Hi all I had a bit of time over the last few days so I thought I would have a look at my Marconi 950. I bought the set some time ago because it was one of the models I used to play around with when I was a kid.
The set was quite dusty inside. previous repairs seemed to be no more than a couple of replacement valves. The PY was cracked so this was replaced, after that the set produced a dark picture with low width, rolling very fast and occasionally collapsing to a line. There was also no sound.
I gave the chassis a careful clean and then started recapping the line output stage. almost every plastic blue capacitor was leaky. Two of the brown moulded ones had swollen and split and read open circuit.
I tried the set after every few capacitors had been replaced and things improved bit by bit, the brightness came up, all the cogging and bending stopped and finally after replacing the capacitors in the frame stage I had fairly good linearity that responded to the controls.
This left the low width with the control not working and no sound.
The low width was just the 1.8 meg in series with the control being very high. I then moved on to the no sound.
A quick flick around the PCL86 showed voltages to be much as expected. I checked the connections to the speaker and then the speaker to find it was open circuit. I can't ever remember having an o/c speaker in a telly before!
To replace the speaker I had to remove the UHF tuner which was a right fiddle to locate correctly when refitting!
After a bit of setting up the set produces very good pictures on both standards, The Mazda "Gold star" has plenty of life left!
However the set has an intermittent line twitch I didn't notice it while it was on the bench but once on the shelf playing a DVD I noticed the picture (or parts of it) sometimes twitches slightly as if the aerial plug was making a bad connection or the line hold pot was scratchy,
It does it on both 405 and 625 both on playback and test card. sometimes it settles down for a while but it is very irritating!
I cleaned the valve pins and holders when I recapped it but that's the sort of symptom it looks like.
I will get it back on the bench at a later date, in the meantime if anyone has any ideas what to look for would be greatly appreciated!
I apologise for the poor photo's I really need better lighting in my telly room!