The MSS1000 occasionally suffers power supply failure, in common
with most other receivers. I've had a few, however, where the power
supply appeared to be dead but produced a faint ticking noise.
Disconnection of the Dolby Prologic Sound board would bring the unit
back to life and the problem has been traced to one of the 4280 power
amplifier chips on the sound board.
Very occasionally, replacement of the 4280 I.C.s has not produced a
complete cure and I've had to change surface mount parts as well: D1
(4v7 zener), Q3, Q4 (BC846B) and Q6 (BC856B). It's also worth
checking the high current diode D54, an FES8FT, just in front of the
main PSU transformer since this can go short-circuit and cause the
same symptoms. Also, as I've mentioned previously, I usually replace
all the electrolytics, as supplied in RELKIT 10..
If the power supply remains dead even after disconnection of the
sound board then you'll need SATKIT 10. However, don't assume the PSU
is dead just because the front panel fails to light up. This could
have many different causes. Always measure the power supply secondary
voltages.
In every town there's a dabbler and ours is no exception. A dabbler
is somebody who likes to "fix" things but really hasn't a clue. All
the dabblers I know have a car registration number after their name
like "G0ZZZ".
Geoff up Castle Street had to pass an exam to get his registration
number. Apparently he is now qualified, not only to practise morse
code, but also to repair anything remotely associated with
electricity!
Unfortunately, he informed his neighbour of this and she believed
him, which is why Mrs Smith's PRD800 was sitting on my bench looking
very sad. Luckily the damage wasn't too severe. At first sight it
seemed that the tuner might be dead, because there was no sound and
no picture. However, there was no LNB voltage, either, and it soon
became obvious that none of the video circuitry was working because
the 12 volt supply was missing. Usually this is caused by broken
tracks to the regulator REG1 but, in this case, the input voltage to
REG1 was less than 5 volts. Again, I would normally assume that one
of the silver "via holes" had gone high resistance, as sometimes
happens, but the knowledge that someone had dabbled made me look more
closely.
In fact the problem was caused by D14. Normally this is a BYW98 or an
EGP30. In this case it was neither and it had become a DUD-1 because
"somebody" had fitted completely the wrong type. I'll never know what
the original fault was but the power supply had had a home-made
junkbox "kit" fitted. It worked but it wasn't safe so I replaced
every component with the correct type. As with most cowboy repairs,
the BUT11A was the under rated plastic version and it was "on
stilts". Why do people think it will run cooler if they mount it like
this? The correct method is to push the transistor down, until the
shoulders of the pins touch the PCB, then bend the pins underneath to
form a mechanical joint before soldering. If it's not fixed
mechanically like this, knocks and vibration can break the copper
tracks.
I don't do many D2Mac repairs most get sent to the experts at SATFIX
in Swansea but the SRD600 is an exception. The faults in this are
often quite simple to fix and I'm prepared to tackle it myself.
However, one particular example had been back to me three times each
time from a different dealer. Clearly the owner was unhappy with my
diagnosis but I had written the same report on the label each time.
Without repeating the exact words, I had implied that reliability
could not be guaranteed because of something the cat had poured
inside!
This time it was Wossname up Church street who brought the same
receiver to me.
"Stinks" he commented.
"Wasn't me, I replied, sheepishly."
"No, this Amstrad stinks. Think the dog did something. You do it for
me. I know nowt about these DeeMacTwo things."
Having pointed my dish at 1 West, I put the unit on test.
Occasionally the picture would appear to lock but most of the time I
could see only a mess of black and white lines.
I repeated the exercise which I'd done before but this time I
scrubbed the Mac board with a toothbrush whilst pouring generous
amounts of isopropanol across it. I dried it with my hair dryer and
had to open the windows because it made me feel quite dizzy. Lucky I
wasn't driving that day!
Finally, I sprayed WD-40 across the board to chase off any remaining
moisture.
Now the unit gave a perfect PAL picture but there was no Mac sound
and it gave strange messages when the card was inserted. Audio
problems are usually cause by the AMU2481 demodulator or the DMA2281.
However, neither of these was likely to cause problems with the card
so I guessed it was a fault in the DMA2286. Now these square chips
are mounted in sockets and there are two ways to remove them without
damaging the socket:
1). use epoxy resin to glue a paperclip to the chip then hook a
screwdriver through the paperclip and lever it upwards, using the
side panel as a fulcrum or
2). use the proper tool. I've seen this tool in a catalogue for 27
plus vat but mine came from SatCure for 6.95. It was worth every
penny because the DMA2286 cured the fault. Unfortunately, this I.C.
itself is rather expensive so the repair was not cheap. A pity
because I still could not guarantee the
reliability.
This D2Mac decoder seems to be "flavour of the month". The problems
stem from the fact that it's actually not a true D2Mac
decoder but a cable box and gives grainy and/or flickering pictures
when used with some receivers and TVs. It also needs a modification
to work with some smart cards. I've had numerous letters and email
enquiries about the CTU900 and most of the time I direct people to
the free information at the SatCure web site
<http://www.netcentral.co.uk/satcure/> or, if they want the
upgrades done professionally, to SATFIX in Swansea (01792
781673).
Most customers are friendly and grateful when a repair is completed
but some are just downright ungrateful! Mr Soditall fell into the
latter category and I almost told him where to put his GRD150. He
insisted that I collect it from his house I normally charge for call
out and, unlike some businesses, I get around this by advertising
"Local call out" instead of "Free call out".
Having collected the receiver, I put it on the workbench to test it.
The mains fuse had melted. This is quite common with this model and
also with the Nokia SAT1700 mk1 and the Cambridge ARD200 (and "badged
clones").
The fuse has actually been chosen to protect the receiver from mains
voltage spikes and does so with alacrity. I tell the customer to
avoid the use of electric hand tools and vacuum cleaners on the same
ring mains or, if this is unavoidable, to fit a spike suppression
plug to the receiver.
I returned the Grundig GRD150 to its owner and tried to explain the
problem to him.
"But it's under guarantee if it fails again?"
"No," I replied. "I recommend that you fit a spike suppression plug
but I still can't guarantee that the receiver will be trouble-free.
It depends on the cause of the surge and the size of the voltage
spike."
With that, he refused to pay me and slammed the door in my face! Now
this was a few months ago and he paid after I had posted him the
invoice twice but only after discussing it with Trading Standards. My
invoice was only for the call out, by the way. I didn't charge for
the fuse or for labour.
In previous articles I have mentioned tuner problems with the
SR950/SRD700 models cause by failure of one or more of the 10 F
capacitors inside. Such failures are now becoming commonplace but I'm
also seeing receivers with faulty EEproms. In the case of these
Amstrad models, the symptom can be either "Stuck in standby. LNB
voltage tripping" or "Autotune works but no channels are stored".
It seems that the EEprom can be damaged by voltages applied to the TV
scart socket by certain models of TV. To prevent reoccurrence,
disconnect R95 and R96 (270 ).
Customers have asked if this model can have a Decoder scart socket
fitted. It can but it might also need about 20 components in
addition! A few had these factory fitted but most did not. A list is
available.
I've mentioned the following fault previously but not in connection
with the MSS300.
Early versions of the Pace MSS500/1000 and also a few MSS300
receivers had a 22 F electrolytic carrying the 22kHz filament supply
to the vacuum fluorescent display. After a few years "on a low gas",
this capacitor can go open-circuit. The display becomes dim and
eventually winks out completely.
Pace recommend replacing this front panel capacitor, C2, with a
multilayer ceramic 1 F/50v device since this is better able to cope
with the current. The MSS300 is easy to fix but the expensive front
panel in an MSS500/1000 is easily damaged and the instructions in the
service manual must be followed to the letter.
Over the months I have learned to recognise the position of C2 and
nowadays I simply solder the new capacitor to the back of the board,
leaving the existing 22 F in place. Done this way it's a two minute
job.