Sony multisystem KV k29MF1 to rescue

[Benyamin39]

Hi,

I recently purchased a Multisystem CRT TV Sony KV k29MF1. This TV is great as it is PAL / SECAM and NTCS and therefore allow me to do retrogaming on european computer systems (PAL COmmodore Amiga, Oric, Amstrad, ...) as well as north american videogame systems (SNES. Genesis, ...).

I tested the TV and the picture is horrible. it needs a lot of work to adjust convergence and geometry but that is not the issue for the moment.

I modded the TV to get RGB, tested with a Mister FPGA and it works great. Either PAL or NTSC systems works automatically.

The problem is that I messed up the TV when I reopened it to do a thorough compressed air cleaning and fix the Red signal that was not soldered properly.

Note that the TV has 2 electronic board : One for the 120V and above (Board D, see schematics) and one for the signal processing (Board A). The design of this TV is pretty neat compared to other TVs I opened (Toshiba, JVC, SAnyo, ...)

I did not not touch the 120V Board, I only worked on the “signal” board. When I reconnected the board I did not properly attached the jumpers. I don’t know if this mistake or the cleaning is the reason I certainly blew up a component.

When I restarted the TV, I got erratic behavior. The picture was heavily skewed like the figure below
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I also got some gentle but prolonged static electricity noise (say 30 seconds to a minute). I can’t say if it is because of the cleaning some dust got stuck on some sensitive parts of the tube or whether a component was already dying somewhere.
Then I got more erratic picture and then no more picture at all.

The TV start. And I can hear the starting buzz as well as relay switch. The IR LED work when I hit keys on the remote control. But I got absolutely no picture at all. The tube has not even any static electricity on its surface.

I am very keen on trying to fix this TV, spending the necessary time and tools (oscilloscope or others) to get it back to life as there are not many of those TVs around. I also have a keen interested in learning this stuff.

I started to measure some voltages using my multimeter.
The power board (board F2) is working fine, giving the required 136V and 12V where needed.
Then I checked straight to the neck board (see my markup)
I got 135V on one of the pin as well as 12 volt on another, which is as expected, I believe.
On H1 and H2 I could barely read 0.1V using my multimeter (not sure how meaningful this measure is)
I could not measure 1000V as I have no tools for that. I believe the issue is on the HV side, but I don’t know exactly where at the moment.

Attached are the diagrams with some markup on voltage measurement I made so far.

My questions are as follows:
1. Is it possible to blew up the HV side by omitting connecting the signal board?
2. How can I check the 1000V? There is a testpoint 8 near the transistor Q2591 that generates 1000V.
3. Could it be the flyback wheel. How can I test this component?
4. Do I need to buy an oscilloscope for this repair?
5. Any other insights are welcome on where to look at for diagnostic

Thx for the help.

https://drive.google.com/file/d/1qOq...ew?usp=sharing

[zeno]

The picture you drew shows a "PIN" or pin cushion problem.

Sony & others had cold solder joints in the following areas.
Horz drive, horz drive transformer, horz output, vert output IC, Small 3 legged regulator IC's also the main power supply board. I would check the HV, CRT & power supply boards for cold joints first.

HV can be detected by checking the 200 VDC at the CRT socket.
If you have 200 V you have HV. Also the H1 & H2 run off the HV.
They are the heaters. If no HV the filaments will not light.

Hope that helps, good luck

Zeno
LFOD !

[Benyamin39]

Thanks that is much helpful,

I looked at the PCB and found 2 locations where soldering points turned yellow, probably due to heat (whether excessive or not).

https://drive.google.com/file/d/1Sbl...ew?usp=sharing

One is the HOT. I need to remove the HOT to test it, which I have not done yet. I will order a replacement part anyway.

The other part is the primary side of the horizontal drive transformer (T2502). The primary side is open. So I need to replace that part for sure.

the part number is 437-195 14 (T?)M

The issue is that I googled on the web and it is very difficult to find replacement horizontal drive transformer. All I found is a close reference
1-437-195-11 Sony Transformer Hori.drive.
I could not find any store where to buy the part. Is the only solution to salvage an existing Sony television?

https://drive.google.com/file/d/1SYq...ew?usp=sharing

[zeno]

The 2nd number looks correct. Most Sony small parts start
with 1- or 8-. Often a partial part number is printed on the part.

Opens are rare on these so look at where the wires hook to the
terminals, may be broken off.

Zeno

[Benyamin39]

Thx Zeno.

You are correct, I retested again the transformer and it is ok! (I get very often false readings when I do this troubleshoot work, I need to practice more I guess).

Silly thing one of the connector between boards was not plugged properly. I realised it after disassembling all the board and reassembling them. I prayed and ... the TV went back to life! Pretty cool and also my RGB modding is working perfectly. I won't touch anything anymore.

Now I need to calibrate the tube.

Thx again

[zeno]

Glad you made progress. If you are doing the PIN problem
next watch the diodes around the Hoz output. Also electrolytics
in the PIN circuit. Its best to use OEM semi's if you can find them.

Adjustments are often done through an OSD service menu. If you
change anything there ALWAYS write down the old number so you
can go back if needed. Also when you exit the menu it wont
save the settings if you dont follow the manual.

C U Later
Zeno
LFOD !

[Benyamin39]

I don't have pin cushion problem anymore. I have started to calibrate the CRT and I get the picture mostly right although it is still far from acceptable. I will post another message tonight with picture.

Thx again

[zeno]

G-2 adjust.
1) Turn up til you see retrace lines then back down til they go away.
2) Turn down the brightness & contrast. In dark room be sure there
are no lines. If there are turn G-2 down til they go away

Notes
Do all CRT set up with color OFF.
Rings for center adj. Tilting yoke for side, T, & B convergence. Little
taped on magnets for corner purity correction when needed.
Its normal for the R,G, & B to have different voltages.
For grey scale use a staircase pattern if you have one.
Run the brightness & contrast about 1/2 - 2/3 to do adj.
Always warm set up 1/2 hr before doing CRT adj.

If your grey scale changes as the set warms its probably the CRT a little weak. Turn off color & watch it as it warms.
A weak CRT will usually look better at lower brightness & contrast
with no bright lights in the room.
Also the 200 V for the RG & B outputs has to be clean or you can get
very small problems. True for ALL brands of solid state sets.
C839 is almost always the problem.

good luck
Zeno
LFOD !

[Benyamin39]

Hi Zeno,

I have adjusted up the G-2 as per your instruction (got the retrace line, and backed off). It is all good on this one and I actually the voltage on the cathode is now close to what the service manual was requiring (185V). So I have cleared this one.

Also to clear any uncertainty I also replaced one the neck board transistor driving on the green line. Voltage on the green cathode is now close to other color values (when no input signal, ie black screen)

I adjusted the white balance and I see some slight improvement. White is getting closer to true white without me having to go all the way up on the green and blue drive settings.

I adjusted convergence (yoke tilt to align left/right, top bottom and then I adjusted and added convergence strips) and I got satisfying results now. I should get across the line on convergence and geometry issues also.

Overall the picture is ok, still on the slight pinkish tones thought.

The remaining issue is that the picture is actually rather dim. In retrospective and after having done all those adjustments I realize that I could have figured out the dim screen symptom right from the beginning.

I run the greyscale picture test and the color does not change when the TV is warming up. No afterglow either.

I did some research and I wonder whether the emission gun is getting weaker. Am I correct? I don't think I have a chance to find a replacement tube for this TV (29in, likely from Europe?), so I am thinking of boosting the heater a bit by lowering R705 and R706 (2 5.6-ohm resistors in parallel) or find someone doing rejuvenation in Toronto area? Do I have any other option?

Thx

[zeno]

One thing USA Sonys have is AKB ( Automatic Kine Bias ).
With this the grey scale is automaticly adjusted. I wonder if
your set has a slightly weak CRT & that is part of the problem.
If you want to see if it has it you can shrink the vertical & see
if it has 3 color lines at the top. R, G, & B. What they do is fire each
gun, measure it then adjust it during Vert retrace. On US Sonys
a weak CRT will cause the video to blink on & off. This happens
most when cold & gets better with warm up. Eventually the
CRT gets so bad that the set wont get a picture.
I asked Sony about this & they said they dont want a Sony with a bad
pic so at a point it just wont work.

Last thing is a bit risky. There is a resistor in series with the heater
about 1 or 2 ohms 1W. It may be the ones you mentioned. If
you jump it out the heater will go up & we often saved sets
for a few years. There IS the risk of damaging the CRT & loosing everything.

73 Zeno

[Benyamin39]

This TV have also AKB. I deactivated it and the picture is very Red, so the AKB has reached its limits. Definitely the tube is very old. Somehow I can understand Sony's policy back then to shutoff the TV past a certain point.

I tried to boost the heater voltage by about 30% but that did not change anything. I read somewhere that not all tubes can be boosted that way.

I ended up dismantling the TV to keep the PCB as spare parts and the yoke and magnetic strips. The good news is I just found recently in my neighborhood someone selling a very similar model TV KV29-J MF1. The tube is still in very good shape, the convergence pretty good. I just had to apply 2 magnets to correct the geometry and I was good to go.

It was a good learning, thx for all the tips.