Barry is an electrician with a rather cavalier attitude towards
safety and a somewhat simplified view of science. His Amstrad
receiver appeared to be well cooked.
"You've had this in an oven!"
"Nah, but I kep' 'im covered up all right. Heat needs oxygen t' burn
an' 'em 'en't 'avin none o' tha'.
I refrained from pursuing this subject and told him to leave his
receiver with me. Barry toddled off to replace Mrs Jenkins' fuse. He
made his own by cutting four inch nails into pieces.
"My fuses is cheap an' 'em never melt" he had once pointed out to me.
I couldn't argue with his logic. While I was thinking about it, I
removed the top from his receiver plug, removed the roll of aluminium
foil and fitted a 3 Amp fuse for my own peace of mind.
The SRD520 had distorted right channel audio which caused distortion
on RF output audio, too, since left and right are mixed before
entering the RF modulator. It took me nearly an hour to trace the
cause of the fault to R89 (15k) which is connected to TR21 behind the
sync-separator board. The resistor was open circuit and hidden under
black glue.
The note on this British Telecom badge receiver said "DEAD" and,
indeed it was. However, this was not surprising because some idiot
had replaced the 4R7 and two 2R2 fusible resistors with 47k high
voltage types! The 10R 5 Watt ceramic resistor was open circuit. That
wasn't surprising, either, because the plastic-body switching
transistor had been replaced with a metal-tag BUT11A, bolted firmly
to the metal heat sink.
I replaced the 10R/5W ceramic resistor and fitted all the parts from
SATKIT 17, including the BUT11AF, the optocoupler and the TL431
variable zener. Measurement of the other primary-side components
revealed no other problems so I connected mains power and was
rewarded with perfect operation.
This was somewhat surprising since the decoder often fails in this
model and requires the fitting of RELKIT 17 to get it working
again.
While I remember, look out for a batch of BUT11A transistors marked
"932" which have been in circulation since early 1997. They are not
correctly rated and cause switch mode power supplies to erupt in an
often spectacular explosion. If you have any in stock or receive any
in a future order, return them to the supplier with a copy of this
article.
I'm a great fan of the Internet, as you may have noticed. Web Site
order forms are becoming common and often provide a quick and easy
way to place an order. Some firms even offer a discount if you use
their web site order form because it allows them to automate the
invoicing system.
One major supplier advertised a discount "if you order via the
Internet". Unfortunately, this description was too broad since orders
sent by e-mail also fulfil the "via the Internet" requirement but
require human intervention in the invoicing process. Consequently the
discount was refused for e-mail orders. One wonders how this would
stand up in court! Unfortunately, the order form system refused to
accept certain order codes, despite the fact that these parts were
listed on the computer (as confirmed by telephone). Promises to "ring
back shortly" to sort out this problem were not fulfilled and orders
were eventually faxed in the usual way to avoid further delays.
Another problem (common with many "professional" web sites) was the
excessive use of pictures which create long delays before the order
form can be displayed on the screen. Luckily I had previously had
excellent service from this company, otherwise I might have gone
elsewhere.
Many smaller companies such as Telepart (www.telepart.co.uk) and
SatCure (www.netcentral.co.uk/satcure) provide easy to use order
forms which list the available spares and appear on screen without
excessive delay.
A lot of repairers still ignore the advantages offered by the
Internet. Nowadays there is little excuse since a suitable computer
or "Internet set top box" (www.satelliteuk.com) can be bought quite
cheaply and used for other purposes as well. Internet connection can
be free and even the cost of the telephone call can be eliminated if
you agree to accept a few adverts each week (www.freecall-uk.com).
The advantages include the availability of free technical help from
manufacturers and like-minded repairers worldwide (contact
satcure@netcentral.co.uk) as well as the possibility of discount on
orders.
Finally, I must mention that my e-mail address is now
"jacksat@netcentral.co.uk". I change it from time to time to
eliminate the build up of "junk mail" (one of the disadvantages!)
Also, it ensures that those people who buy "Television" on a casual
basis do not continue to receive free help for very long! (The old
address will continue to work for a few more weeks for the benefit of
overseas readers who have to wait longer for their favourite
magazine!)
Another receiver from the British Telecom stable, the SVS260 is made
by "The Orient Power Video Manufacturing Company Ltd." based in
Kowloon, Hong Kong. I actually found their Internet web site by using
the "Sherlock" search system on my Apple Macintosh computer.
Unfortunately, they did not reply to my e-mail message so we are
still lacking service information, apart from the booklet from
SatCure.
This receiver came in with a complaint of "humming". I thought that
might refer to a buzzing noise from the transformer laminations (yes,
no nasty SMPSU) but it was silent. The audio from the TV speaker was
perfect so I left the receiver to "soak" for a few hours.
When I returned to it there was a loud hum coming from the TV speaker
on every channel. On a hunch, I squirted the large electrolytics with
freezer spray. This had no effect until the spray hit the rectifier
diodes behind the capacitors. The noise vanished instantly. Replacing
diodes (D405, D406) at the rear right corner of the lower Printed
Circuit Board provided a permanent cure. The diodes are black with a
silver or white stripe (indicates cathode end). I replace these
diodes with fast soft recovery type BYV95A which use glass bead
construction.
I had a telephone call from Wossname up Church Street about an
Amstrad SRD700. This is identical to the Fidelity SR950+ and uses a
different power supply and main board from that employed by earlier
models.
"What's the transistor that's soldered underneath the power
supply?"
"It's not a transistor, it's a TOP202 integrated circuit."
"Ah, OK, I'll see if I can order one." Click. The line went dead
before I could volunteer the SATKIT 16 that I had in stock.
A week later he brought me the offending receiver.
"No joy. Have a look at it for me, there's a good chap. I'll just be
at "The Swan." You can buy me a drink when you've fixed it!"
I muttered under my breath and took the receiver to the workshop.
Thje screws took no time to remove because, as usual, he had lost
them. The power supply actually tried to work but the front panel LED
was flickering, as was the blank raster on the TV screen. I removed
the power supply. He had actually made quite a neat job of the
repair, although I felt that he'd been over generous with solder on
the TOP202. Hopefully he hadn't destroyed it with the heat!
A working power supply from another receiver produced pictures and
sound so I investigated his power supply further. It appeared that he
had used 85 degree capacitors (OK for now) and had not replaced the
optocoupler or the TL431 adjustable zener (judging from the lack of
black treacle around the pins). I replaced both components and the
power supply sprang to life. For reliability I replaced the
capacitors with high temperature types and also those in the tuner
module (as supplied in RELKIT 16) since the decoded pictures were
very "streaky". The "Lion and Swan" now seemed very inviting. I hoped
Wossname had brought his wallet.