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Satellite Workshop 06


A local shop sold an Amstrad satellite system to a customer from Baslow (a rather posh sort of place). A few weeks later he came into the shop wanting to buy another dish & LNB. The shop, of course, sold him one, and away he went. Next of course, was where I became involved. He rang the shop with a question and they told him to ring me!.
Anyway, after I had quizzed him for a while, I got all his story. He has a holiday cottage in France, and had bought the system to use there. However, he enjoyed it so much, he decided to buy another dish for his UK home and take the receiver back and forth with him.
So, now knowing his story, I asked what his problem was. He said he wanted to know how to set his dish up. Being the sort of person I am, I enquired how he aligned the dish in France.
He replied that, from his cottage in France, he could 'see the satellite' and merely had to point the dish at it. My next question, fairly obviously, was what did the satellite look like. He replied that 'it was a bright light in the sky', but that from England he couldn't see it.
At this point, I mentioned to him how far away it is, and that it doesn't have headlights.
Anyway, how lucky can you get, just pick a star at random and point a dish at it!.

Pace fault

Yesterday, a PRD900 came into the workshop with a curious fault. The picture was perfect from all Scart sockets but very dim from the RF output. Tapping the receiver, I noticed, would change the brightness.
I did all the usual checks around the modulator, looking for broken joints and cracked tracks. Visual inspection failed to reveal anything so I resorted to the 'scope. The video level reaching the modulator section was very low, but why? It was a fairly simple task to trace the signal back to the buffer transistor, Q105, which feeds the modulator. This is a surface mount NPN device near the centre of the board. A good healthy signal going in contrasted with a very low one coming out of the emitter. Replacing this transistor cured the fault but I still can't explain why tapping the unit should have had an effect?
Since then I've had two PRD900 Plus with the same problem. One gave no video at all from the RF socket and the other would work for a while then would begin to modulate the picture from bright to dark as if someone was scrolling through the contrast settings. In each case, replacing Q105 effected a cure. A call to Pace elicited the information that this fault had just been flagged in their repairs database. At present it seems to affect only receivers more than a year old (how convenient!) which have been installed with no ventilation. Our summer weather seems to have precipitated the first failures.

Funny Pictures

This morning I had a call out from a lady in distress. She couldn't receive satellite pictures at all and her video recorder wouldn't. Her TV had been "playing up" or, to be more exact, "giving funny pictures". Consequently, she'd tried swapping it for the portable but couldn't figure out how to tune the channels and had swapped it back.
When I arrived, the aerial coax was connected directly into the back of the TV and the VCR was connected to the satellite receiver with two RF leads! A quick swap of the leads got the satellite pictures back. The TV was an ITT model CT1611/2. When tapped, it would produce maximum volume and lose vertical hold. A dry joint which will, no doubt, be found in the workshop later. For the moment I've left the portable connected.

Technisat Kundendienst wir bedanken uns bei Ihnen!*

On Wednesday three weeks ago I had an evening call-out while I was listening to Eric Wiltsher's "Satellite Workshop" (Astra radio frequency 7.56 on the JSTV transponder, 8.10pm for those who are interested). I was a little annoyed because I couldn't very well listen to it in the car!
The problem was a "dead" Technisat 4000ST receiver which I brought back to the workshop for investigation. It didn't take long to find that the mains transformer primary winding was open-circuit. As Technisat no longer have a UK subsidiary I dusted off my German dictionary and phoned the factory in Daun. The girl who answered said that the transformer for that model was obsolete but, if I faxed an enquiry, she thought that a replacement part might be available (at least, I think that's what she said!)
I faxed the information in my best schoolboy German and waited for a reply that didn't arrive. However, a week later my toes were crushed by a battered jiffy bag which arrived unannounced through the letter box. It was a transformer, free of charge, with the compliments of Technisat! Impressed by this service I faxed a letter of thanks. Inside the jiffy bag was a note explaining that their UK agent is now J. D. Electronics in Sudbury, Suffolk. I rang Joe at J.D. and he confirmed that the transformer was now a stock item, together with Echostar parts. Handy to know.

No Connexions

The gentleman who telephoned last week was happy to let me take away his Connexions CX95A receiver for repair and I made the mistake of assuming that he would also be happy to pay for the repair!
However, after I'd ordered and fitted a new decoder board and telephoned him to offer the good news ("only 75 plus vat"), he became quite stroppy and insisted that it should not have gone wrong "after only two years."
Without extended warranty there was little I could do about this. It was well outside the 12 month warranty and I'd been lucky to get a brand new Thomson decoder board so cheaply.
Call me stupid but, to try to reduce the cost, I decoded to try to fix the old decoder. The symptom was the message "Card Invalid" each time I inserted a valid card. I measured the Vpp 5 volt supply to the card reader. It would appear for an instant as the card was inserted but would then drop to zero. This implied to me that the Vpp circuit was all right but that there was a problem with the card reader itself. However, it took an hour to track down the culprit - a leaky 5.6 volt zener next to the card holder.
I compromised on a 45 charge - expensive for a zener but it helps to defray my petrol costs and the fact that I've now got a new, unwanted Thomson decoder board in stock (fits most Echostar and Palcom models).
When I returned the receiver to the customer he asked me to install it back in the cabinet on top of his VCR! I compromised by squeezing them side by side on the shelf. The arrangement still looked tidy and allowed far better ventilation. He paid me without a murmur and seemed grateful.

Cool "Hot Bird"

Although I don't do installations, I'm often called out to sort out some problems. In this instance, the customer had had his 60cm dish swapped for an 80cm Lenson Heath with two LNBs on a bracket. The problem was very sparkly pictures on some Astra channels, plus picture and sound interference on UK Gold.
The "expert" installer had aligned the dish on 13 degrees East for "Hot Bird". Ths meant that the signal from Astra was probably about 6dB down. In addition, side-lobe pickup was giving the interference and increasing the sparklies by swamping the tuner with unwanted reception of other satellite transmissions.
I realigned the dish directly on Eutelsat at 16 degrees, using just one LNB on the standard bracket. Then I fitted the Lenson "Multi LNB" brackets - one on each side of the arm - and screwed the LNBs in place (a fiddly task requiring ultra-thin fingers!) Setting the dish like this can reduce losses on each satellite to just 1.5dB.
Moving each LNB along its bracket produced pictures of a sort. The final alignment required a spectrum analyser to get the best compromise between maximum signal peaks and minimum noise floor. Most "experts" use an ordinary signal strength meter which is about as useful as a piece of wet string for this. If you align for maximum reading you are certain to get maximum noise, too - the meter can't tell the difference!
The LNBs had to be twisted slightly off-vertical to match the "skew" of each satellite and I had to bend the brackets for best readings on the analyser and to reduce co-satellite interference from side-lobes which was quite visible on the spectrum.
Once this was done, the pictures from both satellites were nearly perfect, although I had to warn the customer that he would still see sparklies in bad weather. There was no need for a Link Budget calculation to predict that an 80cm dish was going to be a compromise in Yorkshire!

Première Banger

One of the most recent repairs was a Mimtec Premiere. This arrived, dead, just as Mimtec in Scotland began their summer fortnight shutdown! Luckily, Martin Pickering of SatCure, (formerly Technical Manager at Eurosat Midlands), is offering an on-line help service for satellite receivers.
I contacted him via Internet at his CompuServe address:-(
It transpired that he can supply a power supply repair kit for this model. Since there are about fourteen components which can fail, it saved me a lot of time simply to order the kit and follow the instructions.
Unfortunately, the customer had omitted to send the remote control so, although the receiver now lit up, I was unable to test it. I sent it back, knowing full well that it would return. Sure enough, the following week I received a call from the customer to say that there were no horizontally polarised channels. Back came the receiver (this time with remote control!)
It took only a few minutes to trace the problem to a leaky TR4 (BC547) in the LNB supply circuit. I don't know if this is a common problem but it's worth checking all functions after power supply failure. The last Mimtec I repaired needed a new power supply and had also killed off TR16 and TR17 on the decoder interface board. Those Sorensen power supplies really go bang!
The new replacement power supply is made by Nokia and is said to be more reliable. Unfortunately, satellite owners simply don't want to pay and we will inevitably end up repairing the old ones.

*Technisat Customer Service we thank you!

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