开云体育

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

On Thu, 22 Nov 2018 19:06:41 +0000, you wrote:

I gave my 475 away as it needed fixing and I didn't want any more
projects, a week
later I find myself wanting a scope and nearly buying a little chinese
hand held thing!

I don't recommend the little Chinese cell-phone sized scopes as an
only scope. They are very portable, but quite limited in what they
do.

The Tektronix 2000 series can be nice, not totally familiar with them,
but they have been well rated.

Research would be indicated, I think.

A 2430A is not a bad scope...

Harvey

Guess I might as well buy another proper scope.
Thanks in advance for all the top condition scopes I am going to be
offered..

richard

On Wed, Nov 21, 2018 at 03:20 PM, Chris Smith wrote:

Quick victory photo of the 475A:

Great. I was almost 475ed out with this one here. Well it only had three or four problems...no need to whine about it right ?

What I wanted to mention though is that looking at the 465(B here, not sure about the non B) the 475 sweep has one more range, faster. That may account for the slight difference in the part number. I would figure out a way to check it out on 0.01 uS/div. It doesn't generate the ramp so linearity should be fine, it might be a matter of triggering. Also it is quite possible that specimen of U600 will be fine, but not necessarily ALL of them would do.

Sometimes this type of part is like harddrives. They format them to higher and higher capacities until they start getting errors and set it up for just below that. So in the lower grade (if you can call it that) IC it might or might not work fine but the higher grade IC definitely will. It could be just fine.

I gave my 475 away as it needed fixing and I didn't want any more projects, a week
later I find myself wanting a scope and nearly buying a little chinese hand held thing!
Guess I might as well buy another proper scope.
Thanks in advance for all the top condition scopes I am going to be offered..

richard

On Thu, Nov 22, 2018 at 07:06 PM, Raymond Domp Frank wrote:

Also, ISTR that 1 GSa/s worked but the display quality wasn't 100%. I have to
admit I don't quite remember.
And lots of error messages turned up in the Error Log.

I should add that I didn't spend much time on it before deciding to revert so your results may be better.
ISTR also that the time base setting allowed for a faster sweep than the 720A's. The faster sampling rate and the faster time base were what I was interested in. Still, I decided to revert, maybe just because of the error log growing all the time, don't remember.
The link in my previous message gives access to all the info I had available.

Raymond

On Thu, Nov 22, 2018 at 05:40 PM, garp66 wrote:

Rick,
Please see below.

So... What of the THS 730a upgrade ?

Have a look here:

I think I got all my info there.

What exactly were the problems with that ?

It worked but the bandwidth didn't reach 200 MHz, probably because the THS730A uses different attenuators.
Also, ISTR that 1 GSa/s worked but the display quality wasn't 100%. I have to admit I don't quite remember.
And lots of error messages turned up in the Error Log.

& how can each issue, in detail, be solved ?

If I knew, I wouldn't have returned back to the 720A... setup.

I have a THS720a and would like to upgrade it to the THS 730a.

Raymond

So... What of the THS 730a upgrade ?
What exactly were the problems with that ?
& how can each issue, in detail, be solved ?

I have a THS720a and would like to upgrade it to the THS 730a.

thanks,
rick

Thanks.
I followed the procedure of the service manual: I moved the jumper on "cal" of course, but it is impossible to start the calibration routine: simply at each calibration step, by pressing the "upper coupling" button, the result is "pass" or "fail" in the case of step n. 4!

I'd appreciate copies of those 2 articles as well.

Thanks,

John

If you connect a PC running a terminal program to the serial port
of the THS you can try sending first PASSWORD PITBULL and then ERRLOG CLEAR.

H?kan gave me above advice. It turns out to achieve what I wanted: The error log is cleared.

Raymond

I can help with these if you are interested. They are new tips. $40 US each. Send me email if you want.
Craig