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Old 3rd Apr 2014, 12:11 pm   #1
Andrew2
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Default The ones that got away...

I hope I've put this in the right section.
Have any of the TV engineer bods here got a ghastly memory of a TV, radio or VCR that simply would not fix?
I didn't have many failures in my 20+ years at the bench, but one sticks in my mind.
It was a big plastic Sanyo CTV, a hybrid I think. The complaint on the ticket was 'picture sometimes jumps'. On the bench there was nothing to be seen and the picture was rock steady, so I shoved it on the soak bench to await some action.
The next time I glanced over at it, I saw the picture was jittering up and down like an interlace fault. I let it develop and then removed the back cover. My first action was to gently reset the frame hold and height/lin pots, just in case. No change. Next I re-dressed the scan coil leads away from the PCB. Hmmm...did that reduce it? I think it might have. But it was soon back.
As the fault had appeared after the set had warmed up, I reached for the can of freezer and sprayed over the frame area, expecting an instant return to normal service. No change. Oh oh, time for a trip to the filing cabs to see if there was a manual for this beastie. I knew there wouldn't be one, as I was in charge of the service sheets and I certainly had no memory of seeing anything for this set. Long before the internet of course. So I stared at the PCB long enough to figure out what made it tick.
Further freezing/heating sessions pointed me to a diode in the frame osc department, so out it came. On the meter it was fine, but I replaced it anyway....and still the frame jittered. Staring at the screen to see if the jitter was triggered by picture content was to no avail.
Scoping the output of the sync sep, all looked clean and tidy, and the integrated waveform fed to the frame osc looked nice too. The usual tapping and flexing of the PCB made no odds.
By now I'd spent several hours on this set and I decided to leave it to get on with something that might earn a few quid. The next day was the same story, with me doing a bit on the set every now and then and failing to make any difference.
The customer phoned after a few days and I stalled her by telling her it was very intermittent (it was) and could she hang on for another few days while I attempted to track down the fault. No problem, she said. I think I would have been happier if she had hit the roof and demanded her telly back unfixed.
So more hours were racked up on this unco-operative TV before I finally admitted defeat and delivered it back myself with apologies and no invoice. Bah!
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Old 8th Apr 2014, 12:30 pm   #2
newlite4
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Default Re: The ones that got away...

I remember about 35 years ago I was called on by some elderly neighbours who had some instability issues on their mid '60s B/W 19" set. Try as I might, I could find no way of removing the rear panel. there were no screws, no clips, no flaps, nothing! After about half an hour of searching for a way in, I had to admit defeat and walk away. A rather embarrasing episode resulting in dented pride.
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Old 8th Apr 2014, 12:55 pm   #3
threeseven
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Default Re: The ones that got away...

Way back, during my days at CES, Leeds branch, I had a job on my bench which was resistant to repair! It was a Philips RH720 tuner amp, you see it must have been bad for me to remember for so long! It had touch controls on the top and there was the fault. It would work fine for days, then spontaneously would start changing the input etc at random and the touch pads would change all by themselves with the indicator lights changing from one pad to the next at random.
So, I followed a logical fault finding process in an attempt to track down the problem. It went from changing a few caps, then the touch pad, some transistors, resoldering joints etc but the fault remained. And the worst of it was that apart from one or two occasions it was the customer who ended up finding it was still faulty and returning it. Now, there was a system at CES for returns with the same fault. Returning just once was bad enough for the engineer concerned, it was called RST, returned second time. Too many of those and you were up before the supervisor. Three times and it was a big grilling to investigate your fault finding skills.
This RH720 was a six timer before the super himself took it off me and said smugly, "watch and learn". I did, and it came back to him 3 times!
It was sent back to head office in Croydon for the special fault team to look at it, last we heard was that it was beyond economic repair for the company as it was under warranty, so they gave the customer a new one!
I tried everything I knew, freezer, heat, soak testing, prodding, poking, bulk component replacement, so did the super and nothing worked. I still find myself wondering what it was now! All I can think of is an unstable component being affected by radio signals?
The customer was the most patient bloke I've ever met though!
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Old 8th Apr 2014, 1:18 pm   #4
Nickthedentist
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Default Re: The ones that got away...

Faulty neons on tellies could do things like this.
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