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The same receiver which I mentioned a short time ago came back "under guarantee." It never ceases to amaze me that people will claim "it's the same fault as before" when the symptoms are totally different. I wonder if those people return to the tyre fitter and say "It's the same as before. It won't go!"
In this case, the receiver which was previously "dead" now had a blank screen apart from the channel identifications.
"Told you so", announced the lady. "No picture, same as before."
I didn't bother to argue, even though the German channels produced perfect pictures. She trotted off to Sally's Cafe for a cup of tea while I pushed all the other "urgent" jobs aside to look at her receiver. I fitted the 5 volt link wire to the decoder, since a bad connection in the ten-pin header is a common fault. When this had no effect, I replaced the TEA2029C. No better. I was becoming alarmed by this and replaced the 4u7F electrolytic nearby. I was sure it was lack of sync. pulses that was causing the problem. Finally, I realised I was overlooking the obvious and replaced the 503kHz resonator. Success!
This little fellow is very fragile and can be damaged by knocks.
When the owner returned I greeted her with the bill. She fumed and argued and finally announced: "Right. I'm ringing Trading Standards!"
I'm used to this. I picked up the telephone and punched in the number.
"Hello Trading Standards? Good. Hold, please. I have a call for you."
I handed the 'phone to her and went out the back to make myself a cup of tea.
When I returned she had gone and the 'phone was back on the hook. I pressed "redial" and a familiar voice answered.
"Did you give her the usual story?" I asked. "Oh, good. Thanks, little brother."
We've practiced this over the years. I picked up the cheque and went back to my workbench. I think of myself as a benefactor. She would have lost the case if it went to court. After all, they would need an "expert witness" - someone who really knows his stuff and has written books and magazine articles, you understand. It makes the Prosecutor's life difficult when the defendant is also the "expert witness"!
This receiver arrived with the symptom reported as "no sound" which I confirmed. However, it also had no decoder messages and the pictures scrambled intermittently. I checked the "Contrast" but that was set correctly at "4".
The cause of "no sound" was the MSP3400 - quite a common fault. Sometimes it's caused by excessive voltage on the nominal 5 volt supply. I measured this one as a whopping 5.5 volts, even after I had replaced the 22uF and two 10uF electrolytics near the TEA2018A PSU chip. I turned the board upside down and located the 9k1 surface mount resistor that trims the output voltages. Changing this to 8k2 reduced the 5 volt rail to a more reasonable 5.25 volts. That should improve the reliability.
The cause of the intermittent decoder fault was not obvious so I replaced the PTV111 sync separator I.C. and the 503kHz resonator, as well as the 1uF capacitor C109 (use a Bipolar type) close to the I.C. That almost did the trick but the video level was a little low and the picture still scrambled briefly from time to time. There was a suspicious burn above a surface mount transistor towards the rear of the board. It was marked "3B" - a BC856B - so I replaced it with a BC857C, which has a slightly higher current rating. The receiver now worked correctly.
Another MSS300 arrived and the bald headed owner (join the club) announced that it was "dead". He was correct. The fuse had melted but not soon enough to prevent failure of Q5, the BUT11A, and R49. I replaced these as well as C59, 60 and 61 which gave no reading at all on my ESR meter. The 47uF/400v reservoir capacitor measured 5 Ohms and, although its capacitance was still 45uF, I wasn't taking any chances, so out it came! I'm used to seeing readings of 2 to 3 Ohms for these. Anything higher is a sign of imminent failure.
Now that this receiver was lighting up I could look for the other reported fault of "intermittent scrambling". In fact it was difficult to see whether it was unscrambling or not because the picture was obscured by a mass of dashed lines swirling around the screen. I decided that this receiver had been well cooked - the board looked very dark - so I fitted all 27 capacitors from Relkit 9. This was tedious but it was worthwhile as the resultant picture was free from interference and there was no sign of "intermittent scrambling". I checked and found that the "Contrast" was set to "3" so I changed that to "4" as a precaution. All Pace receivers have the contrast control circuitry before the decoder. Consequently, adjusting the "Contrast" affects the video level going into the decoder which, unfortunately, is a tad fussy about that level!
Pace Apollo 120
This is really an MSS200 without the channel number display and I suppose you could call them both "cut down" versions of the MSS300 with which they share a common circuit board. However, the MSS300 has a twin-input tuner and a vacuum fluorescent display panel, together with a different microcontroller (two, if you count the one on the display panel).
When Wossname up Church Street turned up with the Apollo board under his arm I was less than pleased. The board should always be transported in its metal cabinet to guard against physical damage as well as static electricity.
"No pictures" he announced, sorrowfully. "And it ain't the tuner 'cos I've tried two. Anyway, do it cheap - there's a good chap. I'll be in the Swan."
We have a sort of love-hate relationship. He winds me up and I take it without hitting him! He loves it and I hate it. But occasionally he pays me cash so I tolerate it. I just wish he wouldn't attempt to repair things that he doesn't understand.
The tuner looked to be soldered in securely so I put the receiver on test. The power supply capacitors had been replaced, as evidenced by the vast quantities of brown flux which he'd apparently ladled on with a trowel. Where does he buy his solder? There were flickering pictures from the decoder Scart but no audio at all and no video from any other socket. I looked at the circuit diagram and narrowed down the fault to a small area of board.Once again there was an obvious brown mark above a transistor which I identified as Q42 - a BC856B behind C231. This was the one that I'd replaced in the MSS300 earlier. A BC857C produced a nice clear picture. The capacitors seemed fine so I replaced the MSP3400 and was rewarded with good audio as well.
A month ago I would have said the analogue repair market was dying but there are still people willing to pay money to get these receivers going.