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Toshiba CRT TV fault... what could the problem be?

alex1878

Aug 11, 2016
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I've got an update on the Toshiba TV. I got a local guy who still repairs CRTs to take a look inside for me:
tv.JPG
He says that the PCB is broken in half around the flyback transformer so it is not repairable. :(

Will have more on the colour bleeding one soon.
 

debe

Oct 15, 2011
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Ive repaired plenty of broken circuit boards on TVs that have been droped. Just clean up tracks & bridge with wire on the tracks. Heres a pic of a broken PCB in a Furuno radar transmit board, works fine now. This unit took a hamering on a small planning hull boat.FURUNO 23.JPG FURUNO 18.JPG
 

73's de Edd

Aug 21, 2015
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Sir alex1878 . . . . . . .

An extra "parasitic" winding on the flyback transformer gathers enough 15,734 ~ frequency power to be rectified and then supply an ~ 180 VDC voltage via the YELLOW arrow path to the kine driver board of the kine . . .beside it .

It is then dependent upon the C901 to remove ALL 15,734 artifacts and adjunct trash from that DC supply, or it will modulate and contaminate the otherwise clean video coming in / created for the picture tube . . .kine.

Thassssit

YOUR EXACT SET:

KINE DRIVE BOARD TOSH.jpg


Addenda:

I just now caught that very questionable . . .

" PCB is broken in half around the flyback transformer "

but . . .but . . . BUT . . .BUT . . . BUT! . . .BUT! . . .BUT!
they dont's puts no flybacks on kine drive boards !

Give us a good, sharp, close up of that kine driver board at the rear of the
kine socket.

Aside . .Debe . . .
MMMMMMM . . . . .magnetron . . . .MMMMMMMM . . . .droooll
good save on the PCB . . . .(but I would have used tinned copper foil)


73's de Edd
 
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alex1878

Aug 11, 2016
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Thank you for your detailed replies (and the diagram for my model!), debe and 73's de Edd!

@73's de Edd
-please could you explain to me what you mean by "kine" / what is "kine"? I haven't come across this term before and it seems to be key in understanding my TV! :)

-Are you saying that my Toshiba CRT has no flyback transformer, or just that it is not connected to any boards? What the repair guy actually said was "Toshiba TV is not repairable, the pcb is broken in half around the LOPT" but this amounts to the same thing as what I posted, I'm pretty sure.

-I may not be able to get that photograph you want as the guy has the TV in his workshop and has possibly already replaced the casing ready to give the TV back to me. I don't really want to take the casing off myself due to my inexperience around the high voltages inside.

@73's de Edd and @debe...
-I asked the guy if I could have the broken PCB taken out and given back to me separately when I go to pick up the TV on Monday. He said that this is fine, so I'm going to try and repair it as debe suggested... if I can manage it and there are no other problems in the set, then this should make it work again when put back in, right?
 

davenn

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@73's de Edd
-please could you explain to me what you mean by "kine" / what is "kine"? I haven't come across this term before and it seems to be key in understanding my TV! :)

he's referring to the colour driver board on the end of the tube

Addenda:

I just now caught that very questionable . . .

" PCB is broken in half around the flyback transformer "

but . . .but . . . BUT . . .BUT . . . BUT! . . .BUT! . . .BUT!
they dont's puts no flybacks on kine drive boards !

you mis read ... he didn't say it was !!


@alex1878 ... you really need to do yourself and the poor tech who is going to look at the TV a favour .... get in the with a soft 1" wide paint brush and a vacuum cleaner
and get rid if the thick layer of dust. It's a total mess. That dust can actually become conductive, particularly around the high voltage areas


Dave
 

alex1878

Aug 11, 2016
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Okay, update for everyone... hopefully now we can make some proper progress.

The only thing left in the TV now is the tube itself. I got the TV back today, circuit boards separate:
IMG_20160822_121509.jpg
On Dave's advice, I then got a paintbrush and vacuum cleaner and spent a couple of hours getting it nice and clean:
IMG_20160822_171837562.jpg

The green board on the left and the tube PCB hanging down on top of it are fine. No cracks. The copper-coloured board on the right has a crack at the top and also a long bend (it's very nearly a crack) running from the edge underneath the flyback transformer (top right). You may actually be able to see from the above photos that the right-hand board is lumpy at the top where the damage is. So I removed this right-hand board from the casing - here are some photos of the damage:

CRACK, component side:
100_4469.JPG
CRACK, solder side:
100_4472.JPG

BEND, component side:
BEND component side.jpg
BEND, solder side:
BEND solder side.jpg

I am about to start cleaning tracks and bridging with wire where the crack and bend are, as debe shows in an earlier post. I am also going to check components on the board with a multimeter. I imagine the bend would have affected operation even though it isn't an outright crack?

Do you think that if I correctly bridge the crack and bend, the TV might work again? It was only the picture that didn't show (as you might have seen in the video I posted in my first post). Could the crack and bend have been enough to cause picture loss?
 

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73's de Edd

Aug 21, 2015
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Sir alex1878 . . . . .


I would just like to know WHO dropped / stepped on that board ? (****** BOTTOM OF PAGE)
It certainly didn't get in that shape, just sitting in the cabinet.
Indeed, that crack across the circuit board is being just to the side of the:

AMERIKANSKI's say .. flyback transformer.
(Mamma mia . ..you'a touch'a its'a RED wire and you FLYBACK ! )

Or how you clazee EURO's . . . say . . . . . . . LOPT ( Line output transformer)

And while I am on a roll on some daffy-nitions . . .
Also . . .a kinescope . . .is a . . . CRT (cathode ray tube) . . .is a . . . picture tube.

PROCEDURALS:

Since you already have the chassis cleaned, use a solvent to additionally clean 1/2 in to either side of the length of the exposed crack on both sides of the phenolic circuit board .
Next grasp CLOSE IN on the crack with both hands and VERY (to the power of ten) slowly, micro flex the board crack to let the end flex back and let that very ends slanted fracture overlap again.
( It's currently being cross lapped and thereby being latched apart from surfaces mating flush)
On that rarely created / slanted cracked end, you will have a bit of raw phenolic board exposed, which will give a broader exposed board, whereas, further in towards the center of the board the rest of the board is just having the minimal area of a right angle crack of the board.
Get yourself a small tube of some conventional thin,water clear SUPER glue . . .none of the gels or other variants.
Plan how you can clamp the end of the broken board together. My choice would be either a small"C" clamp or one of the strong little paper clamps.

CLAMPING OPTIONS:
PCB Repair kit.png

Rotate the chassis to place the crack at top, take a deep breath and apply guper slue . . . oooops . . . . . . . my LYS-DEXIA is kicking in again .
The slanted overlap should be a breeze and then just enough glue for capillary action to suck it in on the closed crack down the board to the cracks very end..
IMMEDIATELY clamp the boards very end and let set overnight to assure a rock hard cured setting of the mechanical aspect of the repair..



REPAIR PARTS ASSEMBLAGE:

.Also some jewelers screwdrivers with a standard blade tip, just seem to never get used in one of the dollar kits from a Dollar store.
Its pristine blade end makes an excellent resist scraper of the foil, for either side of a break.
Place its blade tip out about a 1/4 inch from a break line, press into the board at an angle and then draw the blade TOWARDS the crack, repeat for the other side.
Get all of your breaks prepped and then degrease again and initially solder tin across the breaks;
which added wet rosin flux will certainly expedite, and get better solder wetting /adhesion..

PCB EVALUATION . . . . . .by cracky . . . .:

Cracked PCB.png

Next day scrape away/clean any super glue and then overflow a solder bridging of what looks to be about 15 separate foil breaks.

Reconnect connector plugs that go to the board and save the RED ultor lead installation until last.
Find the ultors recessed cavity on the CRT and run a "shorting" wire from one of the the corner metal frame mount(s) over to that ultor cavity for 5 times to see if it had a final weak spark stored away.
(Five times . . . . .because it will keep slightly bouncing back to life . . . . . .weakly.)
Then, you are finally safe to reinstall that ultor lead into its cavity.
In the future, use that same procedure, if you have to remove that lead, but then, you will be having to inch your wire end UNDER the edge of that giant suction cup, that is now blocking connector access..

Any mo' questions ? . . . . .one mo' answer . . . .you say:

Could the crack and bend have been enough to cause picture loss?

I don't see how you got "anything" with its board in that shape . . . .except with an initial shot of high voltage at TURN on that might have caused that weak CRT electroluminescent / illumination,, but for sure, the CRT filament would have not had warm up time, IF it ever was capable of being generated/present.

(*****)
Disregard . . . .I just read back and now I know . . . .QUITE a drop !

I hope that it didn't land straight down on its face and additionally warp the faces internal shadow mask . . . . .with a resultant . . . .permanent distortion of select color reproduction areas.

BUT in the manner of the cracks position and the downward flexure of the PCB mass, from its heavier mounted parts weights, I think that it hit with its very TOP impacting into the floor.



73's de Edd
 
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alex1878

Aug 11, 2016
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Thanks for your help again Edd! I couldn't have asked for more information!

You are correct about the TV landing on its TOP, not directly on the screen. It went from being upright to landing perfectly on its top, doing a 180 degrees flip in mid air.

I have repaired both crack and bend, so as far as I can see, this board is now fine. I was already halfway through the job when you sent me your detailed guide, so I carried on to finish without using super glue or clamps. Despite that, the board is solid now and all of the connections work perfectly!

To repair the bend, I bridged all of the tracks with the bend through them. Some tracks worked okay before the repair and some didn't when tested with a multimeter, but I bridged them all anyway using copper wire from a stripped mains cable. Now all of these tracks work perfectly:
USE 1.JPG

The actual crack went through many more tracks and obviously none of them worked, so this repair was much more time consuming! The first seven tracks were very close together and very small, so I used longer strips of insulated wire (with exposed ends of course) to bridge these. It would have been too fiddly and difficult to make tiny bridges over these first seven tracks. After this, I bridged the rest of the crack using the same smaller bridges of copper wire as before. Now all of the cracked tracks work perfectly.
USE 2.JPG
USE 3.JPG

Tomorrow I am going to reconnect everything in the set and try turning it on. Do you have anything else to suggest I do before doing this? I really don't want to have to take it apart again because it'll have all of the high voltages back once I give it power. :eek: If nothing else in the set is damaged, I think it should turn on... I certainly hope it does after all this!

Just to confirm - by "ultor lead", you mean this lead that comes from the flyback/line output transformer, right? :D
100_4482.JPG

Oh yes, and there was one really big capacitor on the board which sparked when I discharged it with a pen knife. Out of interest... what is this capacitor's role in the TV?
 

73's de Edd

Aug 21, 2015
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Sir alex1878 . . . . .


Ahhhhhhh yes . . . . . . . your top photo confirms the flyback proper almost broken away in a floating island with its foil breaks.
That we didn't see . . . . in the other photos . . .I just concentrated on the portion with almost 15 cross breaks.
Just hope it all works out for you in the test . . . .be ready to immediately yank the power plug on initial power up.
You got the ultor lead identified properly . . . . .its high voltage lineage, being . . . . that its Mama was a car's spark plug wire.
Also you will encounter the opposed spring action of those barbs that constitute the connection that locks down connection within the ultor cavity connector.
Roll the vinyl lip back with fingers across it and then latch one barb into the cavity and press it against that side of the cavity, until it then compresses enough, to let the OTHER barb swing down into the cavity. Then release tension on both and they are then locked internally.
Removal consists of multiple bleeds of stored voltage , until it sparks no more, then a plastic handled standard blade screwdriver pressed internally against one barb lets it then swing in and up and free for a reversal of the install procedure..


Oh yes, and there was one really big capacitor on the board which sparked when I discharged it with a pen knife. Out of interest... what is this capacitor's role in the TV?

That is the sets MAIN B+ storage capacitor that the rectified AC line supplies.
If FULLY charged, it should have made quite a sonic boom and gapped your pen knife blade.

B+ MAIN POWER SUPPLY:

Tosh PS.png



73's de Edd
 
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alex1878

Aug 11, 2016
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I didn't manage to get around to putting it back together yesterday. It will be Friday or Saturday now when I do it, hopefully. I'll keep you updated!
 

alex1878

Aug 11, 2016
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Take a look at this, Edd (and anyone else who is still watching this)... it works PERFECTLY!
IMG_20160826_222714086.jpg

I spent a few hours carefully reassembling the TV last night, and gave the plastic cover a good clean which was full of dust and cobwebs! It's like a new TV in there now.
IMG_20160826_220553983.jpg

The power-on moment was nerve-wracking considering how much time has gone into this over the past week. :D Looks like the cracked board was all that was wrong with it... it works EXACTLY as it did before! Perfect picture!
IMG_20160826_230142323.jpg
Yes... the first thing I did on it was play Chariots of Fire :D

What a rewarding project! I've learned so much doing this. I had very little electronics experience before this but now I know much more about CRTs and electronics on the whole. I think it's a new hobby for me - I even bought a couple of electronics kits while fixing this :).

A big THANK YOU from me to all who have helped me out on this television... I really didn't think I'd see it working again! Thank you to Edd for your detailed explanations and instructions, thank you to debe for letting me know that a cracked circuit board can even be bridged (I nearly gave up on the TV when I found that out!)... and thanks to everyone else who has posted along the way, from early suggestions to the final fix.:)
 

davenn

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What a rewarding project! I've learned so much doing this. I had very little electronics experience before this but now I know much more about CRTs and electronics on the whole. I think it's a new hobby for me - I even bought a couple of electronics kits while fixing this :).

congrats, well done :)


Dave
 
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