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Re: 7000 series carrying handles - how strong are they?
On Sun, Aug 18, 2019 at 05:54 PM, evan foss wrote:
I've carried the 500s and 7000s, for long distances occasionally 1Km plus, and frequently carried them a couple of hundred meters.. and lots of times carried them 10 to 20 meters, from lab to lab, through the halls... or across the lab. (I know... there is a new invention called wheels; but, the scope carts are always jammed up with junk!) The only times a metal strap broke... and that was before I lifted the scope... the steel strap broke (just by pulling on it)... it was very obviously rotted and rusted through, . A couple of times, on the 500s, I braided a rope (1.5 mm rope/string) handle on, just so I could carry it... when I thought the rusty steel handle present might suddenly fail, under inconvenient circumstances. That said... the steel strap is only as "strong", as the fittings it engages, and the bolts (screws really) that hold the whole assembly to the body of the scope. Checking those are sound, and will continue to be sound, seems prudent. I get the willies too, wondering whether the handle is going to break, on these heavy scopes... but under the weight and strain, I quickly start to trust the steel, and I worry more about banging the front panel into something, and bending those little knobs! I have a 1200 series Tek logic analyzer, that has a bail type handle... but it has one corner of the bottom compressed, upwards... like it was dropped, straight down, from letting go of the handle... and then the thing landing on just one corner... so how does that happen?... the handle is fine. Roy |
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Re: 7000 series carrying handles - how strong are they?
On Sun, Aug 18, 2019 at 03:38 PM, Bruce Griffiths wrote:
unless it is cold worked (like stamping it?)... and then it develops a magnetic response. The strength of which [compared to stainless numbers that are magnetic]¡ I guess... depends on the amount of cold working. Roy |
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Re: General Radio 874 Connector, inner conductor "bendies"
On Sat, Aug 17, 2019 at 08:56 AM, Dale H. Cook wrote:
I found a 1001A that I though had a BNC output connector; but, it was an 874 to BNC adapter, inserted into the front panel 874. I have some GR units, mostly older than 1950, mostly audio, 600 ohm stuff, I guess... mostly in wooden cabinets, so old I guess too... like a 546-C, with binding posts. (sometimes seen referred to 546-0, because of the front panel stenciling?). Anyway, even though I have, and have run across GR stuff... my introduction to the 874 was on Tek stuff (like pulse gens, sample heads, and 7000 plugins)¡ which I was not interested in, at the time... so just made a note of that odd looking connector, on the front panel. I guess that was just the peculiarity of my situation... which led me to think it was an old Tek connector, when it was really GR! Best regards and wishes all. Roy |
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2235A Vertical Trace Issue
I'm slowly going through my 2235A scope, replacing the Schaffner line filter and the RIFA capacitors on the Pre Regulator board. The RIFA caps were visibly crazed, so I'm glad I'm replacing them before they failed like the ones in an old computer PSU I have.
Issue I'm having is the vertical traces are very dim compared to horizontal traces. Most noticeable on a square wave, but if you introduce a horizontal element, a sinewave or sawtooth pattern, the trace looks normal. I'm waiting on parts from Mouser to replace the failure prone inlet caps with new ones, so I'm unable to check voltages and ripple at the moment. Is it just an issue with the width of a vertical trace affecting the brightness on the screen, or is there maybe a deeper issue going on here? Thanks Ed Pavlovic KC9MMM |
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Will this capacitor fail?
I have a Tektronix 577 curve tracer and I am recapping the power supply board that is located at the rear of the instrument. I am looking at replacing C744 which is a 250V 1700uF capacitor. I found a 250V 1800uF capacitor but the capacitor installed is a 275V capacitor though the manual states 250V. I am curious how much voltage typically runs across C744 so I don't destroy a capacitor, thanks
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Re: General Radio 874 Connector, inner conductor "bendies"
While it probably isn't "news" IET Labs still sells GR874 connectors along
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with other GR equipment that they still manufacture. On Sat, Aug 17, 2019 at 11:28 AM Roy Morgan <k1lky68@...> wrote:
The GR 1232A Tuned Amplifier and Null Detector has an 874 connector at the |
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Re: 494 and 2756 Spectrum Analyzer questions...
I have no knowledge of the particular component, I use a chemistry hot
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plate that I have roughly calibrated for pre heating, just dandy for certain surface boards where one leg of the component is tied to a big ground plane. 125 - 175 C is the recommendation usually, your mileage and experience may be different..... On Tuesday, August 20, 2019, John Miles <john@...> wrote:
Any suggestions about the best way to open it inI usually use a Dremel tool with a cutting wheel. The filter takes a lot |
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Re: TDS754A
My 754D once had a problem with random reboots. Turned out that a couple of the conductors in the ribbon cables between the boards had burned out. It was fine after replacing the cable, maybe your 754A is constructed the same way.
Cheers, Neil ________________________________ From: [email protected] <[email protected]> on behalf of Stephen Hanselman via Groups.Io <kc4sw.io@...> Sent: August 20, 2019 8:02 AM To: [email protected] <[email protected]> Subject: Re: [TekScopes] TDS754A I would suggest you open it up remove the proc board and PS cover. Then blow out the dust. We have found any ¡°new¡± unit to our facility was fairly dirty. The split wall between the PS and HVPS is perforated but with small holes which clog easily. Regards, Stephen Hanselman Datagate Systems, LLC 3107 North Deer Run Road #24 Carson City, Nevada, 89701 (775) 882-5117 office (775) 720-6020 mobile s.hanselman@... www.datagatesystems.com<> a Service Disabled, Veteran Owned Small Business DISCLAIMER: This e-mail and any attachments are intended only for use by the addressee(s) named herein and may contain legally privileged and/or proprietary information. If you are not the intended recipient, any dissemination, distribution or copying of this e-mail and any attachments is strictly prohibited. If you have received this e-mail in error, please immediately notify me and permanently delete the original and all copies and printouts of this e-mail and any attachments. On Aug 20, 2019, at 07:37, Siggi <siggi@...> wrote: |
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Re: 494 and 2756 Spectrum Analyzer questions...
Any suggestions about the best way to open it inI usually use a Dremel tool with a cutting wheel. The filter takes a lot of vibration, unfortunately, and a respirator is needed unless you want to breathe a lot of lead particles. But it does get the job done. Some have used propane torches successfully, but transferring just the right amount of heat to melt the solder is harder than it sounds. I've done more than my share of damage with propane torches, operating under the usual rationale ("I know what I'm doing, this'll only take a few seconds.") After some time, the rear end with the integratedheat sink gets to hot toGood question, not that I know of. At least some departments at Tektronix used a straightforward watts-per-cubic-inch metric to determine whether something was going to get too hot. Fans were recommended for instruments consuming more than 50 mW/in^3, and the documentation I've seen (Common Design Parts Catalog volume 2 from 1983) indicates that the surface area of the enclosure is also supposed to be taken into consideration. So the thinking may have been that the large surface area of the 275x rack mount enclosure was enough to avoid the need for additional ventilation or a bigger fan, when in reality the instrument might have ended up hotter than the benchtop version. Much of the box is empty, so they would have needed to consider how the heat was supposed to reach the enclosure boundary in the first place. Perhaps that process needed some more work. Maybe someone on the list remembers more about how these decisions were made back in the day? -- john, KE5FX |
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Re: Need Help Troubleshooting Tektronix PS280
daven9ooq
Sent from Mail for Windows 10
Hi the schematic from the TekWiki shows reference to PS28¡ª512-1 my main board showsGPC-848A-1 B the schematic is component wise fairly accurate but all the jumpers and connections are completely different. Some versions had a separate fuse board my main board consists of the 2 variable supplys with filters bleeders rectifiers and 4relays and fuses. Nothing is blown all traces intact. Voltage readings on the main reference 7815 are pin 1-29.7vdc. 2-14.98vdc 3 40.5 vdc this is weird as pin 2 is supposed to be ground even says so on the schematic, but appears to be output pin 3 should be out , but it works! Slave side is similar like a symmetrical reverse image , and looks to be independent but in fact some adjustments do have a relationship with the other side. The last stage before the series pass transistor is labeled dynamic load control. The first 741 op amp readings are pin 1 .0043vdc, 2-14.98v 3-14.98 4 gnd 5.044 6-5.483v. 7- 29.72v 8.NC That is as far as I got so far. Many thanks Dave |
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Re: Fan direction on TEK485
On Tue, Aug 20, 2019 at 5:54 PM Jokken Feldhaar <jochen_feldhaar@...>
wrote: Hey Jochen,designThe 485 has the wonderful temp controlled Siemens motor and impeller you are absolutely right, I just went to look at my 485. My apologies for the (my) confusion. It does have the Siemens brushless motor though :). I was thinking of the 2465, which has the same motor and an impeller, but the opposite airflow direction. The 2465 most certainly draws air in through the case through strategically placed perforations in the case, which are placed over some of the hybrids, and blows it out the back Both the 485 and the 2465 are as close to silent as makes no difference though, which is a great feature in any scope. Siggi |
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Re: Fan direction on TEK485
One reason for positive pressure cooling is that it reduces dust. Air is draw in through the filter which removes the dust (one hopes) and blows it through out the chassis.
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However, positive pressure works when the chassis is designed for it, otherwise cooling may be better with a fan blowing out to exhaust warm air. Positive pressure design is not trivial; you want the greatest cooling where the greatest amount of heat is produced but don't want that air heating up the rest of the chassis. The chassis must be sealed well enough to control the air flow. Sometimes the blower must be some distance away from the hot spots. On 8/20/2019 2:54 PM, Jokken Feldhaar wrote:
fan. It draws the air in through the enclosure and expels it at the back ofThe 485 has the wonderful temp controlled Siemens motor and impeller design --
Richard Knoppow dickburk@... WB6KBL |
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Re: Fan direction on TEK485
fan. It draws the air in through the enclosure and expels it at the back ofThe 485 has the wonderful temp controlled Siemens motor and impeller design the scope. Quite the opposite: The fan will draw in air at the back of the 485, and you can feel the warm air coming out of the case to the left and right front sides of the front panel. BTDT, just last week I wanted to stop my workplace 485 humming loudly. As an extra, you might ask yourselves why the aluminum mesh filter and the foam filter is on the back side of the instrument - because the air enters exactly there. Regards, Jochen DH6FAZ |
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Re: Thoughts on TDS744A
C G
has a fairly unintuitive UIMust fully agree! If you were used in analog or mixed scopes, you might quickly be upset by tons of menussss and their unlogical contents allocation. Own three TDS¡¯s and will sell them out as soon as they¡¯re fully restored. Le 20 ao?t 2019 ¨¤ 12:39, Siggi <siggi@...> a ¨¦crit : |
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Re: Why U800 is such a big problem in Tek Scopes
Whoops forgot. Walter Shawlee used to batch up failed U800 chips and send them away for repair. I don¡¯t know if he still does it. Our friend in Greece sometimes has the IC for sale on his ebay. Other sellers sometimes have the chips but usually very costly. Replacement on the 3 layer board is not difficult.
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Re: Why U800 is such a big problem in Tek Scopes
Very good points Dennis. I would like to add a couple of thoughts. First, I agree that this is an overheating problem. I do not have experience with all 24xx models, but I have repaired a few 2465B models with this problem. The symptom is that after a period of time after turn on, the horizontal trace on the scope disappeared. This can occur instantly or slowly. I have seen it happen in from 3 seconds to 1 hour after turn on. So just turning a prospective purchase on is not sufficient, it should be on for as long as possible to confirm it is ok before purchase.
Turning the scope off for a few hours restores it to normal operation until the U800 IC heats up again. You can confirm that this is the problem by spraying the IC with cooling spray once it has failed. Sweep returning is a clincher. I have used a cpu cooling fan on top of the IC to keep it from overheating. This works for some bad IC¡¯s and could prevent a good one from going bad. I powered the fan from the 15 volt supply through a small resistor. One downside is that the main fan is temperature controlled, I assume to keep the scope from drifting. However I have not seen a change with the new fan in timing, but I would check carefully if that matters. |
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Re: Thoughts on TDS744A
On Tue, Aug 20, 2019 at 11:39 AM Jay Walling via Groups.Io <jayw_comark=
[email protected]> wrote: There's quite a bit of confusion around about the capacitor problems onHey Jay, Interesting - I hadn't heard this before. A quick image search on the Googles doesn't contradict this at all - the few 700A acquisition board images I could find have no telltale electrolytics in evidence. The CPU and front panel PCBs were however common across the TDS5/6/7 series as I understand, and those would be subject to leakage? Siggi |
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494 and 2756 Spectrum Analyzer questions...
1st question.
I have brought a 494 analyzer back to life. Except for the Xtal filter box on top of the CRT, the instrument performs OK. The filter box does not show any temperaturerise when in operation with cover off. Looking in KE5FX service notes, the box must be opened in order to replace the transistor. Any suggestions about the best way to open it in a non-destructive way? Put it on a hot boiler plate and remove the cover when the tin melts or use brute force making the cover unuseable? 2nd question. I have also repaired a 2756P with various problems and the instrument does now work. I am just a bit puzzled by the fact that there is only a very small vent intake on the left side of the cabinet. After some time, the rear end with the integratedheat sink gets to hot to touch. The Bueler fan runs at highest speed. Other 49x analyzers that I have used over the years does not even get close to this high temperature. Easy fix would be to add extra vent intake(s). Did Tek ever made any modifications to the cabinet? Cheers Ulf KylenfallSM6GXV |
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Why U800 is such a big problem in Tek Scopes
I don't pay much attention to the portable scopes that are a very big
portion of TekScopes posts. I have no idea which portables use it but I can pass along a tip that will improve your chances of never needing a replacement for U800 to get your scope to work. The IC itself was originally made by Tek and they would have insured replacements would be available for a reasonable amount of time after the scopes that used them were discontinued. But Tek decided to get out of the IC business and sold their processes and responsibility for providing spare U800s to Maxim. Maxim did the math and quickly decided it wouldn't be profitable to make U800s and that was that. U800 fails because it overheats. The fans in Tek's products have been a source of noise complaints since I can remember. Apparently someone at Tek finally did something about it. The fan in the U800 portable scopes is extremely quiet. It is so quiet most people don't know there is one in the scope. One result is that it never gets cleaned. Eventually Dust and dirt will accumulate on it and some of that will get into the bearings. When that happens the fan comes to a stop. At that point U800 loses its cooling and overheats. Eventually U800 will fail because the fan stopped working. Moral of the story: If you spot a laptop scope for sale at a swap meet ask to plug it in to check it. If the fan isn't working U800 probably failed already. If it still works it may soon fail. Don't buy a portable that has U800s in it if the fan doesn't work. Dennis Tillman W7PF |
Ancel
John Williams
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