Re: Resurrecting a 475 - Request for Guidance
On Wed, 15 Aug 2018 15:25:30 -0700, you wrote: It turns out that C965 (Board A9), a tantalum bypass capacitor on the +15 rail had gone bad; removing brought the +15 rail resistance to ground back to where it should be. Most of the capacitors look to be in pretty good condition; I have not come across any bulges, deformities, leaked electrolyte or burn marks on any of them, even the larger axial lead supply capacitors.
I powered it on, and checked the supply voltages at the test points; all were within specification, although I haven't checked the ripple on each yet. I haven't checked any of the high voltage test points yet, as I'm currently lacking the equipment to do so safely.
A couple minutes into testing the powered on scope (I couldn't find the test point for +105/160), some other component let go, with a loud pop, accompanied by a whistling sound and small quantity of smoke. So, the hunt is on for the culprit. I have removed boards A3, A7 and A8 so far, and have found no obviously failed components on any of them. I thought at first that something on A7 (timing board) failed, given the location where the smoke seemed to come from, but that doesn't seem to be the case. Is there any component in the recess along with the CRT known to fail in such a way? Look for the capacitors across the AC line in the power filter. They can fail, especially if you're in an environment that uses a 220 volt (nominal) line voltage. The value of nominal has been increasing over the years, and will bite you. Harvey
Interestingly, after the component failure, all the supply voltages were still within specification.
Regarding the removal of the two attenuator boards/assemblies, is the best way to get at the nuts holding them to the front panel with a small spanner? I'm having a little difficulty getting them free.
Thanks,
John
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Re: Resurrecting a 475 - Request for Guidance
Look for a tantalum with a small hole in it.
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----- Original Message ----- From: "JR" <jswrussell@...> To: < [email protected]> Sent: Wednesday, August 15, 2018 6:25 PM Subject: Re: [TekScopes] Resurrecting a 475 - Request for Guidance It turns out that C965 (Board A9), a tantalum bypass capacitor on the +15 rail had gone bad; removing brought the +15 rail resistance to ground back to where it should be. Most of the capacitors look to be in pretty good condition; I have not come across any bulges, deformities, leaked electrolyte or burn marks on any of them, even the larger axial lead supply capacitors. I powered it on, and checked the supply voltages at the test points; all were within specification, although I haven't checked the ripple on each yet. I haven't checked any of the high voltage test points yet, as I'm currently lacking the equipment to do so safely. A couple minutes into testing the powered on scope (I couldn't find the test point for +105/160), some other component let go, with a loud pop, accompanied by a whistling sound and small quantity of smoke. So, the hunt is on for the culprit. I have removed boards A3, A7 and A8 so far, and have found no obviously failed components on any of them. I thought at first that something on A7 (timing board) failed, given the location where the smoke seemed to come from, but that doesn't seem to be the case. Is there any component in the recess along with the CRT known to fail in such a way? Interestingly, after the component failure, all the supply voltages were still within specification. Regarding the removal of the two attenuator boards/assemblies, is the best way to get at the nuts holding them to the front panel with a small spanner? I'm having a little difficulty getting them free. Thanks, John
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Re: Resurrecting a 475 - Request for Guidance
It turns out that C965 (Board A9), a tantalum bypass capacitor on the +15 rail had gone bad; removing brought the +15 rail resistance to ground back to where it should be. Most of the capacitors look to be in pretty good condition; I have not come across any bulges, deformities, leaked electrolyte or burn marks on any of them, even the larger axial lead supply capacitors.
I powered it on, and checked the supply voltages at the test points; all were within specification, although I haven't checked the ripple on each yet. I haven't checked any of the high voltage test points yet, as I'm currently lacking the equipment to do so safely.
A couple minutes into testing the powered on scope (I couldn't find the test point for +105/160), some other component let go, with a loud pop, accompanied by a whistling sound and small quantity of smoke. So, the hunt is on for the culprit. I have removed boards A3, A7 and A8 so far, and have found no obviously failed components on any of them. I thought at first that something on A7 (timing board) failed, given the location where the smoke seemed to come from, but that doesn't seem to be the case. Is there any component in the recess along with the CRT known to fail in such a way?
Interestingly, after the component failure, all the supply voltages were still within specification.
Regarding the removal of the two attenuator boards/assemblies, is the best way to get at the nuts holding them to the front panel with a small spanner? I'm having a little difficulty getting them free.
Thanks,
John
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A hot chassis can also be caused by RF filter capacitors connected from each side of the line to the chassis. I would be much more suspicious of these if they exist in the 453 than of the electrostatic shield in the power transformer. There are no such capacitors in the 453. Hence my comment regarding the primary capacitive coupling to the shield. I - er - looked at the schematic before I commented :-) Craig
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Re: 2465B Replace Aluminum Electrolytics with Tantalum
Tantalums are really good when used properly.
1) ESR / ripple current rating MUST not be exceeded, creates internal self
heating that will lead to internal shorts.
2) Use them for high frequency, low voltage switching regulators.
3) De-rate working voltage by 50% as a minimum.
4( Not much available at 35VDC and up
MLCCs are a very reliable alternative to small tantalums
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On Mon, Aug 13, 2018 at 4:38 AM, Mark Wendt <wendt.mark@...> wrote: LOL! LGBTQRC? ;-)
Mark
On 08/13/2018 04:44 AM, Adrian wrote:
Oh but they are!
I've met several who were so conflicted that they thought they were
resistors.
Adrian
On 8/12/2018 11:17 PM, Mark Wendt wrote:
Huh. Who knew tantalums could be emotionally conflicted.
Mark
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As pointed out by others, there are times and places when (at least you think) you need to make a floating measurement (independent of the local ground.)
I¡¯ve done this with mapping sonars that are powered and telemeter commands and data over a 10km coax. The instrument ground and the ¡°topside¡± ground are different. Bench testing has to be done carefully. When we connect between to two (on the bench) e.g. to trigger the scope, we transformer isolate the trigger signal¡..
The can be VERY dangerous - as someone said ¡°you can get seriously killed¡± or perhaps even worse, you can kill someone else.
That said, it can be done safely with care and attention to detail and staying focused (among other things.) A safety observer is an excellent idea - they don¡¯t get wrapped up in the technical problem.
A battery powered scope is a good approach but most of us don¡¯t have them and (often, sometimes, ?) their measurement capabilities aren¡¯t satisfactory.
Clipping the ground inside the instrument (scope or any other) is an excellent way to set someone else up for injury or death in the future.
Just say NO.
A better way is to use (in the US) a ¡°two prong to three prong¡± adapter or a ¡°cheater plug¡± e.g. and external to the instrument device.
You have to set it up, and it¡¯s quite visible - no surprises. Make the measurement(s) and take it out.
-Dale
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On Aug 15, 2018, at 04:52 , Craig Sawyers <c.sawyers@...> wrote:
That would be typical if the chassis is ungrounded. Capacitance between the primary and shield (which
is connected to the chassis) in the mains transformer will cause this. First thing to do is connect
the ground in the mains plug - the previous user did a dangerous thing by disconnecting the ground.
There may be other problems to solve, of course - but make the scope safe first.
Craig
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of f4gny@...
Sent: 15 August 2018 06:02
To: [email protected]
Subject: [TekScopes] 453 trouble
Hello Folks,
Ive trouble on my 453, I discover that AC voltage is running on chassis +/- 75V .........
I opened the main plug and the ground pin was unconnected.
Does anyone experienced the same trouble ? is it normal when ungrounded or internal PSU show a
defective componement ? Thank for your help.
Regards
Alain
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Agree with Jeff for 422 AC, just look around hardware and you might find one to fit without trimming. I trimmed a couple extension cords for mine.
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A hot chassis can also be caused by RF filter capacitors connected from each side of the line to the chassis. I would be much more suspicious of these if they exist in the 453 than of the electrostatic shield in the power transformer. If there are such caps in the 453 lift them to see if the voltage on the chassis disappears. You might want to replace them. There are special capacitors for this service which fail open so they don't connect the line directly to the chassis.
The voltage on the chassis will depend on the amount of capacitance and the impedance of the measuring device.
You can always generate a long argument by discussing the differences between lightening protection grounds, power line safety grounds and grounds to eliminate common impedances in AF and RF circuits.
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On 8/15/2018 1:52 AM, Craig Sawyers wrote: That would be typical if the chassis is ungrounded. Capacitance between the primary and shield (which
is connected to the chassis) in the mains transformer will cause this. First thing to do is connect
the ground in the mains plug - the previous user did a dangerous thing by disconnecting the ground.
There may be other problems to solve, of course - but make the scope safe first.
Craig
--
Richard Knoppow
dickburk@...
WB6KBL
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Hi all,
I acquired a 453 in the spring, which had the ground lug sawed off!? This must surely be a "thing"... I replaced the cord.
Phil
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On 8/14/2018 10:01 PM, f4gny@... wrote: Hello Folks,
Ive trouble on my 453, I discover that AC voltage is running on chassis +/- 75V .........
I opened the main plug and the ground pin was unconnected.
|
One time I picked up a pallet of 465s from an industrial repair service.
All of them had the ground pin cut off.
Paul
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On Wed, Aug 15, 2018 at 01:24:13PM +0100, Craig Sawyers wrote: The way to get around it is to minimise the loop area - plug the two pieces of equipment into the same
power strip right next to each other, and cable tie the mains cables together. Minimum loop area gives
minimum hum.
The brutal and unsafe way is to disconnect the ground of everything except one instrument. Which is
surprisingly common. Alas.
Craig
--
Paul Amaranth, GCIH | Rochester MI, USA
Aurora Group, Inc. | Security, Systems & Software
paul@... | Unix & Windows
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Just done, yes its strange ?
Does something can explain such this action ?
Thank
Regards
Alain To get rid of interference loops. If two or more grounded instruments are connected together via a signal cable, the resulting loop picks up mains frequency interference (or double frequency - 100Hz or 120Hz depending on where the use lives). This is something that plagues audio - a so-called hum loop. The way to get around it is to minimise the loop area - plug the two pieces of equipment into the same power strip right next to each other, and cable tie the mains cables together. Minimum loop area gives minimum hum. The brutal and unsafe way is to disconnect the ground of everything except one instrument. Which is surprisingly common. Alas. Craig
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On Wed, Aug 15, 2018 at 03:04 AM, F4GNY wrote:
Hello Graig,
Just done, yes its strange ??
Does something can explain such this action ?
Thank
Regards
Alain
Le 15.08.2018 ¨¤ 10:52, Craig Sawyers a ¨¦crit?:
That would be typical if the chassis is ungrounded. Capacitance between the primary and shield (which
is connected to the chassis) in the mains transformer will cause this. First thing to do is connect
the ground in the mains plug - the previous user did a dangerous thing by disconnecting the ground.
There may be other problems to solve, of course - but make the scope safe
first.
Craig
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
f4gny@...
Sent: 15 August 2018 06:02
To: [email protected]
Subject: [TekScopes] 453 trouble
Hello Folks,
Ive trouble on my 453, I discover that AC voltage is running on chassis +/-
75V .........
I opened the main plug and the ground pin was unconnected.
Does anyone experienced the same trouble ? is it normal when ungrounded or
internal PSU show a
defective componement ? Thank for your help.
Regards
Alain
Must be coincidence, but this is the third 453 (including mine) I have read about here lately that the previous owner had floated.
|
Hello Graig,
Just done, yes its strange ??
Does something can explain such this action ?
Thank
Regards
Alain
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Le 15.08.2018 ¨¤ 10:52, Craig Sawyers a ¨¦crit?: That would be typical if the chassis is ungrounded. Capacitance between the primary and shield (which
is connected to the chassis) in the mains transformer will cause this. First thing to do is connect
the ground in the mains plug - the previous user did a dangerous thing by disconnecting the ground.
There may be other problems to solve, of course - but make the scope safe first.
Craig
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of f4gny@...
Sent: 15 August 2018 06:02
To: [email protected]
Subject: [TekScopes] 453 trouble
Hello Folks,
Ive trouble on my 453, I discover that AC voltage is running on chassis +/- 75V .........
I opened the main plug and the ground pin was unconnected.
Does anyone experienced the same trouble ? is it normal when ungrounded or internal PSU show a
defective componement ? Thank for your help.
Regards
Alain
|
That would be typical if the chassis is ungrounded. Capacitance between the primary and shield (which
is connected to the chassis) in the mains transformer will cause this. First thing to do is connect
the ground in the mains plug - the previous user did a dangerous thing by disconnecting the ground.
There may be other problems to solve, of course - but make the scope safe first.
Craig
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-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of f4gny@...
Sent: 15 August 2018 06:02
To: [email protected]
Subject: [TekScopes] 453 trouble
Hello Folks,
Ive trouble on my 453, I discover that AC voltage is running on chassis +/- 75V .........
I opened the main plug and the ground pin was unconnected.
Does anyone experienced the same trouble ? is it normal when ungrounded or internal PSU show a
defective componement ? Thank for your help.
Regards
Alain
|
Hello Folks,
Ive trouble on my 453, I discover that AC voltage is running on chassis +/- 75V .........
I opened the main plug and the ground pin was unconnected.
Does anyone experienced the same trouble ? is it normal when ungrounded or
internal PSU show a defective componement ? Thank for your help.
Regards
Alain
|
Funny coincidence as I was out in the garage yesterday and saw my hedge trimmer cord. 10 seconds with my pocket knife and I now have a 50' power cord!
Thanks everyone for replying.
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The non AC/DC version of a 422 needs the same kind of cord as most weed whackers n shit. I have had a few where I had to trim the edges a bit but they connect and they are safe. Some brands f them you don't even have to round the corners off.
Now if you got an AC/DC model that is a whole different story. If you really can't get the cords for those I reluctantly suggest a modification. There are many ways to do it.
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Re: Concentric A and B time-base knobs/interlocking
On Tue, Aug 14, 2018 at 08:53 PM, Colin Herbert wrote:
the B time-base knob is a little imprecise in operation and doesn't seem to
quite click into its detents cleanly.
That sort of imprecise clicking thing normally is easy to correct by loosening the B knob, carefully adjusting the angle of the knob against the A knob, fastening it and repeating if necessary. You do have a nice selection of equipment! Personally, the 466 is one of my favorites in the series, if the storage is adjusted and used correctly. Raymond
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Re: Concentric A and B time-base knobs/interlocking
You may be right about the assembly error, as the B time-base knob is a little imprecise in operation and doesn't seem to quite click into its detents cleanly.
However, I have now checked both the A and B time-bases with my TG 501 and they look to be right, if not wonderfully calibrated. The A time-base is certainly showing the right rates as is the B time-base up to a point. By that I mean that beyond ~20uS/DIV the trace is so dim it can barely be seen. All of the beam-current looks to be in the first part of the sweep, which is the vertical line I mentioned before.
I am no electronic engineer, just a hobbyist, but I do have a working 464, 475A, SC502 and 7623A, as well as this 466 and a possibly ailing 468. I also have PG506, TG501, SG503 and an FG504 with issues. So, I am a little familiar with the operation of the 400-series, if not totally conversant with the theory of operation. But I have no problems with learning "new tricks" and I don't feel insulted. All help is gratefully received.
I am beginning to think that I might raid the parts-donor 466 for its B time-base control parts, if not the whole Timing board. I think my repair wasn't totally successful, considering the imprecise action of the B time-base knob.
Colin.
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of Raymond Domp Frank Sent: 14 August 2018 19:05 To: [email protected]Subject: Re: [TekScopes] Concentric A and B time-base knobs/interlocking Hi Colin, Do you know if the time base speeds of A and B correspond to those indicated on the knobs? Did you try observing waveforms with both A and B? I'm thinking you may have made an assembly error: The max. A and B rotation and the freedom of rotation angles between A and B are mechanically limited by the knob assembly. There is a less-intense portion which can be moved by the "Delay Time Position" control, but it's length isn't controlled by the setting of the
B (delayed) time-base knob, only it's position.
I have no idea how familiar you are with this model and 'scopes in general so please don't be insulted if you know all this: Just to make sure we're talking about the same thing, the smaller, grey knob controls the speed of the B timebase, the clear part behind it controls the A time base. The Delay Time knob controls the time after A's start until B starts. If all is well (assembled), A can never be faster than B. ...no bright-up indicating where the B (delayed) time-base will run from and to
This makes me think we are talking about the same A's and B's but the bright-up should be there. ...it's length isn't controlled by the setting of the B (delayed) time-base knob, only it's position.
That sounds strange: The B (delayed) time base knob (the smaller grey one) should control the length of B on A and not influence the starting position. Sounds like assembly error. Check the speeds of "A" and "B" relating to the indications on the time scale by applying a signal and see if they make sense. Raymond
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Re: Concentric A and B time-base knobs/interlocking
Hi Colin, Do you know if the time base speeds of A and B correspond to those indicated on the knobs? Did you try observing waveforms with both A and B? I'm thinking you may have made an assembly error: The max. A and B rotation and the freedom of rotation angles between A and B are mechanically limited by the knob assembly. There is a less-intense portion which can be moved by the "Delay Time Position" control, but it's length isn't controlled by the setting of the
B (delayed) time-base knob, only it's position.
I have no idea how familiar you are with this model and 'scopes in general so please don't be insulted if you know all this: Just to make sure we're talking about the same thing, the smaller, grey knob controls the speed of the B timebase, the clear part behind it controls the A time base. The Delay Time knob controls the time after A's start until B starts. If all is well (assembled), A can never be faster than B. ...no bright-up indicating where the B (delayed) time-base will run from and to
This makes me think we are talking about the same A's and B's but the bright-up should be there. ...it's length isn't controlled by the setting of the B (delayed) time-base knob, only it's position.
That sounds strange: The B (delayed) time base knob (the smaller grey one) should control the length of B on A and not influence the starting position. Sounds like assembly error. Check the speeds of "A" and "B" relating to the indications on the time scale by applying a signal and see if they make sense. Raymond
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Jeff Urban
Raymond Domp Frank