Repaired my ATU

Merry Christmas!

Not wishing to contend with an evening of dire XYL style Christmas TV (Strictly Come Dancing, Call the Midwife and Downton Abbey) I escaped into the shack and decided to repair my Vectronics VC300DLP Antenna Tuner. I got this ATU second hand last year and while it has been serviceable it had become temperamental of late. The units rotary inductor switch had become stiff and suddenly I was unable to match the OCFD on some bands so it had clearly broken.

I had a 12-position switch (rated at 5A) and knob, originally sourced for an abandoned project and hoped it would be suitable. The existing switch knob on the ATU wasn’t an original, I’d assumed it had replaced one lost or broken. When I removed the cover it was clear that the whole switch had already been changed at sometime.

I also noticed a prominent burn mark inside the inductor coil, caused by a clear break in the insulation of the wire which was resting on the grounded bottom plate.

I know the previous owner of the ATU has a 300W RM BLA-350 linear amplifier, whereas I only normally operate around 30W maximum at my QTH, so not sure how much of this arcing I had caused but it needed sorting! A little over half an hour with the soldering iron and I had replaced the switch and slipped some heat shrink over the broken insulation and re-soldered the wire, lifting it off the ground plate.

The ATU seems to work well, now fitted with a new knob (just missing a cap at the moment) the switch turns nicely. I also cleaned up the SO-239 connectors on the back as they were tarnished and oxidised. I used a small bit of contact cleaner on some cotton buds to clean up the threads and the centre pins, removing a surprising amount of crud. The patch and antenna leads now screws on much better.

With the Mother–in-law staying with us over the festive period I suspect I may be in the shack quite a bit, I have plenty of jobs and half finished projects to keep me busy!

Repairing a Kenwood TR9500, Part4

The troublesome TR9500 has developed another fault, well it has likely had this fault since I’ve owned it but I have only just spotted it.

After making repairs to the microphone amplifier and the receiver pre-amplifier the rig seemed to be working fine, I’d even used it several times during the UKAC contests with some success.

The 70cm band is under used locally and activity seems largely restricted to repeaters. Due to it’s vintage the TR9500 doesn’t have CTCSS tones and so cannot be used to access repeaters without some modification and I’ve been looking at adding a CTCSS board.

In the meantime I really wanted to use the TR9500 a bit more and was hoping to make it part of a satellite station, the TR9500 acting as the UHF uplink transmitter (LSB) and the VHF 2m TR9000 as the downlink receiver (USB) for the AO73 (FUNCube-1) and other satellites.

The satellite portion of the band plan is at 435-438MHz and it was when setting this up I discovered the TR9500 neither received or transmitted in the upper part of the 70cm band (435-440MHz) below this everything was hunky-dory.

It hasn’t taken long to locate the issue, the HET unit employs two crystals L33 (36.6222MHz), L34 (37.1777MHz) which are switched in to the oscillator Q1 depending on the selected frequency. L33 being referred to as low band, L34 as high band the switching occurring around 435MHz.

The switching HL signal (via R10) and transistors Q3/Q4 are working correctly it is just crystal L34 is not resonating. The surrounding diodes, capacitors, inductors and resistors all look fine, no obvious shorts or broken joints.

I have to do some more diagnostics to rule out any of the passive components but if it is the case that the crystal has failed then it may prove difficult to source an economical replacement.

Repairing a Kenwood TR9500, Part3

Back in September I attempted to repair a Kenwood/Trio TR9500 UHF All-modes transceiver for a fellow club member. It had a faulty microphone pre-amp which I replaced and all seemed well but it had further issues with the receiver. Cutting his losses and wanting shot the owner sold it to me for the princely sum of £10.

I have had her back on the bench and initially couldn’t find anything wrong. However in real use it become apparent that she was in fact profoundly deaf! Picking up test transmissions from the nearby FT857D or Baofeng outputting into a dummy load was one thing but it wasn’t receiving anything else!

From the service manual and schematic I deduced that it could be the initial RF receive amplifier. It is a dual-gate mosfet (3SK76) It proved tricky but I managed to source a replacement on eBay and it was a simple job to replace once I’d extricated the PCB.

I can report it is now working and the video below shows it monitoring the GB3EE repeater in Chesterfield. From the coverage map I shouldn’t be able to hear it but I can and reception has been marginal at best using other receivers but it repaired TR9500 doesn’t have any problems.


I wonder if the rig has been subjected to a high RF field in the past this could easily have damaged the receiver amplifier and an induced RF into the microphone lead could have damaged the microphone pre-amp. It just seemed strange it having both faults.

Tuesday night is the last 432MHz UKAC contest and hope to use her in anger.

The TR9500 and her sister come to stay

The shack has gained a couple of ‘new’ radios, one of them look familiar?

It is the Trio/Kenwood TR9500 that I repaired last month for a fellow club member. Having no transmit audio I’d replaced a faulty transistor in the microphone pre-amp. Subsequently it’s owner reported it was still misbehaving and locking up in transmit mode.

I’d offered to give it another look but the owner decided to cut his losses and wanted shot of it. He had just purchased a nice new radio at the National Hamfest and was also selling a 2m Trio/Kenwood TR9000 multi-mode set to make some room.

I liked the look of these pretty sisters and got both of them for a very reasonable price, the TR9500 costing just £10 in lieu of the previous repair work. I collected them at the weekend and got around to checking them out last night.

The TR9000 is a lovely compact rig, the case has the odd scuff but the front is in good condition and has cleaned up nicely. I just need to attend to the microphone plug as it wearing the ubiquitous piece of brightly coloured insulating tape. It is fully functional and I made a few contacts on it during last nights 144MHz UKAC. It is nice sounding and seems to have a good sensitive receiver.

The troublesome TR9500 has been back on the bench and connected to a dummy load and my X-50 dual-band collinear and I cannot find anything wrong. The ALC ‘issue‘ I suspected was a red-herring, the audio does cuts out and the S-meter goes to S9 but only when the RF gain knob is turned to minimum not maximum as I’d thought, the same thing happens on the TR9000.

It is entirely possible the fault reported by its previous owner is intermittent (a bad joint, sticky relay etc) It is also a possibility that RF was leaking back in the rig causing it to lock up. I plan to use it in anger maybe during next weeks 432MHz UKAC especially if the receiver proves as sensitive as that in the TR9000. 

As I mentioned the National Hamfest took place recently and since it is local to me I decided to go along on both days. The Friday was by far the busier day with lots of sellers in the outdoor flea-market with a genuine ‘buzz’ which seemed lacking on the Saturday, there were a lot less sellers outdoors.

The main hall left me a bit underwhelmed, the layout seemed a bit messy and some areas were cramped while others seemed to have acres of spare room. It was also very hot in the main hall especially on the busy Friday, however it was still an enjoyable couple of days and met up with some fellow tweeters and operators. 

My purchases were modest and as well as the usual connectors and cabling I picked up a nice as-new 7A regulated linear power supply, a foot switch, a replacement satellite Quad-LNB, a very sorry looking 70cm linear amplifier and picked up one of those lovely Czech morse-keys for when I brave doing the code!

I also picked up this little 2.4GHz B/W video monitor for a whopping £1 and it works a treat. I have a number of 2.4GHz wireless security cameras (purchased back in 2009) intended for a PC-based PVR CCTV system but the whole PC system proved unreliable so they are sitting idle. This little monitor can receive on the four standand channels and as a bonus runs off 13.8V so ideal for sticking in the car and driving around the local housing estate eavesdropping on other similar cameras – I am joking of course!

The very sorry looking 70cm linear amplifier is a Tokyo Hy-Power HL-60U. I found it hiding away in a box of junk on one stall and after a bit of haggling got it for a fiver! From its appearance I really didn’t expect it work, especially since the warranty seal had been broken. I wasn’t too bothered about the power amplifier I was far more interested if the built in GaAsFET pre-amplifier still worked.

Getting it on the bench I opened the case, expecting to find it plundered and butchered and was pleasantly surprised to find the insides looked almost pristine. I think the main PA transistor may have been replaced, but while it looks a bit messy the flux resin around its joints looks the same as other areas of the PCB so not sure. It looks slightly different internally to some another photographs I found on line and I have searched the web for a manual and schematic with no joy. Tokyo Hy-Power went bankrupt last year and the website and precious data downloads have all but disappeared.

As it looked intact with nothing missing I connected up the dummy load, power meter and fed the input from one of my Baofeng handhelds. It powered up and was giving 15W out for a measured 3W in with no distortion on the audio, so far so good. However after connecting up the FT-857D and slowly increasing the input power is became apparent that 15W seemed to be about the limit of its output, not the 60W as promised.

Removing the dummy load and putting it on the X-50 antenna I had a listen around for weak stations to checked the operation of receive pre-amp and it worked! Should prove useful for the 70cm contests.

Repairing a Kenwood TR9500, Part2 – TX working, SSB RX not

As I suspected the microphone amplifier Q1 in the Kenwood/Trio TR9500 was indeed faulty. The replacement arrived next day and within an hour I had successfully soldered in the new 2SC2240 transistor and it now had audio on transmit.

Transmitting into a dummy load and monitoring on my FT857-D the FM transmission was fine, the SSB was okay, perhaps slightly over driven. I suspected that maybe the previous owner might have twiddled something to compensate for a failing Q1.

In the adjustments section of the service manual VR6 on the IF unit controls the SSB MIC gain. To check the settings it was a case of setting the transmitter to 432MHz and putting an audio frequency signals of 1.5kHz of amplitude 1mV and 10mV from my signal generator on to the microphone terminal, and observing the RF power output, which were the 5W and just over 10W as required. As this didn’t need altering I left it alone and boxed it back up and returned it to the happy owner.

Last night was the RSGB 432MHz UKAC Contest and I was hoping to here it on the air, sadly I didn’t. It now transpires that there maybe another issue with it, something I should have spotted.

I do remember something strange when doing the initial testing. Connected to a dummy load and in SSB mode the S-meter showed S9+ when in receive but with no audio, turning the RF gain control the meter dropped to S0 and normal white noise static could be heard. It received a SSB transmission from the FT857-D with no issue so I thought no more of it. Being over eager and not experienced with using different rigs I had mistakenly dismissed it and should really have read the operating manual more extensively.

The anomalous S9+ meter reading and no audio occured when the RF gain control was set to the maximum which is the normal recommended setting for operating, I’d simply turned the RF gain control to the minimum mitigating the issue.

Obviously the rigs owner had put the RF gain back to maximum and was now reporting it wasn’t switching back to receive. In fact it is but nothing is being heard. Checking the service manual this morning and it appears there is an issue with the AGC circuit (description and block diagram below)

RECEIVER CIRCUIT
…. The signal is picked up from the last stage of the IF amplifier (Q23), then detected and amplified to generate the AGC voltage. The AGC time constant is automatically set according to the mode : FAST for CW; SLOW for SSB. The AGC voltage is applied to IF amplifiers Q21, Q22 and Q23 (3SK73(GR)) and RF amplifier Q51. It is also used to drive the S meter.

It seems the rig may well find itself back on the bench, however this repair could be more problematic!

As I mentioned it was the 432MHz UKAC last night and I had a decent night of search and pounce. Conditions were very strange, lots of fading and strangely some of the usual local operators were not heard. I was very pleased to catch some lift and made a couple of decent DX contacts in Northern Ireland, The Isle of Man, Northumberland as well as Essex and Cambridge.

Who needs a preamp on 432MHz with ears as good as mine? Well actually I do desperately! #ukac pic.twitter.com/WXnMBGY0uw
— Andrew Garratt (@nerdsville) September 9, 2014

In a few weekends it is the National Hamfest, which is held in my home town and I hoping to pick up some bargain gear to improve my UHF set up, however from past experience that may prove difficult.

Repairing a Kenwood TR9500, Part1 – The Diagnosis

A fellow SKARS club member picked up a nice condition Kenwood/Trio TR9500 70cm all-mode transceiver (circa 1980) from the Hamfest last year for not a lot of money and he hoped to use it for the UKAC contests unfortunately it proved to be faulty.

From the description of the fault and studying a downloaded service manual I suspected a relatively simple fault and saw an opportunity to acquire it and offered to buy it for the price he had paid. However I have decided to be more charitable rather than mercenary and have offered to give it a look over and repair it for him if I can.

The fault as described was the rig receives okay but on transmit there was a carrier on FM with no audio and a very quiet SSB signal. A faulty microphone had been ruled out and someone had suggested a bad connection internally. Due to the compactness of the unit and the difficulty in dismantling no one had felt confident to attempt any further inspection. I wasn’t so sure this was the issue so at the last meeting I picked up the rig and currently have it on the workbench.

TRANSMITTER CIRCUIT
The microphone signal is amplified with the microphone amplifier Q1 (2SC2240(GR)), which is commonly used for both SSB and FM transmission modes and is incorporated in the carrier unit (X50-1720-XX). The amplified signal is then fed to both the SSB and FM circuits.

Looking at the block diagram of the carrier unit and the above functional description in the service manual I suspected the microphone amplifier Q1 to be faulty.

I want to confirm the fault first and so I connected up a dummy load and RF power meter and using the FUNCube Dongle SDR I could observe and monitor the output signal. Sure enough on FM there was a nice carrier at 10W with very faint audio, on SSB there was a small visible signal again with very little modulation. Whistling, blowing and tapping of the microphone could be seen on the waterfall… just!

I connected a switch to the Morse key input and confirmed the rig transmitted in CW with no issue.

On the block diagram there is a switchable tone burst oscillator for repeater access and the output of this is joined to the output from the microphone amp. Encouragingly the tone burst can be clearly seen and heard in the transmission again pointing to an issue with the microphone amp.

To get to the carrier unit PCB it was a simple matter of removing the bottom cover. The PCB is held in a metal frame mounted with five screws and can be lifted out, as pictured above. But before I did that I checked the continuity to the microphone socket and the 8V supply to the amplifier circuit and both were fine (see diagram below)

The poor quality image from the scanned service manual shows the bottom of the carrier unit, this is the side of the PCB visible without needing to remove it. The microphone connector is in the top left, putting an oscilloscope on the microphone input (pin1) a signal was observed, however the output (pin8) had an almost identical signal with little or no amplification. Injecting a low level audio signal from the a generator on this pin could be seen and heard in the transmitted signal. This observation together with the tone burst seemed to confirm the other audio circuitry was functioning normally and the microphone amp wasn’t.

Actually removing the carrier unit PCB proved a bit tricky as it has a number of small and very secure connectors with ageing and delicate wiring, but I did manage to extricate it and a visual inspection didn’t show up any obvious issues such as broken tracks or joints.

This is the detail of the microphone amplifier section from the schematic. Using a meter I have checked the continuity of tracks and have checked all the resistors for shorts or open circuits and they all read the correct values. The capacitors all look okay and checking the signals either side of C3 the C7 coupling capacitors show they are functioning correctly. This left Q1 a 2SC2240(GR) transistor as the likely culprit and I have ordered a replacement which should arrive in the next few days. I am hoping this will make it spring back to life.

It worked for three weeks

After seemingly fixing that broken laptop it has failed to boot up this morning!

I noted that it has been running hot again, the heat sink port on the side has been getting seriously warm so if I do attempt another re-flow of the GPU (if that is the fault) I will have to look at improving the cooling. I am thinking I might drill some holes through the bottom casing to allow more air in and might fit an override switch on the fan since it seems to only come on when very very warm.

What is doubly annoying is that over the weekend I managed to receive what I believe are the FITSAT-1 and TechEdSat Cubesats. My earlier attempts last week were only partially successful and the one time I did manage to get really good signals I forgot to set it to record the IQ file.

Over the weekend I was away from home, visiting the in-laws. I had taken a scanner, my FUNCube Dongle and laptop. I appropriated an indoor TV aerial and surprisingly managing to get some clearly audible signals, despite major issues with pager breakthrough and interference caused by the aerials wideband amplifier.
 

As soon I manage to get the laptop working, or recover the IQ files from its hard drive I will post the results.

If at first you don’t succeed… try, try, try again

Hopefully yesterday saw the conclusion to the saga of my broken laptop.

Two weeks ago I had an attempt at reviving a sickly HP/Compaq 6735S a model which is notorious for GPU problems. Specifically the GPU BGA contacts break due to thermal stresses and shoddy manufacturing.

I had stripped the laptop down and using a IR rework station attempted to reflow the contacts with limited success. It survived one power up and then died again.

Like Robbie Burn’s famous spider I was not going to give up that easily so I stripped it down again and this time remembering the 7 Ps adage I didn’t cut any corners.

The picture above shows the motherboard after I removed it the first time, you can clearly see the GPU in the top right. Notice first the pathetic thermal bonding? Also you can see around all four corners of the chip what appears to be red cement.

Initially I was unsure of whether to remove this and indeed it appeared to be tough and nigh on impossible to remove so fearing possible collateral damage I left the cement in place and heated the GPU on the IR rework station attempting to reflow the joints.

This I believe was the mistake as this bonding would have prevent the chip from floating on the reflowed solder pads. So this time I did remove the cement as you can see below. I found heating the cement did make it malleable, the problem being how to heat it without damaging any of the surrounding components?

In the end I used a precision hot-air gun (which they also have at work) on a low-medium heat setting on a very low ‘blow’ setting. Using this and a couple of wooden toothpicks I was able to remove the vast majority of the red gunk!

Once removed I applied a small amount of flux around the chip, working it under the device and then used the IR rework station but on a much higher setting than before to ensure the solder properly melted.

To my pleasant surprise the reassembled laptop booted and it has been successfully been powered down and rebooted several more times since.

While not the prettiest of laptops, or indeed in the best condition it does at least have Windows 7 Professional on it and a nice big hard drive and 4GB of memory so should prove more than capable for my experiments – assuming she carries on working, and she does get a little warm!

Experiments with an SDR4+ and a scanner refurb

Seems the holiday in early June broke the blogging momentum and unfortunately work commitments since and the stresses involved as a major project nears deployment have sapped my time and energy, so not had much to post.

Family commitments too have also eaten into my spare time not leaving me time or inclination to experiment. The FUNCube Dongle and the Ultra-cheap RTL-SDR have been unplugged for several weeks and I am ashamed to say most of my evenings have been sent slumped in front of the TV often nodding off to sleep rather than tinkering away.

That is not to say I have been completely idle! I have spent the last couple of weeks with a Cross Country Wireless SDR4+ receiver courtesy of my younger brother. For a while I have toyed with purchasing one after seeing them at last years Hamfest and have read some decent reviews. The SDR4+ is a HF Software Defined Radio covering 0.85 – 30MHz, the full specifications can be found on their website.

My brother shares a similar interest in radio, probably as he was forced to share a room with me when we were younger and I would subject him to listening to all sorts of strange signals late into the night! Well he decided to purchase one several weeks ago, but was frustrated when it didn’t seem to work. On one of visits to see my Mother I took a cursory look and couldn’t make it work either. To cut a long story short while he went away on holiday I borrowed the unit away to see if I could figure it out.

Following some experimentation and discussions with Chris Moulding on the Cross Country Wireless Yahoo Group turned out the problem was some dodgy USB ports and/or USB leads! The thread can be read at http://uk.groups.yahoo.com/group/cross_country_wireless/message/2136

I strung up a long random-length wire antenna in the loft and have managed to get some decent results on some bands, but interestingly very little on others, probably due to the lack of an ATU. But I have received lots of broadcast AM, some DRM (but not actually decoded) and buckets loads of Amateur transmissions, LSB/USB voice and Morse, RTTY and PSK31 from Europe, and decoded some HF-FAX. Sadly the SDR4+ will soon be off back to it’s rightful owner, but has certainly wetted my appetite.

I have also refurbished my Realistic PRO2022 scanner, as I posted back in 2010 this was my very first scanner and sadly was looking a little bit worse for years of wear. It is still functional, especially for listening to airband but the displays electro-luminescence back light had faded and it was looking a little grubby.

I had already replaced the backlight on my PRO2006, but this was a lot easier due to the display being easily accessible with the simple removal of the front panel, and the EL panel being on flying leads rather than soldered on to a PCB. 

I found a cheap supplier of a suitable EL panel on Ebay and quickly had the new one cut to size and fitted, giving a lovely new blue display.

 The next thing was to clean the grime and grease that was encrusted on the case and knobs, using a small amount of Clit-Bang degreaser and being very careful soon had the case looking almost as good as new!

A bit of a clean up and some repairs

The original plans for the weekend were thrown in to the air for a number of reasons. I spent most of Saturday with a saw, drill and screwdriver rebuilding part of the summerhouse in the garden and ferrying the old rotten parts and other garden waste to the local refuse tip!

Today (Sunday) I had the house to myself as the wife was off visiting her sister. As the weather has been absolutely atrocious, raining most of the day, I decided to have a bit of a clean up in the den. I’d noticed the fans in the main computer have been roaring under the slightest load recently and as I suspected the reason was the air intakes were blocked with dust and dog hair! While not quite as bad as these it was still pretty shocking as I do regularly check them.

As I had to pull them out from under the desk I decided to have a bit of a rearrange. While doing this I removed a redundant ethernet switch and an unused USB 1.1 hub, both were cheap far-eastern ones purchased many years ago. It now turns out they were a major source of interference on my scanners!

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The tidy computer centre (yes the external HD are sitting on a 1980 2001AD annual!)

One other task I achieved today was to replace the backlight on my Realistic PRO2006 scanner.

I purchase the PRO2006 from ebay about four/five years ago, I got it for less than £20 as it was advertised as for repair or spares. It was described as powering up with sound but because there was no display it couldn’t be operated.

When I got it (in it’s original box with manual) and opened it up it was obvious what was wrong as it appear to have spent most of it’s life in a shed or workshop, it was full of fine dust (I suspect from sanding wood) and this has blocked out the LCD display! It also had flecks of paint on the casing. The paint was thankfully emulsion and was easy to remove I just soaked the plastic case in warm water for a few hours. I stripped down the rest of the unit and removed the dust with a can of compressed air and a brush, other than that it worked perfectly!

One downside was the display backlight had faded, the backlight on many of the Realistic desktop scanners is an electro-luminescent panel and their output fades over time. Today I finally got around to replacing the panel, it isn’t as straightforward as it sounds as the spare part is no longer available but using the instructions found here I was able to replace it with a panel cut from a larger sheet purchased from Farnell.

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The display panel removed from the scanner with original backlight

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Original panel removed (top) and replacement panel cut to size (bottom)

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The new panel in all it’s glory!

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The only downside is from this angle you can just see the connector on the panel.

The backlight is now really bright, in fact I have had the ‘dimmer’ switch activated because it is so bright! I also have a Realistic PRO2022 and the backlight on that is fading too, it is nowhere near as bad as the PRO2006 was, but you can see the marked difference below.

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This shows the repaired PRO2006 compared to my PRO2022.

One other benefit of opening up the PRO2006 was I discovered a soldered connector on the shielding behind the front panel had come adrift. I have resoldered this and this has dramatically improved the reception and audio from the unit. Today has been a good day!