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Radiosonde data
An important item to understand in all of this is the conditions in the atmosphere at the time of the event. We don’t have actual data from the exact time the plane was transiting the area but we have a fair approximation. I was able to obtain radiosonde data from NCDC for Fort Worth, Shreveport, OK City and Jackson at 1200 Zulu time, which was shortly after the plane passed through the area (1000-1100Z). I have the original readouts and there may be some transcription errors. If anyone desires the data, I can send it to them in the form I acquired it. I only included up to the data point above 34,500 feet/10,515 meters:
Fort Worth (X indicates no data)
So what do these readings mean? I am not an expert on analyzing these values but I did do some reading on the subject of how they can affect radio waves and how one can calculate the atmosphere’s ability to refract those waves.
The atmosphere normally does refract radio waves allowing their direct wave components to be received at locations farther than the optical horizon. The measure of this refraction is called the “lapse rate” and is measured in “N-units/km”. The normal lapse rate is -40 units/km. I made an attempt to calculate those values based on the radiosonde data using the formulas provided by Dr. Willis’ web site. On page 12, there are graphs showing Temperature and Dew Point vs. Altitude as well as N-Units vs Altitude for two of these sites. There are two points of interest in these computations:
The Fort Worth data shows a significant decrease in the dew point around the 7000 foot level. The lapse rate in this region I computed was about -75 units/km, which is higher than the normal lapse rate for the index of refraction.
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The OK city data had a temperature • inversion of significance up to the 2000 foot (610 meters) level, which had a lapse rate of about -242 units/km. This is also significantly higher than normal but this value is for a narrow band of the atmosphere. The Tinker AFB data for 0600Z (0000 CST) indicated a lapse rate of -53.2 to -58.8 at these levels. It appears that these condition was forming around midnight local time. Is it possible that a condition called a tropospheric duct had formed?
Now these values may mean nothing (I may have calculated incorrectly) but the fact there were some suspect atmospheric conditions in the OK city and Fort Worth area is something that should not be ignored. They could have played a role in the events that transpired.
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RB47 Phase I: The Up-scope incident
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The RB-47 flew from Forbes Air Force Base in Kansas to the south over the Gulf of Mexico. There they conducted gunnery exercises and navigation training.
The next phase of their flight involved flying north towards the gulf coast at Mississippi. As the plane neared the coast, ECM#2 Frank McClure noted a radar signal that confused him.
According to McClure, the radar signal started out from the rear starboard quarter of his scope and moved up to the forward quarter. Thus, the radar signal moved “up-scope”. In some interviews, he also stated that the signal then moved down the port side in a “down-scope” maneuver. This implied the signal was airborne and passed the aircraft on the starboard side or moved around the aircraft in a complete circle.
This part of the case was considered highly unusual and unexplainable. However, Phil Klass thought he explained it by stating that what they detected was the Keesler AFB CPS-6B radar and a faulty relay caused the signal to be reversed. Instead of going down-scope on the port side as it should have appeared, it went up-scope on the starboard side.
Rebuttal
In his lengthy analysis of the case, Brad Sparks makes three significant arguments against the Klass theory that what was detected was the Keesler AFB CPS-6B the statements that they crossed the coast NEAR Gulfport, Mississippi. However, Lewis Chase, the pilot, had told Dr. Roy Craig they crossed the coast NEAR Biloxi. Considering they were recalling details from an event that had occurred a decade earlier, it seems likely there were going to be errors.
Brad Sparks has interpreted this to mean that the plane was flying due north at 89 degree west longitude (Gulfport is at approximately 89.08 deg longitude and Biloxi is at 88.9 deg). This argument appears to be based on the assumption that the Navigator was to navigate by the stars along a specific line of longitude. While this is an interesting theory, why use the 89th meridian? Why not 89.5 or 88.5? What is so magical about 89 degrees?
In fact, how would they know the Navigator was right if he states he was on 89 degrees unless they had a landmark to reach? It seems like the nice round number is the only reason that Sparks chose this path.
Unfortunately, the 89 degree longitude path does not agree with what Lewis Chase put in his UFO report in 1957. He does not describe where they met the coast but he did draw the flight path. It appears to go due north and end at Meridian, Mississippi. The intelligence report appears to confirm this by stating that the plane flew towards Meridian. They were probably trying to navigate towards Key Field on the west side of Meridian as a way point. This would be a recognizable landmark to verify that the Navigator had done his job correctly. Its longitude was 88°45’ 7”W. Had they crossed the coast at 89 degrees west longitude, the due north course would have put them about 14 miles west of Key Field, where there are no known landmarks to verify the navigator’s work (unless you can consider the small crossroads of Hickory at 89.02 an easily recognizable landmark from 34,500 feet).
It will never be possible to determine where exactly they crossed the coast without the navigator’s log but to state they positively crossed at Gulfport and could not have crossed anyplace else, is just wishful speculation. The possibility the plane crossed east of Biloxi on a course due north to Meridian is not an unreasonable to consider and remains a radar and there was a malfunction of the ALA-6 relay causing an error in the signal display:
The aircraft crossed the coast west 1. of Keesler at Gulfport. Therefore, it would have been impossible for there to be an upscope event even with a faulty relay.
In addition to going “up scope”, Mc2. Clure also stated it then went in front of the aircraft and then “down scope” on the port side indicating the object was circling the aircraft.
The Keesler radar was not in operation at the time because it was closed down for the summer break. This seemed to make Klass’ explanation invalid but how good are these arguments and do they positively prove that it could not be a faulty relay and the Keeseler AFB CPS-6B?
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Biloxi or Gulfport? That is the question
The first argument put forth against the Klass theory of the upscope incident has to do where the RB-47 crossed the coast. Early on, Dr. McDonald had interviewed the witnesses and received the statements that they crossed the coast NEAR Gulfport, Mississippi. However, Lewis Chase, the pilot, had told Dr. Roy Craig they crossed the coast NEAR Biloxi. Considering they were recalling details from an event that had occurred a decade earlier, it seems likely there were going to be errors.
Brad Sparks has interpreted this to mean that the plane was flying due north at 89 degree west longitude (Gulfport is at approximately 89.08 deg longitude and Biloxi is at 88.9 deg). This argument appears to be based on the assumption that the Navigator was to navigate by the stars along a specific line of longitude. While this is an interesting theory, why use the 89th meridian? Why not 89.5 or 88.5? What is so magical about 89 degrees?
In fact, how would they know the Navigator was right if he states he was on 89 degrees unless they had a landmark to reach? It seems like the nice round number is the only reason that Sparks chose this path.
Unfortunately, the 89 degree longitude path does not agree with what Lewis Chase put in his UFO report in 1957. He does not describe where they met the coast but he did draw the flight path. It appears to go due north and end at Meridian, Mississippi. The intelligence report appears to confirm this by stating that the plane flew towards Meridian. They were probably trying to navigate towards Key Field on the west side of Meridian as a way point. This would be a recognizable landmark to verify that the Navigator had done his job correctly. Its longitude was 88°45’ 7”W. Had they crossed the coast at 89 degrees west longitude, the due north course would have put them about 14 miles west of Key Field, where there are no known landmarks to verify the navigator’s work (unless you can consider the small crossroads of Hickory at 89.02 an easily recognizable landmark from 34,500 feet).
It will never be possible to determine where exactly they crossed the coast without the navigator’s log but to state they positively crossed at Gulfport and could not have crossed anyplace else, is just wishful speculation. The possibility the plane crossed east of Biloxi on a course due north to Meridian is not an unreasonable to consider and remains a distinct possibility.
Up-scope/down-scope: Two versionsof the same story
Shortly after the crew returned to Kansas, they were debriefed by the wing intelligence officer, Piwetz. He wrote a four page report on what transpired. He described this part of the incident in a single paragraph:
At approximately Meridian, Mississippi, a signal with the following characteristics: Frequency 2995 to 3000 MC; Pulse-width of 2.0 microseconds; Pulse repetition frequency
of 600 cps; sweep rate of 4RPM; Vertical polarity. Signal moved rapidly up the D/F scope indicating a rapidly moving signal source; I.E. An airborne source. Signal was abandoned after observation.1
At this point, there was no mention of a “down-scope” component to the signal. One would think that such a detail would be mentioned.
During the Condon Study, Dr. Roy Craig interviewed several of the crew members.
Frank McClure described this part of the incident as nothing more than an “up-scope” event:
I originally picked the signal up behind me. It went up the right side of the aircraft and then it just hovered out there, out in front of us. The we lost it, and then it turned up on the other side of the aircraft and moved clear around us, as I remember. But we would lose it from time to time.2
McClure, at this point, appears to be describing the behavior of the radar signal over the entire flight. After the upscope incident, according to the intelligence report, the signal did appear on the starboard side of the airplane and, after flying between Fort Worth and Dallas, it moved around to the port side of the aircraft. So, McClure’s description at this point can be interpreted as a recap of the entire incident.
Dr. James McDonald interviewed McClure in February 1969 over the phone. McDonald was the first to get McClure to state the signal also had a “down-scope” component:
…I learned, to my surprise, that McClure first picked up the signal when it was BEHIND HIM going forward! This was when he was northbound near the coast at Gulfport. He stated to me that he called forward to see if anything was seen up there, but they saw nothing, and he forgot it at the time.
Equally surprising was his description that the XXXX( lined out with something inked above – “blip”?) on his scope indicated that the source orbited the B-47 in a counter-clockwise manner. When he first picked it up in the Gulfport area, it was a little bit to their right and it moved UPSCOPE on the right side, went around the front, and then came down on the left side. In reply to my query, he indicated it slipped around at about a constant angular velocity... 3
In his communications with Klass, this description is not as clear as Dr. McDonald described, Klass had him describe the signal’s behavior several times and what he received from McClure was a mix of answers. For instance, in his initial letter to Klass he stated:
I knew that it was not a signal operating from the ground sight (sic), because it moved from 180 degrees to approximately 60 degrees. I asked the pilot if he were in a turn and he replied negative. I made other checks on related signals - looking for other beams etc.....So I considered it as a fluke signal and dropped it.4
At this point, there is no mention of a “down-scope” incident. Because of the letter, Klass was able to conduct a long phone interview with McClure. The descriptions in Klass’ notes are contradictory.
Initially, McClure stated:
This was what we were doing was checking every piece of operating equipment on there. And that’s why I wasn’t particularly alarmed when I saw the signal go up-scope. I just made a mental note of it that something’s wrong with the ALA-6.5
This is consistent with a simple up-scope description. However, McClure then stated:
I noticed that, I can recall that it wasn’t abeam of us exactly, but it was around 30 deg, just ahead of us, and it stayed at the same relative bearing for a long time, and
I know we were flying straight and level. And it did come in front of the aircraft and down the other side. At this time I don’t think we were all mixed up with Utah, Shorthorn, and all those other radars.6
This is the first moment he mentions to Klass a signal went down the other side of the aircraft.
Klass kept pushing McClure to describe the “up scope” signal in more detail and McClure obliged him:
I only worked it 2, 3, 4 minutes, we’d moved quite a way in that time, but it was not too long after that we turned, but that’s just my recollection....It overtook,
well I’d say it went from 180 deg to abeam of us in 50 seconds, you could see it move, I couldn’t___it, becuz it was coming up so fast just like we were standing still, and that’s why I asked the pilot, becuz if he had been in a turn to the left or to the right, I mean that would make it look just like that....7
This continued to be a description of just an up-scope signal. Late in the interview, McClure gave a time line of events that disagreed with the earlier part of the interview:
I first picked it up behind me, and it came up by me, and it came up fast, then it got out to around 30 deg. And just hung there, and then it came around the front of the airplane….So I played around with it for 4 or 5 minutes from the time I first intercepted,
until I left it until about 20 minutes or so later and we were heading west.8
Like, the interview with Dr. Craig, the length of time he described seems to be a combination of the initial incident and the subsequent Duncanville signal. He had stated that he worked the initial signal for just a few minutes but he now describes something that is about 20 minutes in duration.
In a later letter to Klass, McClure continued to describe this incident just as an “up-scope” signal with no “down-scope” component:
I was working the S band when we left the gunnery range and was confronted with a signal moving up scope. I checked it out as to being a spurious response or image and looked for other beams without success.
I called the pilots and asked if it was possible we were turning. The front end said negative so I dropped the signal and leisurely changed to L band to work then when I was alerted, I returned in haste to my original freq-whatever it was-......9
This description is similar to the one he gave in an even later letter to Klass I doubt that it was any thing but a happenstance that the signal went up scope at the onset. I know that no other signal acted that way and when I first came back to the signal it was still moving strangely as it hung about 70 degrees for a while. After that I am sure we were turning so much that it would have made it move funny.10
Once again, McClure seems to be convinced that it was only an “up-scope” signal near the Gulf coast.
What this indicates to me is that we have some memory issues here. He is confusing all the events as one, which is where we probably get this “down scope” business
after the up-scope readings. It seems possible his description of the “down scope” relates to the Duncanville event, when the signal did move to the port side of the craft (around the turn northwest of Fort Worth). The 30 degree bearing he keeps describing is pretty consistent with the signal described in the Piwetz report, which was described as being at 40 degrees.
When asked by Klass, Chase stated they saw no UFO at anytime in this part of the flight. It seems the only source that describes the “down scope” portion of the incident is not very consistent and may be mistaken. As a result, one can not “cherry pick” certain comments to falsify what Klass proposed as the explanation for this part of the case.
Summer vacation and burning the midnight oil
The Keesler radar not in operation is the main argument by Sparks. In his rebuttal he makes the following comment:
The most serious problem with Klass’s explanation is that the Biloxi radar was used only for training purposes and evidently was not operating in the middle of the night in the middle of the summer of 1957….According to ATC, in 1957 only one course operated the CPS-6B – the training course AB300332D, AC&W (Aircraft control and warning) Radar repairman, consisting of 18 weeks of classroom teaching and 18 weeks of training on the various types of equipment (not just the CPS-6B but also the FPS-6 radar and two GPX-6 IFF radar sets so the CPS-6B portion of the equipment training covered less than 9 of the 18 weeks; letter of ATC to Sparks, June 6, 1977.) Since it was a nine-month course it was apparently run during the normal academic term from September to June approximately. In other words, there would not have been a class in session to operate the CPS-6B even in the daytime, let alone nighttime, in the midst of summer vacation, on July 17, when the RB-47 incident took place. 11
Sparks’ argument is stated as if it were factual and accepted by all as being correct.
However, he makes a lot of assumptions that are just plain incorrect. First of all there is no such thing as an “academic term from September to June” or “summer vacation” when it comes to military training. It is year-round (with the exception of breaks occurring around the Christmas holidays). Military courses in enlisted training are done in assembly line fashion such that when one class completes a phase of instruction, another takes its place. There could be as many as 12 or more classes graduating each year in order to keep up with the AF demand for radar technicians because every month, techs are promoted to supervisor positions, exit the service, or are assigned elsewhere for other reasons.
Going through the graduating class photographs available at the Keesler AF graduates forum and communicating directly to two of its members, I was able to find several graduation dates for the training course 300332 in 1957.
Class 31056 graduated January 8, • 1957
Class 05076 graduated February 12, • 1957
Class 19126 graduated July 30, 1957
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Class 30017 graduated September • 10, 1957
Class 27027 graduated October 8, • 1957
(The class numbers appear to be the date the class started. EX: Class 05076 started on 5 July 1956)
The two individuals I directly talked to, who were present at Keesler in 1957, told me that they graduated on March 14, 1957 and June 25, 1957. While this sample is not complete, it appears that there was at least one (possibly two) graduating class every month of the year. There seems to be plenty of evidence that classes involving the CPS-6B were in session in July of 1957.
Additionally, the school had to operate in shifts. Their basic electronics course had at least three shifts of training (06-12,12-18,18-24), so they could cover the course of instruction for all the students there. Communication with various alumni of the Keesler radar training indicated that there were three 6-hour shifts at the annex,
where the CPS-6B was operating, as well. As one alum pointed out, they were long on students and short on equipment at the annex. Maximizing the use of the equipment was a priority.
Klass only became aware of the CPS-6B at Keesler because Frank McClure told him about it in his initial letter to Klass and that he expected the radar to be operating that morning. When Klass asked him about the school in a phone call and if the CPS-6B operated at night, McClure stated:
Yes sir, up to midnight when I was there, I was an instructor there for two years…I was a supervisor instructor there for three years…and they worked from early in the morning until after midnight.13
This brings us to the CPS-6B operating between 0000-0600. I posed the question about it to several individuals and this eventually was forwarded to two Yahoo discussion groups (AF Radar veterans and AF Keesler graduates). Concerned that I would be ignored by bringing up the subject of UFOs, I did not describe this as a UFO event. My request stated:
I am researching an incident where an RB-47 aircraft flew near Keesler and reported a radar signature that was very similar to the AN/CPS-6. However, this was at 4AM on July 17th of 1957. Since the AN/CPS-6 was used only for training, I was wondering if it could have been in operation early in the morning. I also would like to know what groups were using the radar besides the radar maintenance techs.14
The basic consensus was that there were three 6-hour shifts of training (one of which may have involved officers) and that the mid-shift was used for maintenance
on the radar system and getting it ready for the morning shift at 0600. The existence of a 51-week officer course is described (although it is seven years after this event changing the radars being trained upon) by a commentary at radomes.
org. One former student thought it was possible that there may even have been some live student operator training (the radar operator students were referred to as “scope dopes”) after hours. Since the 17th of July was a Wednesday, there would have been classes that morning and it COULD have been operating between 3 and 4AM (CST) so it was ready for the beginning of the 0600 class, as a retest for maintenance performed on the unit, or for training purposes.
We will never know if the CPS-6B was actually operating that morning without the operating logs for the annex on the date in question. However, the argument that it could not be operating because it was summer time or in the middle of the night is not accurate based on what is known about how the annex operated.
What was detected where
A more compelling argument against the Keesler radar was Martin Shough’s argument that the CPS-6 could not be detected as the aircraft passed over Biloxi. This was based on the aircraft not spending enough time in the radiation pattern to determine the revolution rate of 4 RPM described in the intelligence report.
In Klass interpretation of the ALA-6’s sensitivity to the CPS-6B, he states that the upper side lobe of the vertical center beam would only be detected in a narrow 2-mile stretch about 28-30 miles from the radar. Inside that radius, the ALA-6 would not detect the beam. However, these values for the signal actually come from the notes made by McClure the second time he saw the signal near Duncanville and not from any notes he made near the coast:
I did not write anything down until the #3 Raven said the remark about the front end “chasing flying saucers.15
This reference to writing the information down means the signal described in the intelligence report reflects the signal characteristics they saw in Texas. The signal seen during the up-scope incident could have been any of the beam frequencies. In fact, Dr. McDonald stated McClure told him that this frequency was 2800 mhz:
In discussing it with me, his recollection was that the frequency was near 2800 mcs....16 McClure clarified this in a letter to Klass, where he stated: I do recall the signal was in the neighborhood of GCA and the lower end of the CPS-6B, which runs from 2770 to 3200 MC if I remember right. So if McDonald quoted a specific freq of 2800 MC it was a ballpark figure.17
This value of 2800 MHZ was repeated in many interviews with the crew. One wonders why the number was remembered so vividly (while 3000 MHZ was a nice round value). If the signal was near 2800 MHZ, then it would have been near the vertical upper beam’s frequency range of 2740-2780 mhz (or the slant upper beams frequency range of 2820-2860 mhz), which means the plane could detect the signal when it was as close as 11-12 nautical miles or less from 34,500 feet.
According to McClure’s discussion with Klass, the signal moved very fast and he had just enough time to determine the pattern was very much like a CPS-6B. There is no indication that he determined the revolution rate for the antenna at this point. He just noted the frequency was an S-band radar like a CPS-6B and that it moved fast. This kind of angular speed could have been the result of the RB-47 flying very close to the ground radar.
Klass discussed the issue of close proximity detection with Rod Simons, an expert on the APR-9 used to receive the signals that were displayed on the ALA-6. In an October 8, 1971 phone call, Simons stated the RB-47 could detect the side lobes from the vertical center beam at a distance of 20 miles (this distance was suggested by Phil Klass).
...that thing is packing a fair amount of power, so at those distances I think there would be no question about detecting it. That was an APR-9 on the front end and so I’d say there’s no question that you would get a good strong signal.
Even if you had a crystal video receiver when you are in that close you would pick it up…you might even get a signal all the way into the radar. 18
Assuming the aircraft flew directly towards Meridian’s Key field, it would have crossed the coast at about longitude 88°45’ 7”W. At its closest point, the RB-47 would fly by the CPS-6 (located at 88°57’36.00”W, 30°24’26.00”N - see 1992 Google Earth image above) at a minimum distance of about 11 nautical miles (12.65 statute miles). Considering all of this information, it seems possible that the equipment could detect one of the CPS-6 radar beams at that distance.
As stated previously, no visual sighting was ever reported even though, the UFO passed in front of or to the front right of the aircraft. The pilot/copilot/navigator saw nothing. It is really hard to suggest this as a “good unknown” when we don’t even have a visual verification that something was there. Instead, all we have is an anomalous radar signal, which Frank McClure described as an, “...almost a picture-book display of a CPS-6B type signal.”19
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The stuck solenoid theory
Phil Klass proposed an explanation to this “up-scope” signal. After examining the manual for the ALA-6 he identified a faulty solenoid/relay that could have caused a 180-degree error in the signal as the plane flew east of Keesler’s radar. See the table above that comes from the troubleshooting section of the technical manual. Trouble item number 3 appears to describe the symptoms of the 180 degree error.20
In order to explain why the rest of the signals later did not do this, he suggested the fault was an intermittent one (such as a loose lead or relay that was initially stuck/frozen in position) that disappeared.
This seemed to be a reasonable theory.
When McClure read this explanation, he disagreed:
I don’t agree with the malfunction though, because I flew that equipment for 1000 hours in a period of four years and I never saw any sign of a malfunction of this nature, and I never heard any of the hundreds of experienced ravens we had voice any thing which would lead to this conclusion. I do feel strongly that something malfunctioned, but I have no notion of what it could be.21
He repeated this objection, in another letter (apparently after receiving a copy of UFOs: Explained):
I certainly agree the equipment malfunctioned some how, but I can’t quite buy the relay you stated was the cause. It seems to me if it malfunctioned that all the signals would be moving wrong, and that since the tail of the aircraft would have reflected the true heading of the aircraft, the ninety degree and 360 degree points would have been changed.22
McClure’s concern about the equipment failure seems to ignore the possibility that the relay failure was intermittent. In fact, this type of fault was mentioned by a technician the next day according to McClure:
The day after the incident, when several of them were talking to a technician at Forbes AFB and the technician suggested that a loose lead on the ALA-6 might have caused the sweep around signal in Mississippi, Provenzano asserted that he had seen the same phenomenon on his APD-4 monitor.23
It is not clear if the technician found a loose wire and fixed it or suggested a loose wire might be the cause. If he had found the connection loose, he would have simply reattached it correctly and nobody would have ever seen the problem again.
When Klass forwarded his paper on the incident to D.G. Erskine of Bendix, he received the following reply: One of our engineers here, Jim Watson, read the RB-47 case write up and asked that I convey to you his comments. He was an instructor for the Air Force teaching maintenance on the AN/ALA-6 unit and he said, “Had I been asked what could have caused the 180 degree ambiguity, I would have immediately responded that the most probable cause would have been failure of the K-301 relay.24
While the failure of a relay in such a manner seems unlikely, it is not impossible for such a failure to occur and go undetected again for a long time period (see inset box for one of my experiences with troubleshooting such a fault). It is plausible that this could have caused a signal from the Keesler Annex CPS-6B to appear the way McClure described in many of his interviews.
Summary
While Sparks appears to present a good argument, he did not falsify Klass’ explanation and some of his reasons for dismissing it are incorrect. As a result, we have to consider Klass’ explanation for this part of the flight as plausible and more likely than some “unknown intelligence” that was emitting a CPS-6B-like radar beam towards the RB-47.
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Can a bad connection go undetected?
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During my naval career, I was an electronicstechnician. For the nuclear power plant, my division was responsible for the electronic equipment monitoring and controlling various reactor parameters.One of the units was to monitor the reactor power and sending that signal to the protection system as well as to variousindicators throughout the plant. On my first submarine, we had discovered an anomalous trip signal had mysteriously appeared when the power monitoring equipment was powered up. This did not happen every time and was something new. So, as technicians, we were asked to troubleshoot the problem. We found it very difficult to isolate because every time the problem would appear and we would attempt to isolate it to a specific cabinet, it would disappear. Eventually, we did isolate it to a specific unit and removedthat drawer for troubleshooting on the bench. There were three first class petty officers (E-6) involved in the troubleshooting(myself and two others) and one would think it would have been easy. Our effort to isolate the faulty circuit came down to determining which one was responsiblefor limiting positive surges on power up (which is what the signal indicated).However, we discovered that this circuit responsible for this had no faults and we were scratching our heads. One of the other technicians had a wooden stick and he was pointing towards variouscomponents when he touched a diodeand it sprung downward. The diode had been wrapped around its “turret” but had very little solder on it. The electrical solder connection had been essentially broken. Recognizing a potential clue, we looked up what the component did. It limited negative surges and we initially shrugged figuring it did not make sense until we examined subsequent circuitry that would interpret any surge (positiveor negative) as a positive signal and produce the trip signal. Our wise Senior chief asked us to remove the component completely and test it out. This produced the fault signal every time. Apparently, as the cabinet was opened and closed, the component would change its contact and produce the errant signal. This fault (weak/poor solder connection) existed since the installation of the unit over a decade before since there was no mentionof the component being replaced in the material history card. This fault only materialized under the right conditions. Had it not created the spurious signal, it would probably have been ignored for much longer or not even found.
Quelle: SUNlite 1/2012
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