Re: Need Help Troubleshooting Tektronix PS280
Hello Daven9ooq,
I will chuck in my 2 cents worth to help you.
One of the previous posters suggested that you print out the schematics. I am going to adopt a Judge Judy attitude here.
Have you printed out enlarged copies of the circuit diagrams? That is a YES or a NO
Another poster suggested that you start at the transformer and work your way forward.
Have you tested the transformer? That is a YES or a NO
Have you checked the bridge rectifiers as the other poster suggested? YES or NO
The previous helper asked you to make notes on your printed out circuit diagram and component layout drawings?
Have you done as he suggested?
We know your power supply is slightly different from the diagrams. This is the beginning of the "Fun Part." for us hobbyists.
Find a big piece of paper and start drawing the main parts of the circuit as you find it.
Turn this repair job into a learning excercise. Make it fun.
Start with the transformer.
Load test it with say a 2 amp load.
Note the open circuit volatge and loaded voltage as Dave suggested. Write your results down on your big hand drawn diagram.
Load test the ouput of the rectifier stage. (cut the track or wire to the filter capacitor)
Check for a nice fullwave rectifier display on oscilloscope. No Load and full 2 amp Load. This will show up any cracked tracks or
dodgy wiring connctions.
Reconnect the filter Capacitor to the bridge rectifier. Put your 2 amp load resistor across your filter capacitor.
Check the ripple, No Load and Full Load. Record your results as Dave or the other poster suggested.
I want you to tell me that you have tested the transformer, the rectifiers, the filter capacitors and it is all good because you have
test results to prove it. That to me would be a good concrete start on this fun filled interesting repair job.
Regards,
John Crighton
Sydney
toggle quoted message
Show quoted text
----- Original Message ----- From: "daven9ooq via Groups.Io" <daven9ooq@...> To: < [email protected]> Sent: Saturday, August 17, 2019 9:48 AM Subject: Re: [TekScopes] Need Help Troubleshooting Tektronix PS280 Hi Dave, Many thanks! For your comments, I did make some headway today ,haven't found any bad components yet but did get some smooth voltage adjustment from the Master side, No the metering is not working correctly! Could be my fault got some connectors mixed up for the metering shouldn't be too hard to figure out. The metering does light up and appears to work but not reading correctly, I dlo have extra chips if needed.I took my measurements right from the Master output terminals ,in place of relying on the internal meters, seems like at first I has full range to 31volts but when I checked again it was only half of that, not sure whats going on , when you adjust voltage the relays are clicking like a pinball machine! Hope I dont have a bad relay could be hard to replace, actually the relays and the transformer are the only difficult components to replace everything else is commom easy to get stuff. Earlier I took a look at tekscopes for other threads on the PS280 there were some, I would really like to hear what users think about the relibality and Quality of it , I see no one learned their lesson on using counter sunk screws in cheap plastic! How about using a counter bore, And pan head screws! I'm working one handed due to a couple strokes, doing well considering but work is slow! On the plus side there is a Theroy of design in the manual I got from Tekwiki , Many Thanks to whoever did that nice work! Unfortunately the manual is the wrong revision for the one I have. Seems there was 3 versions or revisions mine seems to be the latest and has the heatsink inside and one main board with a zillion connectors. The schematic is usefull in a general way just the connections are wrong fot the revisions, I looked for a different manual but wasn't able to come up with anything usefull. If anyone has one Please post it! I'll do my best to keep you posted on my progress or lack of it. There are a ton of these on ebay most bad which makes me think there is a design flaw ? Any comments welcome! The PS 280 is branded with the Tek Name but wasn't built or designed by Tek , It was aftet sold out to Danaher I think and built and designed by Goodwill a Taiwaneese company Wich explains the Asian capacitors and transistors in it. Best regards to all. Daven9ooq --- This email has been checked for viruses by AVG.
|
Hello, I'm interested in purchasing my first scope and looking for opinions on the TDS744A. I'm not interested in purchasing a Rigol/Siglent, etc - not that they are bad scopes, I've used Teks before at different employers. It's just that I'm not familiar with this particular model. It'll be used for working on amateur radio related radios, experimentation and general messing around :) I know it can be modified to a 1GHz scope and might do that in the future. Thanks for reading. 73! Mark KA6WKE Website: Author: 4NEC2 The Definitive Guide EMail List:: [email protected]
|
Re: Fan direction on TEK485
All I have ever seen draw in at the back. The air passes through the filter first before being delivered to the interior of the cabinet. Here is a bit of fan/blower trivia: A propellor fan needs maximum power when the air flow is impeded or blocked, a centrifugal requires minimum power when the air flow is blocked. The motors on propellor fans are usually cooled by the air flowing over them. A clogged filter not only overloads the motor, it deprives the overworked motor of cooling. Keep the filters clean and free flowing. Don't ignore the filter if it is missing, high voltage attracts dust from unfiltered cooling air, which can cause a flashover.
Bruce Gentry, KA2IVY
toggle quoted message
Show quoted text
On 8/19/19 8:28 PM, Kevin Oconnor wrote: Did the TEK factory have the fan suck air in or blow it out the back?
kevin
|
Did the TEK factory have the fan suck air in or blow it out the back?
kevin
|
Re: TDS460A Will not turn on?
On Mon, Aug 19, 2019 at 04:19 PM, Stephen Hanselman wrote: Other folks, Monsanto, LiteOn, etc, all seemed more stable and reliable.
steve Steve, These optocouplers in the supply have a Small circle made with a dashed line surrounding an "M". It is not a "Motorola M", different from their LOGO. I'll bet these are made by MONSANTO. Thanks for the information! Sincerely, -- Michael Lynch Dardanelle, AR
|
Re: TDS460A Will not turn on?
Roy,
Excellent information! I am not an I.E.E.E member. I'm pretty sure that they don't take old hot rodders and motorcycle mechanics turned electronics hobbyist as members. I have followed a lot of rabbit holes, so this would be no different. I get the gist of what you are saying. The optocouplers can degrade to the point that they cease to turn the device on, but still may test as "good". Sounds like I need to replace these with new ones and mark this off the list of potential failure points. After all, it is less than $2 to replace both of them.
Much Appreciated!
--
Michael Lynch
Dardanelle, AR
|
Re: TDS460A Will not turn on?
Where I used to work, we used optocouplers to Isolate TELCO ring from our circuit and detect ring.
We found that as the opto aged the ability of the photo device to see the emitter decreased.
We replaced a lot of these because of this.
It got to the point that when a board came in for repair and was shown to be faulty in the test set, the first thing replaced was the opto.
This fixed about 90% of the field returns.
It may be that we used optos close to their low limits?
Glenn
toggle quoted message
Show quoted text
On 8/19/2019 5:08 PM, Chuck Harris wrote: Steve,
I have been repairing switching supplies since the
mid 1980's, and I have yet to have to replace an optocoupler.
Not one.
That is very odd, given your statement.
Perhaps, whatever a 6130 is, it uses the optocouplers in
a most severe way?
I must be the luckiest guy on Earth...
-Chuck Harris
Stephen Hanselman wrote:
Chuck,
If the opto-couplers are "HP" I'd have to argue with you. My boss (late '70's) at Opto Elec Div used to do the 6130C's and 6131C's and before he started he poured a little pile of couplers on his bench, and we were the div that made them. We (our company) still see regular failures of these today.
steve
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
|
Re: TDS460A Will not turn on?
On Mon, Aug 19, 2019 at 04:21 PM, Chuck Harris wrote:
A properly functioning colloquially named zener diode will
have a forward conducting knee of 0.5-0.7 volts, and a reverse
conducting knee at the published zener voltage.
Any voltage below the conduction knee will result in little or
no current flow.
I think you are describing a bad zener, which could easily stop
your supply from bootstrapping.
-Chuck Harris
Chuck, Since I cannot tell what the original Zener or avalanche voltage was on this part, I am calling it a Zener. I understand that these diodes over a certain voltage (about 6V) are not truely Zeners, but are actually avalanche diodes, This is something that I just learned regarding what is popularly called a "zener" Diode. It is possible to clearly see the difference in the curve tracer. As you say, Zener is the name they have been given, i suppose in the same way we call all facial tissues "Kleenex"? Strange that they used the same schematic symbol for both. Thank you so much! -- Michael Lynch Dardanelle, AR
|
Re: TDS460A Will not turn on?
Glenn,
I realize all of what you have very clearly stated. However, All of the diodes on this board are marked as "CRxxx". I am not a complete stranger as to how TEKTRONIX schematics have been marked in the past. There are Zener Diodes in clear, red tinted glass packages as well, they look just like the Fast switching diodes (e.g.1N4148, etc.), It may take a curve tracer to tell them apart (thankfully, I have one). While yes, they are all technically "crystal rectifiers", there is no delineation on this board as to which is a Zener, Schotky, High Speed switching, Standard Rectifier or anything else. All of this could have been avoided if they had just seen fit to release a schematic. They wanted to sell complete replacement boards, new scopes and not encourage board level repairs. This really handicaps those of us who need a schematic to follow. I am not one who can look at the loaded board and figure out how it works without a schematic, i wish that I was.
I appreciate your comments and insights!
Sincerely,
--
Michael Lynch
Dardanelle, AR
|
Re: TDS460A Will not turn on?
On Mon, Aug 19, 2019 at 01:55 PM, Stephen Hanselman wrote:
still see regular failures of these [optocouplers] today.
Hi All: I.E.E.E., NASA, and the U.S. Navy, et. al., have published papers citing the significant "failure" of these "critical" components in causing SMPSs not to operate. The authors are claiming that there are "aging" processes that take place in an optocoupler's packaging, and an optocouplers LED. As far as I can tell, the claims are mostly that the performance of some optocouplers degrades enough to prevent the optocoupler from accomplishing its intended purpose, in the design. (They don't seem to imply the aging process causes the optocoupler to fail completely; before the SMPS stops operating.) If you are interested in going down that particular rabbit hole, and you are an I.E.E.E. member too, there are papers on Xplore. Best regards and wishes. Roy
|
Re: TDS460A Will not turn on?
Steve,
As a life long EE, I would not have put up with that for
a minute. Either the circuit would get redesigned, or the
vendor of defective parts get banned.
But, I have always been a bit of a hard-ass about stuff like
that.
-Chuck Harris
Stephen Hanselman wrote:
toggle quoted message
Show quoted text
Chuck,
He would change them 3 or 4 at a time. Now we see two or three over 5 or 6 units. The 6130C uses 22 (or so) and the OEM HP ones were unstable. HP got better, but at the time (1979) they broke at the drop of a hat.
Other folks, Monsanto, LiteOn, etc, all seemed more stable and reliable.
steve
|
Re: TDS460A Will not turn on?
My point was most switching supplies have optocouplers that
send signals in both directions. Typically, one will send
a feedback signal from the low voltage side to the high
voltage side, to regulate the output voltage, and another will
send a power good signal (or other signal) from the hot side
to the low voltage side to help with orderly shutdowns, etc..
You seem to be recognizing optocoupler orientation just fine.
The power resistor is typically almost 1/4" diameter, and 3/4
inch long. Often there are two in series, standing up on the
board (in a "U" shape), and covered with a piece of braided
insulating tubing.
The power resistor is supposed to burn out safely to protect
the supply when a bootstrap failure occurs. It is operating
way over its safe power rating for just a fraction of a second.
As to being a bother, that is what the group is for.
-Chuck Harris
Michael W. Lynch via Groups.Io wrote:
toggle quoted message
Show quoted text
Chuck,
I am trying to learn and NOT be a bother to anyone. I appreciate your help, cannot say that enough.
You are correct on both 1 and 2. See my response, sent before I read this message.
BTW, I have ZERO fear of taking components out of circuit. That seems to be the best and most accurate way to get good test results.
These two couplers have the #1 pin on the "Low" side. So both face the same direction? That is if I am understanding you correctly.
I learned long ago to take pictures and carefully not the orientation of the components. I have messed up in this manner before.
I have posted pictures of the board in the "Photos" section, if you need to see the board lay out.
Your Million$ Hint mentioned Zener Diodes, so I am starting to test the Zeners on this board.
I do not see any "Large" power resistors, but it is entirely possible that I do not know what I am looking for.
Sincerely,
|
Re: TDS460A Will not turn on?
A properly functioning colloquially named zener diode will
have a forward conducting knee of 0.5-0.7 volts, and a reverse
conducting knee at the published zener voltage.
Any voltage below the conduction knee will result in little or
no current flow.
I think you are describing a bad zener, which could easily stop
your supply from bootstrapping.
-Chuck Harris
Mlynch001 wrote:
toggle quoted message
Show quoted text
I would put the odds that the Opto isolators are bad
at under 1%. They are very reliable, and pretty hard
to kill.
-Chuck Harris
Chuck,
You are 100% correct about that optocoupler. I pulled that component out of circuit and it tests good. Don't know why I even trust "in circuit" tests? Moving back to your "million dollar hint". . . .
I do have what the board shows as CR17 and this connects to PIN 1 of UC3844 (PCM Controller). Every diode on this board is labeled as CRxx. So the labels are no help in determining what the components actually are. That being said, CR17 looks like a classic glass package Zener Diode, so I lifted one end from circuit and then hooked it up to my TYPE 576 curve tracer to see what I had, expecting to see a typical ZENER curve. C17 tests as a Zener diode, but it acts in a VERY strange manner, unlike any Zener I have tested before. When I hook it up and increase the collector voltage control, the diode begins to conduct positive at the expected .6V and exhibits the other classic breakdown "knee" fairly quickly. For lack of a better explanation, it is acting like a "variable voltage" Zener. As I increase the collector sweep voltage, the breakdown voltage knee moves farther and farther left on the screen as the positive current increases and the positive current trace stays stationary at about .4V . A "known good" 5.1V Zener does not exhibit this strange characteristic. The known good ZENER knee appears and holds at the correct Zener voltage, regardless of the collector sweep voltage. I am fortunate enough to also have a 577 curve tracer as well, and it shows the same characteristic.
Is this some sort of diode that I have never heard of? Or could this be the troublesome component? Sorry if my explanation is not technically correct or as clear as it could be. I am dealing with something that I have not experienced before.
Any thoughts?
Sincerely,
|
Re: TDS460A Will not turn on?
Chuck,
He would change them 3 or 4 at a time. Now we see two or three over 5 or 6 units. The 6130C uses 22 (or so) and the OEM HP ones were unstable. HP got better, but at the time (1979) they broke at the drop of a hat.
Other folks, Monsanto, LiteOn, etc, all seemed more stable and reliable.
steve
toggle quoted message
Show quoted text
-----Original Message----- From: [email protected] < [email protected]> On Behalf Of Chuck Harris Sent: Monday, August 19, 2019 2:09 PM To: [email protected]Subject: Re: [TekScopes] TDS460A Will not turn on? Steve, I have been repairing switching supplies since the mid 1980's, and I have yet to have to replace an optocoupler. Not one. That is very odd, given your statement. Perhaps, whatever a 6130 is, it uses the optocouplers in a most severe way? I must be the luckiest guy on Earth... -Chuck Harris Stephen Hanselman wrote: Chuck,
If the opto-couplers are "HP" I'd have to argue with you. My boss (late '70's) at Opto Elec Div used to do the 6130C's and 6131C's and before he started he poured a little pile of couplers on his bench, and we were the div that made them. We (our company) still see regular failures of these today.
steve
|
Re: TDS460A Will not turn on?
Steve,
I have been repairing switching supplies since the
mid 1980's, and I have yet to have to replace an optocoupler.
Not one.
That is very odd, given your statement.
Perhaps, whatever a 6130 is, it uses the optocouplers in
a most severe way?
I must be the luckiest guy on Earth...
-Chuck Harris
Stephen Hanselman wrote:
toggle quoted message
Show quoted text
Chuck,
If the opto-couplers are "HP" I'd have to argue with you. My boss (late '70's) at Opto Elec Div used to do the 6130C's and 6131C's and before he started he poured a little pile of couplers on his bench, and we were the div that made them. We (our company) still see regular failures of these today.
steve
|
Re: TDS460A Will not turn on?
Chuck,
If the opto-couplers are "HP" I'd have to argue with you. My boss (late '70's) at Opto Elec Div used to do the 6130C's and 6131C's and before he started he poured a little pile of couplers on his bench, and we were the div that made them. We (our company) still see regular failures of these today.
steve
toggle quoted message
Show quoted text
-----Original Message----- From: [email protected] < [email protected]> On Behalf Of Glenn Little Sent: Monday, August 19, 2019 1:48 PM To: [email protected]Subject: Re: [TekScopes] TDS460A Will not turn on? CRxx indicates "Crystal Rectifier" with a sequence number. Crystal Rectifiers are diodes. CR17 would be the seventeenth diode inserted into the schematic. Due to revisions and other reasons all the sequence numbers may not be used in a schematic. Zener diodes may be marked ZDxx. Zener diodes are usually in a light tight case, either black painted glass or plastic resin. This is because semiconductor devices are light sensitive and light will change the characteristics. Hope this helps on schematic reading and part identification. Glenn On 8/19/2019 3:18 PM, Mlynch001 wrote: I would put the odds that the Opto isolators are bad at under 1%.
They are very reliable, and pretty hard to kill.
-Chuck Harris Chuck,
You are 100% correct about that optocoupler. I pulled that component out of circuit and it tests good. Don't know why I even trust "in circuit" tests? Moving back to your "million dollar hint". . . .
I do have what the board shows as CR17 and this connects to PIN 1 of UC3844 (PCM Controller). Every diode on this board is labeled as CRxx. So the labels are no help in determining what the components actually are. That being said, CR17 looks like a classic glass package Zener Diode, so I lifted one end from circuit and then hooked it up to my TYPE 576 curve tracer to see what I had, expecting to see a typical ZENER curve. C17 tests as a Zener diode, but it acts in a VERY strange manner, unlike any Zener I have tested before. When I hook it up and increase the collector voltage control, the diode begins to conduct positive at the expected .6V and exhibits the other classic breakdown "knee" fairly quickly. For lack of a better explanation, it is acting like a "variable voltage" Zener. As I increase the collector sweep voltage, the breakdown voltage knee moves farther and farther left on the screen as the positive current increases and the positive current trace stays stationary at about .4V . A "known good" 5.1V Zener does not exhibit this strange characteristic. The known good ZENER knee appears and holds at the correct Zener voltage, regardless of the collector sweep voltage. I am fortunate enough to also have a 577 curve tracer as well, and it shows the same characteristic.
Is this some sort of diode that I have never heard of? Or could this be the troublesome component? Sorry if my explanation is not technically correct or as clear as it could be. I am dealing with something that I have not experienced before.
Any thoughts?
Sincerely,
-- ----------------------------------------------------------------------- Glenn Little ARRL Technical Specialist QCWA LM 28417 Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178 QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR "It is not the class of license that the Amateur holds but the class of the Amateur that holds the license"
|
Re: TDS460A Will not turn on?
CRxx indicates "Crystal Rectifier" with a sequence number.
Crystal Rectifiers are diodes.
CR17 would be the seventeenth diode inserted into the schematic.
Due to revisions and other reasons all the sequence numbers may not be used in a schematic.
Zener diodes may be marked ZDxx.
Zener diodes are usually in a light tight case, either black painted glass or plastic resin.
This is because semiconductor devices are light sensitive and light will change the characteristics.
Hope this helps on schematic reading and part identification.
Glenn
toggle quoted message
Show quoted text
On 8/19/2019 3:18 PM, Mlynch001 wrote: I would put the odds that the Opto isolators are bad
at under 1%. They are very reliable, and pretty hard
to kill.
-Chuck Harris Chuck,
You are 100% correct about that optocoupler. I pulled that component out of circuit and it tests good. Don't know why I even trust "in circuit" tests? Moving back to your "million dollar hint". . . .
I do have what the board shows as CR17 and this connects to PIN 1 of UC3844 (PCM Controller). Every diode on this board is labeled as CRxx. So the labels are no help in determining what the components actually are. That being said, CR17 looks like a classic glass package Zener Diode, so I lifted one end from circuit and then hooked it up to my TYPE 576 curve tracer to see what I had, expecting to see a typical ZENER curve. C17 tests as a Zener diode, but it acts in a VERY strange manner, unlike any Zener I have tested before. When I hook it up and increase the collector voltage control, the diode begins to conduct positive at the expected .6V and exhibits the other classic breakdown "knee" fairly quickly. For lack of a better explanation, it is acting like a "variable voltage" Zener. As I increase the collector sweep voltage, the breakdown voltage knee moves farther and farther left on the screen as the positive current increases and the positive current trace stays stationary at about .4V . A "known good" 5.1V Zener does not exhibit this strange characteristic. The known good ZENER knee appears and holds at the correct Zener voltage, regardless of the collector sweep voltage. I am fortunate enough to also have a 577 curve tracer as well, and it shows the same characteristic.
Is this some sort of diode that I have never heard of? Or could this be the troublesome component? Sorry if my explanation is not technically correct or as clear as it could be. I am dealing with something that I have not experienced before.
Any thoughts?
Sincerely,
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
|
Re: TDS460A Will not turn on?
Chuck, I am trying to learn and NOT be a bother to anyone.? I appreciate your help, cannot say that enough. ? You are correct on both 1 and 2.? See my response, sent before I read this message.? BTW, I have ZERO fear of taking components out of circuit.? That seems to be the best and most accurate way to get good test results. These two couplers have the #1 pin on the "Low" side.? So both face the same direction?? That is if I am understanding you correctly. ? I learned long ago to take pictures and carefully not the orientation of the components.? I have messed up in this manner before. ?? I have posted pictures of the board in the "Photos" section, if you need to see the board lay out. Your Million$ Hint mentioned Zener Diodes, so I am starting to test the Zeners on this board. I do not see any "Large" power resistors, but it is entirely possible that I do not know what I am looking for. Sincerely, Michael Lynch?479-226-0126 Home Phone479-477-1115 Cell Phonemlynch001@ [email protected]@...
On Monday, August 19, 2019, 1:18:31 PM CDT, Chuck Harris <cfharris@...> wrote: Hi? Michael, Two things to help further your education: 1) there are almost always multiple devices in parallel, or ? series with every device you may wish to test in circuit. 2) Sooner or later you have to test the courage of your convictions, ? by removing the suspected bad part and testing it out of circuit. ? That is the only sure way of not being fooled by the other parts ? that share its nodes. I find it more likely that you didn't notice that the optocouplers are usually faced in opposite directions... some sending signals to the high side, and others sending signals to the low side. I still put an optocoupler failure in a switching supply at less than 1% probability. -Chuck Harris Mlynch001 wrote: Chuck,
Sorry, I was not at all clear, I should not have used the term "continuity" as I am using the Diode Test function on my DMM.
To be precise:
IC7 is open (infinity) in one direction (Red on Pin 2 and Black on Pin 1) and the meter reads 1.305 (volts) in the other direction (leads reversed from previous).
IC2 reads .512 (volts) in BOTH directions.?
One thing that I have learned is that when two supposedly identical devices test so differently, using the same test instruments, there is a good chance that one of the two is defective.
I have also seen two posts on different web pages that have pointed to optocoupler failures on this particular power supply.
Does this alter your assessment of the situation?
I am always suspect of my knowledge and abilities, NOT questioning anything that you are trying to convey to me.
I appreciate your response and your patience.?
Sincerely
|
Re: TDS460A Will not turn on?
I would put the odds that the Opto isolators are bad
at under 1%. They are very reliable, and pretty hard
to kill.
-Chuck Harris
Chuck, You are 100% correct about that optocoupler. I pulled that component out of circuit and it tests good. Don't know why I even trust "in circuit" tests? Moving back to your "million dollar hint". . . . I do have what the board shows as CR17 and this connects to PIN 1 of UC3844 (PCM Controller). Every diode on this board is labeled as CRxx. So the labels are no help in determining what the components actually are. That being said, CR17 looks like a classic glass package Zener Diode, so I lifted one end from circuit and then hooked it up to my TYPE 576 curve tracer to see what I had, expecting to see a typical ZENER curve. C17 tests as a Zener diode, but it acts in a VERY strange manner, unlike any Zener I have tested before. When I hook it up and increase the collector voltage control, the diode begins to conduct positive at the expected .6V and exhibits the other classic breakdown "knee" fairly quickly. For lack of a better explanation, it is acting like a "variable voltage" Zener. As I increase the collector sweep voltage, the breakdown voltage knee moves farther and farther left on the screen as the positive current increases and the positive current trace stays stationary at about .4V . A "known good" 5.1V Zener does not exhibit this strange characteristic. The known good ZENER knee appears and holds at the correct Zener voltage, regardless of the collector sweep voltage. I am fortunate enough to also have a 577 curve tracer as well, and it shows the same characteristic. Is this some sort of diode that I have never heard of? Or could this be the troublesome component? Sorry if my explanation is not technically correct or as clear as it could be. I am dealing with something that I have not experienced before. Any thoughts? Sincerely, -- Michael Lynch Dardanelle, AR
|
Re: Fan Mounts for Brown Case 545
Mike I stopped looking for the original style mounts years ago. I use a short length of rubber fuel line from the auto parts store and a machine screw. Works for me. If you want a picture let me know.
|
Mlynch001
Michael W. Lynch
John Williams