Satellite Workshop 11
In two previous articles I've mentioned Tardis
Electronics. Flood, Fire and then a Burglary have forced Terry Boyd
to move premises and Tardis now reside at : Station House, Hind Heath
Road, Sandbach, Cheshire.
In recent weeks I've been inundated with receivers which report "Your
Card is Invalid" intermittently. At first I was not detecting any
problem while using my own SKY card but, gradually, I began to see
the problem occur. Finally, it reached the stage where I could put my
card into any Amstrad and it would be fine but several other
receivers reported it to be "Invalid".
However, if I put an old series "09" SKY card into the same receivers
the message would be "Your Card has Expired", as expected. So the
problem seemed to lie with the new card. On closer inspection I
noticed a small black square on one of the card contacts. On my card
this was very worn. I checked it on a customer's card and it appeared
to be a film resistance of about 2k although the actual value would
depend upon the spring contact area inside each card slot.
This resistance is in series with the 3.5MHz clock input to the card.
Could it be that it is needed for some receivers but not for
Amstrad?
I dismantled a Pace PRD900 receiver, which had been giving permanent
"Card Invalid" messages with my card inserted, and cut the track to
the appropriate spring contact. Bridging this track break by
soldering a 2k2 resistor in place immediately cured the problem.
Since then I've carried out this modification to a dozen more PRD
receivers and "clones" such as the Philips STU824, with 100% success.
A call to SKY's technical man elicited the response that they were
unaware of a problem with this model, although they thought there was
a problem with the SS9200. (At least he didn't tell me to "wipe the
card to remove static" the usual response.) Pace were also unaware
but are now investigating. Lest I be accused of anti-Pace propaganda,
let me add that I've seen this intermittent "Card Invalid" problem in
a Cambridge RD480 receiver, too. Oddly, nobody else seems to be
getting this problem. I must have very fussy customers!
Until recently I've been doing only trade repairs but I decided to
run a small advert for "INSTANT SATELLITE REPAIRS" to generate extra
business. I've found that the suggestion of a fast turnaround with a
fixed charge attracts more customers than an advert which says "from
25.00..." or whatever.
Certainly, Mr Wilkinson thought so because he 'phoned me and asked me
to look at his SRD550 which was "flashing red and green". A quick
test at the house confirmed that both LEDs flashed, even with no LNB
cable connected. This could have been a faulty LNB supply transistor
but Mr Wilkinson mentioned that the fault was intermittent. My guess
was that the zero volt connection on the output plug from the power
supply had gone high resistance a common fault on this range of
receivers. Nowadays I can't get away with burning holes in the
customer's carpet and I don't like to work in the back of the van so
I took the receiver back to the workshop and fixed it there by adding
a wire between power supply and decoder screening cans. As a
precaution, I adjusted the low voltage rail to 4.95 volts since I've
seen some rise as high as 6 volts with this earth wire added.
When I re-installed it back at the house The SDR550 worked very well
but the pictures were distinctly grainy. The terrestrial pictures
were better but not perfect. I made up an RF lead using satellite
cable to ensure the lowest possible losses. Connecting this between
satellite receiver and video recorder resulted in "the best pictures
I've had for years", according to Mr Wilkinson. He paid my fixed
charge quite happily and assured me that he would recommend me to his
friends.
According to the installer who brought me an SRD540, it had gone
bang, belched smoke and destroyed the LNB on the dish. I took this
explanation with a liberal pinch of salt until I checked the unit on
the test bench. The LNB output voltage measured fifty
four volts!
After hurriedly disconnecting it I opened the receiver to discover
several capacitors had burst. A quick look at the circuit diagram
confirmed that these were not only on the LNB supply line but also on
the 12 volt rail.
I had an awful suspicion that repairing the power supply fault was
only the beginning!
Now, feedback from the 5 volt output determines the other outputs. If
the 5 volt output is low, the power supply will increase ALL outputs
in its attempt to reach 5 volts. I checked the following:
C622 (2200uF), D608, and the Optocoupler. In addition I looked for
broken copper tracks taking 5 volts to the Optocoupler, since this
has been known to cause high output voltages. In fact, D608 was
open-circuit, although it gave quite a sensible reading in circuit.
Luckily I knew that 0.7 volts was far too high a forward voltage for
this type of diode.
I replaced D608, C622 and the Optocoupler for good measure. The
capacitors on the LNB supply rails and 12 volt rails also had to be
replaced, together with TR303 and TR304. Once this was done, the
receiver lit up but gave a blank screen and very distorted audio.
Replacing the decoder unit resulted in an excellent picture and the
audio fault was traced to IC3. All in all a very expensive
repair!
On the very same day I had an SRD550 with precisely the same symptom,
but this time it was caused by C622, not D608. Somebody had already
attempted to repair it and the power supply now contained several
incorrect parts which I replaced. When I finally got a picture,
however, there were two distinct hum bars travelling down the screen.
I replaced the 68 F capacitor, which smoothes the rectified mains
input, but without effect. It took me a long time to realise that the
fault lay with the yellow-banded transformer which must have
originated in an SRD510. The correct red-banded transformer cured the
problem immediately.
Since I published my "email" address I've had a large number of
interesting enquiries. Most of these I am able to answer but one
question which comes up every week is "Why does my ABC D2Mac decoder
do such and such with my XYZ receiver?" Now, if a man goes out to buy
a tyre for his car, he invariably takes at least the wheel, if not
the car, to make sure that the tyre fits. Unfortunately the same is
not true for D2Mac decoders, consequently problems arise. My first
question is always "has it ever worked correctly with
your receiver?" Some receivers and some decoders are able to accept
various kinds of input signal, provided that the correct baseband
selection is made in the respective menus. Some have no such option
so that choosing a suitable decoder becomes a game of Russian
roulette. Just to make matters worse, sometimes the connecting cable
will degrade the input signal and prevent the decoder from working
reliably.
My advice, therefore, is to buy the decoder only after you've seen it
working with your receiver. Yes, this will add to the expense but at
least it guarantees that you get one which works. Alternatively, buy
a receiver and D2Mac decoder combined or at least manufactured by the
same company. That way you don't get into arguments about which item
is faulty, should a problem arise. Do bear in mind, also, that most
D2Mac programmes use some form of Eurocrypt encoding and the approved
smart cards are generally not available in this country. This fact
puts you into the hands of the pirate card suppliers and, with the
best will in the world, they can't guarantee that their card will
work with your decoder and keep on working.
Keep sending the email enquiries but remember that I answer, on
average, ten per evening after a hard day's work! Include all
relevant information (make, model, connections, symptoms, fault
history, tests carried out, location) but keep it short. Sorry but I
can't handle questions by telephone or ordinary mail.
INTERNET:100613.2105@compuserve.com
Even if you don't have a question, you can send an "email" to say
"hello" or to exchange information about new faults.