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.