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Sunday, 27 December 2015

Replacing the LCD module on a Yamaha DX11 Synthesizer

So here is the problem. The LCD on my Yamaha DX11 synthesizer has faded so much that I can barely see what instrument I am playing - as you can see in the photo above. It appears that the seals around the edge of the glass panel have failed, because the fading started at the outside edges and has progressed inwards. When switched off the LCD is a peculiar pink colour, which you can see in the photo below. The old LCD is on the right, a new one on the left. (Note that I have already transferred the plastic bezel from the old LCD to the new one - it is held in place by a double-sided adhesive strip).
But where do you get replacement parts for an instrument which is probably over 30 years old?
I opened up the the synth and measured the size of the thing and then trawled through catalogues looking for similar devices. I found the Displaytech 162B-BC-BC looked to be the right shape and size, and the row of pins was in the same position along the bottom edge. The Displaytech part has 16 pins instead of 14, but I could see from the datasheet that pins 1 and 2 were connected to the backlight. It was readily available from RS Components at £7.94 (Part number 532-6379) so I ordered one.

While I waited for it to arrive I found the Service Manual for the DX11 on line, and that confirmed that, apart from the two extra pins for the LED backlight, the connections were exactly the same on the two displays.

I had to extend the wires on the LED backlight, and my attempts at desoldering the 14-pin header on the old display were unsuccessful, so I cut the wires one by one, and soldered them to the new display module. The wiring between the connector and the module is 1 to 1, but since the wires are not colour-coded (except for pin 1), it is wise to move them one at a time. In the picture below, you can see the LCD module, nestling in the middle, between the larger PCBs. It is held in place by a metal surround which is secured by a single screw.
 This picture shows the two modules side, by side, before I transferred the wires, so the old one is on the right and the new one on the left.
 The picture below shows the new module in position, with the metal surround back in in place and the LED backlight lead waiting to be connected back in the socket on the main board.
It was a great delight to see the new panel light up with nice clear text. I was expecting to have to make some adjustment to the contrast control resistor, but this was not necessary. The Displaytech module seems to be electrically very similar - even the character fonts seem to be equivalent. A thin metalic strip of the bezel is visible at the top and bottom of the LCD window, and it might be nice to black that out with a strip of black tape or even marker pen. But I couldn't be bothered to take it all apart again.

Happy Christmas and 73 to you all.
Hugh M0WYE

Sunday, 13 December 2015

Apparatus for the Testing of Christmas Tree Light Bulbs

Apparatus for the testing of Christmas-tree light bulbs. I got very frustrated trying to test Christmas-tree light bulbs using a multimeter. Almost impossible to hold the probes on the little wires. I thought about making some kind of bulb-holder, but then hit upon this idea, using a wooden clothes peg. 

Copper tape is wrapped around the ends of the arms and secured with a soldered joint on the outside of the peg. Wires are attached and connected to a battery which can be conveniently carried in a pocket.

The peg is clipped across each bulb as it is removed from the chain. The battery should be chosen appropriate to the Voltage rating of the bulbs - mine are 2.4V - so a part-used "C" cell makes the bulb glow dimly, Note small screw positioned between arms of peg to prevent it closing fully, this is important as it prevents the battery being shorted when no bulb is present

Even though it was dark by the time I had finished it, I was still able to get the set working. The wires on some of the bulbs had become tarnished and so there were multiple"failures" within each series string of bulb. The tarnish seems to be due to age rather than moisture as the new bulbs in the pack had also gone the same way. Happily a little scraping with a craft knife soon got them going again.

Happy Christmas and 73 to you all.
Hugh M0WYE

Friday, 28 August 2015

I am the proud possessor of a Tesco Hudl (Mark 1). For those that are not familiar with this marvel of modern technology, it is an Android Tablet computer, with a 7" screen and all the usual features that this class of computer offer. It has a built-in compass and accelerometer, and of course GPS receiver, so that it knows its position and orientation on the planet's surface. I have been using the "Augmented Reality" App called Stellarium which puts a planetarium on your tablet screen, and, if you enable the feature, when you hold the tablet up against the sky it will show all the stars and planets in their correct positions ... or at least it should do.

Conjunction of Jupiter and Venus on 30th June 2015 (Top left of image!)

Conjunction of Jupiter and Venus on 30th June 2015
It worked when I first installed the app, but recently I have found that the screen won't turn when I do, it always points in the same direction. It was very frustrating, standing out in a field with my son, looking for the conjunction of Jupiter and Venus, and not being able to locate the planets in the sky. Today I realised what the problem was.

On a recent visit to Tesco I noticed a box of nice leather Hudl covers being sold off cheap. Now that the Hudl2 has been released, I guess the accessories for the old model are not selling so well. Ony a couple of quid, so I popped one in the shopping basket. It protects the screen nicely and can even be used as a desk stand. The magnetic catch keeps it closed when not in use ...
Ah ha! - what kind of a product designer puts a magnetic catch on a device which contains a compass?!

I wonder how many other people have been confused by this.

Wednesday, 8 July 2015

0603 Resistor Codes

I was looking at a Printed Circuit Board populated with 0603 size surface mount resistors and puzzling over the markings. In particular R45 and R56 in the photo below. They are marked 18C, but the actual value is 15k.
 Now in the old days resistors were colour coded, and we all knew the code off by heart, Black = zero, brown = 1, red = 2 etc. There were usually three colour bands - 1st digit, 2nd digit and a multiplier which represented the number of noughts. So 4.7k was yellow, violet, red, for example. There might then be a gold band for 5% tolerance, or brown for 1%. Even when "E96" values came in, and many more "preferred" values were needed, it was just a case of adding another colour band to make three digits and a multiplier. This system was carried over onto surface-mount parts, but in numerical form. You can see some examples below - there is a 473 (47k) and a 223 (22k). But there is also 01C  and 30C which don't make much sense.
The answer to this is, of course printed in the data sheet for the resistors. It is is a way to address the problem of marking E96 values - presumably 0603 size parts are deemed too small to put four digits on. 

Perhaps an aside about "preferred values" might be appropriate here (although there is a very good Wikipedia Article about it). When a resistor is manufactured there is a tolerance in the value, perhaps +/- 10%, or 5% or 1%. So a 1000 Ohm resistor might be, say, 5% high (1050 Ohms). So there is no point in making a 1050 Ohm resistor because the value would overlap with 1000 Ohm. The next "preferred value" is 1100, because a 1100 resistor which was 5% low would measure 1050. For 5% tolerance resistors there are 24 non-overlapping values in each decade, and the sequence of values is called the E24 series. 10k, 11k, 12k, 13k, 15k, 16k, 18k, 20k, 22k, 24k, 27k, 30k, 33k, 36k, 39k, 43k, 47k, 51k, 56k, 62k, 68k, 75k, 82k, 91k, For 1% values there is an E96 sequence which requires three digits to represent each value. You can see this sequence in the table below which gives the manufacturer's 0603 resistor code on the left and the E96 value on the right. The Letter is the multiplier code.
So "18C" is indeed 150 x 100 = 15k Ohms. 30C is 20k Ohms, and 01C is 10k. All has become clear.

Now to print out this table and pin it up at my work-bench!

Monday, 6 July 2015

Fully Licensed Wireless Receiving Station

You will no doubt be greatly relieved to know that my two Great Aunts, Ethel and Nora, who lived in Norwood, South London, and who cached all this Crystal Set paraphernalia, were fully licensed. If you wanted to set up even a simple radio receiver to listen to the BBC in the 1920's you had to hold a valid licence. The annual charge for this was 10 Shillings (or 50p in new money). Although this sounds a trivial sum by today's standards, 10/- was quite a lot of money then, not just a coin, but a bank note.
 The paper these documents are printed on is very transparent - almost like tracing paper (or Izal toilet paper!). The conditions are printed on the back, and some of them read in much the same way as the UK Transmitting licence. This licence ran for a year from November 1923 to October 1924.
The design seems to have changed for subsequent years, here is one for 1928 - 9.

If you want to read more about the UK Radio Receiving licence, there is a very good website here: The History of the UK Radio Licence

Sunday, 5 July 2015

Crystal Set

The last of my cuttings gives details for building a crystal set. There were many different designs, mostly trying to improve the "Q" of the coil and so the selectivity. Any of you who have tried to build one of these things, hearing the radio stations is not usually the problem - it is hearing them one at a time. But here the listener is simply trying to get the most volume, and a very simple circuit is described - presumably sacrificing selectivity for output.

Saturday, 4 July 2015

Adding a Thermionic Valve to your Crystal Set

Today's radio cutting describes how to add a thermionic valve (tube) to a crystal set as a radio frequency amplifier.
It is very difficult to describe a circuit in words, and a shame the editor didn't allow a circuit to be printed. However, trying to understand the description as best I can, I have come up with the circuit below ...

I think ATI stands for Aerial Tuning Inductor, and together with the variable capacitor (condensor) which is mentioned, these provide the means of tuning the modified set. (Some values for these components might have been useful!) I assume that a triode valve, with a filament is envisaged (we are talking 1920's - so indirectly heated cathodes were not in use). Again no type number or Voltages for the HT (High Tension) or heater (Low Tension) batteries are given.

It also troubles me that the crystal set is connected into the anode, or plate circuit of the valve - directly connected to the high tension terminal of battery, which might be, say 120 Volts. This could have been an electrifying experience for the listener wearing the headphones if they had come into contact with the terminals or uninsulated wires attached to the 'phones.

An inventive person, with a good understanding of electronics might have made this work, but they probably wouldn't have needed the wordy description in the "Wireless Hints" column!

Friday, 3 July 2015

Choosing the right sort of wire

Today's snippet from "Better Radio Results" describes the different sorts of wire which may be employed with a wireless set ...
"Wireless wire" seems a bit of an oxymoron, but I'm sure we know what he means .

Thursday, 2 July 2015

Extending the tuning range of a radio receiver.

I'm sure we have all wished our radios would tune just a little bit further up the band. Well who would have thought it was so simple ... just put a small capacitor in series with the antenna lead!

Somehow I feel this might not work with modern synthesized radios. Frankly I am a little doubtful that it can even have worked with steam-powered radios, but a simple crystal set may have been detuned a little by the addition of more capacitance in the aerial circuit.


Wednesday, 1 July 2015

Rejuvenating your crystals

During the 1920's, the "Daily News and Westminster Gazette" had a regular column called "Better Radio Results". I have a few cuttings of this column, and since we are all looking for better radio results I thought I might share them.

The first is for the benefit of those employing galena crystals in their crystal set, it describes a way of rejuvenating these crystals. You will be aware that many people relied on entirely passive radio receivers which employed a point-contact semiconductor diode as a.m. detector. A thin wire, known as a "Cat's whisker" was used to probe the surface of a crystal, such as galena, while listening through headphones. Natural impurities on the surface of the crystal could form a semiconductor junction to rectify, and thus demodulate the radio signals. Evidently the galena became tarnished over time and it became harder to find the "sweet spot". Here is a possible solution ...

Hopefully it will make your "cat's whisker" the "bees knees".


P.S. Unfortunately  these cuttings are undated, however this one must be after Aug 1927, because that is when the BBC Wireless Military Band was formed.

Monday, 29 June 2015

Potato Polarity Test

Here's another little gem from "Radio, Television and Electrical Repairs (Illustrated)".
Does this actually work?!

Well yes it does! - I found a small piece of potato from the kitchen waste bin, and poked two stiff copper wires into it. The chapter in the book was talking about lead-acid battery chargers, so I applied 12 Volts from the bench power supply and very quickly heard a fizzing sound and saw a halo of green appear around the positive connection. Looking more closely at the the negative wire I could see small bubbles appearing. I assume the green colour is some kind of electro-chemical reaction taking place with the liquid in the potato to form a green copper compound.

Probably not a good idea to eat the potato after you have turned it green with copper!
As for a "quick and useful" method of testing polarity ... I think I will stick to the test meter for now.


Sunday, 28 June 2015

Fitting the SPF Amplifier in the 23cms BiQuad antenna

Today I installed the SPF amplifier in the dicast box on the back of the BiQuad antenna.

The new amp is MUCH smaller than the old one. Since I want to run the amp from a 12V supply I added the recommended 180 ohm series resistor, however I found that the Voltage across the amp was heading for over 5V once the supply exceeded 12V, so I  upped the value to 220 ohms to be on the safe side. The instructions contain warning about not letting the voltage on the drain of the chip exceed 5V. I'm not happy about the pig-tail on the coax going to the F-connector, but I can't think of a better way of terminating it yet.
At the other end, I kept the ends of the coax as short as possible at the feedpoint of the biquad.

Hopefully, with the nice weather, I might get a chance to try the aerial out this week.
73 Hugh

Friday, 26 June 2015

DXTV via Sporadic E on 50MHz

Nice strong signals from Europe on the 50MHz band this afternoon, I worked:
Jose, EA1HMP, in Spain,
Pinto CT1ANO, from Rio Tinto, Portugal
Uwe CT7AIU, in Portugal, and
Juha - using the OH5C Radio Club callsign in Finland.
But there was a lot of TV buzz. So I hastily connected up my old Plustron 5" portable and got some pictures on the channel marked "3" on the dial  ... but where are the pictures from? Is that Greek text? very few countries broadcast TV on VHF anymore.

All good fun - I haven't received any DXTV via sporadic E for ages ...

Sunday, 21 June 2015

GB1HA - Museums On The Air at Headcorn Airfield

Today we visited the Weald Radio Club at Headcorn Airfield as they operated their special event station GB1HA. Headcorn is the home of the Lashenden Air Warfare Museum, which is a good excuse to activate a station over the weekend. Tony, G4IMP has a 5 element beam for 6m, an ingenious multiband vertical for HF and a longwire which reaches over to the pole with the (ahem) wind-sock on it.

Here is Tony operating 6m (other operators are available). 6m was open to Europe with Sporadic E providing contacts to Spain, Portugal, Poland, and even Russia. There was a lot of contest traffic.

Plenty of light aircraft taking off and landing and the Sky-divers were making frequent flights in their Cessna Caravan.

There were even a couple of buzzards displaying although they weren't calling on the ATC frequency, and they didn't seem to like the parachutes.

73 Hugh

Wednesday, 17 June 2015

Some old radio and electronics books contain beautifully drawn illustrations. Often the artists are uncredited. The images are strangely evocative of a suburban era which has passed. I which I had more shelf space to collect these old books. Here's a picture from "Radio Television and Electrical Repairs (Illustrated)" which is edited by Roy C. Norris, Technical Editor of "Electrical and Radio Trading" magazine. The publishing date is not given, but a book plate indicates 1949. This is an illustration which might help those who are struggling to get rid of interfering "noises" on their radio reception!

73 Hugh

Tuesday, 16 June 2015

Four Meters open to Malta

Just worked 9H1BT on 70.200. Also heard 9H1xT. The skip was very short on 6m, - there was even a French station - that is a usually a sign that the MUF will support higher bands. While 6m was bedlam, 9H1BT was calling and calling on 4m and not getting many replies. Also heard 9H1XT working a UK station, but didn't manage to get him myself.

Sunday, 14 June 2015

Day out at Dungeness

So we've trundled out to Dungeness on the little railway ...
Oh dear looks like rain - better get back to the train.
No walk along the shingle today.
Still sunny out in the Channel.
Winston Churchill at Romney Sands Station.
New Romney Station

Thursday, 11 June 2015

Happy Hour on Six Meters

After a number of quiet days, the Six meter band was busy tonight. I worked:
CT1AVR Manuel, in Portugal,
S59A Drago in Slovenia
TK4LS Laurent on the Island of Corsica
OH1UM Pasi in Finland
OH1Z Juha in Finland
OH2FNR Jake in Finland
YT5TAS Nebojsa Serbia
IK0VWO Giovanni Italy
SM5KWU Hannu Sweden.

Back to the ATV

I got my Amateur TV folder down from the loft, last night. It contains lots of potentially useful magazine articles and datasheets that I salted away when I was trying to get active in Amateur TV ...erm ... 20 years ago!
The original design for the Twin-Quad, Bi-quad or "Bowtie" antenna that I built, is there, and I have scanned it and put it on Google Drive so that I can make it available again. Not sure about Copyright on this, I think the document came from the Kent Television group, but it looks like an extract from another publication. The original design seems to have come from DJ9HO. Anyway, if anyone objects to this being here, post a comment and I will take it down. On page 5 is a diagram showing how my version has the preamplifier mounted on the back, and it is this that I intend to replace with the SPF amplifier that I blogged about a few days ago. I found a very good article, on line, describing how to build a bi-quad antenna for WiFi use - i.e. 2.5GHz. There may be some useful design tips that could be incorporated into the 23cm version. The Author also offers a double biquad design, which offers 13dB of gain. 73 Hugh

Wednesday, 10 June 2015

Trimmer Capacitors

Today I have been looking at the trimmer capacitors that I bought at the Eastbourne Radio Rally. The bags of "10 for £2" are all marked with their values, which is good. I did check them with a capacitance meter, and they measured close to what was indicated.
Need to build some nice tuned circuits now!
I like the miniature air-spaced ones, they have a certain old-world charm, and presumably give quite high Q factor tuned circuits. The vanes are vulnerable to getting bent, but you can see clearly how much the vanes are meshed and estimate the capacitance from that. The ceramic ones are harder to "read".
I bought two of the "piston" style trimmers. They looks to be very low value pF, and can't really be measured on the LCR meter. I guess they are about 1 to 5pF, but I can't find anything quite like them on the internet. The threaded screw is wound down into the ceramic tube to adjust the value. I think I have seen similar components on UHF TV tuners in the days of analogue TV.

Saturday, 6 June 2015

SERFing at Eastbourne

Just got back from the Eastbourne Radio Rally, AKA Sussex Electronics and Radio Fair. Thanks to Peter G8WMZ for doing all the driving. Plenty of stalls, and a quite a lot of visitors, but I suspect some of the stall holders would have wished for more. I don't much like crowds to it was nice not to be jostled as one looked at the goodies. Nice bacon butties and even decaff coffee.
Peter G8WMZ and John G0GCQ looking at Peter's desk mike over a cup of coffee. Some of the stands at the show, which was in a large sports hall.
I came away with aluminium project boxes, trimmer capacitors, some very fine tweezers for surface mount assembly and a nice hand-magnifier. Also bought some books, and a Bench Power Supply for £10.
The bench power supply is a "Maplin Gold" one and seems to work ok. The meter scales are rather faded, and the mains lead is damaged and needs replacing. Also it was full of pet hair! The current limit is a bit strange, it makes a bit of a whistling noise, so i may need to check the output on the scope to make sure it is not oscillating. But a small supply like this was on my "shopping list" as it is a piece of test equipment that I didn't have. All in all a good day out. 73 Hugh