't fade out while the set is on. I will check again.

I have already obtained a brand new STR-S6307, but I didn't replace it yet. I thought it's better to continue troubleshooting for other bad components before replacing IC601. Anyways, IC601 is removed now, and the voltage reading on its first pin (pin #1) was around 320v. Is this the normal input voltage for this power chip?

I have finally managed to find a small 60W (220v) incandescent bulb and it's now soldered to a cable. Could someone please show me on the schematic where and how this has to be connected. I was going to connect it in series from the anode of D604, but I thought it's better to ask first to make sure I'm going in the right direction.

By the way, I have one of the power transistors (Q601, Q603) cracked accidentally while I was trying to remove that rock-solid STR chip and its heat sink. It's on order now, so I won't probably be able to continue testing until I get that transistor.

I'm thinking about ordering couple of other caps, and maybe IC602 and IC603, as long as, I can find them.

Before delving deeper into guesswork, when a power supply like that intermittently runs then stops altogether, it is usually the circuit associated with 'kick starting' it. Some of the supplies used within the PSU itself are derived from it's own output, that means it will only run if something can establish those supplies in the first place. The way it is done is to use the current flowing through a capacitor as it charges up (power switched on) to temporarily provide enough voltage for the circuit to start running.

Given that generally, low grade parts are used in domestic equipment and they are usually run at high temperatures for several hours every day, the start up components are prime suspects. In that power supply, the start-up current flows through R615 then as the oscillator starts to run, it derives the normal running supply by charging C619. As both are likely to be damaged by heat and age, and they cost pennies, change them first before randomly changing other parts.

320V at pin #1 is normal, it is the peak of the AC input voltage minus a small drop in the rectifiers.

I'm not sure the incandescent lamp trick will work on this TV but the place to connect it is in series with the AC power cord. That will limit the amount of power the whole TV can consume but there is a catch - when first switched on you probably notice a brief buzz, that is a surge of power going to the degaussing coils around the CRT to remove any residual magnetism, they are 'DGC' on the schematic. The way the deguass is turned off automatically is by THP601 getting hot (it is designed to run hot) but limiting the input power may leave it cool enough that it fails to work. I would suggest removing JW15 and JW15 before using the lamp. They will have no effect on the TV operation except possibly you will see some colored patches on the picture when you get it working again. Refitting the links should fix that.

Brian.

Hi Brian,

Thank you very much for your detailed, yet very helpful reply. Well, from where you left off, I'm also not sure what the light bulb trick does and how it helps, but it seems it's very common trick for troubleshooting that type of PSUs. So, you do not suggest connecting one in series after D604?

And by the way, I believe you wanted to say JW14 and JW15? Perhaps JW12? Those the only jumper wires I found around the degaussing circuit.

Well, it turns out the problem of the older set is a straightforward fix. As I need to wait couple of days to get the needed components for the KV-2165MT, I thought I might give the older one a shot and see if there's something that needs an immediate replacement so I can order all needed parts for both sets simultaneously. Well, this one has apparently a bulged capacitor. It's a 160V/330uF electrolytic. I don't know if it was the reason the set was making a very annoying high pitched noise when power is switched on. I could hear the noise even after disconnecting the power cord for couple of minutes.

Of course, I will try to eliminate guesswork as much as I can, but as someone else suggested over here, replacing these caps might be the best bet before trying anything else, especially for these old sets.

Hello e-music,

I'm also not sure what the light bulb trick does and how it helps, but it seems it's very common trick for troubleshooting that type of PSUs.

Click to expand...

The purpose of the light bulb trick is to isolate the rest of the set from the PSU to determine if the fault lies within the power supply itself,
or its caused by other stages of the TV. i.e. In the horizontal stage, vertical stage etc.
When the PSU is isolated, and the light bulb glows to a reasonable glow, and nothing else is being affected, then you can more or less
assume that the power supply is good, and the fault is elsewhere. But if the bulb fails to light or is very dim, then the problem will more
than likely exist in the PSU.

Thank you for your reply. Yes, as far as I remember, the 5V is a steady one and doesn't fade out while the set is on. I will check again.

Click to expand...

You're welcome.
Since you are getting 5V on the uC and the IR-sensor, it tells me that your PSU may be working after all, but is being loaded down by the main 115V rail.
The 5 volts present means that the 15V rail of the power supply is working, as its supplying the 5 volts to the uC and IR-sensor. It may not be the full 15V
being supplied to that section though, but enough to maintain the 5 volt rail.

To isolate the TV from the PSU, have a look at the following pictures:



In this picture, you need to lift one leg of R014, which should be a fusible resistor. DON'T just desolder one leg and leave it in place. Lift in out entirely.
This is to ensure that no solder that might still be remaining on the pad can accidentally touch the resistors pigtail.



In this next picture, you need to remove the fuse PS801, shown in the red dot entirely.
I'm certain it will be a chip type fuse and may look like a TO-92 transistor. The fuse would need to be totally removed, to prevent any damage to either of the legs
of the device.



This picture is more of a warning: What ever you do, do NOT isolate any of the components shown. The PSU requires some feedback, and by disabling anything in this
section may cause extensive damage to the power supply.



In this picture I have red and green dots showing. Connect one end of your light bulb to one of the red dots (i.e. attach it to the cathode of D604 or D608).
Attach the remaining wire from your light bulb to one of the green dots, which is basically any good ground point.
Make sure your light bulb setup has the wires coming from it at a fair length, as you need to attach the wires on the solder side of the board.
Ensure you wrap insulation tape around the metal part of your light bulb to ensure your safety, and also from accidentally touching any parts of the TV.
Do NOT use any ground points within the purple shaded area. In other words, any part of the hot side of the PSU.

Once you're all set. Disconnect the deguassing circuit plug (CN602) as suggested by Brian.

Fire up the TV and observe what the light bulb does.
(1) If it comes up fairly bright, then as I've said earlier, your problem lies elsewhere instead of your PSU.
(2) If the bulb fails to light or is very dim, then there's a good chance its the power supply.

If the bulb lights up brightly, then switch off and reconnect R014 back into circuit and try again, with the light bulb still in place.
Once again, if the bulb lit up bright again, (though it may be slightly less brilliant than before), and there were no signs of distress, then go to the next step.

Reconnect the fuse (PS801) that supplies the horizontal stage and fire the set up again with the bulb in place.

If at any time you find one section that causes distress or shut down, then that's the section of trouble.

When you get a chance, can you please perform the above tests and get back to us on your results.
Thanx in advance.
Regards,
Relayer

Hello Relayer,

Thank you again for your awesome reply. That was huge and I'm gonna do all the tests following your instructions precisely. By the way, non of the photos is loading, so please try to check the links because I'm very excited to see them.

Regards

- - - Updated - - -

A quick question that just came to my mind. How a 220v light bulb is gonna glow to its full potential out of a 115V?

Hello e-music,

By the way, non of the photos is loading, so please try to check the links because I'm very excited to see them.

Click to expand...

Strange???

*** Moderator action: removed links to external servers. Uploaded files to edaboard ***

A quick question that just came to my mind. How a 220v light bulb is gonna glow to its full potential out of a 115V?

Click to expand...

Incandescent light bulbs require very little voltage to produce a forward current. Once the potential exceeds the resistance of the filament, the filament will start to glow.
Though admittedly an extremely small amount of light is emitted. Consider the old vacuum tubes only requiring 6.3 volts to get them glowing, though they do use
a different material with their heaters (filament).
With a 75 Watt 240V light bulb, the resistance of the filament is around 60 ohms. I can get a tiny glow coming out of one with 24 volts DC @ around 120mA.
I realize that using ohms law on the parameters I've given above won't really gel, but that's the readings I got from my variable PSU's V and A meters and my
multi-meter for my ohms reading.
So with it applied as a load to your PSU, it should emit a decent glow, undoubtedly not a brilliant light to blind you, but enough to guesstimate that the PSU is
working or not.
The best way to be certain is to measure the 115V rail after attaching the light bulb. It should, (that's if the PSU isn't faulty), give you a reading very close to the
rated main rail voltage.
Regards,
Relayer

Hello Relayer,

Thank you very much for the prompt follow up. Yep, very strange, and even the links you provided did not open either! I don't know if this was a problem at my end, but if you can upload to a different domain, e.g. Google Drive, that would be highly appreciated!

And thank you again for the explanation regarding the incandescent bulb. I can understand it better now!

Regards,

e-music

- - - Updated - - -

By the way, I did not try to upload any content over here yet, but was wondering if the forum doesn't allow uploading these photos here? Perhaps uploading/attaching them here is way better.

Hello e-music,
I'm not 100% on the usage of Google Drive, but see if it works now:

Google Drive

I've placed them in the slide show in the correct order.
I hope it works this time.
Otherwise I can send them to you via e-mail if you like. But DON'T give your e-mail addy in a post.
Send it to me in a Private Message.
By the way, you can post images on the Forum, but you must use a host website like Photobucket, imgur etc.
to upload them to, then get the URL from the hosting site and include that link in you post/s.
Regards,
Relayer

Hello Relayer,

Thank you very much. Yes, it works flawlessly and I've got them now!

Will let you know once I'm done on testing, but it seems I won't be able to find Q603 from the same supplier. Do you suggest any alternative?

Regards

Hello e-design,

it seems I won't be able to find Q603 from the same supplier. Do you suggest any alternative?

Click to expand...

Here are some possible substitutes as per my semiconductor equivalents books.

BC846A, BCV71 or BCV72.

There are a couple of 2SCxxxx’s that are recommended also, but I’ve been unable
to get any reasonable info on them. Thus there’s a good possibility they will be hard
to source.

Strange that your original transistor is mainly used for audio applications, though
I guess your PSU requires low noise, as well as high gain for the error correction
function of the transistor.

I'm certain you’ll able to source the equivalents fairly easily, as the BC846A's are common
to the point of being able to buy them by the kilo. :thumbsup:
Mouser has over 13,000 of the buggers.
Regards,
Relayer

By the way, just a little tidbit info:
2SAxxxx and 2SBxxxx are ALL PNP devices, where as
2SCxxxx and 2SDxxxx are ALL NPN devices.
2SKxxxx are ALL N-Channel FET's and MOSFET's
2SJxxxx are ALL P-Channel FET's and MOSFET's

2SA and 2SC are generally small signal devices
and
2SB and 2SD are generally power devices.
But it seems the Japanese didn't fully keep that standard
and ended up mixing them.