Reducing RF susceptibility for the HamGadgets "Ultra Pico Keyer" - and mimizing RF issues on portable HF stations in general

Note:

While this article describes a modification of the Pico Keyer to reduce RF susceptibility, it also talks about general methods to minimize/reduce RFI-related issues for both portable and "base" stations:  This specific topic is covered near the end of this blog entry.

POTA operation 

Over the past several years I've done a bit of POTA (Parks On The Air) operating, racking up "about" 1000 contacts as an activator in a number of parks - usually as an "activator", and mostly on CW.  Typically, I have operated from a campsite using a portable antenna - usually the JPC-7 loaded dipole (discussed in this blog entry) or the JPC-12 loaded vertical (discussed here) - but I have also used an end-fed half-wave and a simple dipole on occasion - and even the Yaesu ATAS-100 on my vehicle.

Figure 1:
Operating CW POTA from US-0004,
Arches National Park in Utah
Click on the image for a larger version.

In the recent past there has been a revolution in portable power sources in that a LiFePO4 battery - which can supply 20-ish amps - is both light enough to be practical and fairly inexpensive.  For those instances where I may be staying at one location for several days the advent of inexpensive solar to maintain the power budget - and the solar controllers can be made to be RF quiet to make it compatible with HF operation (see this article).  With this in mind it's practical to operate the transmitter at 100 watts much of the time, something that makes it as easy as possible for those who wish to work me.  Despite the ability to run 100 watts, I have occasionally operated QRP (5 watts or less) - again, usually on CW.

A memory keyer

Having used a number of different radios for POTA operation (Yaesu FT-100 and FT-817, Icom IC-706MK2G and even a RockMite) - none of them with a memory keyer - I decided that an "Upgrade" was in order so I got the Ham Gadgets "Ultra Pico Keyer" (Link here).  This device is small, powered by a single CR2032 lithium coin cell and costs about US$40 as a kit (not including shipping) including a (partially) 3-D printed case.  For portable use, I couple it with the "Outdoor Pocket Double Paddle" (with magnets!) from CW Morse (link).

This is a nice, little device in that it provides a consistent interface to the user - no matter which radio you might use - and it has a number of message memories (up to eight), perfect for an activity like POTA where a message (e.g. "CQ POTA") may be repeated many, many times during the course of the operation.

Getting "stuck" 

Figure 2:
The Ham Gadgets "Pico Keyer" (left) along with the
CW Morse Outdoor Paddle.
Click on the image for a larger version.

While the Ultra Pico Keyer works as advertised, I did notice a problem on the first trip out while using a portable antenna:  It would get "stuck".

Clearly, this was an RF susceptibility issue - verified by reducing transmit power and observing that it no longer happened.  In short, at 5 watts there was usually no issue, but at 100 watts  the radio would stay keyed continuously after the first Morse element whether it was sent from a stored message or via the paddle:  While it was "stuck", I could still hear the sidetone - via the keyer's internal speaker - sending the message or what was keyed via the paddle indicating that it was not the microcontroller that had crashed but the circuitry that keyed the radio that was the problem.

Further testing showed that when the unit got "stuck" due to RF and simply unplugging the paddle from the back of the keyer would cause it to release (get "un-stuck").  The fact that this happened using a portable antenna provided further evidence of potential RF sensitivity.

Analyzing the problem

As I'm wont to do, I decided to take a look at the Pico Keyer's schematic to see if there was something about its design and construction that might make it more susceptible to RF interference - and I was surprised at what I found.  Here's the diagram found in the manual that is freely available online on the web site (link):

Figure 3:
Annotated diagram of the Pico Keyer with RF current paths shown.
The components in question are Q1 and Q2, in the upper-right corner.  The lines highlighted in yellow are those through which RF currents will flow (between the radio chassis and the paddle/cable) if no bypass capacitor is installed. 
The added capacitor is shown below the "OUTPUT" jack near the upper-right with the resulting RF current path around Q1/Q2 shown in magenta.
Click to get a larger image.

While there are protection capacitors on the paddle input (C1, C2) my eye was immediately drawn to the output keying (upper-right) where I was, at first, confused as to the arrangement with an N-channel MOSFET in both the keying line and the "common" (ring) of the "OUTPUT" connector (e.g. Q1 and Q2) - but then I remembered that the manual stated that this device would key both positive and negative voltages, explaining the "unusual" arrangement.

While admittedly clever, I could immediately see a susceptibility issue here - the problematic RF current path highlighted in yellow in Figure 3, above:  The "OUTPUT" jack more or less will "float" compared to the "ground" of the keyer itself, which is also connected to the "ground" lead of the cable to the paddle as well as the external paddle itself.  This configuration almost guarantees that there will be at least some RF current flowing from the radio and through the keyer's output circuit for several reasons:

• If you are using this in a portable situation, the radio will surely have some RF on its chassis.  As noted in the final section of this blog entry, it's almost impossible to prevent all RF current from getting onto the feedline - even if you do use a common-mode RF choke and a very nearby antenna is likely to immerse the radio and its interconnecting gear in a rather strong radio-frequency field.

• The paddle and the cable that connects it to the keyer should be considered as part of an antenna - and this situation is made worse if one is sitting at, say, a metal table and also if you, the operator, place your hand at/near the paddle/cable, further encouraging a "through" path for RF.
  

What this means is that there will be at least some RF current flowing from the radio chassis, through the keyer and then, as indicated by the yellow-highlighted lines - via transistor Q2 (and Q1) and then through the cable to the paddle.  I didn't really investigate the exact mechanism by which RF current through this path was causing the keying line to get "stuck" - but here are a couple of possibilities.

• RF may be coupling from the drain of Q2 into its gate - and subsequently into Q1's gate as well, which is tied in parallel with it with the peaks of the RF voltage turning on the FET.  Even if RF through the FET was causing it to conduct only on half of the RF cycle, this would surely be enough to key the radio.  It's also possible that the transistor was turned, on average, only "partially" on by the RF energy - not enough to completely shunt out the RF, but enough to key the radio.

• The RF could also be getting into the output pin of the microcontroller via the FET, causing its totem pole output to get "stuck" on while it was present.

Figure 4:
The added capacitor(s) can be seen soldered between the
"sleeve" pins of the "OUTPUT" and "PADDLE" jacks,
on the bottom of the board.  As you can see, I've made this
modification to both of my Pico Keyers!
Click on the image for a larger version.

Regardless of the cause, the fix was clear:  Add a capacitor to bypass RF current around Q1 and Q2 and the output pin of the microcontroller.  In Figure 3, above, the magenta highlight shows how the added capacitor conducts RF currents around the sensitive components.

When this occurred, I happened to be on a POTA activation, but I had my "electronic toolbox" in the car which included a number of useful items such as a soldering iron and a smattering of useful electronic components (a some common resistors, capacitors, etc.).  Grabbing a 1000pF capacitor, I connected one end to the "sleeve" (ground) pin of the "PADDLE" jack and the other end to the "sleeve" of the "OUTPUT" jack - effectively providing a bypass to RF energy on Q2's drain to the circuit "ground" to eliminate any RF voltage potential between the cable connecting the radio and that going to the paddle.  

This modification completely solved the problem:  It is my opinion that this capacitor should be supplied with the kit.  Additionally, Q2 could be eliminated completely and its source/drain leads jumpered if negative keying is not needed.  ^{See Footnote 1}

Since the topic of "RF on the rig" was already broached, the rest of this article will describe how to reduce it.  It's worth noting that the susceptibility of the memory keyer was such that even with the measures described below, it was affected at 100 watts.

* * * * *  

Suppressing RF on the gear and connecting cables

Some readers of this may immediately say "You are obviously doing something wrong with your set-up if there's enough RF on your gear to cause a problem".  

The problem of RF going somewhere other than out the antenna has been known for many decades and is sometimes referred to as "Hot Mic", a situation where there is enough RF on the radio - and the microphone - that the operator can even get an RF burn from touching the gear.  When this happens RF can get into the radio itself and cause undesired operation (malfunctions, distorted audio, etc.) but accessories connected to the radio - most notably sound interfaces, computers and even keyers - can be adversely affected.

While in the case above there was apparently some RF present on the gear to cause a problem, there isn't anywhere near enough to cause issues with the radio itself, and the radio+microphone (when running SSB) seemed immune.  Some types of antennas - typically ground-plane verticals, random-wires and end-fed half-wave antennas can, by their nature, put RF on the feedline - and thus the radios - unless extra steps are taken to minimize this problem in addition to properly installing/configuring the antenna, namely:

• Common-mode choke on the feedline.  Typically placed near the antenna, this usually consists of coaxial cable wound on a ferrite toroid - typically 6-12 turns on an FT240 or FT140 core with either Mix 31 or Mix 43 as the material - the latter being generally more useful/preferred for portable operations where the higher bands (40 meters and up) are most likely to be used.  Sometimes operators wish to have the feedline itself act as part of the counterpoise/ground - something that can risk a "hot mic" situation and in this case placing the common-mode choke farther along the coax - often near the radio - is the better choice.  (Some operators will put a choke at the antenna and near the radio.)
  

• Use of a "balanced" antenna.  A balanced antenna like a dipole is generally more likely to induce less RF current on its feedline than a purely end-fed antenna (a vertical is included) as it contains its own counterpoise - but having a perfectly-balanced antenna is not really possible and the feedline itself will usually participate in conducting/radiating RF along with the antenna to some degree.  A high-impedance antenna like an end-fed half-wave can sometimes reduce the probability of RF currents on the gear, but note that current can peak at every odd-numbered quarter-wave interval along the feedline and if the radio happens to be at one of these current nodes, issues are more likely to arise:  Placing a common-mode choke at a current node can help.
  

• Counterpoise/ground plane at the radio.  If you are operating in a metal vehicle it's less likely that RFI will be a problem as one is likely to be surrounded (e.g. shielded) - plus the fact that the shield of the coaxial cable feeding the antenna can be electrically bonded to its chassis.  Barring being in a Faraday cage like a vehicle, having a counterpoise connected at the radio (particularly if it's 1/4 wave long at the operating frequency - and if there is more than one of them) this can siphon off some of the RF that might be present owing to its lower impedance.  The use of a common-mode choke prior to the counterpoise at the radio will help to raise the impedance of the conducted RF and will usually improve the efficacy of a counterpoise/ground plane.

• Ferrites only go so far.  At HF, a simple "snap on" choke will probably do very little for the simple fact that there does not exist a common ferrite material that will offer a reasonable degree of choking impedance at, 14 MHz with just one turn (e.g. wire passed through it).  What is required is that multiple turns of a conductor be passed through the device (snap-on choke, toroid, etc.) as the impedance/inductance is proportional to the square of the number of turns.  Even so, there's a practical limit as to the choking impedance of a piece of wire around a ferrite (probably in the hundreds of Ohms for a "casually-wound" device).  As in the case of the keyer, I chose to use a capacitor, instead:  It is a tiny, inexpensive device able to fit inside the keyer rather than a large lump in a cable and it directly addresses the issue at hand by making the circuit intrinsically RF-tolerant.  In other words, it's the correct component for the job!
  

• Place the antenna far away from the radio.  As noted, this isn't always practical - or even desirable during portable operation.  In my opinion, equipment used with a radio transceiver should already have a modicum of resistance to stray RF energy so that even small/moderate amounts of RF on the gear will not cause any problems.
  

If you are operating portable, there's one thing that you probably aren't going to get very faraway from:  The antenna itself.  Almost by definition, portable operating implies being near the antenna owing to the need to have a feedline of manageable length and also due to practicalities of not wanting to lug a long feedline along or taking up more real estate than necessary.  What this means is that it's likely that you and your radio will be immersed in a rather strong RF field - and this also means that anything made out of anything that is conductive (the radio, power cables, microphones, interconnect cables to your paddle and keyer - and even you) are likely to intercept RF energy this will get into everything.

* * * * *

Footnote

1. A 1000pF capacitor has theoretical impedance of about 23 ohms at 7 MHz and it did the job here, but a 10000pF (e.g. 0.01uF or 10nF - ideally about 2.3 ohms at 7 MHz) capacitor would to just fine as well.  For positive keying (which is what likely what any modern radio uses) values as large as 0.1uF (100nF) would work as well - but this large of a value may cause issues with radios that use negative keying (e.g. high-impedance lines on some vintage radios).

 If you never plan to use a radio with negative keying, you could simply short together the source and drain leads of Q2 together to reduce RF susceptibility.

This kit is actually supplied with an "extra" capacitor:  The user can select between a 0.01uF (10nF) and a 0.047uF (47nF) capacitor (C3) on the "headphone" jack to set the loudness.  As I installed the 0.047uF capacitor, I had the 0.01uF left over.  Unfortunately, the specific capacitor supplied was thick enough that it prevent the board from sitting in the bottom of the case, raising it up and preventing the lid from fitting properly.  I could have probably connected this capacitor to the same circuit points on the top side of the board, but as I was home when I made this modification to my second keyer I simply found a lower-profile capacitor that didn't interfere with the board clearance.

* * * * *

This page stolen from ka7oei.blogspot.com

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Repairing a dead Kenwood TS-850S

Recently, a Kenwood TS-850S - a radio from the mid-early 1990s - crossed my workbench.  While I'm not in the "repair business", I do fix my own radios, those of close friends, and occasionally those of acquaintances:  I've known this person for many years and we have several mutual friends.

If you are familiar with the Kenwood TS-850S to any degree, you'll also know that they suffer from an ailment that has struck down many pieces of electronic gear from that same era:  Capacitor Plague.

Figure 1:
The ailing TS-850S.  The display is normal - except
for the frequency display showing only dots.  This error is
accompanied by "UL" in Morse.
Click on the image for a larger version.

This isn't the same "Capacitor Plague" of which you might be aware where - particularly in the early 2000s - many computer motherboards failed due to incorrectly formulated electrolytic capacitors, but rather early-era (late 80s to mid 90s) surface-mount electrolytic capacitors that began to leak soon after they were installed.

The underlying cause?

While "failure by leaking" is a common occurrence in electronics, this failure is somewhat different in many aspects.  At about this time, electronic manufacturers were switching over to surface-mount devices - but one of the later components to be surface-mounted were the electrolytic capacitors themselves:  Up to this point it was quite common to see a circuit board where most of the components were surface-mount except for larger devices such as diodes, transistors, large coils and transformers - and electrolytic capacitors - all of which would be mounted through-hole, requiring an extra manufacturing step.

Early surface-mount electrolytic capacitors, as it turned out, had serious flaws.  In looking at the history, it's difficult to tell what aspect of their use caused the problem - the design and materials of the capacitor itself or the method by which they were installed - but it seems that whatever the cause, subjecting the capacitors themselves to enough heat to solder their terminals to the circuit board - via hot air or infrared radiation - was enough to compromise their structural integrity.

Whatever the cause - and at this point it does not matter who is to blame - the result is that over time, these capacitors have leaked electrolyte onto their host circuit boards.  Since this boron-based liquid is somewhat conductive and mildly corrosive in its own right, it is not surprising that as surface tension wicks this material across the board, it causes devastation wherever it goes, particularly when voltages are involved.

There are some capacitors on the display/driver board on the front panel that should be replaced - but that's not where the majority of the problem lies.

The CAR board - the cause of "display dots"

In the TS-850S, the module most susceptible to leaking capacitors is the CAR board - a circuit that produces multiple, variable frequency signals that feeds the PLL synthesizer and several IF (Intermediate Frequency) mixers.  Needless to say, when this board fails, so does the radio.

They most obvious symptom of this failure is when damage to the board is so extensive that it can no longer produce the needed signals - and if one particularly synthesizer (out of four on the board) fails, you will see that the frequency display disappears - to be replaced with just dots - and the letters "UL" are sent in Morse Code to indicate the "Unlock" condition by the PLL.

Figure 2:
The damaged CAR board.  All but one of the surface-mount
electrolytic capacitors has leaked corrosive fluid and damaged
the board.  (It looked worse before being cleaned!)
Click on the image for a larger version.

Prior to this, the radio may have started going deaf and/or transmitter output was dropping as the other three synthesizers - while still working - are losing output, but this may be indicative of another problem as well - more on this later.

Figure 2 shows what the damaged board looks like.  Actually, it looked a bit worse than that when I first removed it from the radio - several pins of the large integrated circuits being stained black.  As you can see, there are black smudges around all (but one) of the electrolytic capacitors where the corrosive liquid leaked out, getting under the green solder mask and even making its way between power supply traces where the copper was literally being eaten away.

The first order of business was to remove this board and throw it in the ultrasonic cleaner.  Using a solution of hot water and dish soap, the board was first cleaned for six minutes - flipping the board over during the process - and then very carefully, paper towels and then compressed air was used to remove the water.

Figure 3:
The CAR board taking a hot bath in soapy water in an
ultrasonic cleaner.  This removes not only debris, but spilled
electrolyte - even that which has flowed under components.
Click on the image for a larger version.

At this point I needed to remove all of the electrolytic capacitors:  Based on online research, it was common for all of them to leak, but I was lucky that the one unit that had not failed (a 47uF, 16 volt unit) "seemed" OK while all of the others (10uF, 16 volt) had disgorged their contents.

If you look at advice online, you'll see that some people recommend simply twisting the capacitor off the board as the most expedient removal procedure, but I've found that doing so with electrolyte-damaged traces often results in ripping those same traces right off the board - possibly due to thinning of the copper itself and/or some sort of weakening of the adhesive:  While I was expecting chemically-weakened traces, already, there was no reason to add injury to insult.

My preferred method of removing already-leaking capacitors is to use a pair of desoldering tweezers, which are more or less a soldering iron with two prongs that will heat both pins of the part simultaneously, theoretically allowing its quick removal.  While many capacitors are easily removed with this tool, some are more stubborn:  During manufacture, drops of glue were used under the part to hold it in place prior to soldering and this sometimes does its job too well, making it difficult to remove it.  Other times, the capacitor will explode (usually just a "pop") as it is being heated, oozing out more corrosive electrolyte.

With the capacitors removed, I tossed it in the ultrasonic cleaner for other cycle in the same warm water/soap solution to remove any additional electrolyte that had come off - along with debris from the removal process.  It is imperative when repairing boards with leaking capacitors that all traces of electrolyte be completely removed or damage will continue even after the repair.

At this point one generally needs to don magnification and carefully inspect the board.  Using a dental pick and small-blade screwdriver, I scraped away loose board masking (the green overcoating on the traces) as well as bits of copper that had detached from the board:  Having taken photos of the board prior to capacitor removal - and with the use of the Service Manual for this radio, found online - I was confident that I could determine where, exactly, each capacitor was connected.

When I was done - and the extent of the damage was better-revealed - the board looked to be a bit of a mess, but that was the fault of the leaking capacitors.  Several traces and pads in the vicinity of the defunct capacitors had been eaten away or fallen off - but since these capacitors are pretty much placed across power supply rails, it was pretty easy to figure out where they were supposed to connect.

Figure 4:
The CAR board, reinstalled for testing.
Click on the image for a larger version.

As the mounting pads for most of these capacitors were damaged or missing, I saw no point in replacing them with more surface-mount capacitors - but rather I could install through-hole capacitors on the surface, laying them down as needed for clearance - and since these new capacitors included long leads, those same leads could be used to "rebuild" the traces that had been damaged.

The photo shows the final result.  Different-sized capacitors were used as necessary to accommodate the available space, but the result is electrically identical to the original.  It's worth noting that these electrolytic capacitors are in parallel with surface-mount ceramic capacitors (which seem to have survived the ordeal) so the extra lead length on these electrolytics is of no consequence - the ceramic capacitors doing their job at RF as before.  After (later) successful testing of the board, dabs of adhesive were used to hold the larger, through-hole capacitors to the board to reduce stress on the solder connections under mechanical vibration.

Following the installation of the new capacitors, the board was again given two baths in the ultrasonic cleaner - one using the soap and water solution, and the other just using plain tap water and again, the board was patted dry and then carefully blown dry with compressed air to remove all traces of water from the board and from under components and then allowed to air dry for several hours.

Testing the board

After using an ohmmeter to make sure that the capacitors all made their proper connections, I installed the board in the TS-850S and... it didn't work as I was again greeted with a "dot" display and a Morse "UL".

I suspected that one of the "vias" - a point where a circuit traces passes from one side to another through a plated hole - had been "eaten" by the errant electrolyte.  Wielding an oscilloscope, I quickly noted that only one of the synthesizers was working - the one closest to connector CN1 - and this told me that at least one control signal was missing from the rest of the chips.  Probing with the scope I soon found that a serial data signal ("PDA") used to program the synthesizers "stopped" beyond the first chip and a bit of testing with an ohmmeter showed that from one end of the board to the other, the signal had been interrupted - no doubt in a via that had been eaten away by electrolytic action.

Figure 5:
Having done some snooping with an oscilloscope, I noted
that the "PDA" signal did not make it past the first of the
(large) synthesizer chips.  The white piece of #30 Kynar
wire-wrap wire was used to jump over the bad board "via"
Click on the image for a larger  version.

The easiest fix for this was to use a piece of small wire - I used #30 Kynar-insulated wire-wrap wire (see Figure 5) - to jumper from where this control signal was known to be good to a point where it was not good (a length of about an inch/two cm) and was immediately rewarded with all four synthesizer outputs being on the correct frequencies, tuning as expected with the front-panel controls.

Low output

While all four signals were present and on their proper frequencies - indicating that the synthesizers were working correctly - I soon noticed, using a scope, that the second synthesizer output on about 8.3 MHz was outputting a signal that was about 10% of its expected value in amplitude.  A quick test of the transmitter indicated that the maximum RF output was only about 15 watts - far below that of the 100 watts expected.

Again using the 'scope, I probed the circuit - and comparing the results with the nearly identical third synthesizer (which was working correctly) and soon discovered that the amplitude dropped significantly through a pair of 8.3 MHz ceramic filters.

The way that synthesizers 2 and 3 work is that the large ICs synthesize outputs in the 1.2-1.7 MHz area and mix this with a 10 MHz source derived from the radio's reference to yield signals around 8.375 and 8.83 MHz, respectively - but this mix results in a very ugly signal, spectrally - full of harmonics and undesired products.  With the use of these ceramic bandpass filters - which are similar to the 10.7 MHz filters those found in analog AM and FM radios - and these signals are "cleaned up" to yield the desired output over a range of the several kiloHertz that they vary depending on the bandpass filter and the settings of the front panel "slope tune" control.

Figure 6:
The trace going between C75 and CF1 was cut and a bifilar-
wound transformer was installed to step up the impedance
from Q7 to that of the filter:  R24 was also changed to 22
ohms - providing the needed "IF-7-LO3" output level at J4.
Click on the image for a larger version.

The problem here seemed to be that the two ceramic 8.3 MHz filters  (CF1, CF2) were far more lossy than they should have been.  Suspecting a bad filter, I removed them both from the circuit board and tested them using a temporary fixture on a NanoVNA:  While their "shape" seemed OK, their losses were each around 10dB more than is typical of these devices indicating that they are slowly degrading.  A quick check online revealed that these particular frequency filters were not available anywhere (they were probably custom devices, anyway) so I had to figure out what to do.

Since the "shape" of the individual filter's passbands were still OK - a few hundred kHz wide - all I needed was to get more signal:  While I could have kludged another amplifier into the circuit to make up for the loss, I decided, instead, to reconfigure the filter matching.  Driving the pair of ceramic filters is an emitter-follower buffer amplifier (Q7) - the output of which is rather low impedance - well under 100 ohms - but these types of filters typically "want" around 300-400 ohms and in this circuit, this was done using series resistors - specifically R24.  This method of "matching" the impedance is effective, but very lossy, so changing this to a more efficient matching scheme would allow me to recover some of the signal.

Replacing the 330 ohm series resistor (R24) with a 22 ohm unit and installing a bifilar-wound transformer (5 turns on a BN43-2402 binocular core) wired as a 1:4 step-up transformer (the board trace between C75 and CF1 was cut and the transformer connected across it) brought the output well into the proper amplitude range and with this success, I used a few drops of "super glue" to hold it to the bottom of the board.  It is important to note that I "boosted" the amplitude of the signal prior to the filtering because to do so after the filtering - with its very low signal level - may have also amplified spurious signals as well - a problem avoided in this method.

Rather than using a transformer I could have also used a simple L/C impedance transformation network (a series 2.2uH inductor with a 130pF capacitor to ground on the "filter side" would have probably done the trick) but the 1:4 transformer was very quick and easy to do.

With the output level of synthesizer #2 (as seen on pin CN4) now up to spec (actually 25% higher than indicated on the diagram in the service manual) the radio was now easily capable of full transmit output power, and the receiver's sensitivity was also improved - not surprising considering that the low output would have starved mixers in the radios IF.

A weird problem

After all of this, the only thing that is not working properly is "half" of the "Slope Tune" control:  In USB the "Low Cut" works - as does the "High Cut" on LSB, but the "High Cut" does not work as expected on USB and the "Low Cut" does not work as expected on LSB.  What happens with the settings that do NOT work properly, I hear the effect of the filter being adjusted (e.g. the bandwidth narrows) but the radio's tuning does not track the adjustment as it should.  What's common to both of these "failures" is that they both relate to high frequency side of the filter IF filters in the radio - the effect being "inverted" on LSB.

I know that the problem is NOT the CAR board or the PLL/synthesizer itself as these are being properly set to frequency.  What seems to NOT be happening is that for the non-working adjustments, the radio's CPU is not adjusting the tuning of the radio to track the shift of the IF frequency to keep the received signal in the same place - which seems like more of a software problem than a hardware problem:  Using the main tuning knob or the RIT one can manually offset this problem and permit tuning of both the upper and lower slopes of of the filters, but that is obviously not how it's expected to work!

In searching the Internet, I see scattered mentions of this sort of behavior on the TS-850 and TS-950, but no suggestions as to what causes it or what to do about it:  I have done a CPU reset of the radio and disconnected the battery back-up to wipe the RAM contents, but to no avail.  Until/unless this can be figured out, I advised the owner to set the affected control to its "Normal" position.  If you have experienced this problem - and especially if you know of a solution - please let me know.

Figure 7:
The frequency display shows that the synthesizer is now
working properly - as did the fact that it outputs full power
and gets good on-the-air signal reports.
Click on the image for a larger version.

Final comments

Following the repair, I went through the alignment steps in the service manual and found that the radio was slightly out alignment - particularly with respect to settings in the transmit output signal path - possibly during previous servicing to accommodate the low output due to the dropping level from the CAR board.  Additionally, the ALC didn't seem to work properly - being out of adjustment - resulting in distortion on voice peaks with excessive output power.

With the alignment sorted, I made a few QSOs on the air, getting good reports - and using a WebSDR to record my transmissions, it sounded fine as well.

Aside from the odd behavior of the "Slope Tune" control, the radio seems to work perfectly.  I'm presently convinced that this must be a software - not a hardware - problem as all of the related circuits function as they should, but don't seem to be being "told" what to do.

* * * * *

This page stolen from ka7oei.blogspot.com

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