[Amps] Alpha 87A Fault 17

Sun Jan 1 21:23:32 EST 2017

Thanks Larry.

I am familiar with Glenn's stellar reputation, but have been hesitant to bother him with this.  I figure he has a full plate.

Perhaps if we are unsuccessful, we may have to ask Glenn for help.

We are making progress with this. I have received some good input/suggestions  from several  Amps list members.  Bruce W2SE and I have been exchanging troubleshooting ideas.

This is a really nice amplifier. The pin diode switching is not as complex as we expected.  There are only so many places this problem can be, and we are ruling them out one at a time.

I still would like to know what kind of a disparity in the ratio of the wattmeter readings is sufficient to trigger a fault 17.  What is designed into the amp software?   We have concluded this 23% difference is likely not the issue, and now I am about to visit with the input pin diode to make sure it is passing RF to the tube cathode.

The thing kicks offline so fast, there is no Ip led deflection that can be seen.  If this were a conventional amp, I would think it is kicking off before outputting any power.  There is not even a thump like the transformer momentarily loading up.

I am optimistic we will find and fix the problem.  This has surely been educational for me.  Thought when we fixed the fault 1 problem, we were home free.  Wrong!  No frustration so far, I am enjoying this (so far).

73 Charlie N8RR

________________________________
From: Larry Dighera <LDighera at att.net>
Sent: Sunday, January 1, 2017 7:49 PM
To: Charlie Young; amps at contesting.com
Cc: gm5bkc at gmail.com; Alpha87a at yahoogroups.com
Subject: Re: [Amps] Alpha 87A Fault 17

Hello Charlie,

It sounds like your troubleshooting skills are up to the task, but if you need
the input of an engineer very familiar with the Alpha 78A, I wholeheartedly
recommend Glenn Pladsen (AE0Q) gm5bkc at gmail.com.  Glen's patient and
knowledgeable assistance helped me through an issue with my 87A a couple of
yeas ago.  He is often eager to years of 87A experience with other 87A
operators in the Yahoo Alpha 87A group Alpha87a at yahoogroups.com.  Glen's depth
of experience with the 87A is a valuable asset to the Alpha community.

Best of luck with your amp, and throughout the new year.

Larry
WB6BBB

On Sun, 1 Jan 2017 16:39:22 +0000, Charlie Young <weeksmgr at hotmail.com> wrote:

>Bruce, thanks for the thoughtful response.
>
>
>Yes, I was incorrect about the wattmeters being the same.  Last night at dinner I thought about the CT ratios and checked that after coming home, but missed the difference in the voltage divider resistors after the diodes.  Thanks for pointing that out.
>
>
>I have two pairs of tubes, 1990 date code and 2012 date code.   The current condition of these tubes is unknown to me but the 2012 pair was being used by my friend.  He acquired the amp from a SK estate a few years ago.  He has not tried the 1990 pair in the amplifier.
>
>
>The first thing I did after fixing the fault 1 problem that would not let the amp go into operate mode was to run the amp with HV on the tubes and no RF drive.  Yes, I have checked the B+ path from the tube plate back to the HV board.  All 4 tubes were static tested with HV and no problems.  HV was set for the high position and appears normal.
>
>
>Next, I keyed the amp with a footswitch , still with no drive, and tested the various bias voltages to make sure they were proper and that the amp was going from receive mode to transmit mode.  All appeared normal. No faults.
>
>
>Next, I used the computer terminal to monitor the Ip and HV in the transmit and receive state.  0 Ip on receive and 60 ma
>
>Ip idle current in transmit, with no drive.  HV drops a bit in transmit from the standby state due to the load from the tubes pulling idle current.  This all looked normal to me.  Both pairs of tubes were tested in this mode with the same idle current result.
>
>
>At this point I was ready for RF, or so I thought.  Hooked the FT5K to the amp, and the antenna switch matrix to the amp output.
>
>
>First up, with the amp in the operate mode, I confirmed the receive was normal with no attenuation.  The rx pin diodes were working.
>
>
>The amp was on 17M.  I put my very low SWR 20M yagi on it with the RF output on the rig set all the way down, about 10W.  The first dit caused the amp to go to 20M, and both the tune and load capacitors moved to a preset position.
>
>The next dit caused a fault 17 with red plate led indication, and reversion to standby from operate.
>
>
>If the amp is on a different band from the rf drive source, it stays in standby until retuning/band change is done.  It does not go to operate mode until the band and tuning have been reset.
>
>
>After the fault 17 on 20M, I tested the amp on some other bands, including 80/40/30 and 17 meters.  All of these antennas have very low SWR.  With about 10 watts drive, the result was fault 17 on each band on the 2nd dit, after the retuning/band change was complete.
>
>
>Next, I used the computer terminal program to communicate with the CPU and read the input and output wattmeters with the GPIO command, with the amp in standby.  The input wattmeter appeared to be accurate and reads approximately the same power as the exciter.  The output wattmeter reads consistently low, checked at drive levels of minimum to 100W from the FT5K.  For example, with the rig set for 100W, the input wattmeter read 103 and the output wattmeter read 79, a 23.3% disparity.   With reduced drive, the input wattmeter read 19 with output at 13, a 31.5% difference.
>
>
>Last night,  on the microprocessor board, I measured the DC voltage output from both the input and output wattmeter, directly at the plug.  With minimum drive from the transmitter, somewhere in the approximate  10W range, the output wattmeter read  .13V  and the input wattmeter read .49V.  Because of the different CT ratio and, as you pointed out, the different output voltage divider resistance, these readings were expected to be significantly different from each wattmeter.
>
>
>The next test was to disconnect the microprocessor board loads from the wattmeter outputs to see what, if any, loading effects the microprocessor board electronics might be having on the voltage readings from the wattmeters.  With drive level untouched, the output wattmeter voltage remained completely unchanged at  .13V but the  input wattmeter voltage increased  to .55 from .49 volts with the microprocessor board disconnected.
>
>
>We know the input wattmeter is approximately accurate compared to the drive level, so the increased voltage with no load is likely the norm.   Perhaps the fact the output wattmeter was unchanged from load to no load conditions is the sign of an anomaly with the op amp circuit on the microprocessor board.  Not sure.
>
>
>I am going to do some more testing.  The test setup is a 1KW 50 ohm dummy load on the amp output, to verify the wattage levels.  I will test the wattmeter output voltage levels at the microprocessor board for various drive levels, from about 10 to 200 watts and see how the power ratio holds with the internal computer measurement.   I will repeat these tests with the microprocessor board disconnected to see what the internal load does to the wattmeter output voltage.
>
>I will attempt to measure A/D:0 and A/D1 voltage levels and see what that shows.
>
>
>No, I have not verified the input circuit is OK, other than to check and makes sure there is continuity in the RF path through the input band switch.  I would like to get around this wattmeter ratio question first if possible, because we know if the difference between input and output power is too great, it triggers the fault 17.  We just don't know how great this ratio difference must be per the design of the amp.
>
>
>73 Charlie N8RR
>
>
>
>
>
>
>
>
>
>________________________________
>From: bruce at bubble.org <bruce at bubble.org> on behalf of Bruce W2SE <W2SE at QSL.net>
>Sent: Sunday, January 1, 2017 2:24 AM
>To: Charlie Young
>Subject: Re: [Amps] Alpha 87A Fault 17
>
>
>
>On 31-Dec-16 23:25, Charlie Young wrote:
>
>Happy New Year Bruce.
>
>Ditto
>
>
>The 87A has two built in wattmeters, one on the input and one on the output.   Only the output wattmeter reads on the front panel LED display.  The input wattmeter is used for the CPU to monitor the amplifier gain. If the CPU does not see an output level it believes is commensurate with the input level, it immediately puts the amp into a fault condition (17).
>
>
>As soon as the first dit is transmitted, the amp faults giving a low gain fault 17 indication.  So, I have yet to make RF with it that can be measured.
>
>
>The two built in wattmeters can be read with an external computer terminal plugged into the CPU, with the amp in standby.  This monitor says the output wattmeter is reading 23% less than the input wattmeter, with 100 watts applied.
>
>The wattmeter transformer ratios are different as are the voltage dividers after the D1 & D2 1N5711 rectifier diodes for each wattmeter.  A/D is done by the CPU (2 multiplexed analog inputs). Software makes all the decisions.
>
>Try again with 50W and see what the percentage difference is as reported on the external PC interface async serial link.
>
>Can you measure the DCV outputs on the microprocessor Analog I/O board in standby with 100W and 50W drive?   microprocessor schematic sheet 6 right side of page for the output signals:  A/D0 and A/D1 ?
>I think that you may have some of this data already.
>
>I can think of one way to dummy-up the input and/or out-watts voltage to help you figure out the ratios for fault 17 but it will mean a temporary circuit mod with a small pot.
>
>
>
>By design, the amp will kick out on fault 17 if there is too great a disparity in what the CPU thinks the readings should be.  So far, I have been unable to find the factory parameter that is programmed in to trigger a wattmeter related fault 17.
>
>Certainly      OutWatts > InWatts    for normal and correct operation.  It has to be a ratio since input drive can vary.
>I would expect #17 generation is disabled (in software) during tuning.
>I would guess that #17 should expect to see an   A/D0 : A/D1   voltage ratio that equates to at least 6 to 10db amp gain, that's just a guess.  Anything less is either:  soft tubes, bias issue, low HV, input issue (which you have probably ruled out), output tuning/matching issue. and of course wattmeter issue.  I have no idea what this means for the A/D0 and A/D1 voltage ratios and values which would require some testing.
>
>With the amp turned off and unplugged, and the HV bled down and fully discharged, have you tested continuity between the HV supply and the plate caps?  (this tests DC continuity of the chokes feeding HV into the plate circuit, which the amp does not measure).  Be sure to check the  HV R34 10 ohm 25W glitch resistor.
>
>
>
>
>So far, I have run 100W through the amp in standby with a dummy load on the output, and measured the voltage output directly at each of the two wattmeters.  The wattmeters are
>
>NOT
>
>identical but fed with a different ratio current transformer on each input.  I have run the calculations and they confirm the readings on the output wattmeter are consistently low compared to what they should be.  This confirms what the computer monitoring shows.
>
>
>The amp does this on every band.
>
>
>I am about ready to pull the output wattmeter board and check all the components.
>
>
>Fixing the wattmeter may not solve the fault 17 issue, but in order to rule out the wattmeter as a problem, I have to get it reading up to normal level.  So far, no one has been able to tell me how much difference in wattage reading will trigger the CPU fault.
>
>It has to be in an algorithm in the software for the CPU.
>
>If you want to brain-storm via Echolink or telephone let me know.  I like puzzles.
>
>
>73
>Bruce  W2SE
>
>
>
>
>I am optimistic we will find the problem, but the fault 17 may or not be the wattmeter.  It certainly could be.
>
>
>I will post on the Amps Reflector what is found.
>
>
>Thanks for the response.
>
>
>73 Charlie N8RR
>
>
>________________________________
>From: bruce at bubble.org<mailto:bruce at bubble.org> <bruce at bubble.org><mailto:bruce at bubble.org> on behalf of Bruce W2SE <W2SE at QSL.net><mailto:W2SE at QSL.net>
>Sent: Saturday, December 31, 2016 7:40 PM
>To: Charlie Young
>Subject: Re: [Amps] Alpha 87A Fault 17
>
>Hi Charlie,
>
>I haven't worked on an 87a yet but ...
>Just a thought: Did you check/compare the amps' power output to a known good wattmeter connected to the 87A's output?
>Both standby and operate.
>
>Did you get any key-down current and voltage measurements during key-down that confirm that you are getting normal output power?
>
>If you can verify normal power output, the first place that I would look would be the output wattmeter circuit.
>
>Good luck.
>
>73
>Bruce  W2SE
>
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