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Satellite Workshop 01
We get some curious customers in our repair shop and this one was no exception. He hopped from one foot to the other in an agitated fashion as he waited for me to finish soldering a tuner in place.
I looked up and he grinned nervously.
"It's got too much skew," he explained, thrusting a Swedish Microwave LNB and polariser at me.
"I got it from this bloke but it won't work. It's definitely got too much skew and I can't get the channels. Anyway, it got hot when I plugged it in, then the fuse blew."
Occasionally, the mind boggles and mine was boggling like mad.
"Please, tell me what you did and what happened."
"I got it from this bloke in the pub. It's an Echostar but when I connected the wires to the mains it went really hot and there must be too much skew."
Light began to dawn. After further interrogation, I gleaned from him that he had fitted a second hand satellite system but, not knowing where the ferrite polariser should be connected, had joined the wires to a mains cable then plugged it in--and it had become a little warm. Unbelievable!
Equally unbelievable was the fact that I had one in stock. It was a more modern wideband type but it was exactly the same size and shape. I had ordered it last year for an enthusiast who never came back to collect it. I still had his 20 deposit. Mr Agitated seemed happy to give me 38 for it so I fitted it to his LNB and explained how to connect it to the receiver. Armed with the telephone number of a local installer, he trotted away enthusiastically. From the look of his overcoat, I think that "Channel Eurotica" was beckoning.
Back on the repair bench, I had just completed the tricky job of
fitting a Sharp tuner kit to a Pace SS9200 receiver. The old tuner
had expired so that even a nice tantalum bead capacitor had failed to
revive it. Soldering surface mount components is not my favourite
pastime but they are part of the kit and I had made quite a neat job
However, when the receiver clicked into life, the decoded pictures looked distinctly streaky. I'd seen this before after fitting this kit and immediately replaced C21. This is a 2200 F rated at 105 C but the higher temperature rating had not saved it from the cooking it had received. Honestly, I think most customers keep their receivers in an oven! The pictures were better but still a little streaky. This was going to be tricky. I replaced the connector on the decoder board since this can cause the same effect. My 600 desoldering station decided to clog its nozzle at this point. Consequently, a two minute job took fifteen. A pity because the streaky patterning was still there afterwards! In desperation, I began to replace all of the electrolytics around the tuner and the secondary side of the power supply. No better.
At last, I had a moment of inspiration. I increased the value of C125 to 1000 F. Nice clean picture! Since Pace had supplied a 470 F to replace the original 10 F in this position, I guessed that this new tuner was especially prone to noise on the supply rail. Increasing the value still further did the trick. A quick call to Pace technical help line confirmed that they were aware of the problem.
The next receiver was a Ferguson SRV1 a Pace SS9000 in reality.
The customers helpful report said "Goes off sometimes and resets all
channels". It had been sitting on the bench for two hours to warm up
and had not "gone off", yet. However, as I moved it to one side the
picture flickered and appeared to tune through several channels
before coming to rest on an Astra 1D test card! Now, this receiver
can not normally tune as low as that so it was obvious that the
tuning voltage had dropped to zero. I tapped the receiver and it
zipped back to "Sky News".
With the board removed from the chassis, I inspected the tracks for signs of a crack or dry joint. Sure enough, the transformer solder joints looked very grey and close inspection revealed a fine circular crack in two joints. Resoldering these cured the problem, as I proved by gently tapping the unit with a ball-point pen.
Clearly, one transformer winding was supplying the tuning voltage and the other was supplying 5 volts to the microprocessor. Fluctuations in this supply were causing a "brown out" condition and the microprocessor was performing a factory reset whenever it occurred.
Just for completeness, I replaced C9 and C11 in the power supply since these can cause failure if they have been subjected to heat for a few years. Faint, white dashes on the decoded channels indicated that C29 was also degraded. There were no other lines on the picture but I had a pang of conscience and replaced the capacitor inside the tuner. I wished I hadn't after I'd put it all back together because there was now no LNB voltage. It took me another five minutes to see that I had not resoldered the end pin on the tuner!