29-07-2012, 02:28 PM
There is one problem that many sets have that is not caused by a courier's football match. The fact that somebody had 'been there' first. I was thinking this as I finished doing a Pye P116 set that had a simple fault that had taken ages to cure because of the person who had been there before. I sorted it in the end, by fair means and foul. But as it played away in the workshop, I wished for a simple job.
This was rare for me in itself, as I do enjoy fixing what most people would scrap. This comes from my PMR days, when various types of Taxi Driver used to bring in utter garbage and I was the only one in the workshop who would touch it sometimes and I used to get most of it going.
My eyes fell on a portable TV that had sat there for about a year, and the fact that it was supposed to work meant that it would be simple to sort, I thought. So, onto the bench it came and, with me being a man, I just plugged it in and stood back.
The sound, in the form of a hiss, came up but there was no sign of any vision on the screen. I twiddled Brightness and Contrast but still got nothing. So, heaving a sigh and reaching for a screwdriver or two, I disconnected the mains and removed the screws that held the back on. I then looked at the valves, reseated the PL81 and tried again.
Nothing.
One of the happy habits of a neon screwdriver is that when it is held against a LOPT, or any line output valves, it will light if there is any activity in the line output stage. Of course there was none, and not any form of a spark from the top of the PL81.
Putting the set on its front so I could look at the circuit board immediately told me why. Some person had been soldering the line hold control and the power supply with a blowlamp, or so it would seem. Testing round the power supply revealed that one HT line was missing and looking back with the meter showed me where with a loud crack. Dilys was behind me at the time and started singing 'Go and get the fire brigade, get the fire brigade, let the building start to really burn.'
'What do you mean', I asked her.
'Nothing', she replied. 'I was singing a 60's classic as I was dusting'. There are often loud bangs here!
The area needed some work. So I pulled the mains from the set and carried on using the ohmeter. I soldered all the joints I could around the smoothing cap and the nearby fusible resistors, sometimes using wire when the print was not serviceable.
Then I moved to the line hold control and again, using a length of wire and my wits, it soon read OK. Right, time to try again. With the set reconnected to the mains the sound came up, then there was line whistle and a raster. I then set the hold controls mid way and connected up the trusty 405 line generator.
The 1Khz tone came through and a couple of twiddles with the hold control brought in the line hold, but the frame hold was still dodgy and the frame lock could be made to come and go by moving the control. After a few prods with the iron, the frame hold and lock were stable.
The picture was low in width and off centre, so I tried a new PL81 and adjusted the tube controls to re-centre the picture. That improved it a lot, but while I had the set apart, I checked all the other parts that had been replaced. I let the set operate on the bench for a bit as I gave the back a clean.
I'd actually got this far without a circuit. Mainly because I was too lazy to get one. I know that I should have, but working with odd branded stuff often means that I am trained to work without. I would also note that 405 pictures are so good that one does wonder why we bothered with 625. One thing which I do want is a Contrast knob!
Pictures below were taken with a mobile phone – but if you're as much of an anorak as me, you should recognise the programmes here.
Cheers,
Steve P.
This was rare for me in itself, as I do enjoy fixing what most people would scrap. This comes from my PMR days, when various types of Taxi Driver used to bring in utter garbage and I was the only one in the workshop who would touch it sometimes and I used to get most of it going.
My eyes fell on a portable TV that had sat there for about a year, and the fact that it was supposed to work meant that it would be simple to sort, I thought. So, onto the bench it came and, with me being a man, I just plugged it in and stood back.
The sound, in the form of a hiss, came up but there was no sign of any vision on the screen. I twiddled Brightness and Contrast but still got nothing. So, heaving a sigh and reaching for a screwdriver or two, I disconnected the mains and removed the screws that held the back on. I then looked at the valves, reseated the PL81 and tried again.
Nothing.
One of the happy habits of a neon screwdriver is that when it is held against a LOPT, or any line output valves, it will light if there is any activity in the line output stage. Of course there was none, and not any form of a spark from the top of the PL81.
Putting the set on its front so I could look at the circuit board immediately told me why. Some person had been soldering the line hold control and the power supply with a blowlamp, or so it would seem. Testing round the power supply revealed that one HT line was missing and looking back with the meter showed me where with a loud crack. Dilys was behind me at the time and started singing 'Go and get the fire brigade, get the fire brigade, let the building start to really burn.'
'What do you mean', I asked her.
'Nothing', she replied. 'I was singing a 60's classic as I was dusting'. There are often loud bangs here!
The area needed some work. So I pulled the mains from the set and carried on using the ohmeter. I soldered all the joints I could around the smoothing cap and the nearby fusible resistors, sometimes using wire when the print was not serviceable.
Then I moved to the line hold control and again, using a length of wire and my wits, it soon read OK. Right, time to try again. With the set reconnected to the mains the sound came up, then there was line whistle and a raster. I then set the hold controls mid way and connected up the trusty 405 line generator.
The 1Khz tone came through and a couple of twiddles with the hold control brought in the line hold, but the frame hold was still dodgy and the frame lock could be made to come and go by moving the control. After a few prods with the iron, the frame hold and lock were stable.
The picture was low in width and off centre, so I tried a new PL81 and adjusted the tube controls to re-centre the picture. That improved it a lot, but while I had the set apart, I checked all the other parts that had been replaced. I let the set operate on the bench for a bit as I gave the back a clean.
I'd actually got this far without a circuit. Mainly because I was too lazy to get one. I know that I should have, but working with odd branded stuff often means that I am trained to work without. I would also note that 405 pictures are so good that one does wonder why we bothered with 625. One thing which I do want is a Contrast knob!
Pictures below were taken with a mobile phone – but if you're as much of an anorak as me, you should recognise the programmes here.
Cheers,
Steve P.
If we've always had that, why is the car boot open? You aren't smuggling in another old TV are you...?
