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Satellite Workshop 37



When a repair shop some distance away phoned me for advice on an NEC receiver with "no audio" I told them, sadly, that I could not help.
"I may be old, but I'm not THAT old." I pointed out. "It was obsolete seven years ago and NEC pulled out of the satellite business so spare parts and service information are probably unavailable."
"So what do I tell my customer?"
(It amazes me how often I get asked this question! Why are these people in business if they can't speak intelligently to the general public?) I gave my usual, joking, reply:
"Tell him to chuck it in the bin."
"He'll kill me! He says he paid five hundred pounds for it, new."
"Did he buy it from you?"
"Fine, so tell him you'll get it fixed for 499 and bring it to me."
The phone line went very dead. Some people can't take a joke. I would have done it for a bit less than that. Anyway, I carried on working for half an hour then the phone rang again. I noticed that the area code was the same.
"I've got an NEC 4012 with no audio and I wonder if you can help me?"
Oh, boy! He'd given the customer my number. I tried to explain the merits of the new Sky digital system but he wasn't interested. Eventually, against my better judgement, I agreed to have a look at the receiver. It was an hour's drive so he agreed to bring it to me and leave it for however long it needed.
On the bench the receiver worked perfectly so I left it on "soak" while I went out to deliver a tired SRD510 back to a shop. On my return I found that the 4012 was hissing to itself and no amount of button pressing would bring back the sound. However, when I gave what I guessed was the audio circuit a good dose of freezer spray then switched the receiver off and on, the sound came back. With the help of the famous hairdryer (she bought a new one) I traced the cause to a Sony CX-7925B. Unable to find this listed in any catalogue, I fitted a miniature cooling fan above it and phoned the customer with the news. He was delighted to get the receiver back "for the match" but still wanted it fixed "properly". I promised to locate a CX-7925B and he collected the receiver to put back on top of his VCR in its nice warm cabinet (I warned him but he wouldn't listen).
To cut an already long story shorter, I discovered that our very own Grandata stock this I.C. and it arrived next day. The customer's invoice should be slightly less than 499, (but not much less).

Digital Challenge

Now that Sky Digital satellite transmissions are with us, I'm getting a lot of people asking me why their picture and sound disappear in heavy rain while the analogue picture simply used to go a little "sparkly". The simple answer is that digital tends to be an "all or nothing" system. If the installation is not perfect then poor signal and/or cross-polar interference can cause drop-out. The solution is to make sure that the highest quality cable has been used and that the dish is accurately aligned and not distorted. In addition, the LNB "skew" or rotational angle is very critical and ought to be checked with a spectrum analyser, although a rough check can be made with a signal strength meter equipped with a 22kHz oscillator that will switch the Universal LNB to "high band" (10.60 GHz local oscillator frequency).
Recently, a local installer asked me if I could add a 22kHz oscillator to his Manhattan signal meter. This wasn't difficult and I achieved it simply by fitting a 22kHz tone board from SatCure* inside the meter, with a switch to bypass it. It's important to insert the tone board in series with the dc voltage feed and NOT in line with the coaxial signal feed. A normal satellite signal strength meter designed for analogue signals will read 3 to 4 dB low on digital signals because it sees peak signal level. Since digital transmissions have a more even energy spread across the band, the peak reading is lower. This doesn't matter but you should be aware of it. The Sky Digibox gives bar graph indications of signal strength and of error rate in the Installation Menu. There's also a "Lock" indication which should state "OK". If it doesn't then the error rate is too high and the installation needs to be checked thoroughly.

*Box insert if you wish: 22kHz tone board from SatCure can be fitted inside most satellite receivers and signal meters. State make/model. Price 9.95 plus 2.50 P&P. SatCure, PO Box 12, Sandbach, CW11 1XA.

Pace SS9200 IRD

When Wossname from up Church Street waddled into the workshop and presented me with a 90 channel Pace SS9200 I feared the worst. Ever since he bought a copy of the first "Satellite Repair Manual" he's considered himself a first class repairman. That wouldn't be so bad except that he brings me the ones he's messed up and expects me to fix them while he points out what I'm doing wrong!
"Blank screen" he said. "Replaced tuner as per page 77 but no better. Must be the decoder chip as per page 83 but I don't have one. Bung one in for me, there's a good chap. I'll just hold this solder for you."
I pushed his helpful hand away and checked the video output from each socket. There was the normal flickering picture from the decoder scart socket but the TV and VCR scart sockets produced no output at all on any channel. I checked for sync signals going from the TEA2029C sync separator I.C. to the decoder board connector and found none. Replacing U6 cured the fault.
"Oh, that's not in the book!" remarked Wossname. I grinned and handed him the receiver together with his change.
"A quid!" he exclaimed. "Is that all the change I get?"