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Satellite Workshop 13

Working Blind

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....?

Gardening Trouble

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.

SRD500 Audio

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: 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".

SAT 1700 PSU Tripping

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!

SRD510 Low video level

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.

SRD510 "Wiggly graphics"

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.

Card Invalid

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!

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