repairing crt tv, start with recapping

[2takt]

hi,
i have a telefunken palcolor bs 570 dv chassis 619. when i turn on the tv the screen is distorted this will go away after 1hour on(this time will shorten if the tv gets used more frequently).
i think the vertical is the issue because the horizontel lines appear right to me.

sofar i have cleaned the chassis, tube and case. i have reflowed the neckboard. used deoxit on all connectors.

now i want to start with replacing some caps: neckboard, north south modul and the "control and teletext modul". after this i want to recap the mainboard of the chassis including psu and then finaly start with IC swapping.

i dont find any datasheet on my caps, can anybody tell me what they are rated or give a number to the next rated cap? i have phoned rubycon germany, 4 distributors nobody could help me. this is the first time ordering caps by myself, i tryed to get into this stuff for 2 years but only ordered packs for specific electronics.

my caps and series(i think) is:

Rubycon CE W

Tosin TSM

Samhwa SU or SQ(not shure about that)

i have service manual for the tv but there is only the uF rating listed if anybody needs pictures just tell me. thanks for helping me
daniel

[2takt]

forgot to mention i have searched the rubycon site for this series no result, also found a list for old caps but they only go back to 1998. mine are from 1990-93 (1m9310).

tosin i couldnt find the site, only found toshin but i have read they are taiwan and tosin is japan!?

i didnt look up the samhwa cap

[MosherIV]

Hi.
I would advise against replacing capacitors. You might do more harm than good.
The need to replace capacitors came along with switch mode power supplies, they have high freq switching meaning they put capacitors through higher ripple currents, wearing them out faster.
Old crt tvs would have linear psu with fly back to generat the 30KV needed to accelerate the electrons.

Just fault find the bad cap in the vertical or horizontal timing circuits. This may be a ceramic or other non  electrolytic cap.

Good luck 

[2takt]

hi mosher
dont they go bad on theyre own(electrolytic)? and the tv is somewhere at 30 years old.
currently i cant tell you which psu is used on my tv, i will figure this out in the next days.

iam currently waiting on my in series esr tester, hope it arrives till friday. thanks i hope i find something.

one last question i also ordered this cheap oscilloscop dso 138. the service manual says:
the chassis is isolated from line voltage. the isolation point is in the line section.
can i measure the chassis without a isolating transformer?

[vk6zgo]

Hi.
I would advise against replacing capacitors. You might do more harm than good.
The need to replace capacitors came along with switch mode power supplies, they have high freq switching meaning they put capacitors through higher ripple currents, wearing them out faster.
Old crt tvs would have linear psu with fly back to generat the 30KV needed to accelerate the electrons.

Not necessarily, SMPS were commonly used in TVs from the mid 1970s.

A few TVs sold in EU used a SMPS to supply both operating voltages & EHT, but this was unusual.

Most TVs indeed used a transformer variously decribed as a " Horizontal Output" transformer, or an "EHT" transformer, or less commonly (at least in Oz) as a "Flyback" transformer.

The electron beam "flyback" during line blanking requires a very fast transition in the current through the yoke, & hence the transformer.
A multiple turn secondary produces high peak votages during this transition, which in turn, are rectified to provide CRT tube EHT.

Just fault find the bad cap in the vertical or horizontal timing circuits. This may be a ceramic or other non  electrolytic cap.

Good luck 

OP--- Your fault doesn't sound like it is necessarily a capacitor.
I would nominate a dry joint or similar.
If it comes good when the TV warms up there are two ways to approach it.

(1)While the Fault is on, heat up various likely points on the board with a heat gun.
(2) When it is warm, with the fault no longer evident, use "freeze spray" to strategically cool various likely points.

(2) Is usually best to pinpoint the problem, as the heatgun can't target a very small area.

[Brumby]

(1)While the Fault is on, heat up various likely points on the board with a heat gun.

I suggest you don't use your average DIY heat gun you might have in the garage that can be used to strip paint.  It could easily destroy things.

However, if you really must - be very, very, very, very careful.

[vk6zgo]

(1)While the Fault is on, heat up various likely points on the board with a heat gun.

I suggest you don't use your average DIY heat gun you might have in the garage that can be used to strip paint.  It could easily destroy things.

However, if you really must - be very, very, very, very careful.

I have used just such a gun to heat components on boards, or for shrinking heatshrink, many, many times.
Actually, they are pretty lousy at stripping paint.

Their main advantages are that they are, at the one time, much cheaper, & more reliable, than the outwardly similar units especially made for use in Electronics workshops,

It is easy enough to be careful when using them, but if it scares you, a hairdryer is more gentle.

[MosherIV]

I do volunteer work at a computer museum. The stuff we maintain ranges in age upto 50years old.
We never re-cap any of it. Only the stuff 40+ years old do we even look at checking old caps.
Even then, only really bad ones are replaced.

[2takt]

thanks for your replies.

i have an hairdryer and no cold spray but i will order one today!

i have read this chassis has often problems with bad solder joints. what i have thought is a cold joint would always requier the 1 hour warmup, but if i have it on today and maybe tomorrow it would  be fine the next day in 15mins(this testing was done 6-8month ago). so i assumed its a cap thats regenerating itself but iam no professionel electroniks repair man.
one has said it was a ic that caused his issue but didnt write which ic he had swapped.

so the new plan is get this cold spray and see if i find something. if nothing then reflow all the joints.

the boards look good to me the faults i have seen sofar are the big psu cap has little bulge on top.
on the left side of the mainboard is what looks like capacitour fluid(dryed white lines). but there is only the audio board and no H or V stuff.
on the neckboard there are 3 (i think for rgb) big resistors. the pcb it has a darker color here assume its from heat.

ok 40+ years is a point! but i have read capacitor shell life is 2 years so i assumed 30years would make the electrolytik inside not so good anymore.

can anybody tell me if i need the isolation transformer for testing with oscilloskop?

[MosherIV]

Before I got rid of my old 29inch crt tv, I could visually spot the dry joints. Many of them did not cause any noticeable problems, so I left them alone.
The tv did develop a vertical scan problem: top 15 lines would have larger spacing than normal. A good hit to side of tv sorted it out or just left it to warm up. When this stopped working, I looked up the vertical scan circuits, sure enough there was a dry joint in that part of circuit. Re-soldered that single joint and the tv worked perfectly.

If you think there is a bulging cap, change just that one cap. If you have esr meter, confirm tha cap is bad.

Leaking cap electrolyte is normall dark in colour. Still try and trace the source of the whit marks.

Yes, it is normal for large power resistors to generate heat. If it is starting to badly scortch the pcb, that needs investigating. Be careful, the line scan coils are driven with a few hundred volts.
The circuit on the tube rear also has the eht (30KV) so be very careful !

Yes, old crt tvs should be powered through an isolation transformer if you are going to probe with oscilloscope.

[2takt]

here is the big psu cap 330uf 385v rated, so this one is bad

[2takt]

that sounds like my old sony always have to give him a little smack on the side xD
i will check the rest of the caps with my meter then i begin the reflowing.

so the isolation in the tvs psu is not enough for oscilloskop use?



and here is the resistors and the white dryed fluid. hoPe you can see it

[Gyro]

here is the big psu cap 330uf 385v rated, so this one is bad

Nope, that still looks acceptable for a 330uF non-SMPS high voltage capacitor.

[2takt]

ok i found 1 and the display said good if <1000uf the cap was a 1000uf. so this should be good too?

update my esr meter just gave up on me. had serveral zerroing errors. now it show 0L when shorted great

[Benta]

In all the CRT TVs I've repaired (and they were many), the primary fault mechanism was to 99% solder joint failures. Secondary component failures then followed as collateral damage.

The high voltage horizontal and vertical deflection circuit is the part of your main board that's most prone to failure due to high thermal and mechanical stress. Thermal, because it gets hot, and mechanical because the parts are heavy (compared to a resistor).

A simple reflow of the main board will not help. A manual resolder/reheat will also not help.

You'll need to remove the old PCB solder joints under the high voltage components (solder wick, rework station, whatever you have) and resolder them manually with Eutectic electronics resin solder (60/40 or close). Modern lead-free solder will not work on components this old.

Why? The old solder joints have one or two issues.
First, they're oxidized over the years and a simple reflow will not break the oxide.
Second, There's a production issue called "Tin Depletion". Tin has a higher affinity to copper than lead, so when several thousands of PCBs have been run through the wave soldering machine, the solder is no longer eutectic, but lead-heavy. Quality manufacturers monitor this, but it was an issue 50 years ago.

SAFETY ISSUES:
1: make certain that all large capacitors are discharged (easily done with a multimeter).
2: discharge the CRT. Connect a wire between chassis ground and an insulated screwdriver. Press the point of the screwdriver under the "suction cup" on the CRT.

Let us know how you get along. Cheers.

[MosherIV]

Hi.
Agree with Gyro. That 330uF sounds ok.
Generally speaking, most electrolytics caps have esr less than 2 when good.
If you measure more than 10 then it is bad.

Also agree with Benta. Your primary problem is likely to be bad solder joint some where.
I did not know about tin depletion.
I did as Benta suggested, I removed the old solder and re-soldered with fresh 60/40 solder.
I did not do the whole HV section, just found the single faulty joint and re-soldered it.
TV worked for at least 7 years before the next fault. Could have repired it (total loss of vertical scan, just left with bright horizontal line) but it was 20 years old, 4:3 aspect ratio so decided to get shiny new flat screen 

[2takt]

so esr meter had a really bad cold solder point where the probe attaches. need to clean it tomorow, has a lot of loss solder on the pcb. but seamed to work fine.


i did discharge the tv befor doing anything the caps seem empty to me(had a philips cdi psu that shocked me already)

i already ordered a desolder station should arrive next week
my solder is:
https://www.rapidonline.com/stannol-535236-solder-wire-hs10-sn60pb39cu1-0-5mm-100g-50-3997
is this ok to use? what flux do you guys recommend?

i did notice that when i reflowed the neckboard that the solder points didnt look as shiny as normal.



i will keep the 10ohm in mind when further testing. maybe i should ask a friend to look for the joints, 4eyes see more then 2.
same thing happened to my sony 10years ago

[Benta]

That solder is fine, there's no need to use additional flux, it already contains colophonium. You'll get wonderfully shiny joints after removing the old solder.

Don't forget to discharge the CR tube, I'll give you one hell of a whack if you don't (up to 1 J)

[james_s]

Problem that improves as it warms up is a classic symptom of failing capacitors. The most common fault like that I see in old CRT displays is a worn capacitor in the vertical deflection circuit causing foldover when cold.

[vk6zgo]

Another common cause of distorted ("folded over") vertical scans is that the vertical (& audio) output stages are fed with a highish voltage (usually around 150v) derived from an overwind on the Horizontal output/ EHT transformer.
The 15kHz output of this is rectified using a halfwave rectifier, then filtered by a fairly small caoacitance, but high voltage rated Electrolytic capacitor.
(This same system was used in the valve days, when it was called "boost HT")

If the Capacitor fails, the filtering is radically degraded, affecting the vertical scanning.
If the rectifier fails, the same thing happens, but more so, as the vert stage supply reverts to the quite low "start up" voltage, & will be unable to perform its function.

Fix?----Easy, replace the rectifier or capacitor, or both.
But wait! there's more!

A trap for young players exists, in that the capacitor has to be a "high ripple" type.
(Well, that's the old terminology, which I guess, translates to a very low ESR in today's talk!

The rectifier is a "fast recovery" type.

If you fit ordinary old caps or rectifiers, they will work OK for a few minutes then let the magic smoke out! 
No prize for guessing how I know this!

Strangely, I first came upon this problem not at work, but on my Mother in Law's  TV.
It had the classic "fold over" symptoms, but my old Fluke 77 read the largely unfiltered output as around 103 v DC-----Not the 150v it was supposed to be, but, I felt  "not low enough to cause the problem".

When I dragged an old BWD home from work, I was confronted with a "copybook" display of a unfiltered half wave rectifier output.

From this, I learnt  another useful lesson.
DMMs can be fooled by strange waveforms, although more modern ones may be able to tell the difference.
I'm not sure, as I don't have a modern DMM.

 

[2takt]

i have added the pictures of the screen on start up and after it fixes itself

i worked quite a bit with this solder and very happy with it. i dont want to find out how it feels

yesterday i saw a video from retromancave but the other way round, after the pc warming up the screen starts blinking and then goes completly away. he fixed it with recapping the whole board.

i dont know what foldover means or is this my failure in the picture?

the speakers have a bit of hum when the tv is on, so this does matter?
i did find some low esr caps befor the meter quited on me yesterday.
the rectifier is just an arrangement of diodes? like the full bridge rectifier containing 4 diodes

i will post you an update if i find something with my now working esr meter
thanks again for all your help

[xmetal]

Most TVs indeed used a transformer variously decribed as a " Horizontal Output" transformer, or an "EHT" transformer, or less commonly (at least in Oz) as a "Flyback" transformer.

It's also known as a LOPT (Line output transformer) in the UK.

[2takt]

this green yellow white and red pieces in the picture,  are this film capacitors?

i only have found one cap on the chroma modul labeled 470uf 6.3v with esr of 0.219. meter says good if < 470uf

i couldnt read all the values. will have to wait for the desolderstation then i will get the shielding/heatsinks out of the way.

on the front input panel i have 331j (ceramic?) caps the meter just reads 0L is this normal

[xmetal]

I think they're polyester film capacitors from first looks.

[2takt]

the red ones says 0.12j so there are 100pf/0.1uf with 5% tolerance?