Saturday, 30 April 2011

First Swallow of the Summer, etc

THIRTY-odd years ago, early in my professional career I moved up to Central Scotland from Yorkshire, where I remained for about six years.   In the late Spring of the first year I was there I noted the date on which I spotted the first swallow of the summer, it happened to be May 1st, and thereafter May 1st has been the "yardstick" with me for spotting these harbingers of the coming Summer.  For some reason I'd never taken any notice of this phenomenon before.

Having subsequently back to South of the Border, some hundred miles to the south, I usually reckon to see swallows two or three days before that particular date, but unusually this year, it is now April 30th, and no swallows have yet come to my attention (I am not saying they aren't hereabouts!). However, unusually this morning the first house martins I've seen were swooping around the front of my QTH.  Usually swallows are to be seen before the martins in my experience.

TS-180S Repair - Part 2

It is now time to report on the progress with my ailing TS-180S.   Until yesterday evening there wasn't much to report save that I had come to a couple of conclusions.

Firstly, the radio definitely has a problem with the PLL circuitry.   That's enough to make one feel that this could be a long haul!   PLL circuits can be difficult to diagnose and fix, as they only work when the loop is closed, and a fault anywhere in that loop could potentially stop the PLL from working.  This radio has a quite early implementation of the "PLL derived PreMix System" which became popular in era immediately prior to the adoption of full synthesis and continuous coverage.  Trio improved the circuitry for their very popular TS-120 model, but I am left to struggle with their earlier attempt.  The PLL circuitry doesn't lock very well, and when it does lock, for a 100kHz change in VFO frequency, the actual het. frequency derived in the PLL Premix system only changes by 60kHz.

The TS-180S PLL Board
 The second conclusion I came to after probing around the circuitry with a spectrum analyser was that the high gain Wide Band Amplifier between the VCO stages and the prescaler/divider was producing a lot of garbage.

I'd previously checked out the condition of the two electrolytic capacitors in this part of the board on my ESR tester, and they suprisingly appeared to be absolutely fine.

With this knowledge I began to ponder how I might break into the loop and possibly inject test signals from a stable source, (ie replace the WBA with a signal generator and see how things behave), but before doing that I decided I would check the DC conditions around the five transistor WBA.   These checks showed that the first transistor in the chain (Q14) appeared to be short circuit in all directions.  Hah!  That is clearly not going to help!

The 8-40MHz Wide Band Amplifier - things are just a bit tight in there!

Anyhow, the faulty transistor was extracted with no little difficulty, tested, and yes, it is completely dud.

Unfortunately I don't appear to have anything close to it in my spares, so it will have to be an EBay search for something suitable.   The original transistor type is 2SC1907 which has a very high fT (>1GHz), so any old gash BC182 just won't cut it on this occasion!  According to the data sheet the 2SC1907 was designed for UHF TV local oscillator applications.

To be continued ...


  1. Great Martin have been waiting patiently for an update and hope you find a suitable replacement transistor. As for the swallows well we have had them here for just over a week but there again we are a lot more south that you.


    Ken G3SDW

  2. Martin just found what you are looking for, have a look.



  3. Thanks Ken! Saves me looking for an equivalent too. I've dealt with that trader before, and they are OK,

    Somehow I don't think this is going to be the final fault, but one never knows. The WBA needs to hit the prescaler with TTL compatible signals, so it will need to have plenty of gain across its bandwidth of 8 to 40 MHz. I would imagine the first transistor in the chain would probably have the most gain.