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Satellite Workshop 25
Wow! My first digital receiver. This is really neat inside. At a price of £525.00 it ought to be but I was impressed. Less impressed was the gentleman who brought it in.
"Loop through won't work" he announced.
"What, E to E" I said then added "I mean TV aerial loop through?"
"Nah, analogue receiver loop through. You know, you connect your digital to the dish, then you connect your Amstrad through the digital. The signal goes through except it doesn't any more."
I thought I understood so I had a poke around. The fault was not immediately obvious so I rang the supplier, "Satellite Scene" at Derby.
Mike Hancox, Technical Director suggested I check a diode next to the tuner. Sure enough, it had a dry joint. A quick dob of solder and all was well. However I told the customer to come back next week because "I wanted to soak test it to make sure". I'd never seen this "loop through" feature before. It seemed that the Galaxis had to be "parked" in standby on a channel with vertical polarisation so that it was sending just 13 volts to the LNB. The analogue receiver could then control the LNB itself. Interesting. No need for a twin-output LNB or an additional cable.
MSS500 and MSS1000 receivers are beginning to appear more often. It's the usual problem: the customer has kept his pride and joy nice and warm for two years and now the electrolytics have dried out.
The symptoms can be wonderfully varied, however, so it becomes quite a challenge to work out exactly why a capacitor might cause a particular fault. However, I now replace the entire set of capacitors using the "Relkit 6" kit from SatCure. If the fault still persists then I start to hunt it down by conventional methods. Fitting the kit, however, usually fixes the problem.
Such was the case with an MSS1000 which arrived by carrier last week. The customer's lucid description was all of two words long:
"Intermitant dekodering" (sic) it said. There was no sign of a fault during a two hour soak test but the diagonal, dashed lines swirling across the picture indicated that the electrolytics were beyond their "sell-by" date!
I fitted the power supply capacitor kit and, for good measure, C208 1 F next to the PTV111 sync-separator chip, which often causes decoder "dropout" if it has been "cooked."
The receiver now gave NO decoder messages and the channel name and on-screen menus drifted gently from right to left! Oh, dear! After spending a fruitless hour with an oscilloscope in one hand and a helpful Pace engineer at the end of the telephone line in the other, I had to give up. There comes a time when you "can't see t' wood fer t' trees."
I packed the unit carefully and shipped it down to Ian at Satfix in Swansea. He, of course, spotted the problem immediately and phoned me to gloat.
"A tiny thread of solder isn't it, you left it across a surface mount capacitor. Want me to post you my magnifying glass do you? Perhaps new spectacles are required? And by the way, you know you always complain that I leave the screws out? Well, tell me, why is the Dolby board hanging loose inside?"
Touché. I just threw a stone in a glass house. I wondered where those extra screws on my work bench had come from!
I had more success with the MSS500 which turned up in the arms of a local TV aerial chappie.
"LNB short" he announced, "but it ain't, I checked it and the cable is all right, too." Sure enough, on the work bench the MSS500 flashed the magic words on the screen as soon as the LNB cable was connected. I tried the usual cure-all by pressing the reset sequence "MENU, ZERO, STORE, RIGHT-ARROW, LEFT-ARROW" on the remote control. This corrects the installation settings without changing the channel tuning. It had no effect on the fault symptom. I was disappointed. I love to see the installer's face when I perform this feat of "magic."
I could find nothing wrong with the LNB current-detect circuit, so, it had to be capacitors. Fitting the kit provided a cure. One of the reasons that the fault had occurred was that "someone" had already replace C11 and C12 with 1000 F capacitors of the correct voltage rating. Unfortunately, they were not low ESR types and had quickly given up in service. The SatCure kit I use includes the Pace recommended replacement for C11 -- an Ultra High Reliability 1500 F electrolytic. I guess it's not cheap but I don't like to have receivers bouncing back within my guarantee period!
A nice excuse to increase my profit is the "Silent, Miniature Cooling Fan Kit". This ticks over very slowly when connected to the 5 volt supply. It's especially good for the version with internal positioner board which runs rather warm. Although not approved by receiver manufacturers, the fan takes negligible current, is made of plastic and can't short out anything should it become dislodged. It provides just enough air movement to get rid of "hot spots." My customers think it's a marvellous idea. One of them even fitted one to his TV cabinet and used a 6 volt dc adaptor to power it. I found this fan kit at SatCure's new web site, by the way: http://www.netcentral.co.uk/satcure/
Capacitors are also earning me money from the older PRD800 and PRD900 units. Apart from power supply failure, the symptoms vary but one obvious sign is low LNB voltage. It can have other causes (check the 1 R543 resistor which protects the LNB supply next to the tuner) but I like to replace the full kit. This time it's "Relkit 2" from SatCure. It's nice to see the customer's face when you point out that, not only is the fault cured but the picture no longer has that annoying streakiness which developed so slowly that the spouse didn't even noticed it!
You don't see many SRD2000 receivers, although they were the rival to Pace's MSS1000 with surround sound connections and other nice features. Recently, they have been sold at ridiculously low prices. This worries me because the owner is less likely to pay me lots of money to fix it!
Anyway, this one was brought to me from a town about ten miles away. It was dead. The fault was not too difficult to correct since it was only the TOP204 device which had failed. You need a really hot soldering iron to do this job because the I.C. is a TO220 case device which is soldered to a broad area of tinned copper on the underside of the power supply board. The first time I repaired an SRD2000 it fooled me. I fitted a TOP202 by mistake. This has a lower current rating than the TOP204 and the result was that the receiver would work only if the audio board was disconnected. Guess who wasted an hour fault-finding the audio board!