Sony Trinitron KV32FV27 Suddenly Dimmed

[cmonkey]

A couple of days ago I finally got my hands on a locally sourced Trinitron and after lugging all 175 LBS home I gave it a good cleaning inside and out. The guy said it had been in a shed for 2 years, but the outside wasn't too bad. The inside was another story and while there was no evidence of mouse, it had certainly been kept in a VERY dirty home.

I cleaned it to an acceptable level of grime, at least clean enough to where nothing would heat up from the dust insulation. I then tried it out and it worked!

I'd say I had it on for about 15 minutes or so and then lugged it to it's final resting spot and hooked up my PS1. I was in heaven for about 5 minutes when the screen brightness just took a nosedive. My heart just sank.

Now when I turn it on, it's brighter for perhaps 1 second or so and then just drops back down to being barely visible.

I'm hoping something other than a bad tube could cause this? Could bad caps or a resistor? I'm thinking I'll start by poking around at voltages on the neck board and see what they are.

I did check the brightness setting in the menu and turned it all the way up. Once I did that I can make out the screen pretty well but it's certainly no solution.

I found the service manual here and have started poking around - https://www.manualslib.com/download/...Kv-32fv27.html

Ultimately I'll try to post back after I've learned more.

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

Well I've been studying the schematics for this TV quite a bit and reading and have focused on the G2 circuit specifically. I wanted to see if there were any resistors that may have shorted and caused a drop in voltage.

There is only one resistor on the G2 circuit (from what I can see) - R1797. It tested fine at exactly 100K. Bummer.

Next I tried just turning up the G2 voltage using the potentiometer on the flyback as shown on page 13 of the manual. The result is shown below. I turned the knob maybe 15% from a factory setting of being at zero.




Now I'm not enough of a CRT expert to know what to do after adjusting that G2 control, or even if it's a good idea to do it. The colors are obviously off and need adjusting as well but I'm not sure how at this point. There are instructions on page 13, but they go quite a bit beyond me at this point. It would require more equipment I think and time to learn.

I'm wondering if the flyback is just starting to go out and not generating enough G2 voltage at this point. Maybe I'll try looking for a replacement and swapping it in and see what happens. Not sure yet.

Another option might be to replace that 100K resistor with a slightly higher resistance one. Has anyone done that?

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

One other thing is that the technical manual doesn't tell what G2 voltage should even be and so I don't know if I can test it with a multimeter. I don't wanna blow up the meter or shock myself obviously.

Does anyone know what G2 voltage should be for this model?

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

Did some more testing today on the filament circuit and it looks like this might be the problem.

Not 100% sure I tested right as it's hard to find info on whether these are AC or DC coming off the flyback, but DC doesn't give me any voltage at all and AC gives me 1.3V AC coming off the flyback and 1.1V AC at the actual heater element. I've seen references that CRTs need to be at least 5V AC and that 6.3V AC is ideal.

So I guess I need a new flyback and lucky me, they are all out of stock....

[R_J]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

The flyback is not your problem, if it was bad you would not have any high voltage and as a result would not have any picture. What are you using for a meter? The heater voltage is high frequency AC. Check the solder connections on the flyback, they could be bad especially the one for the heater.
There are two voltages that are easy to check, they are the +12v (TP98) and the -15v (TP99) Check that they are correct.
Also check that you have +200v on CN1764, pin5 on the C (neck) board

How did you clean this tv and what did you use, that my be the cause of the problem.
You can turn down the G2 control to eliminate the retrace lines that you have in the picture.

[stj]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

check all the soldering

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

What are you using for a meter?

How did you clean this tv and what did you use, that my be the cause of the problem.

Using a Mastech MS8268 multi-meter.

I used an air compressor to blow it out and a vaccuum to suck up the bigger chunks. No liquid was used.

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

There are two voltages that are easy to check, they are the +12v (TP98) and the -15v (TP99) Check that they are correct.
Also check that you have +200v on CN1764, pin5 on the C (neck) board
.

TP98 is +14V
TP99 is -14V

The board says they should be -15 and +15 respectively.

Pin 5 on the neck board is 202V.

Is the flyback an 'all or nothing' package? Can't certain parts of it fail?

[R_J]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

The +/-14vdc are ok, also the +200v is close enough, I suspect the heater voltage is ok as well, For a test check the AC voltage on the anode of D531 (+12v diode) see what ac voltage you measure, this will check if your meter can read 15khz AC.
I suspect your meter can't read the heater voltage accurately.

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

So D531 measures 19.8vAC on the AC side and 14vDC on the DC side.

The +/-15 V pins on the flyback itself also measure 19.8vAC. Does that mean my meter isn't able to read AC coming off the flyback since the DC side measured right but not AC?

Any recommendations for a meter that could read it?

[R_J]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

It looks like the meter has a problem reading the high frequency ac, so it is hard to say what the ac voltage on the heater really is I would think the meter would read the heater voltage high as well,
It is supplied by the flyback so I suspect it is ok. even one shorted turn on the heater winding would likely cause the high voltage section to shut down. and if the winding was open, you would not have any picture at all. You did have a picture in your first post, in your second post the g2 is up too high so turn it down so you don't see the retrace lines.

Locate TP85, C531 or D519 and check the Dc voltage, It should be around 8~10 vdc, that should tell you if the heater voltage is ok or low.

Do any of the menu settings affect the picture, ie: color, brightness, contrast?
try using a different input, or select an on air channel and see if the screen is brighter.

Best way to see the ac voltage and to trace the video signal is with a scope.
try looking in the crt neck to see if you can see the heater glowing, you may need a darkened room to se it.

On these Sony's there is a chance of cracking the circuit board if it was not supported properly when you had the rear cover off, Check at the point on the board where the front plastic supports the board and where the back cover meets it. (near the indent on the side of the board)

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

Locate TP85, C531 or D519 and check the Dc voltage, It should be around 8~10 vdc, that should tell you if the heater voltage is ok or low.

Do any of the menu settings affect the picture, ie: color, brightness, contrast?
try using a different input, or select an on air channel and see if the screen is brighter. .

On these Sony's there is a chance of cracking the circuit board if it was not supported properly when you had the rear cover off, Check at the point on the board where the front plastic supports the board and where the back cover meets it. (near the indent on the side of the board)

The menu settings do change the screen, it's just far too dim even with the brightness maxed. It was much brighter before. It's not just the one input, it's everything including the menu.

TP85 - This one is hard to pick out on the board but it kinda looks like it's a point that's measuring 14 vdc but that doesn't make sense based on the diagram, it should be the same as the other two points.
C531 - 22 vdc on the positive point.
D519 - 22 vdc

I double checked I was on the correct test points for each of these since they are different than you had posted.

I don't see any cracks. It was held in place very well actually, 80% of the board was supported by rails.

There is a glow in the back of the tube, doesn't seem super bright but it is there. I'd say it's comparable to other CRTs I have from what I can see through the backs of some of them.

I've also looked for bad joints on the flyback and I don't see any.

[R_J]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

That test point is fed by the heater supply and then rectified and filtered so the heater voltage is likely good, it seems your meter is reading it a bit high.
Check that R543 is not open (0.47Ω) that supplies the abl pulse to the video circuit but it is likely ok.
Check that you have +200vdc all the away to C1751 on the neck board.

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

R543 is bouncing between .5 and .6 ohms.

C1751 is indeed +200vdc.

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

Just out of curiosity I measured pins 1,2,3 and 5 on IC1701 on the neckboard and they are different than the diagram. Not sure if it means anything though.

1 - 2.44 vdc
2 - 2.54 vdc
3 - 2.52 vdc
5 - 3.9 vdc

Edit - Nevermind this was because I was messing with the G2 voltage. I had it slightly high and lowered it now pins 1-3 are around 2 vdc. Pin 5 is still 3.9.

[momaka]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

Just subbing to monitor this thread, as I do remember having spare boards from a KV32FV___ Sony set of some sort in my junk parts bin. Doesn't look like the issue is flyback or some other unobtanium part... but if it is and I do happen to have it, I can let you know. I saved a number of CRT boards from some dumpster-picked Sony TVs (most were broken by scrappers for their yoke / copper.) Anyways, I did always wonder if those TVs were thrown away back then because they didn't work or because they were just not wanted. Some research back then suggested a lot of the newer (2000's) Sonys suffered from bad solder joints, so probably a good idea to inspect all boards very carefully. Also try removing and re-seating the neck board several times, just in case some of the pins have developed corrosion / oxidation from sitting. If the TV was really dirty and also stored in a shed, there's a chance moisture might have affected contacts on some of the connectors and/or potentiometers. On that note, it would be a good idea to pull apart and re-seat all connectors. For potentiometers, remove all that are removable and measure their resistance. Also see if their variable output produces "scratchy" resistance. Don't forget to mark their factory setting before messing with them, though.

Aside from that, I believe these TVs are pretty reliable. The caps might be coming to an old age now (especially any small ones near any heat sources) being 20+ years old or thereabouts. But that's about it. If the tube was weak, you would likely have seen either very poor focus (blurry picture) or very dim picture from the get-go. The fact that the set was working OK at first suggests it's not a tube issue. It also wouldn't be a flyback issue, as those are pretty much indeed an all-or-nothing affair. Usually when one voltage rail tanks, the whole flyback supply/PS goes down.

I'm surprised about the heater being AC voltage-fed. IIRC, on Sony CRT monitors, it's usually rectified to DC and regulated. But I haven't played with too many CRT TVs to know about this.

[R_J]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

Pin 5 of ic1701 is ok, it is the IK output and if there is a bit of imbalance in the R.G.B current the IK voltage will be different. If the crt was bad the RGB would not balance and the IK signal would blank the crt video completely.
Not sure what else to check without having a scope to check the actual video signal.
Did you remove any sub boards when you were cleaning it? if you did, recheck that the connections are ok
Also R453 is ok

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

No I just cleaned where I was able to maneuver. It still needs a lot of cleaning and so I might just do that next and work on re-seating all of the connections and testing them as momaka suggested.

In the mean time, if anyone has any suggestions for a scope that would work for what I need but also not break the bank I would be thankful. I've wanted one for a while so this is a good opportunity.

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

Bumping this because I'm finally getting back to it now that indoor season has arrived again. I still have high hopes I can get this thing to work eventually.

It's still behaving the same way so the first thing I'm going to do is just re-seat every connection I can find and check for corrosion. Next I'm going to clean each board in detail and reassemble and see if that does anything.

[cmonkey]

Re: Sony Trinitron KV32FV27 Suddenly Dimmed

Concluding my testing for tonight, re-seating all the connections didn't work so I started testing off the B+ voltage rail coming off the flyback.

Made it to R547 and couldn't get a good reading on it in circuit. Took it out and it's completely open, I can't get any reading. This resistor looks like it connects the B+ line and the ABL line, but I'm not skilled enough to understand what it going on with these two circuits.

Not sure if it's the cause but I'm going to keep checking each component so if I find more I can order them all.