KB 027 Help wanted

[marcus 3500]

Hi All

Over the last 3 or more months I've been staying in my old bedroom at my parents' house and not at home; so late on a night I've gone in my workshop and started to look at some of my faulty sets.
This one is a KB 027 dual standard B&W set that uses the VC52 chassis, I think.

The fault is the picture is not stable; it's running too fast sideways. None of the controls at the back ( H hold V hold ) make much difference, but the worst thing is it looks like the EHT overwind over the years has been slowly melting away - the set was used on Saturday for over an hour, while checking to see if the lopt would start to melt again, but it didn't.

I think I can remember reading about a similar fault in an old copy of tv mag (readers' help section) and the cure for the sideways rolling picture was a valve?

Any help would be appreciated: this is my first B&W valve set repair; most B&W sets I've had over the years have simply worked first time or have had the odd valve missing only.

I'm going back up to my parents soon. Im looking at a HMV 8000A tonight, but will take some pictures of the KB switched on and try and post here tomorrow.

Regards

Marcus........

[Steve_P]

Hi Marcus. Glad you're OK. Seen it all on Sky News...

The sync separator is part of V8. (PCF80). The line pulses are fed via C71 to the line oscillator. The frame is fed to the cathode of V7 (PCL84) - The triode section - Pin 3.

Cheers,

Steve P

[Brian R Pateman]

Hi Marcus,

Thought you weren't going to be around much

I always liked these KBs and found them to be pretty reliable, right through to the late 80s when I packed up. When I got rid of my rental fleet I still had two of these out which I gave to the renters as a sign of long service!

Try the simple thing first and give the standards switch a good clean.

Regards and good luck,

[marcus 3500]

Hi All


Here is a pic of the KB.
I'm going to spend a couple of hours on it tonight. I didn't get a chance to look at it last night - decided to have a few drinks instead, as it was my birthday yesterday.

Regards

Marcus........

[Tazman1966]

Hello Marcus and belated birthday for yesterday

I take it that the picture on your KB would've looked like that even if it was perfect after a few beers.

It looks like the frame is synchronised and as you say the line is running too fast. First off does the horizontal hold control do anything at all? Can you get a picture to sort of float across the screen sideways if you very carefully adjust it. If not check the control itself and the series resistor. You could always try changing the line oscillator valve (PCF802?).

Not much help I know but let's keep the encouragement going!!!

Regards,

[Focus Diode]

The KV025/1 model I used to have was identical in style but fitted with a 19" CRT.

Looks as if the line hold is miles out. As Brian says check the easy things first such as the system switch. Do you have 405-line facilities?

The usual cause is R131 (47K) from the HT line to pin 8 of the PCL802 or the discriminator diodes. It's also been reported that the anode coils occasionally suffer from s/c turns in extereme cases.

This is, of course, assuming the PCF802 and PCF80 are ok.

The melted overwind pitch could've been the result of the set operating in hot conditions, if it ran cool after an hour's operation I wouldn't worry about it. It certainly has nothing to do with the line hold problem.

Hope that's some help.
Cheers,
Brian

[Zelandeth]

Unfortunately I'm on holiday at the moment, so my net access is a bit sketchy...wanted to reply here though.

Doesn't look like it should take too much to get that up and running, probably just a couple of caps and/or resistors needing changed. These sets are a bit daunting to the uninitiated at first glance thanks to being hand wired, but in reality are easy enough (if at times a bit awkward - the component you need to change is always the one most deeply buried in the ratsnest).

I wouldn't worry too much about the appearance of the LOPT, my KV024 (VC51 Chassis) has a rather sorry looking LOPT, but it works just fine, despite a puddle of wax having collected on the bottom cover of the cabinet over the years. Shame the same wasn't true of the CRT in my case. Looks like the VC51 and 52 are very similiar, took a few seconds of looking at the photos to start noting the differences.

Will be watching this thread, nice to see a set similar to mine being revived.

First thing I'd probably try would be to sub the PCF802 and PCF80 (assuming you've got known good spares to hand). Other than that, start having a hunt around for suspect looking capacitors and resistors.