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Re: KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...

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ke9uw

Re: KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...

Yes the W6 point gets 8 volts either thru the diode D2 or D6 depending on whether in receive or xmit. I think I have an oscillator at Q5-Q6. I am checking all the feedback chokes and capacitors. I may need to unsolder C118 and see if it is infact a capacitor inside the shell and maybe also C120. RFC6 checks ok, R49, R470, etc.
Thanks for the interest and help.

Chuck, KE9UW

---- Original message ----

>Date: Tue, 20 Oct 2009 23:40:36 -0400
>From: Don Wilhelm <[hidden email]>
>Subject: Re: [Elecraft] Just built K2 and finals seem to be oscillating...
>To: [hidden email]
>
>Chuck,
>
>I have given you about all the info I can until I can refer to the
>schematics and make a guess about where the 450 Hz might be coming
>from. I am currently thinking that there should be no DC at W6, but I
>could be wrong on that.
>
>As far as the sidetone source - yes, with firmware 2.04r, you must add
>the sidetone source wiring change to obtain sidetone for all control
>boards below SN 3000 - whether or not you have the KIO2 or KPA100
>installed. The statements in the firmware document override since they
>are dated later than the A to B upgrade or the KIO2 or KPA100
>instructions. Version 2.04r firmware eliminated the U6-25 sidetone
>output option and will save a lot of support effort in the future.
>
>73,
>Don W3FPR
>
>
>C. J. Hawley wrote:
>> Thanks. I went back and re-read his note and he did mention K2-T2 as well. Then I went to the newest manual and K2-T1 and K2-T2 are now shown wound the way he did them for me. All reverse from the original manual. So that's not an issue I see.
>> I still don't have a solution though. I checked 8T, 8R, measured all the D1 thru D4 diodes, took out the 160M board and shorted J14 to restore W1, resistance checked to see that all the chokes, etc. are installed in the T-R switch area.
>>
>> After more careful checking with the power knob all the way down, I get about 3 vpp at W6 riding on 8 vdc. I get very small voltage at BPF on transmit and as well on Xmixer and buffer. 40 vpp with 8 vdc on D3-D4 cathodes, 60 vpp at 0 vdc on W1 (with 160 removed), and the same 60 vpp at 0 vdc on the output ant jack. Fundamental freq is about 450KHz.
>>
>> I also read the instructions for rev 2.04 firmware which said to revise the A board according to KIO2 mod details for sidetone, but I kept going back to rev B mod page where it said I didn't have to if I didn't have KIO2. The issue is that the new rev 2.04 firmware does not have the option to use U6-25. It only allows U8-4. Once I cut the trace, etc. all works well for the sidetone.
>>
>> Beats me...
>>
>> Chuck, KE9UW
>>
>> ---- Original message ----
>>
>>> Date: Tue, 20 Oct 2009 17:56:27 -0400
>>> From: Don Wilhelm <[hidden email]>
>>> Subject: Re: [Elecraft] Just built K2 and finals seem to be oscillating...
>>> To: [hidden email]
>>> Cc: elecraft <[hidden email]>
>>>
>>> Chuck,
>>>
>>> The winding sense that The Toroid Guy was referring to is T1 and T2 for
>>> the KSB2 board, not the base K2.
>>> The winding sense on those transformers will make no difference.
>>>
>>> From your previous post, I see you have an oscillation that appears as
>>> far back as W6. That can be a problem muh earlier in the transmit
>>> chain, like at the TX mixer or the Transmit buffer. Check the RF levels
>>> of the VFO and BFO at the transmit mixer (see the Receive and Transmit
>>> Signal Tracing sections in the back of the manual for the normal levels.
>>> Also check the frequency at TP2 and TP1 to be certain they are correct -
>>> the VFO frequencies for each band are listed on the Schematic Key page.
>>>
>>> 73,
>>> Don W3FPR

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Chuck, KE9UW

Don Wilhelm-4

Re: KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...

Chuck,

Since you have a 'scope, I would suggest you remove the PA transistors
from the picture and see if the oscillation persists. You can easily
de-solder T3 which will remove voltage from the PA collectors.
If you still have the oscillation at the base of Q7/8 (or at the
collector) of Q6, then you can more easily troubleshoot it without fear
of damaging the PA transistors.
Q6 can similarly be taken out of the operating condition by removing a
choke or resistor. I don't have the schematics with me while on
vacation, so you will have to find out which one on your own.

73,
Don W3FPR

C. J. Hawley wrote:
> Yes the W6 point gets 8 volts either thru the diode D2 or D6 depending on whether in receive or xmit. I think I have an oscillator at Q5-Q6. I am checking all the feedback chokes and capacitors. I may need to unsolder C118 and see if it is infact a capacitor inside the shell and maybe also C120. RFC6 checks ok, R49, R470, etc.
> Thanks for the interest and help.
>
> Chuck, KE9UW
>
>
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ke9uw

Re: KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...

Good idea...I'm at that stage where I need to check parts and try to isolate. The receiver and all works well.
Thanks, Chuck, KE9UW

---- Original message ----

>Date: Wed, 21 Oct 2009 08:42:52 -0400
>From: Don Wilhelm <[hidden email]>
>Subject: Re: [Elecraft] KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...
>To: [hidden email]
>Cc: elecraft <[hidden email]>
>
>Chuck,
>
>Since you have a 'scope, I would suggest you remove the PA transistors
>from the picture and see if the oscillation persists. You can easily
>de-solder T3 which will remove voltage from the PA collectors.
>If you still have the oscillation at the base of Q7/8 (or at the
>collector) of Q6, then you can more easily troubleshoot it without fear
>of damaging the PA transistors.
>Q6 can similarly be taken out of the operating condition by removing a
>choke or resistor. I don't have the schematics with me while on
>vacation, so you will have to find out which one on your own.
>
>73,
>Don W3FPR
>
>C. J. Hawley wrote:
>> Yes the W6 point gets 8 volts either thru the diode D2 or D6 depending on whether in receive or xmit. I think I have an oscillator at Q5-Q6. I am checking all the feedback chokes and capacitors. I may need to unsolder C118 and see if it is infact a capacitor inside the shell and maybe also C120. RFC6 checks ok, R49, R470, etc.
>> Thanks for the interest and help.
>>
>> Chuck, KE9UW
>>
>>

Chuck, KE9UW

ke9uw

Re: KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...

In reply to this post by ke9uw

Thanks so much for the help. The problem was C120...the one in the middle between two close in caps. Hard to see the value. Had to get serious and bend one over. Figures it would be that one. I had the value .001uF instead of .01uF.
You were so correct. Made me look closer.
Thanks for your patience, ability, and experience.
The alignment seems to be going well so far. Perfect tuning wand for those inductors. All done on that and buttoned up. All works and works well. I need to do the filters now...maybe Spectrogram. I'm a little confused if it is free or what, but I'll figure it out.
I have made use of the latest manual on line for some of the later clarifications and info. Thanks for having these on line.
And thanks Don and Michael for your suggestions along these same lines.
Chuck, KE9UW

---- Original message ----

>Date: Wed, 21 Oct 2009 11:39:06 -0700
>From: Gary Surrency <[hidden email]>
>Subject: KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...
>To: [hidden email]
>
> If a close inspection does not find it, a scope or
> an RF probe can be a big help too.
>
> There should be just a little RF leakage at the
> junction of D3, D4 when in transmit, but next to
> nothing at the anode of D3 or D5. D5 and C110 shunt
> any T-R switch leakage to ground through C108. See
> the schematic. If there is RF present at these
> points, it usually means the T-R switch has poor
> isolation.
>
> Sometimes it helps for troubleshooting to remove T3
> so the PA transistors do not have 12V to operate and
> become damaged. Place a 10 ohm resistor across the
> base lead of Q7, Q8 to provide a load for Q6 and T2.
> Now you can leave off the bottom cover for easier
> troubleshooting if the removal of the DC supply to
> PA transistors did not stop the oscillations.
>
> But in almost all cases I have repaired, there is an
> incorrect part or bad connection in the Q5-Q8 area
> if the PAs are oscillating and it is not being
> caused by poor T-R switch isolation (removal of
> jumper W1 will show if the RF feedback is from the
> output of the PAs to the input of Q5.
>
> An open RFC can be the problem too, if the DC bias
> is not getting to some of the T-R switch parts.
>
> D1, D5 are biased ON in TX, where D2-D4 and Q2 are
> biased ON in RX.
>
> Some builders have left out the two sets of ferrite
> beads at Z1, Z2 on either side of T3. Be sure they
> are there, and it is OK for them to touch the pins
> of the PA transistors since they are non-conductive.
>
> Some folks wind T4 correctly but then install it in
> reverse. It has to be installed with the green wires
> closer to T3, and the two bare wire links go
> straight thru each hole of the core, and are not
> wound around to the other hole (just a link from
> 5-6, and 7-8 on the PCB.)
>
> I've also see many rigs with Q2 reversed which will
> definitely cause self oscillation of the
> transmitter. Its wider side should align with the
> flat on the PCB.
>
> Either of the caps across the secondary of T1 or T2
> will cause oscillation if they are damaged,
> incorrect values, or missing.RFC6 is critical for
> stability too, and must not be open nor missing the
> correct parts at C120 or R48.
>
> All caps around Q5, Q6 are critical as to value,
> esp. C115, C119. Be sure you did not use a .001 for
> a .01 or 0.1 for example.
>
> Also check the DC bias on Q6 as I mentioned, and if
> it is more than 1.0 to 1.1VDC, replace R46 with a
> 390 ohm resistor. The 2SC5739 we now use for Q6
> often needs a lower bias.
>
> Again, look very very closely at the PCB, parts, and
> soldering and you might find the problem just with
> your eyes.
>
> --
> 73, Gary AB7MY
> =========
> [hidden email]
> Elecraft Technical Support
>
>
> C. J. Hawley wrote:
>
> Thanks again for the help. I checked all the 4007's with a Simpson 360 just to make sure the cathodes were where they belonged. I can still see the outline on the board as well. I will check them visually again.
> Not discouraged...as an EE I designed and debugged electronics for chemistry research for 35 years at the U of IL. So I have had my share of late Friday nights trying to get something running before the chemist's sample died over the weekend.
> Thanks again again. I'll follow these ideas and I have been avoiding disassembling anything to diagnose (lazy). But that will just have to be part of the fun.
> I'll let you know what I find...embarassed or not...heh.
>
> Chuck, KE9UW
>
> ---- Original message ----
>
>
> Date: Wed, 21 Oct 2009 08:50:07 -0700
> From: Gary Surrency <[hidden email]>
> Subject: Re: KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...
> To: [hidden email]
>
> Are you sure there are no reversed 1N4007 diodes in
> the T-R switch?
>
> Try clipping jumper wire W1 behind T4. If there is
> any feedback path from the output of the PA state
> back through the T-R switch that is causing self
> oscillation, this will stop it. Note this also
> disables the receiver input. Removing the 160m
> adapter does the same thing, which I think you have
> tried. The 160m option should not be installed until
> the basic rig is working OK. (reinstall jumper W1).
>
> Look at each and every part in the Q5-Q8 area
> because any mistake in even a cap value, can cause
> problems with the transmitter.
>
> Reheat every connection too.
>
> Also, if the cap across the secondary of T2 is
> damaged, open, or missing - the Driver will self
> oscillate. This is C122, the 56pF cap.
>
> If the transmitter starts self oscillating
> immediately as soon as it is placed in Tune or the
> Power knob is advanced, there is a strong feedback
> path.
>
> MCU version 2.04R allows only U8-4, since we had way
> too many people setting it wrong to U6-25 and then
> losing their sidetone. We had to do this change even
> though it meant some older rigs prior to sn. 3000
> would have to have the sidetone mods done even if no
> KIO2 or KPA100 option was going to be used. (loss of
> sidetone was an everyday event!).
>
> The minimum we charge for any repair is $99 + return
> shipping. It always takes at least an hour to find
> and fix what is wrong, align and test the kit, and
> then write up the repair report and package it for
> shipping. This also helps encourage the builder to
> spend some time looking for the problem without
> immediately giving up and sending in a lot of kits
> for us to repair. In almost every case, there are no
> bad parts - just an assembly or soldering error. In
> order to send in the kit, you need to email
> [hidden email] or call 831-662-8345 to get
> authorization and the needed RSA# and form.
>
> Keep a positive attitude and look over ALL of your
> work, and you will likely find what is wrong.
> Remember to not transmit when the bottom PA heat
> sink panel is removed, or the PA transistors will
> burn up in a few seconds - even if there is no RF
> output since there is always DC bias current when in
> transmit. Check there is 0VDC base bias on the PA
> transistors when in RX, and not more than 0.62 to
> 0.65 VDC when in TX. Try each band too in transmit.
>
> --
> 73, Gary AB7MY
> =========
> [hidden email]
> Elecraft Technical Support
>
>
> C. J. Hawley wrote:
>
> I went back and re-read the toroid guy's note and he did mention K2-T2 as well as the T1-T2 ssb toroids. Then I went to the newest manual and K2-T1 and K2-T2 are now shown wound the way he did them for me. All reverse from the original manual. So that's not an issue I see.
>
> I have 1089, rev A board, ssb, nb, and 160m installed.
>
> I still don't have a solution though. I checked 8T (0 vdc to 8 + vdc), and 8R (8+ vdc to .267 vdc). I even loaded 8R to around .225 vdc, but no help. I measured all the D1 thru D4 diodes, took out the 160M board and shorted J14 to restore W1, resistance checked to see that all the chokes, etc. are installed in the T-R switch area.
>
> I know I am missing something...somewhere...
>
> I think I have an oscillator at Q5-Q6. I am checking all the feedback chokes and capacitors. I may need to unsolder C118 and see if it is infact a capacitor inside the shell and maybe also C120. RFC6 checks ok, R49, R470, etc.
>
> After more careful checking with the power knob all the way down, In xmit, I get about 3 vpp at W6 riding on 8 vdc. I get very small voltage at BPF on transmit and as well on Xmixer and buffer. Q5 base, about 6 vpp, Q5 collector about 10 vpp with about 13 vdc, Q6 collector, 30 vpp with about 13 vdc, 40 vpp with 8 vdc on D3-D4 cathodes, 60 vpp at 0 vdc on W1 (with 160 removed), and the same 60 vpp at 0 vdc on the output ant jack. Fundamental freq is about 450KHz.
>
> As to the sidetone, I read the instructions for rev 2.04 firmware which said to revise the A board according to KIO2 mod details for sidetone, but I kept going back to rev B mod page where it said I didn't have to if I didn't have KIO2. The issue is that the new rev 2.04 firmware does not have the option to use U6-25. It only allows U8-4. Once I cut the trace, and installed the wire(s), all works well for the sidetone.
>
> Switch on the control board was on battery. Thanks for that.
>
> I'm kind of exhausted from hours of checking. If you have any further ideas...
>
> I noticed there is no R4 on the RF board even though it's on the schematic and board. Correct?
>
> Not giving up yet, but if I sent this K2 in, roughly what kind of issue is this? $? That's probably a dumb question. You might see the glaring problem right off. I guess I am looking at all the obvious things...maybe I should return it to stock without the 160, NB, and SSB so I can check easier. But I keep thinking the problem is in the area of Q5, Q6, and the finals. Receive works perfectly and I can hear the carrier when I transmit on another receiver in the shack which makes me think the xmit VFO is working ok...just swamped by the 450KHz.
> Thanks for all your time and help,
>
> Chuck, KE9UW
>
> ---- Original message ----
>
>
> Date: Tue, 20 Oct 2009 11:24:19 -0700
> From: Gary Surrency <[hidden email]>
> Subject: KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...
> To: [hidden email]
>
> In MCU firmware version 2.01 and above, there is an
> option in the St L menu for selecting
> either of two ICs for the sidetone source. Edit St
> L, and then press the DISPLAY
> button until you see U8-4 as the sidetone source.
> Only older K2's before sn. 3000 use the U6-25 entry,
> and then only if they do not have a KIO2 or KPA100
> option installed. We left this selection in place
> for backwards compatibility.
>
> If this doesn't fix it, then Q5 (2N7000) may have
> failed. It is a MOSFET, and is very easy to damage
> by ESD, or static electricity. A BS170 may be used
> in place of a 2N7000, if you turn its flat side
> around 180 degrees since its Drain and Source leads
> are reversed from that of the 2N7000.
>
> NOTE: It is sometimes necessary to cycle the power
> off and on after making the sidetone source change,
> while you are still in the "St L" menu and editing
> the entry. You should try this first, as it is often
> all that is wrong. Several attempts may be needed.
>
> The power supply needs to be good for at least 4
> amps too.
>
> Keep the transmit testing time to not more tha 2-5
> seconds until you nail down what is wrong.
>
> Lo Bat can be caused by the slide switch on the
> control board not being set to the correct position
> (12V). Later boards have a jumper block here.
>
> --
> 73, Gary AB7MY
> =========
> [hidden email]
> Elecraft Technical Support
>
>
> C. J. Hawley wrote:
>
> Thanks, I'll check all. Gives me some place to start. The finals never got warm, I restricted the xmit time to less than 10 seconds each time.
> One other thing that I haven't dealt with yet is a Lo Battery display on occasion. I measured the supply and have a solid 13.8 at the rf board...about 13.4 when it oscillates in tune.
> The third thing is the lack of a sidetone. I measure 2.5 vac at pin 4 of U8, and 2.04 is calling for U8-4, but no sidetone. I have an early (ser #1089) rev A board...I finally got back into this project. Nine years goes by fast. Lots of fun though and thinking of a K3 next.
> Thanks again, Chuck Hawley, KE9UW
>
> ---- Original message ----
>
>
> Date: Tue, 20 Oct 2009 10:10:07 -0700
> From: Gary Surrency <[hidden email]>
> Subject: KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...
> To: [hidden email]
>
> Hi Chuck,
>
> NEVER transmit with the heat sink removed, or the PA
> transistors will be damaged. If there are any signs
> of heat on the tabs or the PA transistors, or if the
> nylon shoulder washers are melted, the PAs are
> probably damaged and will need to be replaced. If
> one of the PA transistors is bad, the transmitter
> will still have near normal RF output on the lower
> bands, but it will drop off rapidly on the upper
> bands.
>
> Check to see if the 8R and 8T lines are working
> properly.
>
> In RX, 8T is near zero and 8R is close to 8.0-8.3VDC
>
> In TX, 8T is near 8.0-8.3VDC and 8R MUST go below
> 0.3VDC or the T-R switch isolation is not enough to
> prevent PA feedback.
>
> The 8R and 8T points are easiest to measure, at J13
> which is the Xverter header near the back of the RF
> PCB. Pin 1 is 8R, and next to pin 6 is a pair of
> pads labled "X" and "8T" on K2s after sn. 3000. 8T
> is the empty hole to the right of J13 pin 6.
>
> Problems with 8R and 8T not switching properly are
> usually related to a problems with Q1-Q4 on the
> control board, or something is wrong or parts are
> missing around Q23, R113, C111 at the right front of
> the RF PCB, near the power switch and underneath the
> control board.
>
> Also look to see if any of the 1N4007 diodes in the
> T-R switch near the rear of the RF board are
> reversed or if Q2 is are reversed. The pictorial
> near the back of the manual shows how these parts
> must be oriented.
>
> An open or missing RFC6 under driver Q6 will also
> cause this.
>
> See if the DC base bias on Q6 is more than 1.0 to
> 1.1VDC. If so, change R46 near the U1 IOC from 270
> to 390 ohms.
>
> --
> 73, Gary AB7MY
> =========
> [hidden email]
> Elecraft Technical Support
>
>
> C. J. Hawley wrote:
>
> I just finished this K2 rev A with most all mods incl B and cannot do the transmitter alignment.
> The finals seem to be oscillating at about 450 KHz on all bands.
> The power goes to max (17 watts), power control all the way down, the current goes to 3 amps, on the Bird meter (50 watt slug) I get about 13 watts showing. The frequency on the scope (and aux counter) appears to be about 450 KHz. I get this frequency on W6 (about 5 vpp and as well larger at the collector of Q6 (about 25vpp) and of course at the collectors of the finals but with a lot of ringing at a higher frequency and at the input to the low pass filters, about 40 vpp...same on all bands.
> I've checked the transformers, etc for wiring and they appear to be ok.
> No shorts on the final collectors, etc. Kind of looking for some previous experience with this or some idea of where to go.
>
> I also have the latest firmware, rev 2.04 and have no side tone. With the firmware from March 2000, rev 1.04 I have sidetone. The instructions (various years) say the side tone comes from U8 pin 4, I get ac voltage there, the menu says U8-4, but no sound.
>
> Thanks,
> Chuck
> KE9UW

Chuck, KE9UW

Don Wilhelm-4

Re: KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...

Chuck,

Spectrogram version 5.17 is freeware and matches the screenshots for setup.
See the information (and download) at Tom Hammond's website www.n0ss.net.
If you want extended information about K2 dial calibration and filter
setup, take a look at my website article on K2 Dial Calibration -
www.w3fpr.com

73,
Don W3FPR

C. J. Hawley wrote:
> Thanks so much for the help. The problem was C120...the one in the middle between two close in caps. Hard to see the value. Had to get serious and bend one over. Figures it would be that one. I had the value .001uF instead of .01uF.
> You were so correct. Made me look closer.
> Thanks for your patience, ability, and experience.
> The alignment seems to be going well so far. Perfect tuning wand for those inductors. All done on that and buttoned up. All works and works well. I need to do the filters now...maybe Spectrogram. I'm a little confused if it is free or what, but I'll figure it out.
> I have made use of the latest manual on line for some of the later clarifications and info. Thanks for having these on line.
> And thanks Don and Michael for your suggestions along these same lines.
> Chuck, KE9UW
>
>
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