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CG551AP Low SAC Uncal
I have 1 CG551AP which is having issues with its Low SAC that I
can't seem to understand. The output of the Low SAC is being driven to -12.5V, after some stuffing around I have found that the output of U1311 which provides offset adjustment for the Low SAC has is output at about -13V despite the inverting input (roughly -13V) sitting well below the non-inverting input (roughly -4.5V). I have tried removing U1311 which allows the Low SAC to function normally apart from there being an offset which is unable to be corrected for. I have also tried replacing both U1311 (LM725) and U1211 (LF356) which did not help at all. The big mystery for me is why the output of U1311 is not at positive saturation rather than what appears to be negative saturation given that the voltage of the inverting input is below that of the non inverting input. The input voltages appear to be in the specified range for the supply voltage being used i.e. +/-13.5V (worst case) for a supply of +/-15V. I am even considering the possibility that the circuit may be going unstable due to the frequency compensation components going out of spec. Has anyone experienced this problem before with the Low SAC in the CG551AP or had similar issues with OP-Amps? |
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Re: [TekScopes2] Re:Replacing caps
Jonathan Thornton
Re: [TekScopes2] Re:Replacing caps
Hi everybody Hurrah, I just got my TDS 544A working, usual acq fault, replaced all the electrolytics on the acquisition PCB - still same fault, so I replaced all the double and quad SOIC op.amps (TL 02/04 )--fault finding by attrition I removed the caps by making a 2 pronged fork out of wire for the tip of the soldering iron, to unsolder both sides of the cap simultaneously. You can alternate the iron from one side of the cap to the other whilst lifting the cap, but there a serious risk of pulling a pad off. For the ICs I made a U shaped tip for the end of the iron out of brass sheet, which with a bit of adjustment gripped the IC and unsoldered both sides at the same time, very quick. I then cleaned up all the pads with desoldering (the spellcheck tried to change this to 'disordering' braid) and cleaned the board with isopropyl alchohol. For replacement i used solder paste and a very fine iron tip, all helped enormously by a great purchase on XXXX, a nearly new Leica StereoZoom 4 binocular microscope for under $180, it's one of those things you don't know how you managed without Finally a wash in the dishwasher. Jonathan -- I am using the free version of SPAMfighter for home users. SPAMfighter has removed 12850 spam emails to date. Paying users do not have this message in their emails. Get the free SPAMfighter here: |
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Re: [TekScopes2] Re:Replacing caps
Jonathan Thornton
Hi everybody
Hurrah, I just got my TDS 544A working, usual acq fault, replaced all the electrolytics on the acquisition PCB - still same fault, so I replaced all the double and quad SOIC op.amps (TL 02/04 )--fault finding by attrition I removed the caps by making a 2 pronged fork out of wire for the tip of the soldering iron, to unsolder both sides of the cap simultaneously. You can alternate the iron from one side of the cap to the other whilst lifting the cap, but there a serious risk of pulling a pad off. For the ICs I made a U shaped tip for the end of the iron out of brass sheet, which with a bit of adjustment gripped the IC and unsoldered both sides at the same time, very quick. I then cleaned up all the pads with desoldering (the spellcheck tried to change this to 'disordering' braid) and cleaned the board with isopropyl alchohol. For replacement i used solder paste and a very fine iron tip, all helped enormously by a great purchase on XXXX, a nearly new Leica StereoZoom 4 binocular microscope for under $180, it's one of those things you don't know how you managed without Finally a wash in the dishwasher. Jonathan -- I am using the free version of SPAMfighter for home users. SPAMfighter has removed 12850 spam emails to date. Paying users do not have this message in their emails. Get the free SPAMfighter here: |
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TDS460A display intensity?
Just acquired a TDS460A.
Display intensity seems low (I have is set to 100)?and the contrast adjustment does nothing (on both internal and external monitor). Is this a common problem? ? Is there an hours counter on it somewhere? wondering if the CRT is going out or some other problem. Seems to work perfectly otherwise. ? Thanks, ? David. ? [Non-text portions of this message have been removed] |
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THM565 rear connector
Folks,
I bought two Tektronix THM565 portable scopes at a local surplus dealer for a very cheap price. However, the units came without batteries. I could download the operating manual and found that there is an ac adapter for this model, the THM5AC, but the only source I could find for them was charging a modest value of $365.00 for one. Since I do not even know if the units are operational, it makes no sense trying to buy one. Does anybody knows the pin assignment for the THM565 rear connector in order to allow me to build a DIY power supply and test the units. Thanks in advance for any help. Roger |
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Re: Somewhat OT: HP 8553B/8443A system needs new home (Los Angeles area)
All of the items are now taken.
--John Gord --- In TekScopes@..., "johncharlesgord" <johngord@...> wrote: California.)
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Re: Type 111 Pretrigger Pulse Generator not up to speed
Craig Sawyers
I have heard thatThat is one of the reasons that I prefer scopes from the steam age. What you see is generally what is happening, rather than something that has been digitised and processed using a process I have no control over. Mostly I'm just glad it works at all, actually, I shouldn'tYeah - that sounds a good move. The 111 is actually a really nice pulser, and should do nicely. I also have a very odd avalanche pulser of more recent vintage that fits in a TM5xx series power unit. The part number is not marked on the front, and by all accounts there are several variants of this rather rare, and somewhat prototypic beast - I've only heard of another two, and all three are different. Over 4 years ago I put some pics on the tekscopes gallery, including some sampler traces of the rise time, which measures an aberration-free 250ps on an S6 sampling head (<30ps rise) - it is a fast beastie. Gallery is called "Wierd TM500 plug in". Craig |
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Re: [TekScopes2] Re:Replacing caps
davec
If I have a whole bunch to replace, I use solder paste, hot air, and a-=-=-=- No hot air SMT apparatus or oven. Will be using fine tip iron. Can you actually touch the tip to the caps' leads while the cap is resting in place? Or do you heat the pad while pressing down on the cap? (Flux paste is probably a good idea, too, I'd think...) Thanks, Dave |
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Re: Replacing caps (was: Help with Tek 2445)
davec
Chuck,
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What about the small SM electro caps? Seems to me that these might be difficult to solder (being originally wave soldered) -- getting an iron in there might be difficult. I read that some folks use radial caps with very short, bent leads soldered to the pads. Your experience? Thanks, Dave -=-=-=- Hi Dave, |
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Re: Type 111 Pretrigger Pulse Generator not up to speed
--- In TekScopes@..., "Craig Sawyers" <c.sawyers@...> wrote:
I've got a chicken-and-egg problem here. I have a pile of 560-type sampling plugins thatSubject: [TekScopes] Type 111 Pretrigger Pulse Generator notTrying to deconvolve a fast rise time from a longer one is fraught with I want to fix up, and need to get the 111 going to help do that :) Right now I'm borrowing time on a modern Tek TDS4000 series. 350MHz digital phosphor unit. I have heard that the frequency response of the recent digital scopes is not guassian - that the rise time is somewhat faster than bandwidth alone would indicate. That makes me think that my estimate of 111 risetime is actually erring on the high side. Mostly I'm just glad it works at all, actually, I shouldn't complain too hard. I suppose the 3S gear and the 111 can bootstrap themselves up to speed, one step at a time. |
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Re: Tek 315D Oscilloscope Instruction Manual
--- On Fri, 9/19/08, Pierre F1BLF <pierrot8254@...> wrote:
From: Pierre F1BLF <pierrot8254@...> Subject: [TekScopes] Tek 315D Oscilloscope Instruction Manual To: TekScopes@... Date: Friday, September 19, 2008, 9:29 PM Hi Tekscopers, I'm looking for a Tek 315D Instruction Manual, preferably in a scanned form of PDF. Many thanks in advance. Pierre F1BLF I could use one of those manuals too as I have one of those fine old relics in my collection. It is the only scope I have that I seriously thought of washing as it's the filthiest. Has broken fan mounts thanks to UPS but otherwise it is in very good physical condition. Complete with stacks of selenium rectifiers with a sticker that fell off stating that those had been replaced ages ago. Also contains plenty of "bumblebee" caps. Think I might be missing a cover plate over the HV section though. Occasionally I'll look at the scope but not planning on restoration any time soon, mainly due to the washing issue keeping me from even getting started. I?have?the scoped?wrapped in plastic so it doesn't get any dirtier! ? ? Sorry to hijack the message. A few good pics in?there of the little beast if you care to look. ? ? Dave |
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Somewhat OT: HP 8553B/8443A system needs new home (Los Angeles area)
All,
I posted this on the HP/Agilent group and haven't had anyone jump at the chance to pick this stuff up: I have upgraded my spectrum analyzers and I no longer have room for the old units. The following items are available free to anyone who can use them and is willing pick them up. (I live in Venice, California.) 140T/8552B/8553B system with a 8443A (late model, LED) tracking generator. 2 each 8556A 8250A storage normalizer Tek 604 monitor (use with 8250A) HP 1331A variable persistence display Let me know if you are interested. -- John Gord ( johngord(at)verizon.net ) |
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Re: Type 111 Pretrigger Pulse Generator not up to speed
Craig Sawyers
Subject: [TekScopes] Type 111 Pretrigger Pulse Generator notTrying to deconvolve a fast rise time from a longer one is fraught with problems. 500ps on a 1ns instrument response is a nominal 1.12ns - which is only 14% different from your measured 1.275ns. Are you sure your timebase is that accurate on the fastest sweep ranges (they often aren't). The only sure way to measure it more accurately is to use something with a response much faster than what you are trying to measure - ie a sampling set up (which is precisely what the pretrigger of the 111 is for - getting the sampling timebase up and running before the measurement event). To get a good grip on the rise time and potential aberrations, you need a rise time at least three times faster than what you are trying to measure (for a 10% error). So at most at 170ps rise time. An S2, S4 or S6 sampling head will do this, or a 1S2 from the earlier generation. My main scope is set up with a spectrum analyser at the moment, or I would get sampling up and running and measure my own type 111. It would just be confirmation though - I've measured it before, and know for certain that it gives less than 500ps rise. Craig |
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Option 13 in an R7912?
Jose V. Gavila
Hello!
Today I have received my last Tek toy, an R7912 mainframe :-). It has a label in the plug-in compartment base which says 'Option 13'. I wonder if someone know what does it mean. Thanks! JOSE ------------------------------------------------- 73 EB5AGV - JOSE V. GAVILA IM99sm La Canyada - Valencia (SPAIN) Vintage Radio and Test Equipment European Boatanchors List Amateur Repairs List |
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Need 475 scope
Dave_s
Hi folks,
The repair of my sick 475 scope is not occurring EASILY despite SO AMNY HELPFUL suggestions from members of this group. It is possible that the repair may occur. Just in case, I am now searching for a replacement usable 475, 475A, or 485 in good working condition. What is available? Never having used EBAY, I am also interested in other sources that refurbish, calibrate, offer good used scopes, etc. Still optimistic that I will find the fault parts. Thank you, 73, W6MIK, Dave |
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Re: 2215 Problem
tom jobe
Hello Gary,
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For what it's worth... That same capacitor, 285-1222-00, was also used in the military version of the 2235, It was used directly across the incoming AC lines just before the full wave bridge rectifier as part number C904, and it did not have a resistor in series with it.. I have a few partially stripped military 2235 mainboards, and they are all missing C904, so I would guess that it must have been a component that had problems. Other 22XX scopes I looked at use a .0022 uF (2200 pF) 250 V capacitor for C904. tom jobe... ----- Original Message -----
From: "Garey Barrell" <k4oah@...> To: "Tekscopes" <TekScopes@...> Sent: Thursday, September 18, 2008 7:55 PM Subject: Re: [TekScopes] 2215 Problem Stefan -come fingersfrom singapure, and worked just fine for a few hours beforehand. module.for days. The cap was actually inside a Schaffner brand mains filter <k4oah@...>wrote: toI was using my 2215 for an hour or so the other night, and moved over likethe desk to look at something else. About 30 minutes later I heard a thea Rolodex. P/N 285-1222-00, 0.068 uF @ 250 VDC, 20%. This is a tiny one.million and a half capacitors that I have will even come close to ------------------------------------ |
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