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Re: TEKTRONINX P6139A shorted, metalic, Grow Metal Crystals? any definitive solution?

Roy Thistle
 

On Sun, Sep 12, 2021 at 10:50 AM, Jeff Dutky wrote:


but I struggle to imagine what else could cause the short, and return
annually.
Hi Jeff:
There is another phenomenon that causes observations like tin whiskers to occur... and that is dendrites: an electro-chemical process that is well understood, relative to tin whiskers.
I'm not claiming it's not a tin whiskers phenomena (or that that P6139As don't have a tin whiskers problem)... just that what I see on the video 'suggests?' it might be a dendrite problem.
Maybe that hasn't been considered before?

--
Roy Thistle


Re: Thoughts About Modern Tek Scopes

Roy Thistle
 

On Fri, Sep 10, 2021 at 07:23 AM, Jeff Dutky wrote:


Maybe a modern consumer DSO is all marketing fluff, and they're all really 200
MHz scopes under the hood, with just a few jumpers to tell the scope to limit
itself to the bandwidth
The Chinese... or the Taiwanese... low cost scope manufacturer's have been known to do that...that is... offer hardware/software that is 'crippled'... and can be user 'unlocked.'
I suppose those manufacturers are copying Western ones who've offered significant upgrades to functionality though the enabling hardware/software through entering special codes into an options menu.
For a very general example of 'hidden capabilities'... AFAIK... almost all Chinese phones come/came with an FM radio... the software, and the hardware, is part of the chipset. But, many don't have the FM radio enabled in the phone's menu.
Substantially priced user installable 'codes' to unlock hardware, as well as unmarked 'cuttable' links... or just unidentified removable jumpers... to unlock hardware/software... these have been a thing for a long time... which I'm sure many people posting well know. Tek, Anritsu, HP, Fluke, et. al. have done it.
I'd say a significant number of hobbyists feel cheated by this 'trick'... but industrial and educational users don't seem to care? They just pay.
All and all it's sometimes... maybe always... easier with modern chipsets... where extra functionality is just there already... to manufacture a thing that is easy for a user to upgrade by entering a code, or altering a jumper.
Discovering how to do it, without paying for it... or 'hacking'... is something that is quite popular.


--
Roy Thistle


Re: TEKTRONINX P6139A shorted, metalic, Grow Metal Crystals? any definitive solution?

 

Roy,

Ive watched the video multiple times. I admit that the resistance value he is seeing is not what I expect from tin whiskers, but I’ve only had one experience with them, and I did not try to measure the actual resistance of the short they caused (it was in a 2N2207, and I cleared the short by rapping the case on a hard surface. Since the mechanical cure “fixed” the issue I took it as read that the cause had been tin whiskers).

The method he used to clear the short is clearly not the method mentioned on TekWiki, but I struggle to imagine what else could cause the short, and return annually. You would think that if there were some environmental factor causing the short that it would cause problems with all sorts of other equipment, and to a much greater degree that with part of an oscilloscope probe that is protected by a screw thread.

It’s not clear from the TekWiki article where the tin whiskers usually happen in the P6139 cable. I had merely assumed that they occurred in an open space an either end, and could be cleared mechanically.

— Jeff Dutky


Re: Repair of a 7S14

Ed Breya
 

Oops - correction needed. In my previous post where I described using transistor optocouplers as generators, the output is taken from the B-E junction, not B-C. Ed


Re: Zener diodes on 475?

Dave Voorhis
 

Per the usual online service manual for the 475, the four tunnel diodes are designated CR556, CR566, CR776 and CR786.

The first two appear on the A8 Trigger Generator and Sweep Logic circuit board (fig 7-12) at locations 7C & 7D.
The second two appear on the A8 Trigger Generator and Sweep Logic circuit board (fig 7-13) at location 7B.

CR556, arming TD, is on the 'A' Trigger Generator schematic 5, to the middle right.
CR566, firing TD, is on the 'A' Trigger Generator schematic 5, to the lower right.

CR776, arming TD, is on the 'B' Trigger Generator schematic 6, to the middle right.
CR786, firing TD, is on the 'B' Trigger Generator schematic 6, to the lower right.

I have found discrepancies between the schematics and my 475 too. For example, the schematic shows the intensity control as a single-gang pot. Mine is a dual-gang pot. The front gang has the part number and circuit matching the schematic. The rear gang is part of the HV regulator circuit, which doesn’t match the schematic.

On 12 Sep 2021, at 17:32, Simon <tenareze32@gmail.com> wrote:

I have discovered that they are tunnel diodes (152-0386-00) and cannot be tested with a multimeter. I am wondering where I can find a circuit diagram that marks them. There are also many discrepancies between my board and the 475 or 475A schematics I have. Maybe there were modifications.
Simon


Re: Suggestion for our group Administrator

Jim Adney
 

It was just a suggestion, and I believe this list's owners have done a good job explaining why editing causes problems. Many of you clearly have long history with this list that I lack.

I'm very familiar with listservs and I'm also very fond of them. None of the lists I own have as many listees as this one does, and I've never run into the kind of OCD that got brought up here, generating multiple reposts. I was thinking more about the long term problem of having incorrect part numbers, etc. become part of our permanent record. I communicate almost exclusively via email. I reread my messages before sending and make corrections and additions if necessary. Nevertheless, I'm not perfect, so occasional mistakes slip thru.

I take the digest form of this list, and I'm VERY aware of the problems that this can cause if someone top posts and quotes the whole digest with the wrong subject line. I'll never make THAT mistake. Yes, that happens on another list I'm on and it's really annoying. It's good that groups.io has instructions at the top of each digest that discourage this. I've found it hard to add proper replies from the digest, but I'll catch on. Up to now, I've just gone to the web site, searched for the message I want to reply to, and then written my reply. THIS reply comes via the individual message link within the digest. I hope this worked as intended.

I wish groups.io did a better job of showing threads on their web site. They are there, but you have to dig down to find them. That's something we can't fix.


Re: Zener diodes on 475?

Simon
 

The trigger circuit seems to be working properly. My problem si a lack of Z axis signal to turn on and off the trace.in sync with the time base.The time base is running and I have X deflection, but no trace as the DC restore circuit cannot function without a Z axis signal.
Simon


Re: "mottled effect" on anodized front panel

Tom Norman
 

I recently acquired the calculator keyboard for my 7854 that had some mild mottling on the surface. The usual mild cleansers didn't help, so I tried using a very mild plastic polish with good results and the mottling has not returned. It didn't seem to hurt the silk screened characters at all. The product I used is called Novus, but I don't recall if it was the #2 or #3 (#3 is least aggressive). Your milage may vary, and just reporting what worked for me.

Tom


Re: Zener diodes on 475?

Simon
 

I have discovered that they are tunnel diodes (152-0386-00) and cannot be tested with a multimeter. I am wondering where I can find a circuit diagram that marks them. There are also many discrepancies between my board and the 475 or 475A schematics I have. Maybe there were modifications.
Simon


Re: Zener diodes on 475?

Mlynch001
 

Simon,

Those are indeed Tunnel diodes for the trigger circuit.

--
Michael Lynch
Dardanelle, AR


Zener diodes on 475?

Simon
 

I have found, a couple of short circuited zoner diodes on my 475. They are gold plated and fit into sockets on the triggrer Z axis board, both anodes to ground. They are marked GE 0386, but I don’t know their value. I am wondering if they might be tunnel diodes, although they are marked zeners on the board but I cannot find them on the 475 or 475A schematics. Does anyone have any idea what they might be?
SImon.


Re: Suggestion for our group Administrator

Jared Cabot
 

What could be a good compromise is a 5 minute delay on the emails going out after the 'reply to group' button is clicked.
In that 5 minute window, an edit button could be available, but once 5 minutes has elapsed, the message is set in stone.

That would probably require the feature to be made available by the groups.io team though maybe?

In any case, I have no strong feelings in either direction.


Re: Suggestion for our group Administrator

SCMenasian
 

My 2 cents worth: Let the the administrator choose whatever option is the easiest to manage. I am very thankful for all the effort put into keeping this group going smoothly and would not want to add additional complications. I can adapt to anything.

I try to avoid making mistakes in the first place; if a serious one creeps in, I mark the correction with an initial "Oops". If it is possible to let a poster remove one of his/her own messages from the site, we could keep bad information from cluttering up the site.


Re: Suggestion for our group Administrator

toby@...
 

On 2021-09-12 2:04 a.m., Brian Cockburn wrote:
Could I perhaps suggest a short trial. Maybe just 2^9 hours. Then ask again to see if the "No" team might have some members change to "Oh alright then".

Mods please step in in both groups, meta thread needs to end.





Re: Suggestion for our group Administrator

John Griessen
 

On 9/12/21 8:28 AM, Alex wrote:
I have no desire to operate this forum through multiple never ending stream of emails when I can simply and easily do it on this simple and easy to use web interface. I know opinions vary. Perhaps I am missing some advantage, but can't imagine why
Advantages of using an email reader:
sorting emails into buckets by list name
killing messages from certain senders and with certain subject words
ease of response to individuals off list.
search through your current set of incoming emails for keywords, (and maybe dump the rest).
use threaded setting to see subject lines and decide to read some subject threads without looking at the rest.

By using a few tools as above, dealing with the volume of posts is better time management than with the web interface, and the web interface has an annoying login required every so often, but email reader has logins automated in a secure way.

--
John Griessen
no editing


Re: Suggestion for our group Administrator

Alex
 

In forums when posting, it helps me to read (and sometimes to re-read) my own message with the PREVIEW feature and that usually allows to catch any required corrections or changes before the message gets posted. But of course at times there is the inevitable small mistake that sometimes still gets through, or 5 minutes after posting I change my mind on how I wrote some part and want to try to change it to make it clearer, or update some information, etc, so I can sympathize with people wanting to have an edit feature added. Perhaps it might help a few people to share how I operate this forum.

I am writing these lines (on a laptop) while the thread is open in Firefox, which has a build in spell "check as you write" feature and will automatically highlight common spelling errors with a red underline. Of course when a change to the post ends up being needed not because of a spelling mistake but rather the way some part of the content is expressed, then spell checkers are of no use. Also most email programs have a build in spell checker that does the same (mine does), but I have no desire to operate this forum through multiple never ending stream of emails when I can simply and easily do it on this simple and easy to use web interface. I know opinions vary. Perhaps I am missing some advantage, but can't imagine why anyone, other than perhaps an admin, would want to do it the hard way by having to deal with untold number of emails just to read and follow a thread. Also not sure either why any adult, unless they are in a airport lounge waiting for their flight, would want to regularly use a phone keyboard to send sometimes lengthy forum postings. I gave up and left behind trying to type on a damn phone keypad years ago and left it to the teenagers. And no, my finger size is not the problem by a long shot. But then again, perhaps some persons just don't have any other option but to type on a "smart" phone, or even enjoy it. But for me, even if the only other option would be a basic $100 laptop, that would be a million miles ahead of typing or reading postings on a phone.

Not sure how others operate this group, but I find that receiving a single and compact email in the morning with all the latest posts of the previous day is the most convenient and efficient way as there will be one link per thread, and I can easily open any thread of interest in Firefox. Then its up to one to get to the tail end of it to see the latest post or postings, but it works for me. And all this in a single short email. If I want to save the email to preserve a link because of a specific thread of interest for future reference, my email program allows me to edit both the body and subject of inbound emails, so I can delete all the body text that is not desired around the link of interest, and then just simply change the subject to the name of the thread. I really have no need to follow any exchange live and up to the minute, I assume others need or want to, but when I am interested to keep taps on postings of an ongoing thread, I just leave it open in Firefox and set it to refresh every 30 minutes or whatever seems reasonable, and it will automatically show any new posts for the duration. And no email deluge.

Just my $0.02.


Re: TEKTRONINX P6139A shorted, metalic, Grow Metal Crystals? any definitive solution?

Roy Thistle
 

Hi Jeff:
Well... in his video... he cleared the short by washing out the socket on the cable where the probe tip screws in... with a brush soaked in alcohol.
Did you watch the video?
Maybe it's not a "tin whiskers" problem?
--
Roy Thistle


Re: Help needed bringing a 555 back to life

Morris Odell
 

The voltage across C640 is close enough to normal as is the parallel combination of R646/647. But something doesn't make sense. The 5651 is a voltage reference tube that should be at a constant 85-86 volts when lit. It gets its feed from the -150 line through R608 so even if it's open circuit or faulty the voltage across it can't be more negative than the -150 volt line which you say is at -148 volts. Likewise the grid of V634 is fed from a divider that has the -150 as it's most negative end and a plate of V624 as it's positive end so it can't be -153.5 volts if the -150 line is at -148. If the plate of V634 (connected to the grids of V647) really is at 0 volts then V634 will be cut off and V647 will be conducting hard, making the -150 more negative which is clearly not happening. Under these circumstances the voltage there would be slightly positive as it's pulled up by R633 but V647 could be pulling grid current and sucking it down to 0 volts. Make sure pins 3 and 6 of V647 really are at chassis potential. You need to check that what's in your 555 corresponds to the schematic.

Morris


Re: FG502 No wave

Ozan
 

Hi Chris,

U200 Starting point around "1" on the frequency adjustment dial = +0.1V. turning the control CCW increases the voltage gradually to +9.7V. It then >jumps suddenly to +17.85V and as I turn another 2-3 sub-divisions, it jumps back to +0.1V, the starting point.

U135 Starting point around "1" on the frequency adjustment dial= +7.28V. turning the control CW increases the voltage gradually to +19.7V

U140 Starting point around "1" on the frequency adjustment dial= +6.67V. turning the control CW increases the voltage gradually to+16.43V when it
jumps suddenly to +19.1V, stays there a few sub-d-visions and jumps back to +6.67V, the starting point.

U170 Starting point around "1" on the frequency adjustment dial= +7.2V. turning the control CW increases the voltage gradually to +18.00V.

U175 Starting point around "1" on the frequency adjustment dial= -6.49V. turning the control CW increases the voltage gradually to -18.15V.
----

These voltages are OK. Once all the issues are fixed calibration will make them more accurate. R110 (frequency control) pot seems to not stop at the end and continue past the contacts. Probably a mechanical issue but it is not the cause of the stopped oscillations.

Oscillator could be one of several states so instead of a lengthy flowchart if you can measure few voltages we can narrow down the issue.

Setup: Turn the dial so that output (pin 6) of U135 is about +10V, pick triangle waveform, pick 10^3 range.

Measure the voltage across R140 and R175. This tells us if current sources are working.

Measure the collector voltage of Q292. In normal operation it should be a square wave with +/-5V amplitude but since your unit is not oscillating just note the voltage.

Measure the collector voltages of Q315 and Q325. This tells us if gating circuit is stopping the oscillation.

Measure base voltage of Q230A. In normal operation it should be a square wave with +0.5V/-0.6V amplitude.

Measure gate voltage of Q200. In normal operation we expect ~ +1/-1V amplitude triangle wave. This tells us how the oscillator is stuck (railed high, railed low, floating in the middle).

Measure emitter voltage of Q210. This voltage is expected to be same as gate voltage of Q200. Tells us if Q200/Q204/Q210 buffer is working.

Ozan


Re: Suggestion for our group Administrator

Brian Cockburn
 

Could I perhaps suggest a short trial. Maybe just 2^9 hours. Then ask again to see if the "No" team might have some members change to "Oh alright then".

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