At 5:49 AM +0200 7/18/12, Stefan Trethan wrote:

It may be different with ceramics, there are some dielectric materials
that have rotten voltage coefficient and the capacity will be way low
much below rated voltage.

Other way'round. Capacitance might drop to 1/3 at rated voltage, but will be okay at, say, 20% WV.

After I changed the first bad tantalum last week, I left the PG506
running for a couple days while I watched it. Last night I was
contemplating how to modify the trigger out signal so that it occurs
75 ns before the fast rise or high amplitude signals. That would
allow it to be used in place of a Tektronix 284 pulse generator and
make it much easier to calibrate my 7S11/7T11 sampling system. The
PG506 was sitting on my desk and just after I hooked up my 2232 to
make some measurements, the fast rise output failed because the other
tantalum capacitor shorted.

The only visible evidence was a hairline crack in the epoxy which I
could not see until I removed it from the fast rise PC board. I was
disappointed that embryonic alien beings or superpower granting toxic
fumes did not erupt from the shorted tantalum.

--- In TekScopes@..., tubesnthings@... wrote:

549s aren't all that wonderful to use - kinda like a 545A, but with 6cm
vertical deflection.
The trace is much more coarse. Like the 564B, the 549 has a "programmable"
storage display feature allowing a stored trace to be displayed for a time
before arming the trigger circuit for new trace acquisition. Top and bottom
storage areas can be so alternated, giving the impression that the 549
really does get up and dance for you. Unusual level of autonomous behavior for
the time!

As stated on tekwiki, the 549 is probably most useful with a 1L5 lf
spectrum analyzer.
Or, perhaps a transducer setup with a type Q...

Bernd

Adding to Bernd,s comment, 549 used a different phosphor in the stoarge target than the 564. It has a faster writing rate, but was very easy to burn and has a shorter working life. Tek abandonded the use of this phosphor after the 549 and developed other techniques to improve writing rate, while maintaining more robustness than the 549 system had.

- Steve

One advantage of a SMPS over a linear PS is that the secondary caps get charged current driven rather than voltage driven. So with larger caps you won't have the situation that charging is done with larger current and smaller duty cycle; ripple current nearly doesn't change. Start-up is another story of course.
Some polarized caps are timing caps. For instance the cap at pin 1 of the SMPS control IC is a timing cap with different values among 'scopes/versions for whatever reason. I would be reluctant to change the value.
Albert

as long as we are sticking to the same type of capacitor (eg, tantalum, ceramic, mica, mylar, electrolytic...) size usually the only thing that increases as you increase its rated voltage. A physically larger capacitor might also have less ESR (equivalent series resistance) and larger and fatter leads will also have less resistance.

the only thing you should worry about is you are for example, replacing a tantalum capacitor with a mylar capacitor, as the ESR and ESL (equivalent series inductance) will vary with the materials used in the capacitor. electrolytics for example, have a higher ESR and leakage current compared to other types.

as far replacing what was a 10uf cap with a 22uf cap, it might be fine, but then you might potentially run into trouble. If all that was done on the later model was change that particular cap from 10uF to 22uf, then you're probably ok. but if they also changed that particular circuit that the cap was in, then the upgraded circuit probably required the extra capacitance, where as the older circuit with the 10uF cap could have been different. If that 10uf cap was electrolytic, you will probably be more likely to be ok, since electrolytics are usually only used to filter out AC and prevent sags or transients for a DC line.


I still have a lot to learn in this area, so if I am mistaken anywhere, hopefully no one will hesitate to correct me. :)

-Robby

...while you were watching? I want the incantation you must have
pronounced over it. :-)

Congrats - nice job!
-ls-



David <davidwhess@...> wrote:

Higher voltage is generally OK (even better) with electrolytics.

It may be different with ceramics, there are some dielectric materials
that have rotten voltage coefficient and the capacity will be way low
much below rated voltage.

Higher capacity depends on the circuit, if a later model uses more it
is most probably OK. There is a high tolerance on electrolytic caps
and circuits should not be too sensitive to the exact value anyway.

ST



On Wed, Jul 18, 2012 at 5:44 AM, doswoodman@...
<rgwood@...> wrote:

As I have shared before my electronics experience is some 20 years ago in the Navy and then some time working on consumer electronics in the later 80's. All the gear I worked on was not certifiable the way O'Scopes are.

Anyway, to the question. Are there any limits (beyond the obvious physical size, and economical limitations) when dealing with capacitors and suitable substitution? For example replacing a 10uf 25V capacitor with a 10uf 50V of suitable tolerance. Is size/money constraints the only thing keeping one from subbing a 10uf at 100V or 200V, or 1000MV <---got'a love taking things to the limit as that cap would likely be a large as a house as a guess ? --->

Along the same lines. If one is replacing a capacitor in a scope and scopes with later serial numbers show that the value has moved. i.e. a 10uf cap in the board but manual shows the value was upgraded to 22uf at some serial number after the one you have. Is the best sub another 10uf or a 22uf of suitable voltage in this situation?

Seams like this last part was touched on relatively recently. However, I could not find it with my search skills. Unfortunately my memory is not up to the task either.

I hope this is not to far off topic. Thank you as always for the bandwidth and replies.
Rob



------------------------------------

Yahoo! Groups Links

As I have shared before my electronics experience is some 20 years ago in the Navy and then some time working on consumer electronics in the later 80's. All the gear I worked on was not certifiable the way O'Scopes are.

Anyway, to the question. Are there any limits (beyond the obvious physical size, and economical limitations) when dealing with capacitors and suitable substitution? For example replacing a 10uf 25V capacitor with a 10uf 50V of suitable tolerance. Is size/money constraints the only thing keeping one from subbing a 10uf at 100V or 200V, or 1000MV <---got'a love taking things to the limit as that cap would likely be a large as a house as a guess ? --->

Along the same lines. If one is replacing a capacitor in a scope and scopes with later serial numbers show that the value has moved. i.e. a 10uf cap in the board but manual shows the value was upgraded to 22uf at some serial number after the one you have. Is the best sub another 10uf or a 22uf of suitable voltage in this situation?

Seams like this last part was touched on relatively recently. However, I could not find it with my search skills. Unfortunately my memory is not up to the task either.

I hope this is not to far off topic. Thank you as always for the bandwidth and replies.
Rob

C1062 on the +16.5 volt supply was the first shorted tantalum. C1067
on the -16.5 volt supply which I was thinking of replacing shorted
today while I was watching.

On Tue, 17 Jul 2012 03:43:22 -0000, "Patrick Wong" <patwong3@...>
wrote:

Hi David,

Congratulations on restoring proper operation to your unit.

Since a spec is the high amplitude output is adjustable up to > 5V into 50 ohms, I suppose that is the reason that the adjustment procedure has you setting the max output at 5.2V, giving you 4% over-range.

If you are asking what is the utility of the high amplitude output, there are at least a couple of uses in the analog 24xx scope calibration procedure:

1. CAL 06 - Vertical Transient Response, where the high amplitude output powers a tunnel diode pulser. A maximum voltage setting is required from the high amplitude output here.

2. Adjustment of CH1 and CH2 input capacitance, although in this case it looks like only 300 - 600 mV signal is required.

Patrick Wong AK6C

--- In TekScopes@..., David <davidwhess@...> wrote:

...My question concerns the high amplitude output calibration. Why is it
even adjustable via R790? The output level has no important
application that I can see so why bother adjusting it to 5.2 volts
into a 50 ohm load?

开云体育

549s aren't all that wonderful to use - kinda like a 545A, but with 6cm vertical deflection.

The trace is much more coarse. Like the 564B, the 549 has a "programmable" storage display feature allowing a stored trace to be displayed for a time before arming the trigger circuit for new trace acquisition. Top and bottom storage areas can be so alternated, giving the impression that the 549 really does get up and dance for you. Unusual level of autonomous behavior for the time!

?

As stated on tekwiki, the 549 is probably most useful with a 1L5 lf spectrum analyzer.

Or, perhaps a transducer setup with a type Q...

?

Bernd

?

In a message dated 7/17/2012 2:55:37 P.M. Pacific Daylight Time, childwhereugo@... writes:

A while ago I traced high-TC drift in a Fluke 540B Thermal Transfer Standard to an electrolytic cap wired from signal to ground. The electrolyte and electrodes had begun to act like a battery.

HTH,
Dave Wise

________________________________________
From: TekScopes@... [TekScopes@...] On Behalf Of David [davidwhess@...]
Sent: Friday, July 06, 2012 6:07 PM
To: TekScopes@...
Subject: Re: [TekScopes] Re: OT: J511 current regulator diode (FET) temperature coefficient

I guess board contamination is unlikely then since you thoroughly
cleaned it.

I combined the split page schematic in the publicly available service
manual:



I went back through the discussion threads about your 7081 problem. It
looks like you have ruled out board contamination, a bad OP16, and a
bad offset null potentiometer.

I would try disabling the offset null trimming circuit by either
removing the potentiometer or lifting one leg of R715 and R714. Then
measure the output drift and noise. Is the offset null jumper in the
correct position?

I would also look at the output with a sensitive oscilloscope. A 7000
series with a 7A22 would be ideal but a AM502 with any oscilloscope
would work also. Maybe the noise is line synchronous or more than
just random. If it was popcorn noise from a bad transistor or other
source that would be easy to see.

On Fri, 6 Jul 2012 09:23:03 +0100, "David C. Partridge"
<david.partridge@...> wrote:

You might have missed my much earlier recommendation posted to the
volt nuts list to clean the board around IC705

The whole board has been through the dishwasher at 70C (no detergent, no rinse aid)
and then sat in an airing cupboard for a month).

Dave
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of David
Sent: 05 July 2012 22:14
To: TekScopes@...
Subject: Re: [TekScopes] Re: OT: J511 current regulator diode (FET) temperature coefficient

I am appending my response from the other list at the end of this post.

I think C704 is just to help with transient response. Most of the frequency compensation will be from C714. I would check that capacitor to see if it dried out.

It might also be worth looking at the TP705 output with an oscilloscope and checking the transient response which will give an indication of how stable the amplifier is. A low frequency square wave would make a good test source.

You might have missed my much earlier recommendation posted to the volt nuts list to clean the board around IC705 and the circuits at the non-inverting input with an aqueous solution to remove ionic contamination. The schematic shows that they went to considerable effort to shield them from leakage. Board contamination of electrometer circuits can cause something that looks like a combination of noise and drift when the changes in humidity cause changes in leakage.

You can test for this by using a soda straw to blow on selected areas of the board. The moisture in your breath will cause noise and drift if the board is contaminated. Clean boards will be much more stable.

On Thu, 5 Jul 2012 21:40:20 +0100, "David C. Partridge"
<david.partridge@...> wrote:

No, I didn't see it as for some reason I often seem to miss messages from that list.

Yes I had noticed that the output and hence the feedback comes from the "top" of R718.

I think there is a danger of low frequency oscillation which I think C704 is supposed to control.

So if you believe that the drift should be irrelevant, what might the fault be?

Thanks

Dave
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On
Behalf Of David
Sent: 05 July 2012 19:06
To: TekScopes@...
Subject: Re: [TekScopes] Re: OT: J511 current regulator diode (FET)
temperature coefficient

Dave, did you see my reply over on volt-nuts@... ?

It looks to me like D717 serves to bias the output of the cascode where its effect will be inside of the negative feedback loop. Its drift should be irrelevant if the circuit is working correctly.

I suspect they reason the designer did it that way is so that the operating current of the cascode would not change and because of the low compliance available. I expect the circuit is prone to oscillate because of the voltage gain inside of the feedback loop so the frequency and phase response had to be very carefully controlled.

I would have included a resistor between the emitters of TR702 and
TR703 to better control the gain although with the output shunted by at most 5KOhms, maybe that is not necessary.

On Thu, 05 Jul 2012 07:04:36 -0500, David <davidwhess@...>
wrote:

I doubt the temperature coefficient of D717 matters in this circuit.

Feedback is taken off of the output through TR705 or TR706 (x10 mode)
back to the inverting input of IC705. The current source was used to
prevent any significant shift in the operating point of TR703 for
frequency compensation reasons because the switched cascode has voltage
gain which is inside of the operation amplifier feedback loop.

The drift in the cascode bias from D716 is irrelevant for the same
reason.

Having voltage gain inside of the feedback does suggest another failure
mode that could cause drift or noise in the output. Could
IC705 or TR703 be oscillating? Maybe C714 dried out and has low
capacitance.

------------------------------------

Yahoo! Groups Links

------------------------------------

Yahoo! Groups Links

It is. I just confirmed on the physical box itself.
-ls-




"Albert" <aodiversen@...> wrote:

just outta curiosity, how good are those scopes?

how does the 549 compare to the 564 storage scope? I see from tekwiki that it has a greater BW. and is the 543 similar to the the 545 or 547?

-Robby

No, it doesn't look right. I have the same scope (also NOS, maybe
from the same MOD source ?) and mine looks like the first image.

IIRC, the character generator has 2 sets of adjustments, some on
the board itself (position, hight , width etc) and more adjustments
on the V-output amp where the vector is summed (and possibly on
H-output as well). I bet the lead routes make a difference too . I
also have a 7603 with a similar looking defect (it resisted my
attempts to adjust it / fix it - but it's a spare so I didn't look too hard)

You will need the serial numbers as there are serveral different versions ...

dc

17/07/2012 21:54

Thanks David, mine came from a charming lady re seller in Somerset,
one of a pair she was selling. I'm going to get David Partridge to
cast his expert eye over it shortly, it's a shame not to set it to
rights, being such an otherwise mint example. It's perfectly usable as
is, but things like that frankly bug the hell out of me ;)

--
Best Regards,
Chris Wilson.

On 17/07/2012 19:56, ROLYNN PRECHTL K7DFW wrote:

Note: There is no difference among the sockets 499-P44-10 (REV.B), 499-P44-20 (REV.A) and
499-P44-00, it is the same socket which marked "499-044-00".

Thanks, missed that.

Gordon

Hi John,
At Kurt's Tekwiki you will find a 10 MB text-searchable pdf:

You can even search for U722 in the pictures!
Albert

What made you choose REV-B? REV-A is the most recent (2/10/06) according to the drawings. REV-B has
4/11/01 as the drawn date.

----------------------------------------------------------


From the web site.

Note: There is no difference among the sockets 499-P44-10 (REV.B), 499-P44-20 (REV.A) and
499-P44-00, it is the same socket which marked "499-044-00".

Hi John,
I'm not at home where I have a paper manual, but I could download the BAMA manual here. It looks like we are talking about different things. At page 102, figure 8-11, all 3 ICs are shown, U722, U842 and U416. The A1 board layout is shown 3 times in the pdf and all 3 occurences show those 3 ICs. I didn't check traces, so I don't know whether the FP control is really connected to the IC which is labeled U722 at the board.
Albert

I made my own out of copper tape and a proto-board. The commercial socket does look just a tad more professional.

Thank you.

Mine are all above S/N B069999, so I guess I don't get to play !!

73, Dick, W1KSZ