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
of them.
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!