Saturday, 8 October 2016

TS-790 Repair

Sometime ago (in fact over nearly a year ago!) I purchased a Kenwood TS-790 from eBay. It was described as for parts only or repair -which if you read my occasional post's you will realise its how I like  them !

I've repaired three of these for others and I own one which I love. In the repairs I've carried out previously no PA blocks had failed but one had ALC problems (faulty diodes in the 144mhz section), one had poor soldering the PIN diodes of the PA and one had been transmitted into (!!!) and so needed the front end of the 2m section rebuilding.

This one was especially interesting as it had the rare UT-10 (23cm) module, the pictures of it showed that it was in a dirty state and un-loved, the sub receiver LCD display was not working. The advert did say that it received on 144Mhz (the only band they tested) but there was no output on transmit at all, the inference being that the PA blocks in TX section were blown.

So when the auction ended I found I had won it for a very, very good price, especially remembering the UT-10 module faulty or otherwise !!!

Upon receipt the 790 was as described - dirty, unloved and definitely in need of work but did indeed have the UT-10 module !   

Initial testing proved the advert accurate, no transmit at all, it did receive (actually really well to spec on the Stabilock 4031) and the sub display was indeed dead.

Easy bits first - the Sub LCD display was working just not illuminated - the two 12v bulbs had were blown. I ordered (a long time ago!) 100's of the right bulbs with wire ends and current and so, 20 mins later the sub receiver was illuminated evenly and working nicely.

I also noticed that on SSB there was no ALC action at all, and regardless of the mike gain, the ALC was end stop (!).

At this point work intervened and I put it away for another day !

Fast forward nearly 12 months, my conscience pricked me and I had some time so I thought I'd take a closer look.

I started on the 144mhz, sure enough no output. I'm lucky enough to have a genuine service manual and so set about checking it against that, basic's first, voltages, tx switch voltages, all were OK. I went through the setup process, all were there or there, with a little adjustment all were put as per the service manual, but no output at all, checking the PA section everything looked fine. I disconnected the input to the PA stage just in case it should spring into life and to aid fault finding.
I checked again and the ALC on SSB was end stop and so started to check the ALC area's of the circuit (below)

(Copyright Kenwood)
It has a fairly standard approach to ALC with feedback from the PA sections being fed into the ALC board within the IF unit - its not unusual for this to fail, but the voltages were within reasonable levels. However on pin 7 of the unit the ALV should have been around .62v but there was none. Checking where this is derived from the 'SW' unit which turns out to be the RF power and Mike control board. 

So I have a close look at the RF Power / Mike control, it seems very slightly loose (i'd assumed it needed the collet ring tightening up) but upon closer inspection its the pot itself. Now all have a little movement, but this seems slightly more that usual.

I remove the board from the front panel and have a closer look. The front of the pot is definitely not quite right (see below)

So I de-solder the pot from the board and test it - sure enough the dual gang power pot (front one) is open circuit.

Luckily these are fairly often used in Kenwood kit and I know that I have one in a damaged front panel that I replaced on a TS-850 for someone else. - result !

I remove it from the panel, check its working (it was) and then put it in the SW board and re-assembled the front panel. 

I check the voltages now as sure enough they are correct now, the ALC isn't end stop on SSB and so I reconnect the PA stage, connect to the Stablilock and sure enough there the right output that can be controlled by the RF power control. 

Result - Fixed :)

So 144Mhz fixed and onto 433Mhz

Start again checking all the usual voltages and suspects - they are again all correct, I work back from the PA and check the input to it from the 433mhz RF section - there is an output (ie input to the PA section) but it seems very low (according to the service manual). I check and reset / tune the whole 433Mhz sections . PLL, 430Mhz section etc and get a massive output of 0.2w (200mW) output (according to the Stabilock !)

There clearly isn't enough output from the 433Mhz section to drive the PA blocks, so I disassemble the 430Mhz RF board so I can get to the bottom (all surface mount of course!) where the active components are and start checking the voltages vs the service manual (below is the section from the manual).

(Copyright Kenwood)

Prior to this element of the circuit all the inputs and voltages on each active device were correct, I expected the final pre driver (Q244) to be faulty but the voltage were correct, working back I then checked  Q223 - again all voltages correct, then Q222 (2SC3357) and found that the emitter voltage (.75v) was not present - I then check the bias components - all were OK, these are all SMT so I checked all the soldering - all were OK, so a possible faulty transistor.

I didn't have stock - so ordered up a replacement (in fact 5) NEC equivalents.

They arrived a couple of days later, genuine NEC ones (watch eBay for fakes there are lots of them!), I removed the 'offending' transistor with the hot air rework station, and replaced it then cleaned the flux off.

I re-assembled the board and tested the bias on TX and - nothing :(

Oh dear - I Then realised that in turning on and off the 790 I had selected 144 not 430 (!) 

I then set the right band, and voila the right bias was present and the output of the driver board was about the right level.

I reconnected the 433 PA unit and there was the correct output.

I noticed on this 790 as with ALL the others I've seen there was no heat sink compound on any of the PA units and so I will ensure that there will be some before I finish,

I spent some time doing a complete setup from the service manual, and all was well

RESULT - fixed.

Now onto the 1.2Ghz section..


Sunday, 24 July 2016

TS-950SD repair

Long time - no post !

Well, I've been buzy, changed jobs (twice) and so any time I've had I've concentrated on home and fixing radios.

But now things have settled down a little, I will return to occasionally blogging about fixing kit that I've acquired - in order to help others and record how they were repaired.


I found this lovely radio on the UK website which was out for a swap and clearly labelled as non working with an interesting fault.

After a little thought I contacted the poster (a lovely guy named Mike) and a deal was done for the transceiver.

I picked it up (never trust couriers even for a faulty radio) as whilst the fault might not get worse the physical condition of the radio may well do so !!

The fault as described was the receiver had a 60db carrier (FSD on the S meter) after warm up and no signals could be received regardless, the TX was perfect - full output on FM and SSB. On the bench sure enough on switch on there was no receive (also no FSD on the S meter), TX was indeed perfect in all modes. So the description was (unusually in many cases in my experience) spot on :)

So left the transceiver on for a few hours and sure enough after a while the s meter went to FSD. During the warm up I checked controls etc - all were fine with the exception of the RF gain control (which apparently didn't function) and a total lack of audio / signal receipt. I also checked the sub receiver - which did have audio and did receiver albeit at a poor (insensitive) level.

So I'd already down loaded the service manual and familiarised myself with it and so I started to look at the receive chain / receiver gain control parts of the transceiver due to the symptoms noted above.

I checked the audio amp by injection a suitable signal into it on the main receiver  input to the AF amp and sure enough it worked fine. So onwards.

I doubted that it was a PLL problem as the sub receiver (which shares elements of the PLL) was working fine with low receive, but thought I would check, by carrying out an alignment as per the manual all was fine.

This looked more and more like an AGC type fault (as there was no RF gain control operative) effectively the RX looked liked it was turned hard off when the fault was present. I checked the manual to see where I could check the voltage and noted that there was a couple of nice test points used on the alignment that would give me a good start (see below).

So Fluke to fore, measured on main AGC and to find that it was way off (can't remember the actual voltage and didn't make a note - D'oh!!!) , the sub rx was sligtly off but was adjustable to the required level (2.8V).

Making progress :) 

So started to measure voltage in the AGC area and established that they were not correct in the fault state - also they weren't stable (to be expected in an agc circuit - but these varied by volts not mv and were not signal related!). (circuit below)

the voltage (13.5, 14.5 circled in red) were all over the place and are derived from the 15v line (red on the right).

So why is the 15V line variable and where does it come from ?

Answer it comes from a sub board on the control unit called the trx board (circuit below)

And sure enough its a right pain to get to :( - its location is below

So removed the Control unit and decided to remove the trx board from the unit (thank you decent desolder station - makes this a breeze!) to take a look at the board - sure enough R156 and R157 solder flow was poor (in fact when I touched R157 it fell off the board !!

The components check out OK but I decided to replace them both just in case, I also re-flowed the rest if the components on the board as well - just to be sure.

Replaced the trx unit onto the control unit, and ensured that both that unit and the one close to it were bent away from each other to help with any heat issues - although I'm sure sooner or later (an certainly in hot climates) this fault will re-appear, the control unit is located behind the front panel as so there is not much (if any) air movement and so this almost certainly is the root cause. - I considered a small fan but in the decided that this wouldn't really work effectively.

I re-assembled the control unit with all its connectors, rechecked all and then tested again.

First thing I noted was there was noise in the receiver (I forgot to turn down the AF gain!!) and it blasted me :), secondly (when I turned the audio gain down!) - was the the RF gain control now worked correctly - ie as I reduced it the s meter slowly lit up until it was fully lit (ie fully reduced gain).

I checked the test point on the signal unit and it was still wrong (to high at 6.3V) but I could now reset it to the correct level (2.8V).

The receiver was now functioning correctly - I then did a full re-alignment of the transceiver as per the service manual - and it is now totally within spec and working exceptionally well.

Hope this might help others in the future.

Job Done :)


Friday, 28 June 2013

So did the mast work ?

So, the question needs to be asked......

Did it work ?

Well the answer is ( I Think ) a resounding yes :)

The reason for no posts recently (other than being busy at work) is that I have entered two yes two contests.
Ground Level (more or less!)

The Practical Wireless 144Mhz low power and the 50Mhz Trophy contest.

Here are some pictures of the 144Mhz set-up the first one is it ready to be pumped up and the second one is it fully pumped up and ready to use.

Did it work - well I think the answer is definitely yes ! I ended up with 77 contacts (remember this is a low power - in this case 3W) contest, the furthest away being GI4 which is 419Km away, also some first for me with my first GM station on 144Mhz, as well as my first Isle Of Man station and my first French station on two - for me a brilliant personal result - I've entered the contest but as it is predominantly a portable contest I'm unsure how a fixed station like myself will be placed, several portable stations I worked had very large serial numbers !!!!
Final Height - and in use.

The best part was 30 minutes after the contest had finished, I had dismantled the antenna, the mast was 'let down' and stored away and everything was back to a 'normal' garden.

So it absolutely hit the mark with regard to the design spec that I set myself on both the time to get ready and the time to remove it.

It was so successful that I decided I would try the next weekend the 50Mhz Trophy Contest  (RSGB), This is a 24 hour contest, but does have a six hour fixed station section (6F) that seemed reasonable.

So I removed the 6M antenna from the loft space (this is a dual band 6M/4M with 3 elements for 6M and 4 for 4M).  I used the same arrangement that I  used for the previous weekends 144Mhz contest, but learnt that I could use the step ladder to aid the mounting of the rotator and antenna, and help make this truly a 'one man' operation. Here are a couple of pictures of the antenna in place and at the full height.

50/70Mhz Dual Band Antenna @ full height

As you can see it looks good (well I think so!), it was pretty gusty and so this time I took the precaution of putting two guys in the direction of the prevailing wind.

I'm pretty sure it didn't need it as it wasn't moving at all before I deployed them, but better safe than sorry.

Again, did it work ?

Well I think again a resounding yes !

I worked 38 stations, with a combined score of 340825 (claimed) , conditions were very poor, with only one or two sporadic E openings, my best DX was ES1MM/2 in  locator KO59DI this is a distance of 2045km. I also worked my first GM on 6M, and into Iceland. 

50/70Mhz Antenna close up
Whilst I was very pleased with the overall set-up and how things went the conditions were truly dire. Considering I only have a 3 element antenna and only use 100W I did pretty well, I'm currently 4th in the 6F part of the contest. Others are running larger antenna's and much more power (2 or 3 times more) so not too bad in my view.

Again the mast came down really quickly and within 25 minutes, it was back to a 'normal' garden with no mast or antenna visible.

So is the mast a success - On balance I think yes, two contest entered, both pretty convincingly - which I wouldn't have been able to without the mast. result :)

Now to up the power on 6M and get a better antenna - onwards and upwards - literally !!!!

Tuesday, 4 June 2013

Ordered my 144Mhz antenna

After all my hard work on the mast, I thought I would give it an airing in the PW 144Mhz low power contest this weekend (Sunday).

This is a low power (3W) contest and so it will be interesting to see how it goes. Of course to do this I need an antenna and so after looking around I thought I would try the 9 element 144MHz OWL Super-Light Yagi made by.innovantennas in Essex ( to a G0KSC design.

Looks like a good gain figure and also a reasonable boom length as well. I will be picking it, as they are quite near where I am during the week, up so that I will have it ready for the weekend.

Now just to get the feeder and the rotator all sorted :) - I've got both (including the rotator cable) just got to get them all connected and sorted out. Something for Saturday I think.

Monday, 3 June 2013

50Mhz - what a band !

You've got to love it !

For most of the week, well all of it actually I'm located away from home and recently i've put one my FT817ND's in the flat so I can have a tune around when I feel like it.

With 50Mhz being open a lot recently I thought I'd have a quick listen when I got in from work, it was open, and unbelieveably with just the standard antenna connected to the front panel I made a contact.

It was with IC8TEM located in JN70CN - Capri Island  he was strong here (JO01IM) and gave me a 59 I returned the complement. 

That was with 2.5W (max) to a rubber duck antenna indoors -  a distance 1597Km as the crow flies

Not a record but pretty amazing really :)


Sunday, 2 June 2013

Lovely weekend - more work on the mast

So last Monday (Bank Holiday) I fixed the seals in the Mast (see my last Blog post) , it was a lovely day yesterday, and so I set about putting the plan for the mast in action.

Mast, small Granddaughter, and black Lab,
and yes I know the mast's not vertical, its
just a test !!
First I got the ground mount sorted.

As discussed in my last post I used a fence post spike 600mm long, which after grinding, drilling and welding provided a great ground connection for the mast.

I then set about thinking how to make sure the mast stood vertically and safely. In the end I decided on a three legged tripod which can be taken apart when not in use, I again cut, welded and drilled three legs (adjustable using butterfly nuts - a nice touch I thought :).

Lovely blue skies :) 
I hammered the ground spike in the ground, and test fitted the mast, all looked good, I then test fitted the legs, a bit touch and go, but after some re-engineering on the fly, all looked good, although I couldn't find the right size butterfly nuts and so final test assembly would have to wait until Sunday.

Mast from another angle, minus
Granddaughter and dogs :)

So Sunday arrives, bright and lovely, I decide to go to the Spalding Radio Rally in the morning, where I spend a pleasant hour or so wandering around, by a couple of things, got hold of a Gigatronics power meter which needs a remote head for £25 which I think is a good buy.

Return home via hardware shop to get right size butterfly nuts and bolts, complete final assembly, and then for the first time, try it out, mast pumps up beautifully, holds up without locking it, but I lock it anyway for safety. With the tripod it's really sturdy, even in the gusty wind, a real result, even the family are impressed :)

Basically it works !,perhaps  a little 'agricultural' in engineering terms, but then I'm an electronic engineer by training not a mechanical one !!. I still have some fine tuning to do but as you can see from the pictures dotted through the blog showing the fruits of my labour it worked, any comments most welcome :) . At this rate I might make am entry into the Practical Wireless low power 144Mh contest next weekend,  if I can find a suitable 2M beam 
Mast what Mast !

To top it all of course, 6M was wide open again into Europe in the afternoon via Sporadic E, worked way down into Greece, Italy, Spain and quite 'short skip' E into Germany, France and Austria. If only I'd done this earlier I might have been using the mast with a decent 50Mhz antenna on the top !! - ohh well never mind perhaps that's only a week or two away, might be ready for the 50Mhz open contest !!!

Below are a few final of pictures showing the ground mount spike / swivel and the mast in its stowed position, I haven't bothered removing it from the ground spike at the moment. Also considering if it needs to have guys as well as the tripod mount, might do so just in case, especially with a rotator and beam on top :)

Just goes to prove, where there's a will there is most definitely a way !!! 

It certainly fulfilled the design brief I set myself ...

Ground mount, mast vertical
Mast lowered and horizontal (can be removed from
ground spike if needed)

Close up of ground spike, the mast can be removed from
this by undoing the knob on top and the two silver machine
screws on the side

Monday, 27 May 2013

Bank Holiday Monday - Mast preparation :)

After my last post on 6M I got to thinking about how I could get a better antenna for 6M, and perhaps 4M and then there's always 2M as well isn't there !

I've had in my mind for several months the idea of a 'temporary' mast to enable me to quickly get some decent (perhaps 6 element 6M beam) up in the garden for weekends and contests.

The basic criteria would be -

1 - Temporary - most important after studying the planning regulations, I didn't want to apply for permission for a mast, especially as I live in a conservation village, whilst I might find antenna's pretty special others (including the xyl) might have other ideas. A 'temporary structure' is defined as one that is not permanently fixed to a building - or other structure.

2 - It must be fast to put up and take down - I want to do radio not build masts etc.!

3 - Would be high enough to get above the house from the back garden

4 - Would be able to be assembled as dis-assembled  by one person (me!)

5 -  Would have minimal impact when taken down (ie must be temporary, not visible and not a structure when taken apart)

I've been thinking about it for some time and in the end decided that an ex mod pump up mast would be best.

Not a SCAM12 - those are massive, and whilst built like the proverbial 'brick out house' they weigh a ton and are designed for a small army to assemble, so what next ?

Then I came across (again via eBay what would I do without it) a Hilomast NK9, a lot more manageable - when pumped up 9M, 2.3M when retracted, 22Kg's of head weight and it weighs approx 21KG, which whilst bulky is manageable for a lard ass like me :)

It was advertised as "possibly in need or refurbishment"  I took a punt and won it just over £100, with semi local collection, I picked it up in my 7 series - couldn't do that with a SCAM12 :)

This was autumn of last year, I got a seal pack from SMC Communications (£70+ ouch!), and then did nothing with it.

Then my 6M post |(and an upcoming 2M low power contest), and I thought I take a closer look at how I could use it.

Well after 6 hours or work, I've replaced all the seals, and now know intimately the inner
The construction of a Hilomast
(c) Hilomast (SMC)
workings of the Hilomast !! - if you've any questions just ask !

I'm was very impressed with the build quality, really good stuff, great to work on, perhaps the equivalent of a BMW or Audi in engineering terms, when I dismantled it, I discovered a hand written note on one of the upper tubes, that it was re-built in 1994, so I doubt that its been touched since then. The top section is slightly damaged, but has no effect on the use of the mast at all.

I did check before working on it and it didn't pump up at all :(  and now after working on it, it not only pumps up, but also stays up (without using the locking handles), so now all I've got to do is work out how to put together a ground mount to help me put it up, and also how guy it to make sure it doesn't fall over with the antenna's on top !!

I've already decided that the cables would be permanent from the house to ground level down the wall in a weather proof box. I've already go a method of getting cables from the loft to the outside world using the a waterproof hole in the soffit (or is it barge board) of the roof, with a removable, flying cable up the mast, including the rotator control cable, to enable quick set up, and keep things tidy.

I recon that I should be able to get it set up for weekend working (I'd have to choose the antenna obviously !) in about 45-60 minutes and then take it down in about the same.

That should give me great gives flexibility  (Contests are only at the weekend, and actually I'm only around then to play radios's), a reasonably good antenna for my favourite bands 6M,4M,2M, and no planning problems as its temporary, I can even drop it down to 7ft when I'm not using it to avoid neighbour problems.

I should be able to store the antenna vertically at the side of the house safely and so not too much disassembly should be needed, and if it does need this its a small price to pay I think.

So next step now I've got a working mast is to get the ground mount sorted out, and get the cables put in permanently. Thinking cap on, I've a few ideas already.

Sorry there's no pictures, I didn't really think until I was finished, that I'd write it up on the blog, silly me :( - I will when I do the ground mount, and of course the final result.

Now how big is a 40M three element beam (!!!) :)