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On Tue, Nov 13, 2018 at 07:31 PM, Chuck Harris wrote:

I had a consulting contract years ago to help a
Swedish company with a problem they had in converting
from European 240V to the USA 120V. The engineer that
did the conversion didn't understand the ratings of the
molex connector.

He saw the 17A rating, and saw the 15A drawn by the heater,
and said, "Looks good, ship it!"

And, then the problems began. In the US, the connectors
burned up after the third or fourth cycle of the instrument.

The customers were not amused, and even less amused was
the guy that relocated his family to the US to become the
president of the USA division... My customer.

What happened?

Well, molex rates their connector at 17A with the following
stipulations:

1) 25C ambient temperature.
2) 12 inches of #14ga stranded wire on each side of the
connector with everything suspended in free air.
3) only one pin set per connector shell.

Does that sound like what you are doing? If so, you will
be fine.

It didn't sound like the Swedish company's 4 circuits in a
shell, with 3 inches of wire between connectors, and placed
next to a 700W heater... OOPS!

-Chuck Harris

Harvey White wrote:

On Wed, 14 Nov 2018 07:33:38 +1000, you wrote:

...

On the current ratings, from what I understand, the current rating is
good, but goes down with the number of insertions.

I completed the overhaul including the installation of Molex connectors for the transformer leads. I posted before and after pictures here: /g/TekScopes/album?id=79113

Overall, it went well. A little crowded now inside with the addition of the Molex connectors.

I still have other issues with the 577 I need to track down - traces look OK for diodes but don't line up for transistors; as other have stated "the out and back I-V curves do not lie on top of each other". I saw other posts on that topic and will pursue this next. And the storage option doesn't work either (it's a D1).

Thank you,
Wolfgang

Thanks a lot everybody. It seems just for my 2465B it's not a very useful part...
But the link from Dale Chayes was very interesting i didn’t find it. Thanks
Rolf

I to would like this link if available.

The “low” side of every BNC instrument I’ve looked at closely is tied to the AC power ground.

Sometimes there are good reasons to disconnect that ground and make a measurement that is not relative to the AC power input ground.

This link will take you to a Tektronix “white paper” about making floating measurements.



-Dale

It would only work if your input was already floating, say for example a
TPS2024 or scope meter, and allow you to attach two probes in a
differential configuration.
The shell is unlikely to present a useful input impedance to attenuator
probes, so it would only work with X1 probes.
Quite limited use, I would say.

ST

On Fri, 23 Nov 2018 04:26:56 -0800, you wrote:


For measuring AC ripple at 120 Hz, I'd look at the ripple, but
triggered on line. Measure anything that stands still....

Ought to get you close.

Harvey

On Tue, Nov 6, 2018 at 08:03 AM, Chuck Harris wrote:

Hey! Don't muck with the DAC adjustment, unless you are prepared
to do a full calibration!

It is not supposed to be +1.25 and -1.25 volts, but rather a 2.500V span.

Sure, if you are a perfectionist, and diddle with the 10K reference
resistor values, and put in perfect opamps, it can achieve those values,
but that is not a necessary goal: 2.500V span when doing the calibration
routine is the necessary goal. -1.25 and +1.36V references that are *stable*
is the goal, as any errors in them get stored in the calibration constants,
and as such calibrated out, when the scope is calibrated.

Any tweaking, or replacement of DAC parts that you do will require a
full calibration of your scope. Why? Because you have no idea what they
were like when it was last calibrated.

If they were on the low (or high) side of spec when last calibrated, and
you adjust them to be right on, with a DVM that was on the high (low) side
of spec), they errors could add up to be wrong enough to perform poorly.

-Chuck Harris

OK understood. I have not touched the adjustment at R2010. Only replaced both 10K 0.1% resistors (the original ones where both open). Also replaced R2016 1K 1% because I pulled it out by mistake and one of the contacts looked a bit iffy, so that one was also needing replacement anyway. The original value of this last resistor checked on my HP3478A was 1.00248K and the substitute measured 1.00302K, so only a 0.0539% difference between them. The voltages from the +1.36 and -1.25 references did not vary very much from what the where while still using the temporary 5% resistors. I initially had +1.3848 and now it is 1.3836v. And -1.2688 went to -1.2681v. Not much of a difference.

I was looking at the procedure to check the 2.5V DAC voltage span in the service manual (page 5-3) and plan on verifying it at pin 13 of J119. But I will not be making any adjustments to it, since as explained above this might actually be detrimental and worsen the calibration state of the scope. So for now I will only record the voltage range, and they will stay as is.

I have received my new GQ-4X4 programmer, and the DS1225 from Mouser, but before I pull out my original NVRAM still need the machined 28-DIP socket which I had to reorder as I messed up the PN, and also ordered a FW16W08 FRAM to play with and an Aries SOIC to DIP converter board.

After getting the cal data rewritten on a fresh D1225 I am assuming I will have to tackle the power supply caps next. Sometimes see a very small almost unnoticeable horizontal jitter on a displayed waveform, so this is probably ripple in one or more power supplies. I last time the scope was open also took a glance into the power supply board and noticed I do have the infamous RIFA exploding caps and at least the one that sits closer to the angle I was able to peer onto the board shows the typical small cracks. I'm on 120V so I understand the risk of them exploding is less than on 220v mains, but I will replace them asap once I have all the other PS caps on hand as well. Already have the replacements for those, but since pulling out the PS boards as a pair its not exactly easy, will probably wait until I have all the required elco caps on hand as well and get it done once.

BTW can someone please explain how does one take the power supply ripple reading for 120Hz only, as opposed to the total ripple reading? By using the HF reject triggering option?

Thanks.

On Fri, 23 Nov 2018 05:40:12 -0800, you wrote:

Picture of the part here:

I'm going to guess, and an ohmmeter would tell you. One BNC is
straight through to the male BNC. The other center pin is wired to
the ground on the male BNC. The two shells are connected together,
but not to anything else.

It floats your scope.

Best used on a battery scope if at all.

Another option (if there's a short on the pin to ground, and the
wiring is not as described) would be for a 7A14 and a current probe
(needs an adaptor to tell the difference between a P6021 and a P6022).

Unlikely, though.

Harvey

Picture of the part here:

I got for free such an adapter. Ha anybody an idea how to use such a floating ground. I know what floating ground is but I have no idea for what the double BNC should be useful.
Google didn’t help me and a manual or application has not been around.
Any hints would be helpful.
Rolf

Link above is only for one picture. Full album is really here:

/g/TekScopes/album?id=76874&p=Name,,,20,1,0,0

Added 4 pictures to my photo album showing rise time measurements of the 2465B (o.57nS) and also my 2247A (~2.0nS). BTW the 0.57nS rise time was confirmed with the corresponding parametric measurement, the result was exactly 0.57nS as well. Also included a close up of the 2N2369A avalanche pulse generator I build (last picture), and that requires around 90V to work, but I just use my Heathkit IG-4505 with DC output set to the 100V scale, and it works just fine. Much easier that having to build that cumbersome DC-DC converter used in the original pulser article.

/g/TekScopes/photo/76874/1?p=Name,,,20,1,0,0

BTW is it possible to reorder the pictures? I could not find a way to do it through the web interface.

On Tue, Nov 6, 2018 at 08:03 AM, Chuck Harris wrote:

Hey! Don't muck with the DAC adjustment, unless you are prepared
to do a full calibration!

It is not supposed to be +1.25 and -1.25 volts, but rather a 2.500V span.

Sure, if you are a perfectionist, and diddle with the 10K reference
resistor values, and put in perfect opamps, it can achieve those values,
but that is not a necessary goal: 2.500V span when doing the calibration
routine is the necessary goal. -1.25 and +1.36V references that are *stable*
is the goal, as any errors in them get stored in the calibration constants,
and as such calibrated out, when the scope is calibrated.

Any tweaking, or replacement of DAC parts that you do will require a
full calibration of your scope. Why? Because you have no idea what they
were like when it was last calibrated.

If they were on the low (or high) side of spec when last calibrated, and
you adjust them to be right on, with a DVM that was on the high (low) side
of spec), they errors could add up to be wrong enough to perform poorly.

-Chuck Harris

OK understood. I have not touched the adjustment at R2010. Only replaced both 10K 0.1% resistors (the original ones where both open). Also replaced R2016 1K 1% because I pulled it out by mistake and one of the contacts looked a bit iffy, so that one was also needing replacement anyway. The original value of this last resistor checked on my HP3478A was 1.00248K and the substitute measured 1.00302K, so only a 0.0539% difference between them. The voltages from the +1.36 and -1.25 references did not vary very much from what the where while still using the temporary 5% resistors. I initially had +1.3848 and now it is 1.3836v. And -1.2688 went to -1.2681v. Not much of a difference.

I was looking at the procedure to check the 2.5V DAC voltage span in the service manual (page 5-3) and plan on verifying it at pin 13 of J119. But I will not be making any adjustments to it, since as explained above this might actually be detrimental and worsen the calibration state of the scope. So for now I will only record the voltage range, and they will stay as is.

I have received my new GQ-4X4 programmer, and the DS1225 from Mouser, but before I pull out my original NVRAM still need the machined 28-DIP socket which I had to reorder as I messed up the PN, and also ordered a FW16W08 FRAM to play with and an Aries SOIC to DIP converter board.

After getting the cal data rewritten on a fresh D1225 I am assuming I will have to tackle the power supply caps next. Sometimes see a very small almost unnoticeable horizontal jitter on a displayed waveform, so this is probably ripple in one or more power supplies. I last time the scope was open also took a glance into the power supply board and noticed I do have the infamous RIFA exploding caps and at least the one that sits closer to the angle I was able to peer onto the board shows the typical small cracks. I'm on 120V so I understand the risk of them exploding is less than on 220v mains, but I will replace them asap once I have all the other PS caps on hand as well. Already have the replacements for those, but since pulling out the PS boards as a pair its not exactly easy, will probably wait until I have all the required elco caps on hand as well and get it done once.

BTW can someone please explain how does one take the power supply ripple reading for 120Hz only, as opposed to the total ripple reading? By using the HF reject triggering option?

Thanks.

Richard,

Would a 2245A be suitable? Where are you located? I am not at all keen on packing the scope.

Roger

On 23/11/18 06:18, Brian Cockburn wrote:

At the CATS rally (South London) ...

I'm in Cambridge but I'm not familiar with 'CATS Rally'. Googling didn't turn up anything non-feline. Could you elaborate a bit pleas

The canonical source for these rallies is

Since the Couldson (Surrey) rally was last month, it no longer appears there.

George,

At the CATS rally (South London) ...

I'm in Cambridge but I'm not familiar with 'CATS Rally'. Googling didn't turn up anything non-feline. Could you elaborate a bit please?

Thanks, Brian.

Good idea

I found that pressing against the surface with a soft point I believe I found the screw holes hiding behind the label. I believe they should be Philips, I might use a small precision screw driver to make a minimal incision.

I am now curious if in fact the screw holes are behind the label, perhaps when the probe with made at the factory the case is screwed together the label is glued on top. Thus to tamper with the inside of the probe the front label would be damaged.

I would like a link to the articles too.

Thanks
randy.ab9go

Here is one of the 2430A that I have available.
Shown on Ebay listing #202376811343

Craig

Hi.a thought, ..do get a very clear un-astigmatic photo of it in case you need to have another created.
My Regards
Jack

I have a P5205 differential probe that has a offset issue when switching the attenuation from 500x to 50x and the overage light doesn't seem to come on or any sound either. I would like to open up this probe up for inspection but I have a question in doing so. From a previous post it is from my assumption the screws are hidden below the front label and in order to get to them I would have to puncture the label? Is it possible to peel the label without damage? Thanks