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Re: Little ceramic trimmer caps that always break... A fix.
On Wed, Aug 19, 2020 at 07:58 AM, Chuck Harris wrote:
Chuck, You always have a way to make me laugh, learn, or in this case; to feel better. I'm glad to hear that I am not alone. -- Michael Lynch Dardanelle, AR
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Re: Little ceramic trimmer caps that always break... A fix.
Dave Wise
We're all aging, one day per day. I swap keystrokes and beat the shift all the time.
Five years from now someone will search for "FG504" and if not for pedantry, they would miss your helpful note. Dave Wise ________________________________________ From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Chuck Harris via groups.io <cfharris=erols.com@groups.io> Sent: Wednesday, August 19, 2020 6:21 AM To: TekScopes@groups.io Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix. I am mid sixties as well, but to further my stress is a little dementia thing that runs down my mother's side of the family... I have always edited myself, but lately there is way too (just typed as "oot") much red on the page. Anyway, I wanted this to be a little helpful note for folks suffering from the trimmer capacitor plague. I apologize for turning it into an exposition on my degrading capabilities... -Chuck Harris n4buq wrote: Mid-sixties here and having some of the same issues. I work with a lot of various systems and am constantly crossing up numbers and letters (or conflating one system's numbers with another, etc.). Very annoying. I have had to resort to carefully rereading what I've typed to pick out the nits (just like I did for this one). It is indeed frustrating if not downright embarrasing at times.<snip>
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Re: A possibly sick 7904A
On Wed, Aug 19, 2020 at 12:12 PM, Roger Evans wrote:
I remember my disappointment when I started collecting 'scopes in 2012/13: I fed the < 1ns rise time signal from a PG506 into my newly acquired 7904A at a fast time base setting, expecting to clearly see the wave shape. The brightness was very disappointing, even at 1 MHz repetition rate. It turned out that the CRT had seen better days and had grown a bit tired. At normal repetition rates, as encountered by the ham that had sold me this instrument, all was fine. The 7904's and 7904A that I acquired later were much better but the limitations in writing rate were obvious. In the analog 'scope realm, apart from the 7104 or the 2467 with their MCP CRT's, nothing beats a 7834 or 7934 analog storage 'scope in this respect: Even single-shot 1ns edge speeds can be seen clearly. Raymond
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Re: Little ceramic trimmer caps that always break... A fix.
Paul Amaranth
I could type 40 wpm on a manual typewriter all day with very few mistakes.
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I suppose that dates me. Now I can't type a line without a couple of typos. My theory is that as the cost of a mistake decreases we just get lazy. Making a typo in an editing program has essentially zero cost (other than finding and fixing it). Add in spell check and you don't even have to remember spelling (I'll ignore auto-correct). Age has nothing to do with it. That's my take and I'm sticking with it :-) Thanks for your service notes Chuck. Whenever I see one I file it away. They're always full of useful information. Paul
On Wed, Aug 19, 2020 at 09:09:42AM -0400, n4buq wrote:
Mid-sixties here and having some of the same issues. I work with a lot of various systems and am constantly crossing up numbers and letters (or conflating one system's numbers with another, etc.). Very annoying. I have had to resort to carefully rereading what I've typed to pick out the nits (just like I did for this one). It is indeed frustrating if not downright embarrasing at times. --
Paul Amaranth, GCIH | Manchester MI, USA Aurora Group of Michigan, LLC | Security, Systems & Software paul@AuroraGrp.Com | Unix/Linux - We don't do windows
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Re: Little ceramic trimmer caps that always break... A fix.
Chuck Harris
I am mid sixties as well, but to further my stress
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is a little dementia thing that runs down my mother's side of the family... I have always edited myself, but lately there is way too (just typed as "oot") much red on the page. Anyway, I wanted this to be a little helpful note for folks suffering from the trimmer capacitor plague. I apologize for turning it into an exposition on my degrading capabilities... -Chuck Harris n4buq wrote:
Mid-sixties here and having some of the same issues. I work with a lot of various systems and am constantly crossing up numbers and letters (or conflating one system's numbers with another, etc.). Very annoying. I have had to resort to carefully rereading what I've typed to pick out the nits (just like I did for this one). It is indeed frustrating if not downright embarrasing at times.
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Re: SC502 With Display Issues
tekscopegroup@...
On Tue, Aug 18, 2020 at 11:02 AM, Dave Wise wrote:
Just out of curiosity, Mouser.com in the US does not ship to Paris? I know there is a Mouser.eu, but it should be easy to get around that limitation if need be.Am I missing something?https://www.mouser.com/ProductDetail/Central-Semiconductor/2N3565-PBFREE?qs=%2Fha2pyFaduixFoFz41ximubJVln7aNMI0hWYPb32rxc%3D
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Re: Little ceramic trimmer caps that always break... A fix.
n4buq
Mid-sixties here and having some of the same issues. I work with a lot of various systems and am constantly crossing up numbers and letters (or conflating one system's numbers with another, etc.). Very annoying. I have had to resort to carefully rereading what I've typed to pick out the nits (just like I did for this one). It is indeed frustrating if not downright embarrasing at times.
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Thanks, Barry - N4BUQ
----- Original Message -----
From: "Chuck Harris" <cfharris@erols.com>
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Re: 7854 display set up procedure without the calculator keyboard
Martin Whybrow
On Tue, Aug 18, 2020 at 08:40 PM, redarlington wrote:
All in the USA unfortunately, but bit the bullet and bought one. Cheers guys.
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Re: Little ceramic trimmer caps that always break... A fix.
Chuck Harris
It is becoming a touchy subject for me. All my life I have
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been a very fast touch typist. I spent a lot of time writing programs, and later writing documentation, and could always type quickly and effortlessly... But in my 60's, I am noticing coordination problems in my typing, I "slur" my shift control, and swap adjacent letters. FG504 can become FG540, Chuck can become CHuck... I even do a little weird thing where small common words, like "the" come out backwards "eht", and other words always gain an extra letter, such as "ratio" always getting typed "ration". I always find it amusing when I type a long treatise on some subject or other, and the only comments that get made are about a misplaced comma, or a typo. I am getting older. I can't see as well as I once did, I cant type as well as I once did... And I don't like it. I am working through a couple of FG504's. If I can help, just ask. -Chuck Harris Colin Herbert via groups.io wrote:
No, the typo doesn't matter in so far as that is what it was. I was just curious because I am trying to get a FG504 working correctly and not doing too well at the moment. I didn't mean to insult you or anything like that; please forgive me if that's what it came over as.
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Re: A possibly sick 7904A
Chuck Harris
Your description is pretty accurate.
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The more modern scopes have compensation circuitry that changes the focus voltage with the instantaneous intensity setting.... and changes the instantaneous intensity settings for the different beam uses... So, the intensity is separately controllable for the A horizontal plugin, the B horizontal plugin, the readout, and in some cases, the "intensified" horizontal A vs B settings... but FOCUS, and ASTIGMATISM, each have only one user control. Each of these settings result in a different beam current, which require a different focus/astigmatism voltage. For the 7904A, which was one of the earlier adopters of this enhancement, they have a circuit called Auto Focus, and in the Performance check and Adjustment procedure, page 5-12 of my manual, they explain how it gets adjusted. The do the main focus adjustment with the beam very dim, and then they adjust the Auto Focus circuit with the beam at full intensity control position. -Chuck Harris Roger Evans via groups.io wrote:
I am not an expert on this, trained in physics not electronics. When you look at a low rep rate signal at 500ps/div the beam is on a very small fraction of the time, about 5ns every msec so one part in 200000. The readout is being triggered automatically and runs around 1kHz or so, I don't remember the actual clock speeds. So for the same brightness the signal trace has to carry maybe 1000 times the current compared with the readout, this means a higher density of electrons and the space charge can affect the beam focussing compared with a low current beam.
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Re: Little ceramic trimmer caps that always break... A fix.
Stephen
On Wed, Aug 19, 2020 at 01:22 AM, Chuck Harris wrote:
I make typos all the time. Especially with multi spellcheck in different languages. It writes whatever it wants... If I don’t double check... Don’t worry, it’s okay. I understood you were talking about the FG504. But maybe Colin did believe an actual FG540 existed and was confused when he did find it. Mistakes happen.
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Re: Little ceramic trimmer caps that always break... A fix.
Colin Herbert
No, the typo doesn't matter in so far as that is what it was. I was just curious because I am trying to get a FG504 working correctly and not doing too well at the moment. I didn't mean to insult you or anything like that; please forgive me if that's what it came over as.
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Colin.
-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris Sent: 19 August 2020 13:22 To: TekScopes@groups.io Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix. Honestly, does it really matter that I mistyped FG504? I am talking about ceramic trimmers that exist in hundreds of Tektronix instrument models. -Chuck Harris Colin Herbert via groups.io wrote: Do you mean an FG504? I can't find any FG540 on TekWiki.
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Re: Little ceramic trimmer caps that always break... A fix.
Chuck Harris
Honestly, does it really matter that I mistyped FG504?
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I am talking about ceramic trimmers that exist in hundreds of Tektronix instrument models. -Chuck Harris Colin Herbert via groups.io wrote:
Do you mean an FG504? I can't find any FG540 on TekWiki.
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Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal
Roger Evans
Luis,
Since both channels are equally affected the fault must be either in the beam switching circuitry (not very likely) or in the Y amplifier stages following the beam switching. There is a fairly simple test on the beam switching that you can do with just a DMM. If you locate test points TP364 and TP 374 on schematic <3> and the example waveform shown in <21> and <22>, you should be able to replicate the DC values ( +1V and -1V) by setting the horizontal mode to ALT and the timebase to its slowest setting so the voltage flips every half second or so. Set both traces to somewhere near the middle of the screen and trigger to AUTO. This is not a definitive test but if these voltages are wrong the diodes may not switch correctly. I only just now noticed you have Trig View option on the 465. Try feeding the calibrator signal to Trig In, set Trig Source to Ext or Ext/10. Push the trig view and you can move the trace up and down with the Trig Level control. Does the vertical height of the displayed trigger signal change with position in the same way as do the Ch1 and Ch2 signals? If Q322 and Q324 are socketed then remove and test them. The Service manual schematic <3> shows various voltages around Q322 and Q324, set up the scope as best you can to the conditions defined in the manual at the start of the Schematics section under the heading 'DC Voltages'. See how well your measurements match the figures in the manual. Farther down the Y amplifier chain there was a change from discrete transistors to an IC based Y amplifier. Which one do you have? Regards, Roger
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Re: Little ceramic trimmer caps that always break... A fix.
Colin Herbert
Do you mean an FG504? I can't find any FG540 on TekWiki.
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-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris Sent: 19 August 2020 05:15 To: TekScopes Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix. Just to clear up some confusion: This note is about subminiature ceramic disk type trimmer capacitors. Tektronix equipment from the 1980's onward is littered with these little timebombs. It is a "modernization" of the old style ceramic trimmers that had a silver plated half circle on the lid that was soldered to the adjusting screw. In this case, the silver plating is inside of the trimmer, and the ceramic disk is held on by very temperamental magic. The moving ceramic disk sticks to its ceramic base, and the magic disappears. -Chuck Harris Chuck Harris wrote: Hi All,
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Re: A possibly sick 7904A
Roger Evans
I am not an expert on this, trained in physics not electronics. When you look at a low rep rate signal at 500ps/div the beam is on a very small fraction of the time, about 5ns every msec so one part in 200000. The readout is being triggered automatically and runs around 1kHz or so, I don't remember the actual clock speeds. So for the same brightness the signal trace has to carry maybe 1000 times the current compared with the readout, this means a higher density of electrons and the space charge can affect the beam focussing compared with a low current beam.
I tried putting a fast rise square wave into my 7904 at 1kHz and qualitatively I see what you see. I have to turn up the brightness a lot to see the trace at 1ns/div and it does defocus compared with the readout. I can improve the focus slightly and that worsens the focus of the readout significantly. Maybe if we get some more comments we can decide who is unrealistic and who is easily satisfied. I have no idea what the factory specifications were. Regards, Roger
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Re: Little ceramic trimmer caps that always break... A fix.
Chuck Harris
Just to clear up some confusion:
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This note is about subminiature ceramic disk type trimmer capacitors. Tektronix equipment from the 1980's onward is littered with these little timebombs. It is a "modernization" of the old style ceramic trimmers that had a silver plated half circle on the lid that was soldered to the adjusting screw. In this case, the silver plating is inside of the trimmer, and the ceramic disk is held on by very temperamental magic. The moving ceramic disk sticks to its ceramic base, and the magic disappears. -Chuck Harris Chuck Harris wrote:
Hi All,
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Re: Little ceramic trimmer caps that always break... A fix.
Chuck Harris
Hi John,
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This is normal stuff when you calibrate an instrument for the first time in decades. These little subminiature trimmer caps break all the time. Every time I try to turn one for the first time, my jaw clenches up, and I give it a gentle turn. Either the ceramic part breaks free and the cap turns, or the screw breaks free of the ceramic disk. It is fixed, and the generator impedance is now adjusted. I am about half way through the calibration adjustments... All is good. I just like to put out repair notes as my local reality reminds me of them. -Chuck Harris John Ferguson via groups.io wrote:
Wow, Chuck, it was worse than I thought, but it sounds like you have prevailed.
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Re: Little ceramic trimmer caps that always break... A fix.
Chuck Harris
Trimmer caps is short for trimmer capacitors.
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-Chuck Harris keantoken via groups.io wrote:
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Re: Little ceramic trimmer caps that always break... A fix.
Stephen
On Tue, Aug 18, 2020 at 03:21 PM, keantoken wrote:
I believe he’s talking about precision adjustable capacitors, not trim pots... 🤷♂️
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