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Re: Peter Keller's Book Mailing Status (Minor Correction)
In this present world of ¡°instant gratification¡± utilizing electronic means to send messages and documents I do realize that it is somewhat difficult for some people to understand the sloggingly slow process of the US Postal Service. I wanted to make a few comments regarding this.
1. Media mail is expected to be slower than normal mail approaches. 2. The US Postal Service has been crippled by the pandemic, funding, volume and politics. 3. I have recently experienced packages sent via Priority Mail to take over a week to be delivered. 4. Delivery times will vary depending upon the delivery areas and route conditions. 5. I am a patient person. 6. I have plenty of things to read until my book arrives. 7. If I die before it does, I have others who may be interested in receiving it to read. ¡°Nuff said. Greg |
Re: Tek 7904 In Pulse Mode Related to C1511 on LV Regulator
Thanks for the reply Tom. I thought better of the change as well since Tek made a boat load of these with absolutely no change in component value over the lifetime of the instrument. My load board was a purely resistive implementation initially and I decided to add the shunt capacitance the main interface board applies to this rail and that solved the problem. The supply now correctly drives the artificial load perfectly. On to the rest of the mainframe.
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Re: Intermittent power on problems with 2465B
Bob Albert
I am late to this party but I fixed one smilar unit by replacing the power FET in the switching power supply.? Perhaps yours has a similar problem.
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On Tuesday, January 5, 2021, 04:29:44 PM PST, Mark Hatch <mark2382@...> wrote:
I *really* appreciate all the views here. Lots to think about. I am ok with replacing the LVPS e-caps and those x2's too. And it will be good to look at the infamous SMD's on A5. Haven't done that yet and I *really* should... In terms of simpler solutions, anybody think that it could be the power switch on the front? When it first started acting up, I thought sticky relay. But threw that idea out the window when I found no relay in power lines. Having worked on boat anchors (like I suspect most of you), right after e-caps the next set of problems are caused by dirty/corroded switches. And given that the last (and worst) incident was after I had to put the scope in my shed during are most recent set of rain storms here in No Cal it got me wondering. The shed is dry, but I suspect it still would be damp over that 2-3 days. Perhaps that could lead to corrosion on the switch contacts?? Or am I just having wishful thinking.... I did see in the archives that the switches do go bad, but nobody mentioned intermittent powers. Reading between the lines it sounds like the switch failure was something hard. Currently, the scope is behaving itself and turning on with the button push like it should...? Would be nice if it failed hard instead of playing "hide and seek" with me.... Regards, Mark |
Re: Intermittent power on problems with 2465B
Mark Hatch
I *really* appreciate all the views here. Lots to think about.
I am ok with replacing the LVPS e-caps and those x2's too. And it will be good to look at the infamous SMD's on A5. Haven't done that yet and I *really* should... In terms of simpler solutions, anybody think that it could be the power switch on the front? When it first started acting up, I thought sticky relay. But threw that idea out the window when I found no relay in power lines. Having worked on boat anchors (like I suspect most of you), right after e-caps the next set of problems are caused by dirty/corroded switches. And given that the last (and worst) incident was after I had to put the scope in my shed during are most recent set of rain storms here in No Cal it got me wondering. The shed is dry, but I suspect it still would be damp over that 2-3 days. Perhaps that could lead to corrosion on the switch contacts? Or am I just having wishful thinking.... I did see in the archives that the switches do go bad, but nobody mentioned intermittent powers. Reading between the lines it sounds like the switch failure was something hard. Currently, the scope is behaving itself and turning on with the button push like it should... Would be nice if it failed hard instead of playing "hide and seek" with me.... Regards, Mark |
Re: Intermittent power on problems with 2465B
On Tue, Jan 5, 2021 at 03:36 PM, John Williams wrote:
for my 0.01 dollar worth... it was an intermittent power cord... when I had dozens of "good" ones... but not the imagination to imagine that could be the problem. Lesson learned... I hope. |
Re: Slightly OT: How can I dissolve Potting Compound?
On Tue, Jan 5, 2021 at 08:39 AM, George Kerber wrote:
Like... with bottled water... one is relying on the company/manufacturer's claim the product is "safe" and "effective." I note that according to public information the product mentioned allegedly has dichloromethane... and also ... another chemical component. The effects of dichlormethane (a.k.a. DCM) on cured epoxy compounds have been discussed in the current thread. The other component... which is added... and which I suggest, is added to allow the DCM to remain in solution longer (as DCM evaporates readily)... and also to allow washing with water. If you have experience with a commercial/industrial product, or the product's manufacturer, and have received training, or "adequate" instructions in how to "safely" use the product... and are willing to spend more money (sometimes a lot more)... then sometimes these industrial/commercial products can be a better fit. If you go with a commercial/industrial product... then IMO, good luck in recovering your losses, should their be any. If you just want to go with "generic" strait DCM... then perhaps the onus is on the user, as to whether they understand what DCM is, and known to do, and could do. |
Re: Early 7904, no readout
Look at the TekWiki site. There are several manuals there. I don¡¯t know what S/N ranges they cover.
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DaveD On Jan 5, 2021, at 17:30, Bruce Atwood <CCDman1@...> wrote: |
Re: Intermittent power on problems with 2465B
I hate to interject into this very interesting and exciting thread which I am finding much more interesting than CNN, but one thing does concern me. That is I have spent many hours searching for a trouble when the answer was far simpler. I would want to make absolutely certain that the problem wasn¡¯t in the AC side of things. I would take off the cover and set up to both measure the ac inside the scope and use a probe or clip lead to jumper the switch. If it doesn¡¯t help no harm no foul. But I would certainly check these two things before ripping the poor scope apart. Jm2?.
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Re: Troubleshoot TEK 465
Bob Albert
Seems like an unblanking issue.? Trace the signal that is supposed to raise the CRT control grid potential during sweep.? Sweep gate.
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On Tuesday, January 5, 2021, 03:24:13 PM PST, wes Bolin <k5apl41@...> wrote:
I am trying to repair a TEK 465 oscilloscope that my friend bought from ebay.? It does not have a trace unless I push the Beam Finder button.? A trace then appears that I can move vertically, horizontally, focus and vary intensity.? I do have the sawtooth output from the Horizontal Amp that varies with the front panel switch position.? Where do you suggest I look next? I do have some test equipment to be used for troubleshooting.? I'm used to using scopes, not repairing them, so any help is sure appreciated.? Thanks. Wes Texarkana,? AR |
Troubleshoot TEK 465
I am trying to repair a TEK 465 oscilloscope that my friend bought from ebay. It does not have a trace unless I push the Beam Finder button. A trace then appears that I can move vertically, horizontally, focus and vary intensity. I do have the sawtooth output from the Horizontal Amp that varies with the front panel switch position. Where
do you suggest I look next? I do have some test equipment to be used for troubleshooting. I'm used to using scopes, not repairing them, so any help is sure appreciated. Thanks. Wes Texarkana, AR |
Re: Peter Keller's Book Mailing Status (Minor Correction)
I don't dispute the issues you are experiencing with mail delivery but it is not like this .
Dennis Not that it matters but my latest Media Mail experience is I shipped a book to Southern California Dec.8th. As of today it is just left a post office in NewJersey. USPS is really complicated anymore no reliability. Craig |
Re: Intermittent power on problems with 2465B
Chuck Harris
Histrionics, I love it!
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You must live in an alternate universe from the rest of us. I would rank electrolytic capacitors as being the second least reliable part in modern electronics, narrowly being bumped from first place by incandescent light bulbs... But, I know of something that leaves even more damage in its wake than bad electrolytic capacitors: People who are not skilled in electronics construction and repair, replacing good parts they heard someone on the internet say might be bad. I have been a practicing electrical engineer for 40 years now, and I have seen just about every sort of part failure that can happen over that time, but I have not seen electrolytic capacitors take off like rockets and stick in a ceiling 8 feet up. The closest I have seen to that is back when I used to do my annual December 7th sacrifice of a Japanese electrolytic capacitor in honor of those who lost their lives on Pearl Harbor day. Those were hooked directly across the power line, and blew instantly. Your hyperbolic warnings will probably do more damage in the long run than the capacitors you rant against. -Chuck Harris David Campbell wrote: Re. recapping 2465B |
Re: Tek 7904 In Pulse Mode Related to C1511 on LV Regulator
I haven't looked at the schematic, so I can only speak in general terms. If that cap is indeed part of a loop compensator, I think it's ill advised to go about modifying it in any ad hoc way. Whether 0.1uF is "high" or "low" isn't related just to its value, it's a function of the impedance it sees, and of the gain of the loop. Speeding up the loop by dropping the value of the cap could endanger loop stability. A wildly oscillating switcher is not what you want!
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-- Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 1/3/2021 16:05, rgpierce1@... wrote:
Hey Guys, |
Early 7904, no readout
My new (to me) s/n B041515 7904 arrived DOA. (ebay, "not working, for parts".) With the help of my mostly trusty DSO138 I found the shorted 47/25V dipped tantalum on the -15 supply. Replaced it with a 470/25V aluminum electrolytic, 'cause that's what I had. It now has a beautiful and bright trace. I have ordered what I hope is an original paper manual for the early 7904s. The read outs do not work and all the manuals I have found online are for the later version, s/n B26000 and up. While waiting for USPS is there a downloadable version of the early manual somewhere? Point me to it please. thanks
PD I'm in the market for a 7A19 and a 7A26, any advice welcome. |
Re: Intermittent power on problems with 2465B
Let's see your stats for Tektronix equipment. I have never seen tants from Tek gear eject into ceiling tiles. I reject any dogma that is uninformed by relevant data.
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-- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 1/5/2021 13:56, David Campbell wrote:
Re. recapping 2465B |
Re: Intermittent power on problems with 2465B
David Campbell
Re. recapping 2465B
Youre on the cusp of learning the *hard way* why advice to NOT replace caps is extremely bad. Out of the multiples of semi load after semi load of equipment I worked on "back in the day" (very high volume consumer electronics from tube to fine pitch SMT)Ive seen too many electrolytics and some tantalums go 'knees up' and leak, explode, literally take off like rockets and stick in a ceiling 8 feet up, blow confetti across the room, destroy power supplies and even turn power transformers into smoking piles of tar and iron. And do circuit board damage... Only a* FOOL* thinks they can get away with NOT recapping and I do mean ALL of the caps. Its a crap shoot, a losing gamble to trust any old cap. Its a false Meme from the antique radio world that says "I can get away with not replacing caps/ just testing them" That Meme is from the world of working on an old AM broadcast or SW receiver and attempting to keep it as near "stock " as possible. The adventurous remove old caps and hide new ones inside. The foolish ignore old caps... Its EXTREMELY bad practice in anything worth keeping, such as high end equipment like Tek. Its a second Fools Errand and false meme to play the "bring it up on a variac" or "Ill reform a 50 year old cap." Delusional. The "bring it up on a variac" meme was for finding shorts that were hiding in equipment with linear power supplies where just turning the thing on instantly blew the fuse. It is NOT a valid or useful procedure for dealing with old caps, no matter how hard the True Believers want it to be. Ignore those advising anything but a total recap. *They wont be paying for the damage their foolish advice causes.* This is (presumably) high end, near scientific Tek (and other) test equipent. If its not worth $100 in caps and a days work, why bother? Just throw it in the dumpster. Signed, replaced more leaky, shorted and open caps than " theyll" see in 5 lifetimes..., |
Tek 7904 In Pulse Mode Related to C1511 on LV Regulator
Hey Guys,
I'm in the process of (mostly done I think) repairing a 7904 power supply that goes into pulse mode. I replaced a number of the bad tantalums on the cap rectifier board which brought some supplies closer to where they needed to be but but did not keep the supply from going into pulse mode. Continuing to diagnose things I found that pulling C1511 on the LV regulator board solved the problem, however the cap I pulled isn't reading as a short and replacing with a known good causes the pulse mode to return. C1511 seems to be working as a speed up capacitor for the regulator (allowing high frequency transients to bypass R1514 in the ladder) but seems awful high at 0.1 uF for that purpose. I'm considering replacing with a much smaller value ceramic (like 100 pF). Does anyone have any experience/thoughts/suggestions with this? Could my -50V supply have a lot of noise on it from somewhere else that it shouldn't which is causing this cap to be a problem? I'm currently running the supply into a bank of resistive loads so it would have to come from a connection to one of the other supplies if this was the case. Thanks for the help. Ricky |
Re: Peter Keller's Book Mailing Status (Minor Correction)
I don't dispute the issues you are experiencing with mail delivery but it is not like this everywhere.
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I mailed the books on Saturday morning. Monday afternoon I received an email from a member that they received Peter's book within my state (Washington). Today (Tuesday) I received another email that their book arrived. Dennis Tillman W7pF -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Vince Vielhaber Sent: Sunday, January 03, 2021 9:44 PM To: [email protected] Subject: Re: [TekScopes] Peter Keller's Book Mailing Status (Minor Correction) Media mail from my house to anywhere, even 20 miles away, will first go to Pittsburgh, PA. I'm about 40 miles north of Detroit. That said, I've seen Media Mail packages get to the same city before both a priority and first class package around the same weight. (I sell used DVDs and have anywhere between 10 and 30 packages in transit at any given time). Vince. On 01/04/2021 12:24 AM, Jack Reynolds wrote: Hi EJP,-- K8ZW -- Dennis Tillman W7pF TekScopes Moderator |
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