Satellite Workshop 18
I had my first look at a Prima when a local installer brought one in
for repair. "It's dead" he announced and scarpered. I did wonder why
he didn't simply return it to Pace under warranty but it was too late
to ask. I soon found out why: several cracks radiated outwards from
the PCB mounting pillar, close to the power supply. Luckily, none of
the cracks had reached the live side of the circuit so I decided that
a safe repair was feasible. I did not attempt to solder fine wire
directly to the damaged tracks but, instead, soldered "Kynar" wire
(teflon-insulated single-strand) across solder pads nearest to the
breaks. I used blobs of glue to secure the wires to the board
("Tak-Pack" is best). This is an essential operation from the safety
aspect because a loose wire might conceivably touch part of the live
circuit.
When the installer returned he seemed surprised that the receiver now
worked. "Spaghetti junction underneath?" he asked. "Wires everywhere.
Will it be reliable?" Since I had reinforced the board with epoxy
resin, cured with the aid of a hair dryer, and I was happy with my
neatly soldered "spaghetti", I assured him that it would be perfect.
However, I spoke too soon. Within half an hour he burst angrily into
the workshop and slapped the receiver down on the bench. "Won't
respond to the remote!"
I connected the receiver and tested it with my own handset. No
problem. On questioning, he admitted that he was using an MSS200
handset which, although similar in appearance, uses a different code
set. The Prima handset can be distinguished by the designation
"RC-10" at the bottom right corner of the keypad.
Remote control handsets have many uses: apart from dislodging the
cat, stirring tea and throwing at the spouse, they are often used to
change channel! The small, uncomfortable-looking man, who trailed in
after a contrastingly large and domineering lady, clearly fell into
the "spouse" category.
"'E 'it it wi' 'is 'ead" explained the lady, demonstrating the point
by tapping a handset on the poor guy's bonce. "Now it's gone dead.
We'll be back for it in an hour, shall we?" she commanded.
I decided that this job was urgent and pushed aside a FilmNet decoder
to make room on the bench. The handset was for the Pace PRD range. I
checked the batteries which measured a little over 3 volts in series.
There was no infra red output when the buttons were pressed. Pace
handsets are not the easiest to take apart and many people either
wreck them or give up. My method is to warm them up with a hair dryer
which makes the plastic less brittle. I twist the casing with both
hands until I can see the split line start to open. Then I insert a
blunt penknife blade and gently ease it along, unclipping the two
plastic shells as I move it. Don't be afraid to twist the handset
hard. The circuit board will not suffer and the plastic won't break
if you have made it nice and hot. This method works with Amstrad
handsets, too.
The usual problem is that the 455kHz ceramic resonator legs snap.
Simply solder two wires into the board and solder the legs of a new
resonator to the wires. Glue it down, unless you like repeat
business! Occasionally the LED fails instead. I test it by connecting
12 volts across it via a 1k resistor. An infra-red sensitive key fob
is all that's needed to see if it works.
The lady owner returned after 59 minutes, snatched the handset from
the counter and demanded a fiver from the small man whilst testing
his cranial reflexes with the newly repaired weapon.
"'Ow much?" she demanded.
"Erm, a f' fiver will do nicely." I stammered. Not to appear too
downtrodden I qualified that with "Special discount, of course."
No sooner had she gone than the milkman appeared with a handset. This
was for an Amstrad SRD510 and extremely sticky to the touch.
"Dropped it in the milk, did you?" I inquired.
"Coke" he countered, waving a bottle of well known fizzy drink in
front of my face. "Spilt half the blooming bottle, darn it. Low
sugar, too."
I dismantled the handset, using the hair dryer to soften the plastic.
Inside was brown goo. I used a toothbrush and Isopropanol to clean
the silicone rubber keypad and the conductive contacts on the circuit
board. Then I scrubbed the plastic housing shells with warm water and
detergent. The hair dryer quickly removed the moisture from all the
parts and when I reassembled the handset it worked perfectly.
"Just a tenner," I told the milkman on his return. (He's smaller than
I am. Anyway, he'll get some of it back as his Christmas bonus!)
A dealer brought an SRD500 to my workshop last week. It bore the
label "LIVE" but no other information. The dealer was reluctant to
explain, muttered something that sounded like "kit" and scurried back
to his van. Being a cautious sort, I did not plug it in but removed
the cover instead. Just as well; the white ceramic radial-lead
surge-limiting resistor had been replaced with an axial-lead type.
The live wire had been pressing against the steel top cover. I
resolved to ask the dealer if his public liability insurance was up
to date.
My brother is manager of a local trout farm. He brought me a PRD800
which belonged to one of his lads. Apparently it would decode "Sky
One" but no other channel. The card had tested all right in a
different receiver. Suspecting a problem with the contrast setting, I
plugged the receiver in. It didn't light up at all but there was a
nasty smell of fish. Fearing the worst, I removed the cover. The
receiver was perfectly clean inside so I reconnected the power and
tried again. This time the display lit up dimly. I could change
channel but there was no picture or sound. The dim display and fishy
smell gave me a clue. I measured the microprocessor supply and found
it to be only 3 volts! Sure enough, C15 had leaked, hence the smell
and the low dc measurement. Replacing C15 restored the receiver to
normal and the card produced clear pictures on all encrypted Sky
channels.
Some customers won't settle for medium-rare; they like their
satellite receivers to be well done. The MSS1000 which arrived by
carrier from Birmingham was one of these. I knew it had been cooked
when I saw that the rubber feet had disappeared, leaving a sticky
mess behind. The circuit board had gone completely black in places
and my first move was to replace every single electrolytic capacitor
in the power supply section. This cured the "dead" fault (actually it
was "tripping" at high speed). I left the receiver on test and, after
an hour, the decoder messages disappeared. Liberal application of
freezer aerosol pinpointed the culprit as the PTV111 sync separator
chip. However, replacement (twice!) failed to eradicate the fault.
After some thought, I replaced all the electrolytics around the I.C.
and, as usual, it was the very last one a 1 F. Next time, I really
must remember to replace the last one first!
From time to time I still see Ferguson SRV1 receivers (the Pace
SS9000 clone). The large, buxom lady who brought in the latest one
obviously meant business as she thumped it down on the counter and
informed me:
"I just collected this from that silly sod, Wossname, up Church
Street, you know, anyway he said the power thingy's dead but he
couldn't fix it and he's had it six weeks so I've got it back now and
I want it tomorrow otherwise HE's going to go bonkers 'cos of the
football, you know."
I took advantage of this pause for breath to inform the large, buxom
lady that it would certainly be ready tomorrow, yes definitely,
madam, without fail and no, we don't close for lunch.
An hour later I was beginning to regret the rash promise and starting
to understand why Wossname, up Church Street, had been unable to fix
it. Something was Wrong with it and I
couldn't figure out what. I'd replaced every single component in the
power supply, including the horrible little surface mount ones, and
still it wouldn't work. All the dc voltages on U23 were correct but
it simply refused to oscillate.
With the aid of a cup of tea, I compared the board with a scrap one.
About to give up, I suddenly spotted the problem! Pins 14 and 15 on
U23 are supposed to be joined via a common pad but, on the offending
SRV1, somebody had run a knife between them, neatly dividing the
copper pad. Clearly Wossname, up Church Street, had assumed a short
circuit was present and had removed it. So skilful was his work,
however, that it needed an eyeglass to confirm it. A blob of solder
cured the fault at once.
I've mentioned this model previously because it tends to suffer from
memory corruption if the power supply fails and also because it seems
prone to dry joints on the infra red sensor pins. A variety of
symptoms is produced but most common is that the LNB voltage can not
be changed or else odd things happen in the menu settings. Martin
Pickering of SatCure has asked me to point out that his new
"Satellite Repair Manual edition IV" incorrectly lists a factory
reset code which is actually for an earlier model. Unfortunately, the
STU824 actually has NO reset code so the only way to reset it is to
download the information from an identical model or to replace the
EEprom which is a 24C16.
picture supplied on disc
It seems that every person in Scotland owns one of these; possibly
because they were produced there. Unfortunately, they do not seem to
tolerate the moderate warmth of Glasgow, and the plastic cases become
brittle as a result. The Scotsman who dispatched one to me clearly
didn't understand that "packing" means more than a Sainsbury carrier
bag with my address glued to it. The receiver was well and truly
smashed. Luckily, I still have a few "unrepairables" in the workshop
and I was able to use the mouldings from these. The initial fault
symptom was that the screen was black, apart from the top few
centimetres which were white. This looked like a power supply fault
so I replaced all of the large electrolytics.
The improvement was noticeable but the picture was still obscured by
hum bars and interference lines. I removed all fourteen 1N4003 diodes
by the usual method of cutting each lead flush with the board then
poking the remainder through with my soldering iron. This is the only
way to avoid damage to tracks and pads. With new diodes neatly formed
and soldered in place, the picture was almost perfect. However, the
sound was extremely crackly and a loud hiss was apparent in the
background.
I replaced the middle crystal, the U2829 FM demodulator IC and all
the electrolytics around it. The sound was much improved but still a
little sibilant. Since I'd already spent an hour on the job, I
decided to call it quits. I've heard worse sound, straight from the
factory.