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Satellite Workshop 39


BT SVS250/Matsui OP10

Don't you just hate it when the telephone rings while you are in the middle of a really brain-taxing repair! It was a local number so I answered the call.
"I've done everything in the book but now it's dead so can I bring it along for you to look at?" said a male voice.
"What, a dead book?"
"No! it's a statallite I mean.
"What sort of 'statallite'?"
"Oh pee ten" said the voice, proudly.
"I beg your pardon?"
"I read it on the front panel; it's a Matsui oh pee ten."
"Oh, good, you can read then," I murmered then, louder, "you'd better bring it in.
"Can I watch?"
"Watch what?"
"Can I watch while you do it?"
"While I do it? Oh, while I repair it! Yes, certainly, I charge an extra ten pounds an hour for an audience. It's the insurors, you know. They worry."
"Ah. Never mind then. I'll drop it off."
Meanwhile, I was struggling with a later version which had a regulator heatsink on the rear panel. The early version has a large, black heatsink inside with a horizontal projection that "cooks" the decoder board. Putting the heatsink outside the box seemed like a good idea. However, this receiver was giving a hum bar across the screen and I could hear a 100Hz hum in the audio. Obviously it was not an individual rectifier diode at fault because that would have caused a 50Hz hum. It had to be an electrolytic, a regulator I.C. or simply excessive load caused by a partial short-circuit.
Since the receiver looked almost new I decided that the capacitors should be all right. The problem was intermittent and, since the new design heatsink was so small, I opted for the regulators. My oscilloscope showed a ripple on the output from the centre regulator that supplies 6 volts. I replaced this semiconductor, applying lots of heatsink compound to all three. Drat! The symptom remained. I could see a fairly large ripple on the input to the regulator and it had, perhaps, 0.5 volt "headroom". Most regulators like at least a volt to spare so perhaps the fault was caused by a capacitor after all.
To save a lot of time, I soldered a new 2200uF electrolytic directly between the regulator red input wire and a zero-volt connection on the decoder board (see photograph). This cured the fault so I secured the capacitor with glue and left it in place. It wouldn't do any harm to leave the intermittent electrolytic in place.
At that moment, my telephone customer arrived with his Matsui "oh pee ten statallite". He left it on the counter and beat a hasty retreat.
On inspection, I saw that the cover screws were a bit mangled and there were what looked like teeth marks around the plastic cover! It didn't light up.
There were no secondary voltages reaching the regulators on the heat sink. It took ten minutes of probing with a multimeter to trace the cause of the problem to a cracked board. One track was cracked right through. It was located beneath link W94 to the left of the rear, right, hexagonal, brass support pillar for the decoder. Clearly the owner had leaned on his screwdriver with some considerable force.
Once I had cured this problem, the receiver lit up but, as is comon with this model, there were no decoder messages. It's a waste of time to try to trace this symptom to just one component since it is usually caused by the demise of a dozen capacitors. I opened a RELKIT 17 and changed all the capacitors, including several on the main board. The 503kHz ceramic resonator was covered in glue so I desoldered it and scraped away all traces of black stuff.
Finally, to improve reliability, I removed the horizontal heatsink plate that "fries" the decoder board and refitted the 6 volt regulator to the main heatsink, using thermal grease and the nut and bolt supplied in the kit.

Pace MSS1000-IP

Herr Mueller phoned me and explained the problem with his MSS1000-IP receiver. "Ven I turn it on, I get ze rrollink pictures, ja. Und ze schcreen ist ferry dunkel - dark as you say - mit no decoder nachrichten. Und sometimes I see ze 'motor error' message."
Now, my father spent five years in a German prisoner of war camp. No, he doesn't hate them; he learned the language and, as I grew up, he would speak to me in German. In addition, we Yorkshiremen naturally speak with flat vowel sounds and rather weak "Rs". Consekvently - I mean consequently - what Herr Mueller said made perfect sense to me. I told him to bring the receiver to my workshop.
I rather expected a short, rotund man in "lederhosen" so I was a little surprised to meet a tall, gaunt man in a business suit. He left the receiver and headed for the nearest bank as I told him the repair could be expensive.
I was right. Inside, everything looked black. It had been well cooked!
My TV screen remained blank, although I could hear sound and there was a weak, flickering picture available via the decoder Scart socket. Fitting all the capacitors from RELKIT 10 made very little impression, although the nasty interference which my 'scope had shown on every secondary voltage supply was greatly diminished.
Q58 is often a cause of low video level so I replaced that. Now I had a weak, rolling pictre from the TV Scart but nothing from the VCR Scart socket. Replacing Q35 buffer transistor produced a weak, rolling picture from the VCR Scart socket but all was still not well. I inspected the board carefully. There was a very dark spot above the position of what the service manual identified as Q41, so I replaced that transistor as well. At last I had good, bright pictures and decoder messages! The front panel vacuum fluorescent display looked dim so I replaced C2 with the Pace recommended 1uF/50v multilayer ceramic capacitor.
Finally, with the Dolby Prologic audio board replaced, everything was functioning normally. The "motor error" problem had gone - probably thanks to C216, 1000 F/63v in the RELKIT. This capacitor is a common cause of problems. Later production models use an ultra-low ESR type which seems to last a lot longer.
When Herr Mueller returned I smiled at his nice fat wallet.
"Es war etwa gekocht" I said. "Das heisst ganz durch!" ("It was rather cooked - in fact it was well done")
He smiled and said that magic word to me: "Wieviel?" ("How much?")

Pace Prima

I can't imagine why a Mexican family should settle in England - let alone in the frostbitten wastes of North Yorkshire - but Pablo Rodriguez did just that.
He whittled a living out of wooden artifacts and pottery and generally seemed content. Certainly, much of his life appears to be spent in sleeping in front of his cottage while his eight children play joyfully by the river.
Now, Pablo is a "Simpsons" addict and was distraught when his Pace Prima failed.
"Hola, senor Arm Sterong."
"Ah, Pedro, Que tal todo?"
"Ah, no es bueno", he replied, sadly. "Dos cervesas, por favor".
He sank sadly into my chair as I poured him the requested beer and put a spare can beside him. This seemed to cheer him up. He handed me a Pace Prima receiver.
"No va!", he explained. I promised to have a look at it and he taught me some interesting new Mexican words as he drank his beer and cursed technology in general.
After Pablo had left, I tested the Prima.
"LNB Short!" it announced, on the TV screen, as soon as I connected my dish cable. To inhibit low LNB voltage detection, I lifted the cathode of zener D15 and linked it to D5 cathode. That allowed me to make some measurements. The LNB voltage supply passed through PNP transistor Q1 (FXT749) all right and reached the collector of NPN transistor Q2, a TIP31A on a heat sink. Curiously, there was no output voltage from Q2. I discovered that the track to Q2 centre leg was fractured just as it joined the solder pad. A quick repair with thin, teflon-covered wire and all was well. It must have been damaged by a knock or vibration.

Pace MSS100

Wossname from up Church street brought me two Pace MSS100 receivers for repair.
"No hurry", he said. "Just for stock. Won't cost much will it?"
I assured him it wouldn't, provided that he wrote the actual fault symptoms on a label on each unit. He looked a little "put out".
"OK, I'll just fix every darn fault I can find, then, and charge you accordingly?"
He scribbled notes, furiously, then departed!
The label on the first one said "Blew screen No sigernal." I could tell which school he had attended. The receiver lit up with a blue screen and displayed the "no signal" message. There was no LNB voltage coming out of the tuner but a quick measurement proved that the supply voltage was reaching the appropriate tuner connection beneath the board. I desoldered the tuner and found that the "F" connector centre pin was disconnected inside.
The second label said "Chanle names float leftwords and no please insert card message".
I confirmed the symptom and set about trying to find the cause. A few prods with the oscilloscope indicated that the PTV110 was not functioning correctly. Replacement effected a cure.