Author Topic: EEVblog #803 - HP1740A Analog Oscilloscope  (Read 22353 times)

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Offline nfmax

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #50 on: October 05, 2015, 07:16:49 am »
Quote
Presuming you have a manual, you could start by looking at some of the voltages with a voltmeter. It may even be possible to use the scope to look at its own internal waveforms, but I haven't considered that in detail.
Actually I have three additional working oscilloscopes, (as well as two copies of the 1740A manual, and the user guide). It's the principle of the thing, you understand...
 

Offline tggzzz

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #51 on: October 05, 2015, 08:19:54 am »
It's the principle of the thing, you understand...

Yes, I do understand  :(
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline Jay_Diddy_B

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #52 on: October 05, 2015, 10:14:42 am »
Hi,

I have seen problems, with this family of scopes, where the connector on the secondary side of the line transformer has overheated and become bad.

I suggest checking the connector for discoloration.

Regards,

Jay_Diddy_B


 

Offline helius

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #53 on: October 05, 2015, 11:15:01 am »
I've got one of these. Really nice scope. Of course, all of the feet are broken off. One of these days, I need to make some new ones in my shop, because it's a LONG scope.
Here is a site with fantastic pics of test equipment repair, including this HP scope series. You can see the replacement wooden feet:
http://www.amplifier.cd/Test_Equipment/Hewlett_Packard/HP_other/1725A.html
 

Offline SilverSolder

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #54 on: October 05, 2015, 11:20:36 am »
This is a great scope, although if I had one I would probably 3D print a new bezel around the screen (probably in some hipster color for kicks). As that bromite aging effect looks kind of bad on that plastic.

Yeah it looks pretty crusty, kinda spoils it.

Apparently, it is possible to remove that yellowing "nicotine look" - I haven't tried it myself yet, but looks plausible:

http://www.exisle.net/mb/index.php?/topic/59657-de-yellowing-plastic-the-stain-isnt-permanent-after-all/

 

Offline edpalmer42

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #55 on: October 05, 2015, 01:27:31 pm »
Apparently, it is possible to remove that yellowing "nicotine look" - I haven't tried it myself yet, but looks plausible:

http://www.exisle.net/mb/index.php?/topic/59657-de-yellowing-plastic-the-stain-isnt-permanent-after-all/

I don't know who did it first, but the web site for this process is http://www.retr0bright.com .

Ed
 

Offline Tothwolf

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #56 on: October 05, 2015, 06:24:09 pm »
Apparently, it is possible to remove that yellowing "nicotine look" - I haven't tried it myself yet, but looks plausible:

http://www.exisle.net/mb/index.php?/topic/59657-de-yellowing-plastic-the-stain-isnt-permanent-after-all/

I don't know who did it first, but the web site for this process is http://www.retr0bright.com .

It was a community project involving quite a number of people from the Vintage Computer community. The follow up to the material at retr0bright.com can be found here: Retr0Bright (or RetroBright) treated plastics re-yellowing even with minimal light exposure?
 

Offline han

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #57 on: October 05, 2015, 06:56:56 pm »
I haven't read whole thread. Is anybody already suggest watt meter at the whole unit.
Is the power dip/spike when the error occur?


 

Offline EEVblog

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #58 on: October 05, 2015, 11:44:40 pm »
REPAIRED!
I bet no one can pick it before I upload the next video...
 

Offline krivx

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #59 on: October 05, 2015, 11:50:44 pm »
I didn't see the manual posted, so I think this is it.

http://cp.literature.agilent.com/litweb/pdf/01740-90909.pdf

Those are good scopes, it is no wonder they are still working going on forty years later.
I have my doubts those LCD all digital scopes we have around us today will have the same longevity.

Any predictions on failure modes? Apart from electrolytic caps I would think they could last a long time, the LCDs are not as fragile or as consumable as a CRT are they?
 

Offline krivx

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #60 on: October 05, 2015, 11:56:44 pm »
REPAIRED!
I bet no one can pick it before I upload the next video...

Percussive maintenance
 

Online Fungus

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #61 on: October 05, 2015, 11:58:13 pm »
Apart from electrolytic caps I would think they could last a long time, the LCDs are not as fragile or as consumable as a CRT are they?

Lower power consumption should mean the caps last quite a while.

Plus they don't have all that high voltage circuitry, etc.
 

Offline PA0PBZ

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #62 on: October 06, 2015, 12:02:22 am »
REPAIRED!
I bet no one can pick it before I upload the next video...

So either all suggestions given are wrong or you already uploaded the video  :)
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Offline EEVblog

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #63 on: October 06, 2015, 12:14:22 am »
So either all suggestions given are wrong or you already uploaded the video  :)

All the suggestions are wrong.
 

Online Andy Watson

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #64 on: October 06, 2015, 01:00:07 am »
There appeared to be a fault with the channel/trace multiplexing logic - my guess would be either faulty logic chip or decoupling cap eventually taking the supply down - either directly operating on the +15V, or overloading the +5V and causing thermal problems in the PSU. All the supplies are referenced to +15V so once it is compromised they all fail.
 

Offline AF6LJ

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #65 on: October 06, 2015, 01:03:41 am »
I didn't see the manual posted, so I think this is it.

http://cp.literature.agilent.com/litweb/pdf/01740-90909.pdf

Those are good scopes, it is no wonder they are still working going on forty years later.
I have my doubts those LCD all digital scopes we have around us today will have the same longevity.

Any predictions on failure modes? Apart from electrolytic caps I would think they could last a long time, the LCDs are not as fragile or as consumable as a CRT are they?

From my mobile radio experience LCD displays degrade in the sunlight. While interior lighting is less destructive  florescent light does contain some UV. Plastics age with heat nad time, and this is an issue with all electronics, again drawing from my two way radio experience flex cables will de-laminate over time. Some of the newer flex cable designs are better than the ones made even a decade ago they still are made of plastics and will fail sooner than other connection means.

pots can be cleaned and repaired, some rotery encoders like the ones on some of my amateur radio gear are repairable others not so much, and that may not be a big deal in the decades to come, they could actually outlast pots.

As far as rotary switches go, HP and others have done a great deal to eliminate the conventional rotary switches which require some degree of skill to clean, just spraying crap on one of those old pheonlic rotary switches will do more damage over the long term, when they get wet they swell up, the rivets holding the contacts loosen up and you have intermittent contact. You can see what HP has done in this scope to make rotery switches more reliable.

Over the decades silicon has replaced a lot of discreet components including switches and pots, this is not necessarily a bad thing, but it has its drawbacks. Fifty years ago the mainstay scopes were scopes like the HP-170 and the Tektronix-545. If you have one of those today, you can find replacement parts for just about everything in that scope without robbing parts from another 170 or 545. Each successive generation that fraction of specialized parts has grown The scope mentioned in this thread is on a par with a Tek-465. You can argue til the cows come home how reliable those custome chips are used in both scopes but when one dies, you cannot go to Mouser and buy one, you have to rob it from another 1740 or 465. Sadly this trend toward custom chips is all the rage in test equipment, add to that all that firmware. How do you back up that firmware that runs a modern digital scope? We haven't even touched on the subject of calibration, if the scope in question relies on an external means to access "soft pots" in order to make adjustments the failure of that must also be considered, when was the last time you saw a screwdriver, or a hex head alignment tool fail?

We have test equipment with enormous power at our disposal now, the new stuff is truly great in terms of preformance and in some cases makes gear of a generation ago look like junk. Consider the full price that goes with having that gear, how many here have a Rigol service manual for their scope?

Sadly our whole civilization is going this way Figuratively speaking all our gear will end up in a landfill (or recycled as raw materials) sooner or later. The trend in consumer electronics is that amount of time before end of life is shorter and shorter, in many cases it is due to fashion trends, in others it is because that TV or cell phone uses a chip that someone once made and no longer does cost of repair being factored out; the trend in how we design gear of all types is toward less repairability while the level o9f reliability remains fairly constant.
That ends with a shortened service life for the item in question.

 
Sue AF6LJ
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Offline AF6LJ

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #66 on: October 06, 2015, 01:04:33 am »
So either all suggestions given are wrong or you already uploaded the video  :)

All the suggestions are wrong.

I for one am looking forward to seeing what you found.
Sue AF6LJ
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Offline MarkL

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #67 on: October 06, 2015, 01:10:04 am »
The voltages on the twitter photo were all down by roughly the same percentage; there wasn't one that was extremely out of line with the rest.  I would start looking for something in common to all the rails, like on the primary side.

Intermittent candidates: 120/240V selector switch, power switch, connector, bad solder joint.
 

Offline AF6LJ

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #68 on: October 06, 2015, 01:12:12 am »
The voltages on the twitter photo were all down by roughly the same percentage; there wasn't one that was extremely out of line with the rest.  I would start looking for something in common to all the rails, like on the primary side.

Intermittent candidates: 120/240V selector switch, power switch, connector, bad solder joint.

That's the easy part and the part that must be taken care of before anything else.
I am of the mind there are two problems, but with so little data it is hard to say.
Sue AF6LJ
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Offline PA0PBZ

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #69 on: October 06, 2015, 01:13:38 am »
I've seen this posted before but I find it very unlikely that all secondary voltages will drop the same percentage if you lower the primary voltage. I fail to see that if 4 different regulators are going out of regulation they will drop the same %.
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Offline AF6LJ

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #70 on: October 06, 2015, 01:33:51 am »
I've seen this posted before but I find it very unlikely that all secondary voltages will drop the same percentage if you lower the primary voltage. I fail to see that if 4 different regulators are going out of regulation they will drop the same %.

I have seen the actual symptom before and repaired it.
Yes it can be something as simple as a primary side fault, especially if the voltage sources are referenced to a single source that has a higher drop out voltage than the others. Then they all will track the reference voltage.
The bad news is; that may not be all that is wrong with this scope.
Sue AF6LJ
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Offline MarkL

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #71 on: October 06, 2015, 01:38:25 am »
I've seen this posted before but I find it very unlikely that all secondary voltages will drop the same percentage if you lower the primary voltage. I fail to see that if 4 different regulators are going out of regulation they will drop the same %.
The unregulated inputs to the regulators would track the primary voltage.  Once you were below drop-out voltage for the regulator, they would track eachother.

I would look at the primary voltage input to the transformer as the next step.  Or some of the unregulated rails.  But we don't have that data.

If not, it could also be something with the +15V supply, since the other voltages are referenced to that voltage.  Looking more closely, they're all almost exactly 20% down.
 

Offline han

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #72 on: October 06, 2015, 01:53:06 am »
let me guess, bad main switch contact?
 

Offline AF6LJ

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #73 on: October 06, 2015, 02:15:13 am »
let me guess, bad main switch contact?

Maybe....
Something low experience techs would overlook in search of a vastly more complex fault. ;)
Sue AF6LJ
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Offline Len

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Re: EEVblog #803 - HP1740A Analog Oscilloscope
« Reply #74 on: October 06, 2015, 03:15:55 am »
Spider carcass in the power supply causing an intermittent short.
 


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