KV-1800UB barn find

[djrm]

Yes you were quite right Trevor.
Photo shows cause and effect, leaky supply decoupler caused resistor failure.
There is now snow showing n the screen. I think my test generator is on the blink or there is still a video problem.
The faulty capacitor is hidden between two signal boards, not far from the video output transistors and collector load resistors.
I'll try another signal source next, tomorrow I may clean the cabinet if it looks like its going to work.
Kind regards, David.
   

[djrm]

Yay, its showing a picture now. There is something wrong with my colour bar generator,it just shows a blackscreen.
I should have bought that nice Philips one when I saw it for sale.

The photo is taken from an old VHS tape I have - Mr Motivator actually.
However the screen is too dark, even withthe screen control turned up full.

I cleaned the case and tried to wipe the black mould spots off the front of the tube - I was very suprised to find it was inside the glass.
Either there is an implosion shield or the tube is so flat its let damp in ;-)

Something to look at tomorrow, I'm going to struggle now without a schematic.
A bonus is that last time I tried the VHS recorer it wasnt working, today I wound the tape on a bit and now its ok
.
Kind regards, David.
   

[Murphyv310]

You'll never get black mould inside a CRT. Also these are not twin panel tubes.
I've had many arguments with customers who demand a new tube only to curl up in a corner when the face of the tube is cleaned with an abrasive cleaner like Jif cream cleanser.

[Mark Hennessy]

Agreed - there's no way it could form on the inside of a still-working CRT. To me, the first of the 4 images shows quite convincingly that it is on the outside. Time to get a bit more aggressive with it

Good progress so far - pretty amazing when you think about how it's been stored. Not surprised at the picture at this stage; I wonder how much better it will get when you've had a go at setting it up?

[djrm]

Hi Trevor,
I was, of course, joking about mould inside the tube.
However the black marks are definateley not on the outside of the glass.
This morning i have adjusted the main power supply to the reccomeded voltage, this has perhaps slightly lightened the picture but it still looks dark. i.e. the black level is too dark. There is enough contrast and focus is so-so. Last night I cleaned the case and today I put it all back together again. 
I cant do much else until I get a decent test signal into it. I have a colour bar program on my CP/M computer, I'll try that when I unpack it.
Kind regards, David.

[ppppenguin]

I've got a (monochrome) CRT with a small black mark inside the glass. Just one small mark, alas near the centre, not a whole load of marks. It was due to a less than perfect CRT rebuild. Since the rebuild had been done as a favour I wasn't going to complain. In case anyone's wondering, this was in the mid 1980s when tube rebuilding was still available commercially.

As an alternative to Cif you could try Brasso or T-Cut.

[Mark Hennessy]

This picture shows what I see as dirt/mould on the outside of the glass. Are you talking about something different to this?

I don't think I've come across problems with the phosphor layer breaking down on a colour TV before, but that's the only fault mechanism I can think of. Or perhaps contamination on the shadowmask, at a push. But in a working CRT that still has a good vacuum? I guess anything is possible, but it would be a new one on me. My experience is later sets though - the oldest sets I have significant experience with is the KV1820, as mentioned earlier. Probably saw about a dozen of those - I worked in a TV shop for a couple of years around the turn of the 80s/90s, and helped deliver countless new TV sets, and usually took away the old one. There were large numbers of KV1820s - they obviously sold well in the area, but then our competitor just a few doors up was a Sony centre, which might explain it

Couldn't resist a quick look on Google Maps - was slightly surprised to see both stores appear to be there. I knew the one I worked for was still going (they're a Euronics store now), but didn't think there would be room for 2 on the same street in such a tiny town (though the website of the other one is not exactly forthcoming about what they might do).

[djrm]

Greetings, thanks for the comments. 
At first I thought I must have been mistaken and have tried again to remove some of the marks by rubbing with wire wook in the corner, no change.
Just now Ive tried a more scientific experiment, I marked a dot with a cross and took a video moving aroung from left to right, you can clearly see the dot is not on the surface of the glass. It is also aparent thet the dot is not on the phosphor surface, there are shadoows of the dots on the phosphow which move around when a torch is shined ontot eh scvreen - these appear brownish on my video here: https://photos.app.goo.gl/zEUfUBc52FKZkMRb8
I wonder what it could be? David.
   

[Murphyv310]

That is very very odd.
How that can happen beats me. It has to have been like it from new. I'd like to see the set in the flesh to be fair.

Try giving the screen a hard slap with the Palm of your hand and even turn the set upside down and repeat the slap and see if they move.

[ppppenguin]

It's as if there was some loose stuff in the CRT and it's landed on the aperture grille. One suspect would be a faulty getter.

If you can turn the set on its back and support it without damaging the back, tapping the CRT face might cause some of those bits to drop back towards the gun.

In any case, if this stuff is in the CRT, the CRT is realistically a goner.