Sunday, 27 November 2011

TS-180S - this is getting ridiculous!

I knew it was a mistake putting the lid on properly.
Having restored the functionality of the frequency display I decided to run the radio for a few hours over the weekend to evaluate performance further.   Still no tx, of course or any PLL locking on 28MHz but I knew that already ...
I was listening to a QSO on 7MHz this morning between a very strong Belgian station and a string of UK stations, most of whom I could hear reasonably well when I realised that the frequency seemed to be locked on to 7.150.0MHz.  Tuning either side by a kHz or two made no difference to the display.   I had a funny feeling about this, so I tuned up and down the band to find that lo and behold that the display was only displaying frequency to a 10kHz resolution!
To see whether this was a heat related issue I switched the radio off and let it cool down for half an hour or so, but on re-powering the fault was still present, so I have concluded that I have ANOTHER dead chip!  More than likely a duff 7490 in the counter chain, and that's TTL not CMOS, so another theory goes down the pan.
It is now only sheer stubbornness which is sustaining my interest in this project.  In all the years of building and repairing equipment, I don't think I've ever come across a project like this.   Trying to fix up a radio with numerous faults is one thing (and what I thought I was dealing with here), but fixing one which keeps breaking seemingly randomly whilst under repair is quite something else.   It's a case of either "nolum illigitimus carborundum", or chuck the bloody thing in the (recycling) bin!  I don't give up easily though.  What kind of trauma has this radio suffered in the past?   It's anybody's guess.

Saturday, 26 November 2011

TS-180S Display Fixed (Again!)

As I reported previously I discovered that the display in my TS-180S which is currently undergoing major restoration was again faulty.

The symptoms were either that it displayed just the "base" frequency of the band in use when it was powered up, "1.500.0" for example on Top Band, "3.500.0" on 80m, or another sequence of numbers unrelated to anything.  None of these numbers changed when the bandswitch was operated with the set switched on.

A couple of nights ago I decided to have a look with my test gear to find out what was going on, or not.

The trickiest part of the whole operation is extracting the display from the radio, and conversely refitting it after investigation, and this struggle led me to suppose before I started that the fault was induced during the arduous refitting after the previous repair, and the consequential tidying up of the cable harness.

This was soon proved not to be the case as investigation with an oscilloscope quickly led me to the conclusion that (a) there was plenty of 40-40.5 MHz signal from the premix unit but (b) there was no gate signal in the digital counting chain.

So attention returned to the previously repaired divide unit which sits underneath the main counter board, and so consequently the whole caboodle had to be extracted once again from the radio so I could get at it.

Well at least I was well practiced at this, and knew what to do (familiarity doesn't imply enjoyment!), so eventually, after cutting some of my nicely installed cable ties, and much cussing, I had the recalcitrant unit upended so I could investigate.

TS-180S Display Divide Unit
The marked up drawing above shows what I found, and I quickly came to the conclusion that either Q8 or Q9 would appear to be faulty, with the balance of probabilities suggesting Q8.
Fortunately a trawl through my spare parts revealed that I had a 4013 (Dual D-Type Flip-Flop) and also a 7400 if required, so I had a "cunning plan" to replace these parts in the radio the following evening.
Divider Board - Q8 Bottom Right
And so it came to pass.  The following evening Q8 came out as sweet as a nut (it was helpful that it was in the corner of the board and no immediately surrounding components, a new 14-pin turned pin socket was soldered in and the new chip installed.
Powering up the radio followed and to my great delight the correct frequency display appeared!  Yay!
Display Correct (note - upside down!)

Display ready to go back in ...

The display has now been refitted and is working as I type this, so after much effort, I am now back where I started and wondering (a) what on earth will go wrong next? and (b) how can one radio have had so many seemingly unrelated faults?    The only connection I can think of between this fault and the previous repair to the divide unit is that both of the faulty chips were CMOS types of presumably similar vintage?  Maybe the anti-static handling precautions at the factory weren't up to much at the time?

Faulty Q8 - Innocent Looking, eh?


Sunday, 20 November 2011

A New (Old) Direct Conversion Receiver

For a while now I've been participating in the "QRSS" aspect of the hobby, mainly by streaming my "grabber" or sometimes "grabbers" (I can run two simultaneously if I am feeling keen!).

Each of these grabbers ties up a radio and a PC.   As you may have realised I have quite a number of each of these commodities, a ridiculous number, if you were to ask my wife, but being brought up in post-rationing Yorkshire (though not of such Noble birth), I always felt that tying up a sophisticated multi-band multi-mode transceiver just to stream a Spectrum Laboratory grab onto the Internet was "overkill".

I've been pondering for some time knocking up a direct conversion receiver for, say, 10MHz which happens to be the most popular band with QRSS enthusiast.  I've built a few of DC receivers over the years.  They tend to be fairly "minimalist" devices, and yesterday it struck me in a flash that I have already got, gathering dust on a shelf, a 14MHz single-band receiver built back in the 1980s which would potentially fit the bill.

The receiver in question was dubbed the "RC-14", and was a project featured in Rad Com back in 1987, described as a "beginners receiver".   When built at the time it worked reasonably well, and I reworked it slightly to fit it into on of those ubiquitous die cast boxes as the one which came with the Cirkit (remember them?) kit was rather flimsy to say the least.  In my opinion, the nicest feature of that particular design by Steve Price GW4BWE was the AF stage which featured a nice two stage active low pass filter'  The performance of this filter meant that the radio sounded like a "proper" SSB receiver, when the received signal was strong and in the clear.

It hasn't had a great deal of use since then and it occurred to me yesterday that it would be relatively straightforward to "wavechange" it to the 30m band.

QRSS stations tend to operate around a single 200Hz channel either side of 10.140MHz, and just below the WSPR segment.   In  view of this, simply moving the built-in 14MHz VFO to 10.1MHz would probably not be the best thing to do.  Instead a fixed oscillator on the right frequency would fit the bill, or maybe a "VXO" to give a little more operational flexibility.

Now I haven't got a suitable 10.14MHz - ish crystal to hand at the moment, but as proof of concept I have temporarily modified the radio to accept an external oscillator, and used a synthesised signal generator as that external oscillator tuned to 10.1387MHz instead.   This puts the wanted frequency of 10.14 plus or minus right in the middle of the receiver pass band.  A slight tweak to the receiver's input tuned circuit was all that was needed to get the receiver up and running, and in this way I've been streaming this new (old) grabber receiver onto the Internet all afternoon with satisfactory results.

I am now wondering at the practicability of using this principle as the basis for a two or possibly three band dedicated QRSS receiver.  And so another project is born!

Saturday, 5 November 2011

Good News, Bad News

First the Good News.

I believe the PC which was whacked by a virus/trojan/bot last weekend, courtesy of a "driver site" is now back up and running having been seemingly "de-loused".

As it was still partially crippled, even after a Windows XP "repair" from the OEM CD, whilst I was driving up to the top of Scotland at the beginning of the last working week I figured that one way of dealing with the problem was to connect the affected PC's hard drive as an additional drive to a fully functioning PC, and to virus scan it from that PC.

This is what I did yesterday, and the virus scan found a few suspect files and zapped them.

Once the "cleansed" drive was reconnected to its proper PC and that was booted, it was immediately evident that the nasties had in fact been purged.

I then fixed the on board virus checker (this PC runs Microsoft Security Essentials) with a "hotfix" downloaded from Microsoft, and then let Windows Updater catch up with everything, including re-installing Service Pack 3.

I took the opportunity to vacuum out the PC, a Dell Dimension 3100, which always has been blissfully quiet and generally tidy up all the cabling associated with it, no trivial job I can assure you!

Anyhow, it all seems to be in reasonably fettle now, and I have once again started up my QRSS grabber, though I think I won't reinstate the Apache Web Server.

As part of the rescuing of the situation I moved all affected sites off site, and I will leave them there for the moment.

Now the Bad News.

On a whim, I extracted my TS-180S from the shed with a view to giving it a little exercise as it has been lying discarded for a few months.

To my horror upon firing it up I found I once again had a "dead" digital display.   The receiver is still working as it was when I put it to one side, but when last used it had a fully functioning display.   My favoured theory at the moment is that I disturbed some wiring when I tidied it all up before putting the covers on.  

Knowing the previous track record of this radio, that might be wishful thinking!

Bother ... !!