HP 1725A Oscilloscope--Curve Tracer Function?!

thefragger

thefragger

Certified Crazy.
Hi all,

I bought this oscilloscope five years ago locally and it's been great! I lent my oscilloscope out to a friend for his grandfather to use. When I got it back I was re-integrating it into my bench and getting my setting back to where I keep them until I noticed one function that I hadn't taken note of before...

OQQ6f.jpg


fTh4Z.jpg


3SO0a.jpg

As far as I can tell there are no curve tracer specific inputs, additionally the manuals I've been able to find state nothing of an option H01 (option 101 includes the 1607A logic-state analyzer inputs), but if you look at the first photo, this was a unit built for amdahl.

Pulling the intensity knob to enable the curve tracer mode, the line becomes a point, and it positions itself on the far left of the screen, one major division from the edge, and one major division below the horizontal zero line.

This is a photo of what I consider to be a 'normal' 1725A: http://www.amplifier.cd/Test_Equipment/Hewlett_Packard/HP_other/images/1725A_front.jpg


I have yet to play with this mode (bit busy) but I thought I might post it up here just in case anyone has seen this before! I'm quite excited as I've been shopping for a Tek curve tracer, but they tend to sell for 5x my budget!


Philip.
 
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thefragger said:
Hi all,

I bought this oscilloscope five years ago locally and it's been great! I lent my oscilloscope out to a friend for his grandfather to use. When I got it back I was re-integrating it into my bench and getting my setting back to where I keep them until I noticed one function that I hadn't taken note of before...

OQQ6f.jpg


fTh4Z.jpg


3SO0a.jpg

As far as I can tell there are no curve tracer specific inputs, additionally the manuals I've been able to find state nothing of an option H01 (option 101 includes the 1607A logic-state analyzer inputs), but if you look at the first photo, this was a unit built for amdahl.

Pulling the intensity knob to enable the curve tracer mode, the line becomes a point, and it positions itself on the far left of the screen, one major division from the edge, and one major division below the horizontal zero line.

This is a photo of what I consider to be a 'normal' 1725A: http://www.amplifier.cd/Test_Equipment/Hewlett_Packard/HP_other/images/1725A_front.jpg


I have yet to play with this mode (bit busy) but I thought I might post it up here just in case anyone has seen this before! I'm quite excited as I've been shopping for a Tek curve tracer, but they tend to sell for 5x my budget!


Philip.
Click to expand...

I used to own that scope, and it came with a voltmeter attached to the top of the enclosure, as seen in your photo I suspect the curve tracer likewise lives there. Since the scope says, "Built for Ahmdahl," it probably is a semi-custom that isn't available off-the-shelf. Have a look under the top cover to see it there are connectors that look useful.
 
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Alrighty! So there's another HP 1725A on eBay (#290760536448) right now with the 1607A inputs on the back, but without the curve tracer writing on the faceplate... ?!

I think you're right, Ken, I'll have to pop the top open again, and take a closer look at this thing!
 
DCinDC said:
I don't think it is what you think it is.

:popcorn:
Click to expand...

I'm not real familiar with this scope.
I'm wondering if curve tracer mode is more like X-Y mode-one vertical channel is the x (horiz.) axis, and one is the Y (vert.) axis. Used for instance to observe lissajous patterns.
Not a curve tracer as such to test transistors, etc.
I could be wrong, though...
 
HackerJohn1 said:
I'm not real familiar with this scope.
I'm wondering if curve tracer mode is more like X-Y mode-one vertical channel is the x (horiz.) axis, and one is the Y (vert.) axis. Used for instance to observe lissajous patterns.
Not a curve tracer as such to test transistors, etc.
I could be wrong, though...
Click to expand...

Nope, at least not using the probe inputs--there's an XY button at the bottom of the line of blue buttons in the centre of the scope. I was looking at the Lissajous figure of a tuner's MPX output when I notices the 'curve tracer' function and turned it on with just the one dot appearing.

Very strange... :scratch2:
 
I suspect there was a curve tracer accessory to connect somehow - I'd guess this puts the scope in the correct display mode and scale for an accessory that produces the required drives to test transistors.
 
I've got one of those old Leader curve tracer's, which utilizes a scope's X/Y inputs to view the curves. I'm thinking the hp is built around that type of a model.

It makes sense that hp put some kind of control around the Intensity adjustment. You don't want a curve tracer (or X/Y) display mode to burn a hole in your phosphor.
 
Even more interesting... on the eBay oscilloscope with the 101 option (1607A inputs), the Z input on the back has a sticker over it stating that it's a 1697A input, while mine does not have this sticker. Another 'built for amdahl' model is also on eBay right now (#180646030393) and it shows the same sticker missing on the back; this is at least a bit of confirmation that the sticker on mine wasn't peeled off!

Maybe the X, Y, and Z inputs are used for the C, B, and E inputs... :scratch2:

There really needs to be more hours in the day--I won't be able to pop the cover until mid-to-late next week.


opt101 and opt003:


d2SlD.jpg


KlEjV.jpg

​



Amdahl optH01:


BdGAo.jpg


6IcGc.jpg

​
 
Oh! Another thing I noticed is that on the 'normal' (opt101) oscilloscope, the time interval area (top right) has a multi-turn potentiometer with what appears to be a vernier dial (labelled as 'STOP'), while on my 'scope and the other optH01 example, that appears to be replaced with a dual-concentric potentiometer (labelled 'OFFSET').

Another round of spot-the-difference and we find that the CAL test point on the bottom edge, in the centre, states 'CAL 3V' on a 'normal' 'scope, and 'CAL 1MHz/1uSEC' on mine as well as the other amdahl unit on eBay, although I imagine that this is insignificant.
 
Have you tried contacting HP? They may keep archives of documentation, even on special order units. I've found that some companies are very good about digging that stuff out and supporting individual users long after the unit is "obsolete."
 
JonL said:
Have you tried contacting HP? They may keep archives of documentation, even on special order units. I've found that some companies are very good about digging that stuff out and supporting individual users long after the unit is "obsolete."
Click to expand...

Ha! Interestingly enough I just send off three emails to different parts of Agilent (HP spin-off of it's test equipment division). Emailed the calibration, obsolete parts, and repair sections.

While I do have the 1725A manual, there's no mention of an option H01.

Fingers and toes are crossed!
 
A possible feature of the curve tracer option is that it reduces the intensity when both X and Y inputs are zero, to reduce spot burn at the origin.
 
Jon_Logan said:
I've got one of those old Leader curve tracer's, which utilizes a scope's X/Y inputs to view the curves. I'm thinking the hp is built around that type of a model.
Click to expand...

Was thinking the same... Thinking of it,my Tectronix scope has X and Y inputs at the back as well, I'll have to check the manual what they are for, but will take couple of weeks before back home.
 
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