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Satellite Workshop 34


Thorens TSR205

After the second world war a large number of Polish immigrants remained in Britain. All the ones I know are really nice people and Edward is no exception so, when he announced that the receiver he'd just brought back from Germany didn't work, I had no hesitation in agreeing to look at it, despite having no service information.
Inside, this 205 channel Thorens receiver is pure Samsung. It's very nicely put together and uses a mains transformer and NO surface mount components. The problem with Edward's box was that he had shorted out the LNB connection and there was no LNB voltage coming out of the tuner.
Luckily, the LNB supply circuit was recognisable as it is very similar to that of the old Amstrad SRD400 - but with a 22kHz tone inserter board added.
I found a protection device in the form of a posistor but this was intact. Instead, the 7812 regulator (U601) had died. There was 30 volts going into it, 1.1 volts on the middle reference pin and nothing on the output. Unfortunately, my test probe slipped and shorted 30 volts to the centre pin, after which this, too, had zero volts on it!
Your careless scribe traced his damage to a 2SA733 PNP transistor, Q303, on the tone board and replaced it with a BC557B. With the 7812 plastic regulator replaced with one rescued from an SRD400 chassis, the repair was almost complete. To improve the protection, I replaced the posistor with a 1 Ohm fusible resistor which would simply go open-circuit in the event of a fault; much easier to replace than the regulator!
Edward was delighted: "Now I can watch de Polsat channel again!" he announced. "Czesc!"

Pace Apollo 120

This Apollo came to me with what looked like a decoder fault but it wasn't because German channels were also affected. Difficult to describe in words but it appeared that the picture scan lines were spaced too far apart or every other line was missing ("no interlace" to use a technical term). In addition there was distortion at the edges of the picture ("cogging" I think you call
it?) and the picture would roll or jump dependent on the contrast setting. Decoder wouldn't decode. After some time, I traced it to Q97, a BC846B in the buffer before the clamp circuit. No idea why it failed.

Pace MSS1000

I had two MSS1000 to repair last week. BOTH had been in an oven on a moderate heat for a couple of years and, curiously, both had ceased to function! Capacitors were so black that I could not even read the markings on them. I had to replace quite a lot. Luckily I keep RELKIT 10 in stock.
The first MSS1000 had come from Mrs Fu at the Chinese Chippy. Even with capacitors replaced and power supply functioning perfectly, it would not work at all. I plugged in a new front panel assembly and it was perfect. Replacing the microcontroller on the old front panel got the receiver working but the display would not light up. I scraped off the chip fat, replaced the vacuum fluorescent tube, capacitor C2 and transistors on the display board and still it wouldn't light up. Eventually I gave up and quoted customer a silly price for a new display assembly. She decided to manage without that but I get a free Chicken Chow Mein for the next six weeks!
Second one was the MSS1061 D2Mac version. I got it running but D2Mac was very intermittent. Decided to replace ALL electrolytics on the D2Mac board. (Careful! One of them is non-polarised). On refitting the board I found it wouldn't work at all! Thinking that I'd shorted something out, I put it to one side until I was "in the mood". Three days later I looked at it and found that I'd plugged the D2Mac board in slightly too far to the left. Each of the connector pins was displaced and in the wrong hole! Luckily no damage was done and it worked perfectly once I'd installed it correctly.

This week two more arrived. An MSS1001 had clearly been treated to a drink of coffee. Luckily this had washed over the power supply without touching anything else. I flushed the board with soapy water, followed by Isopropanol and a blast with the hair dryer. Surprisingly, it worked perfectly after I had fitted the Satkit.

The other was an MSS501-IP which, the customer reported, kept displaying the message "Motor Error" and lines on the picture. Both of these symptoms are typical of capacitor faults so I simply fitted the complete "Relkit". That seemed to do the trick.

Pace PRD800

A repairer brought me a PRD800 which he had been given by his customer as "whistling then dead". He replaced C5, C7, C8 which fixed this fault but was left with horizontal lines across the picture on most (but not all) channels. Some horizontal and some vertical channels were not obviously affected. After spending hours replacing every capacitor in the unit, he brought it to me in desperation.
"It's not affected by heat or cold" he volunteered. "Used a whole can of freezer."
I removed the PCB assembly and looked underneath.
"Where's the RF modulator screening cover?" I asked, innocently.

Write me an Essay

I receive quite a few letters and Email and, provided that an address is given, I reply to them all. Some of them are interesting and amusing I like those but some are simply frustrating and I have to force myself to reply politely.
The worst is the one-liner that says "My BTxxx123 must have a faulty crystal because it won't tune in. All I get is snow and squiggles. Thanks. J. Bloggs".
Firstly, this is boring. I like a friendly, informal style that tells me about the person and, secondly, the description of the symptoms is abysmal, there is no mention of tests carried out or of the level of expertise of the writer. I am hardly inspired to write a technical essay if J. Bloggs has no soldering skills or electronics knowledge. He might as well go to his local repair shop!
If you want a useful reply, tell me a little about yourself so I can judge your level of expertise. What equipment have you? Tell me if the LNB supply voltage is correct and what happens if you swap the receiver for a known good one.
Finally, the best way to contact me is by email. "No computer" is no excuse nowadays you don't need one. I notice that you can get a simple Internet box that plugs into your TV and offers free Internet access for just 299 from Satellite Scene in Derby (01332 812588).