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
with other GR equipment that they still manufacture.
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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
input. It receives audio signals from diode mixer/detectors used in RF
measurement systems that mostly had 874 connectors.
Roy sends.
On Aug 17, 2019, at 11:56 AM, Dale H. Cook < bridgewaterma@...> wrote:
On 8/17/2019 11:40 AM, Roy Thistle wrote:
I don't recall seeing any of them using the 874... probably because
they are AF, or RF units?
874 connectors were pretty much universally used on GR RF instruments
manufactured after 1948.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
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Re: 494 and 2756 Spectrum Analyzer questions...
I have no knowledge of the particular component, I use a chemistry hot
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.....
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On Tuesday, August 20, 2019, John Miles <john@...> wrote: 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? I 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 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? Good 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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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:
Hey Dana,
IIRC the standby power supply that allows soft-power on is also responsible
for powering the main switcher. Maybe the standby supply needs recapping.
The TDS5/6/7As are also well documented to suffer from capacitor plaque.
There are SMD electrolytic capacitors all over the acquisition, CPU and
front panel boards. If yours hasn't been re-capped, then that's also a
possible explanation for what you're seeing.
Siggi
On Tue, Aug 20, 2019 at 10:25 AM danadak <danaaknight@...> wrote:
This scope has been excellent to date. Now when turned on it
power cycles. It will start up, most of the time complete the POST,
then power itself off after a minute or two.
Before I spend the next century trying to find the problem anyone
have a similar experience ?
Regards, Dana.
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Re: 494 and 2756 Spectrum Analyzer questions...
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? I 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 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? Good 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
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: The 485 has the wonderful temp controlled Siemens motor and impeller
design
fan. It draws the air in through the enclosure and expels it at the back of
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.
Hey Jochen, 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.
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.
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On 8/20/2019 2:54 PM, Jokken Feldhaar wrote: The 485 has the wonderful temp controlled Siemens motor and impeller design
fan. It draws the air in through the enclosure and expels it at the back of
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
--
Richard Knoppow
dickburk@...
WB6KBL
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Re: Fan direction on TEK485
The 485 has the wonderful temp controlled Siemens motor and impeller design
fan. It draws the air in through the enclosure and expels it at the back of 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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has a fairly unintuitive UI Must 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 :
has a fairly unintuitive UI
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Re: Why U800 is such a big problem in Tek Scopes
Here's my project link regarding the 2465 series and U800 cooling mods are included.
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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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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 on
the TDS500, TDS600, and TDS700 series of scopes.
The scopes that had all those leaky caps on the acquisition board are:
TDS500 (non suffixed) and TDS500A. The TDS500B scopes did not have this
problem as they went to all ceramic and Tantalum types. TDS6XX (non
suffixed) and TDS6XXA.
None of the TDS700 scopes had the problem. They also used ceramic and
Tantalum types on the acquisition board, except the TDS784D, TDS794D and
TDS754D with serial prefix B04XXXX and up. I've never seen those leak,
though.
Hey 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
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Re: Fan direction on TEK485
The 7854 (and maybe other 7000 series scopes) draws air in through strategically placed perforations in the covers (top and sides but mostly bottom) and blows it all out the back. There are no filters. The fan is a propeller type. Regards, Cliff Carrie ________________________________ From: [email protected] < [email protected]> on behalf of greenboxmaven via Groups.Io <ka2ivy@...> Sent: Monday, August 19, 2019 8:58 PM To: [email protected] < [email protected]> Subject: Re: [TekScopes] Fan direction on TEK485 All I have ever seen draw in at the back. The air passes through the filter first before being delivered to the interior of the cabinet. Here is a bit of fan/blower trivia: A propellor fan needs maximum power when the air flow is impeded or blocked, a centrifugal requires minimum power when the air flow is blocked. The motors on propellor fans are usually cooled by the air flowing over them. A clogged filter not only overloads the motor, it deprives the overworked motor of cooling. Keep the filters clean and free flowing. Don't ignore the filter if it is missing, high voltage attracts dust from unfiltered cooling air, which can cause a flashover. Bruce Gentry, KA2IVY On 8/19/19 8:28 PM, Kevin Oconnor wrote: Did the TEK factory have the fan suck air in or blow it out the back?
kevin
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Re: TOPIC CHANGE: Pro's and Con's of the 576 and 577 Curve Tracers. WAS: 5xx 'Scopes
On Tue, Aug 20, 2019 at 06:53 PM, Dennis Tillman W7PF wrote:
I forget what I wrote just a day earlier.
Dennis
Keep spreading your knowledge, Dennis and don't police yourself! Raymond
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Re: 2467B focus/astigmatism anomaly...
On Tue, Aug 20, 2019 at 05:14 PM, Chuck Harris wrote:
I tested the cap's leakage at 1KV, and it was 0.3uA.
1uA is 1V on 1M. And here we have impedances around 10M.
It is concerning, especially since the cap has 1.4kV
across it.
Good news! Raymond
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Re: TOPIC CHANGE: Pro's and Con's of the 576 and 577 Curve Tracers. WAS: 5xx 'Scopes
Mea Culpa! It appears I was the culprit. Life is flying by too fast. I forget what I wrote just a day earlier.
Dennis
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of Raymond Domp Frank Sent: Tuesday, August 20, 2019 3:05 AM To: [email protected]Subject: Re: [TekScopes] TOPIC CHANGE: Pro's and Con's of the 576 and 577 Curve Tracers. WAS: 5xx 'Scopes Hi Dennis, On Tue, Aug 20, 2019 at 09:41 AM, Dennis Tillman W7PF wrote:
Hi Dave,
What does a 7704A with a P7001 have to do with curve tracers???
The reason I changed the topic was to separate the discussion about
500 series scopes from the discussion going on about transistor curve
tracers with the same subject.
Dennis Tillman W7PF
You're right, we strayed. This is how we got here: While discussing the modular construction of the 577 curve tracer and the possibility of changing a 577D2 into a 577D1, this happened: Hi Dave,
Tek sometimes uses this modularity in very interesting ways. I think the 7704 was the first scope they designed to be modular from the start.
The top section is completely removable and held to the bottom section
with only a few screws. This was done so Tek could insert the
interface section of the DPO (Digital Processing Oscilloscope) in between the top and bottom of the 7704. The DPO used a DEC PDP-8 minicomputer to capture data from the 7704 lower section plugins and display the results on the 7704 upper display section.
Tek listed the DPO in its catalogs from 1974 to 1981. In 1981 Tek
introduced the 7854 which does all of this in a normal size 4-wide mainframe using a microcomputer instead of the PDP-8 minicomputer.
Dennis Tillman W7PF Very relevant historically, interesting and significant but you're right, not ideal for posterity unless searching for content, not topic. Raymond -- Dennis Tillman W7PF TekScopes Moderator
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Ancel
John Williams
Raymond Domp Frank