Author Topic: HP 1741A oscilloscope - restoration project  (Read 98040 times)

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Offline BravoV

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Re: HP 1741A oscilloscope - restoration project
« Reply #25 on: October 10, 2011, 07:38:22 am »
Love this thread, thanks for sharing this tekfan.

This is making me to re-think about an offer locally for this exact beauty about US$150 complete with front cover, really itching to grab it.  ::)

Offline tekfanTopic starter

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Re: HP 1741A oscilloscope - restoration project
« Reply #26 on: October 10, 2011, 02:15:42 pm »
I hope I can upload more pictures about the progress soon. I also got a HP 1740A from school (non workong of course - same as this one only non storage).
One can never have enough oscilloscopes.
 

Offline appsman

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Re: HP 1741A oscilloscope - restoration project
« Reply #27 on: October 12, 2011, 06:10:17 am »
Wow! I have to admit, when I saw the start of this post I thought, "No chance", but you are clearly not to be denied! Very impressive work. I think even Jim Williams would have been impressed.
 

Offline dfnr2

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Re: HP 1741A oscilloscope - restoration project
« Reply #28 on: October 13, 2011, 06:09:59 am »
Great thread, and beautiful pictures of a beautiful scope.  We are all waiting for the pics of the restored scope.

The HP 1700 series are really marvelous scopes, I bought a nice "untested" 1725A on Ebay about 10 years ago and repaired it, and it's been a reliable workhorse ever since.  These scopes are a pleasure to have at the bench.  They also have great manuals and are a joy to work on and repair (unless a hybrid dies, but they don't seem to be as failure prone as the Tek 24xx hybrids.)

Dave
 

Offline tekfanTopic starter

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Re: HP 1741A oscilloscope - restoration project
« Reply #29 on: October 16, 2011, 07:41:46 pm »
Onward:

After replacing the CRT and turning it on:
Lo and behold a trace!


The trace was very unfocused at first:


After some fiddling around with the HV supply:


The trace after calibrating the HV supply, astigmatism, focus...  MUCH better


After some calibration:
The trace is the pulse from the Jim Williams pulse generator
The rise time is slightly over 2ns as opposed to the specified 3.5ns
This scope can easily display signals well beyond 100MHz



The trigger source can also be displayed on the screen. Giving the scope an ''almost'' third channel.


All that's left now is to put the covers back on


And since it's a storage scope you can even play Etch A Sketch on it:

One can never have enough oscilloscopes.
 

Offline lowimpedance

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Re: HP 1741A oscilloscope - restoration project
« Reply #30 on: October 17, 2011, 03:15:49 am »
Fantastic restoration.
Another quality peice of gear rescued from the scrap heap.
There is a 1741a in the instrument store at work collecting dust, now I am motivated to get it out and fire it up  :).
Great final photo.
Now you can sit back and sip a nice cool beer and admire your work, you have definately earned it.
BTW are you now going to be called HPfan ?? :D
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline vk6hdx

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Re: HP 1741A oscilloscope - restoration project
« Reply #31 on: October 17, 2011, 06:55:22 am »
Nice work and great result, thanks for sharing this restoration project with us.

Troy
 

Offline BravoV

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Re: HP 1741A oscilloscope - restoration project
« Reply #32 on: October 17, 2011, 07:04:32 am »
Thanks for sharing this restoration job, well done and congratulations too !

Btw, what Jim Williams pulse generator ? Link ?

Offline tekfanTopic starter

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Re: HP 1741A oscilloscope - restoration project
« Reply #33 on: October 18, 2011, 07:29:56 pm »
Btw, what Jim Williams pulse generator ? Link ?

http://cds.linear.com/docs/Application%20Note/an47fa.pdf

Page 93-95

I've tried to make it as small as possible for my self for the convenience. A little flimsy on the stripboard but it works:

One can never have enough oscilloscopes.
 

Offline BravoV

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Re: HP 1741A oscilloscope - restoration project
« Reply #34 on: October 24, 2011, 10:57:51 am »

http://cds.linear.com/docs/Application%20Note/an47fa.pdf

Page 93-95

I've tried to make it as small as possible for my self for the convenience. A little flimsy on the stripboard but it works:

Thank you for pointing that Jim's circuit, guess with my recently acquired 400Mhz old analog tek scope, I will make one to see how much it's rise time, should be interesting to observe.

Yours looks so cool and compact sized, love the front transistor and the trimmer cap position, a dead bug style but the best for high freq stuff.

Looks like I will substitute the 90 volt generator with common popular MC34063 and probably with 9 volt battery instead of small 1.5 volt like yours, also I'm thinking it might not easy to find that old 2N2369 transistor anymore, do you still have one to spare ? ;)

Offline Omicron

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Re: HP 1741A oscilloscope - restoration project
« Reply #35 on: October 24, 2011, 05:06:31 pm »
Btw, what Jim Williams pulse generator ? Link ?
http://cds.linear.com/docs/Application%20Note/an47fa.pdf

Page 93-95

Be careful, the pulse generator described in this app note is not suitable for rise time measurements. I think this has been discussed on this forum before. The pulse it produces is too narrow. For a correct rise time measurement the scope trace MUST be able to reach the full amplitude of the step input. If the input pulse disappears before the scope trace has achieved the true amplitude of the input signal then your reading will be wrong (i.e. far too optimistic). The pulse from this generator is so fast even a 400MHz scope has no hope at all of showing it's real amplitude.

Jim himself undoubtedly knew all this as he made several modifications to the pulser in later app notes to achieve a wider output pulse.
 

Offline tekfanTopic starter

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Re: HP 1741A / 1740A oscilloscope - restoration project
« Reply #36 on: December 28, 2011, 11:48:15 pm »
Recently I got another HP scope. This time an HP1740A. This was on it's way to the dump at my school. The sides were unscrewed and put beside the scope so obviously someone tried to repair it. It is very similar to the 1741A storage oscilloscope. The 1740A is a dual channel 100MHz analog oscilloscope with delayed time base and 1mV/div maximum sensitivity (5mV/div full bandwidth).

This is basically how it arrived. It would blow the fuse when turned on.


After a bit of searching I found two rectifiers shorted. This seems to be a common problem in these scopes.


Then I found two burned resistors on the Z axis board.


Looks like the ceramic capacitor went short circuit and caused the two resistors to blow.


Replacing the resistors allowed the Z axis amplifier to unblank the beam and suddenly a trace appeared.


The time/div switch shaft was also worn. Looks like this scope had a lot of use.


Contacts of the time/div switch are still in great shape but the center hole where the shaft goes trough
is worn so that the contacts on the switch are misaligned with the contacts on the PCB.
This caused severe timing errors in the horizontal time base.
One can never have enough oscilloscopes.
 

Offline FenderBender

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Re: HP 1741A oscilloscope - restoration project
« Reply #37 on: December 29, 2011, 02:45:44 am »
Awesome work. These scopes really look like great pieces of equipment. I was debating between one of these and a old Tek scope. I wound up going with the Tek, but this is a lovely piece of equipment.
 

Offline BravoV

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Re: HP 1741A oscilloscope - restoration project
« Reply #38 on: December 29, 2011, 09:31:03 am »
Great finding and awesome restoration job as usual, thanks Tekfan.

Btw, about this particular model 1740A, does it have custom ics ? Cause I'm being offered the same exact model by local surplus shop here.

Offline tekfanTopic starter

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Re: HP 1741A oscilloscope - restoration project
« Reply #39 on: December 29, 2011, 02:19:13 pm »
Btw, about this particular model 1740A, does it have custom ics ? Cause I'm being offered the same exact model by local surplus shop here.

The 1740A has four custom ICs. Two hybrids. One for the vertical preamp and the other for the vertical output amp and two ICs in the trigger circuit. One for main sweep and the other for triggered delayed sweep.

I've never had any of these fail no matter how dirty or misused the scope was. The primary problem seem to be the shorted rectifiers.
One can never have enough oscilloscopes.
 

Offline wkb

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Re: HP 1741A oscilloscope - restoration project
« Reply #40 on: December 29, 2011, 05:45:18 pm »
Nice job Tekfan!

Reminds me of the Tek 2213a that I have sitting here and still needs fixing  :( 

It only displays a partial time base line, like 70% or so of the screen width.  Using the x10 on the timebase things get better, like 90% or so.

We (a friend of mine and your's truly) were under the impression the CA3046 on the time base module went south but a replacement CA3046 did not help.

So more digging to do I'm afraid.  It is a nice little scope that I handed down to the aforementioned friend.  Initially the time base problem was intermittent, sensitive to gentle tapping.  Now it has become a solid fault.

Any suggestions maybe?
 

Offline tekfanTopic starter

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Re: HP 1741A oscilloscope - restoration project
« Reply #41 on: December 29, 2011, 06:29:53 pm »
Nice job Tekfan!

Reminds me of the Tek 2213a that I have sitting here and still needs fixing  :( 

It only displays a partial time base line, like 70% or so of the screen width.  Using the x10 on the timebase things get better, like 90% or so.

We (a friend of mine and your's truly) were under the impression the CA3046 on the time base module went south but a replacement CA3046 did not help.

So more digging to do I'm afraid.  It is a nice little scope that I handed down to the aforementioned friend.  Initially the time base problem was intermittent, sensitive to gentle tapping.  Now it has become a solid fault.

Any suggestions maybe?

First try reseating all the possible connectors in the scope.
It may have shorted horizontal output transistors. The gain for the horizontal amplifier might be off due to a wonky trimpot or drifted resistors.

When using 10x time base, the gain for the horizontal amplifier is just increased by 10. If one of the driver or output transistors is shorted that may be the cause of the problem.

If you have another scope you can use the add both channels and invert one channel trick to get differential inputs and probe around the horizontal amplifier.
One can never have enough oscilloscopes.
 

Offline amspire

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Re: HP 1741A oscilloscope - restoration project
« Reply #42 on: December 29, 2011, 11:11:52 pm »
I've never had any of these fail no matter how dirty or misused the scope was. The primary problem seem to be the shorted rectifiers.

My 1740A was blowing fuses when I purchased it.  A new rectifier and it has worked perfectly ever since, so you are right - it does look like those rectifiers are the weak point in the design.  I replaced them with larger higher current ones - not pretty, but I hope it is more reliable.

Richard
 

Offline tekfanTopic starter

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Re: HP 1741A oscilloscope - restoration project
« Reply #43 on: December 31, 2011, 02:48:28 pm »
Cleaning time for the HP1740A

This is how the front panel looks before cleaning


And after
Now I just have to find a printer or something to rob it of its HP badge


Found some cold solder joints on the Z axis amplifier board


And this is what happens with a signal at the fastest time base setting
This should be a nice sinewave.
One can never have enough oscilloscopes.
 

Offline tekfanTopic starter

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Re: HP 1741A oscilloscope - restoration project
« Reply #44 on: January 06, 2012, 06:57:36 pm »
Since I've got a HP1741A that is very similar to the HP1740A I tought that it would make troubleshooting a bit easier.


The upper trace is from a working scope and the lower is from the still defective HP1740A


After a bit of searching I found a defective IC. IT contains six separate transistors. I made an adapter so that I can plug it into the curve tracer.


And sure enough one transistor was defective.


Here is the trace for a good transistor inside the IC


I found a discrete transistor with very similar carachteristics as the ones in the IC and soldered it over the IC so that it can be inserted back into the socket.




One can never have enough oscilloscopes.
 

Offline firewalker

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Re: HP 1741A oscilloscope - restoration project
« Reply #45 on: January 06, 2012, 07:09:12 pm »
Very nice!

Results?

Alexander.
Become a realist, stay a dreamer.

 

Offline BravoV

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Re: HP 1741A oscilloscope - restoration project
« Reply #46 on: January 06, 2012, 07:20:18 pm »
Really enjoying your work on fixing old scope TekFan, its an epic. ;)


I found a discrete transistor with very similar carachteristics as the ones in the IC and soldered it over the IC so that it can be inserted back into the socket.


I guess you're going to insulate the replacement transistor pins against touching those cut pins right ?

Offline tekfanTopic starter

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Re: HP 1741A oscilloscope - restoration project
« Reply #47 on: January 06, 2012, 07:25:38 pm »
Very nice!

Results?

Alexander.

I don't know yet. This is as far as I've come.

I guess you're going to insulate the replacement transistor pins against touching those cut pins right ?

Once the IC is in the socket it can't move nearly as much as to touch the cut pins. And even if it does nothing will happen since it's all low voltage low current stuff.
One can never have enough oscilloscopes.
 

Offline wkb

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Re: HP 1741A oscilloscope - restoration project
« Reply #48 on: January 06, 2012, 10:20:57 pm »

And after
Now I just have to find a printer or something to rob it of its HP badge


Heh... thought of scanning my ol' HP corporate badge.  But that won't do, you need the old, classic HP badge!
 

Offline amspire

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Re: HP 1741A oscilloscope - restoration project
« Reply #49 on: January 06, 2012, 11:03:55 pm »
TekFan,

That HP IC with the blown transistor (HP part no  1821 0002) is a CA3045 transistor array. Costs about $5. Probably worth getting a proper replacement.

Richard.
« Last Edit: January 06, 2012, 11:08:56 pm by amspire »
 


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