Satellite Workshop 13
Two magicians were born in my home town of Middlesbrough: [note
correct spelling!] One was the famous Paul Daniels. Not so famous
but well known locally was "Blind Des". I first saw Blind Des perform
at my Grannie's house in Longford Street. The Television, a Decca
DM4-CA, had developed a rolling picture fault. (OK, I know it's
supposed to be satellite but you'll like this!)
"Run and get Blind Des" my Mum told my Uncle. "He'll fix it."
Uncle returned ten minutes later with an elderly lady who had a
white-haired gentleman and suitcase in tow. I knew he was blind
because he tapped things with a white walking stick.
At the impressionable age of seven I quite expected him to wave his
white stick and mutter some magic words which would instantly cure
the jittery picture. Instead, he sat down in the armchair and
directed his wife to kneel down by the TV. She described the symptoms
to him in colourful detail.
Blind Des listened intently then sat back and clasped his hands to
his chest. This was better than cinema!
"Swap th' ECC82s" he pronounced. If that dun't fix it, replace grid
bias resis'uh under th' Flywheel Sink Valve." The little woman
squatted on the floor and followed his instructions. Apparently it
was the Sink Valve resistor because she produced a large soldering
iron from the suitcase and plugged it into a wall socket. With
amazing dexterity and much smoke she replaced the offending resistor
in seconds.
"Well I'll go to the foot of our stairs" pronounced Grannie as a
perfect picture appeared. "'Ow much?"
I remember being seriously impressed by this performance and decided
at that early age to be a TV repair man. I would learn all about Sink
Valves before I went blind! (In fact I'm still not blind, despite the
evil invention of Surface Mount Devices!)
The moral of this story is that you can fix things even when you
can't see them, provided that somebody can "paint a picture" in
words. Most of my headaches arise from telephone calls or e-mail
where the other person simply can't describe accurately what he sees
and hears. Of course we put up with this from ignorant customers but
when other "engineers" in the trade perpetrate the same mistakes, it
becomes frustrating. So the next time you report to me "interference
lines", shut your eyes and paint a verbal picture: how many lines;
how far apart; what orientation; what colour; solid, dotted,
dashed....?
It was Good Friday. The population had split into two groups. One
group was counting red and white cones while sitting in parked cars.
The other half had donned gardening gloves.
When the 'phone rang I removed my gloves to answer it.
"My satellite's gone off" said an anonymous voice. "You advertise
same-day repairs so will you come and fix it? I was in the garden and
when I came back in it had gone off."
"Did you plug your lawnmower in next to it?"
Hesitation. She sensed the presence of a magician. "How did you
know".
"Magic" I confirmed, grinning. "I'll come straight away.Tell me your
address".
The receiver was a Grundig GRD150. In the workshop I replaced the
fuse and then tested it. The receiver now worked perfectly but I
could hear a beep beep from the TV loudspeaker when the smartcard was
inserted.
Soldering the recommended 100nF capacitor between links J72 and J80
cured this problem and I returned the unit to the customer who now
had her entire family in the house, all waiting to watch a programme
on satellite TV.
"I fixed the power supply but I also noticed a bleeping sound with
the card inserted. Did you know about that?"
"Yes" she said. "But the man at (well known high street chain) said
it was normal".
"Ah!" I replied. "Well it's not normal any more. I've fixed that,
too".
The lady was delighted and paid my price without argument. I made a
mental note to visit (well known high street chain) to offer my
services.
Very occasionally I get calls from other dealers who get my number
from goodness knows where! Clive was having problems with an Amstrad
SRD500. It took about half an hour to warm up before a picture could
be seen and, even then, several audio channels were missing. Now, I
remembered having this same problem previously and tackled the
picture problem first. This was caused by C13 in the power supply. By
the time I had replaced all the capacitors which looked brown, the
audio problem had gone away.
Consequently, I suggested this method to Clive who had spent two
hours probing around the audio section but to no avail.
"Power supply!" he said, incredulously. "I'll ring you back!"
True to his word, he did. Replacing C13 and C14 had fixed both
problems. Thanks, Clive. If you are reading this, you didn't leave me
your number.
I've had several faults with this model. If you have picture
problems, it's invariably caused by electrolytics. Try replacing
those near the tuner first. Last week I had one with no audio at all.
It took me a ridiculous two hours to trace the problem to invisibly
cracked tracks at the rear of the board. If the owner had told me
she'd dropped it in the first place the final bill would have been
much less.
My E-Mail address changed as you will have noticed. So popular is my
technical advice service that it was costing me a fortune to reply
via CompuServe whose local number was horribly unreliable. I asked
them to sort it out but all I received was empty promises.
A small, local company went out of its way to help me. I now have a
lower-cost access point and, in return, I've been recommending this
company to friends. It's all about caring for your customers. The big
players find this very difficult. You may not care for the Internet
and I'm sorry if it bores you! However, I find it incredibly useful.
For instance, in the newsgroup called cryptically:
sci.electronics.repair I can get information from repairers all over
the world. We all help each other to solve problems. It works like a
"bulletin board." You post a question and (sometimes within minutes)
somebody posts a reply. One nice fellow who seems forever to be
helping people with problems is Nigel Cooke. I've never met him,
other than via the Internet, but he runs a shop called "Diverse
Devices" which stocks obscure/obsolete components, second hand test
equipment, schematics and other stuff. (I do manage to find them for
you!) Send Nigel two stamps for his catalogue. Diverse Devices, 75
Priory Rd, St Denys, Southampton,England. SO17 2JQ. There is a
newsgroup for just about every type of hobby and business. Don't give
up your subscription to "Television" but you might find it useful to
"get connected".
This Nokia receiver is generally one of the most reliable. However a
local dealer had a problem with this one and brought it to me after
replacing most of the power supply parts. I checked his work which
seemed all right and I could find no components which measured
incorrectly. However, the power supply made a rapid ticking noise.
This is usually caused by a shorted output diode or, if the tripping
is much slower, by a dead TL431 adjustable zener.
On a hunch, I removed the decoder board and the receiver worked
perfectly. Now I was faced with discovering precisely which component
on the decoder board was drawing too much current. I considered
rigging up a separate power supply but this was too much like hard
work. Recently, I'd fixed a couple of Thomson Videocrypt decoders in
which the sync separator IC had gone short circuit. In these it was
easy to find because the transformer power supply had burned out the
series resistor which feeds the IC.
I removed the TEA2029C on the Nokia decoder board and the short
circuit disappeared. A new chip cured the fault. The dealer was quite
surprised to hear that the power supply had not been to blame!
This is such a common fault with many well-known causes but I thought
I'd mention this one because I've come across it only twice. Checking
with the oscilloscope showed that the video level was low quite soon
after the tuner. I actually replaced the tuner to begin with but
without effect.
Finally, I traced the cause to TR42. This transistor is near the back
of the board and clamps the incoming signal if low LNB voltage is
detected. To further confuse me, however, the electrolytic C5 was
also faulty. Replacing both these devices brought the video level
back to normal.
This fault has plagued me since this model first appeared. Again, it
can have a number of causes. This particular one was traced to a high
12 volt supply. The problem arises because the 12 volt supply comes
from the 13 volt supply, regulated by TR304, a large plastic
insulated TO220 device at the front of the board. If the 12 volt rail
is adjusted too high, TR304 has insufficient "headroom" to regulate
and the high frequency ripple gets through. The remedy is to reduce
the value of R319 which sets the 12 volt rail lower.
I've also had instances where TR304 runs terribly hot. This happems
because the 13 volt supply track is shorted to the 23 volt track!
This is a manufacturing fault. You can see that the two tracks run
closely together and the etching has failed to separate them. These
receivers can run for months like this before TR304 finally
melts.
I mentioned in a previous article that the series 10 Sky card seems
to "play up" in some receivers. The card has a resistance spot on one
contact. In some Pace PRD receivers (and clones) an intermittent
"Card Invalid" message can occur. Only a tiny percentage of receivers
is affected and, usually, only as the card wears with use. However,
I've seen it happen with brand new cards.
My answer in the PRD receiver was to cut the track which goes to the
"black spot" contact and insert a 2k2 resistor. However, Pace have
stressed that they do not recommend such a modification.
In other receivers such as SS9200 and Cambridge RD480 Extra, I've
solved the same problem by carefully scraping the black spot off the
card.
However, Sky have stressed that they can not authorise tampering with
the card.
The official line is to request a replacement card, insert it in the
decoder slot and, once it is working, to leave it there.
[At this point I'm really tempted to type "Draw your own
conclusions!" But I'd better not. I need to keep in with these
guys.]
previous article...
"In common with the other new Amstrad models, the SR950 and
SDR700"
should read ".....SRD700". Finger trouble!