Author Topic: HP 1741A oscilloscope - restoration project  (Read 98037 times)

0 Members and 1 Guest are viewing this topic.

Offline tekfanTopic starter

  • Frequent Contributor
  • **
  • Posts: 385
  • Country: si
HP 1741A oscilloscope - restoration project
« on: June 27, 2011, 10:06:17 pm »
This is to all of you who are afraid to spend too much money on a scope that they don't know if it works or not. I'll try to show (hopefully) how to restore a scope in the most awful condition you can imagine.

OK so recently I got a HP 1741A 100MHz dual channel analog storage scope from ebay for an insanely low price. This picture was in the auction. Although a bit dirty, it looked quite promissing.


The package arrives. The scope was very well packed indeed. The box was almost a meter high.


This is how the scope looked when taken out of the box. As for the picture in the auction, appearances can be deceiving.


Shot of the scope from above. Notice I immediately unplugged the anode lead and touched it to ground just incase.
As for the carpet......dot't ask.


So first thing to check in an analog scope is the CRT. Prying off the rusty base connector wasn't easy.


Tube lifted to slide out from the CRT shield.


CRT on the table. It doesn't look good. The getter evaporated.


The neck of the CRT is broken so this one is useless. :'( (unless you've got an induction heater, diffusion pump, glass blowing lathe.... you get the picture).
Sadly I don't so what now? The electron gun makes a nice ornament though. ;D


It's a too nice scope to throw away or just use for parts so after a bit of searching I found a used CRT on ebay and the restoration will continue.

I will post more information as the restoration continues. Comments appreciated.




« Last Edit: June 29, 2011, 07:39:32 pm by tekfan »
One can never have enough oscilloscopes.
 

Offline Bored@Work

  • Super Contributor
  • ***
  • Posts: 3932
  • Country: 00
Re: HP 1741A oscilloscope - restoration project
« Reply #1 on: June 27, 2011, 10:31:14 pm »
What did you pay for it on eBay?
I delete PMs unread. If you have something to say, say it in public.
For all else: Profile->[Modify Profile]Buddies/Ignore List->Edit Ignore List
 

Offline saturation

  • Super Contributor
  • ***
  • Posts: 4787
  • Country: us
  • Doveryai, no proveryai
    • NIST
Re: HP 1741A oscilloscope - restoration project
« Reply #2 on: June 27, 2011, 10:44:11 pm »
Very nice tekfan,  if you photograph the before and after as you move forward, it would make a great documentary!
Best Wishes,

 Saturation
 

Offline Kiriakos-GR

  • Super Contributor
  • ***
  • !
  • Posts: 3525
  • Country: gr
  • User is banned.
    • Honda AX-1 rebuild
Re: HP 1741A oscilloscope - restoration project
« Reply #3 on: June 27, 2011, 11:15:45 pm »
I love restorations, but among the others damages, looks that there is too much salt in there.
This item looks to was near to sea water for long time.

I wish you all the luck of this world, you will need it.  :)
 

Alex

  • Guest
Re: HP 1741A oscilloscope - restoration project
« Reply #4 on: June 28, 2011, 12:01:58 am »
Lovely scope, shame to the seller! Nice HV connection too. How much was it? Have you restored any valve scopes like...

 

Offline tekfanTopic starter

  • Frequent Contributor
  • **
  • Posts: 385
  • Country: si
Re: HP 1741A oscilloscope - restoration project
« Reply #5 on: June 28, 2011, 10:47:56 am »
What did you pay for it on eBay?
It was slightly more than 30 EUR. Which for an oscilloscope is cheap, especially in europe. They normally go from 100 to 150 EUR.
America is a different story. I've seen better working scopes go for 0.99USD (shame really)


I love restorations, but among the others damages, looks that there is too much salt in there.
This item looks to was near to sea water for long time.
It looked like salt but it really isn't. It doesn't have that salty sea smell. I don'tknow what it is. It came from Germany so it can't be sea water damage.


Lovely scope, shame to the seller! Nice HV connection too. How much was it? Have you restored any valve scopes like...
I don't think it was the seller's fault. It must have stood in water somewhere (flood maybe?).

Sadly I haven't got a 547. Even the tube Teks are getting more expensive in europe. The Tek 555 can sometimes reach 300 EUR!!!
I've only got a Tek 561 with a missing HV transformer. Might restore that one in the near future.
One can never have enough oscilloscopes.
 

Offline Neganur

  • Supporter
  • ****
  • Posts: 1138
  • Country: fi
Re: HP 1741A oscilloscope - restoration project
« Reply #6 on: June 28, 2011, 11:06:15 am »
It came from Germany so it can't be sea water damage.

Oh, there's the Baltic Sea and the North Sea. It's salty too
(not trying to be smart, I was born there :))

Good luck finding a replacement, the scope looks really nice otherwise.
« Last Edit: June 28, 2011, 11:08:14 am by Neganur »
 

Offline tekfanTopic starter

  • Frequent Contributor
  • **
  • Posts: 385
  • Country: si
Re: HP 1741A oscilloscope - restoration project
« Reply #7 on: June 29, 2011, 07:38:30 pm »
Sorry for the wait. I was at a concert the other day.
Anyway now the scope is being dismantled so each individual part can be cleaned.


I've found out that you can unscrew the back half of the scope off. The power supplies can now be easily accessed.
The 4 long extender shafts  can also be seen. (top to bottom: focus, intensity, beam finder, power)


Power supply board with many filtering capacitors. I figure it's easier to start troubleshooting some components at this stage since everything is easily accessible
Transformer is disconnected and checked for shorted or open windings. Capacitors checked for ESR and capacitance. All test good.


Crystalised deposits from water damage (probably). It is not salt and doesn't smell of anything. Maybe mineral content from hard water?
The scope must have been standing face up with water dripping on it.


Luckily the scope is all made from aluminium so there's no rust on the chassis but the only thing that's iron is of course the transformer which looks like this...


Back plate, power supply board and transformer cleaned and ready for assembly.


It came from Germany so it can't be sea water damage.

Oh, there's the Baltic Sea and the North Sea. It's salty too
(not trying to be smart, I was born there :))

Good luck finding a replacement, the scope looks really nice otherwise.

The scope actually came from Stuttgart so I think it's safe to rule that one out.

More later.
One can never have enough oscilloscopes.
 

Offline Frant

  • Regular Contributor
  • *
  • Posts: 54
Re: HP 1741A oscilloscope - restoration project
« Reply #8 on: June 29, 2011, 08:56:52 pm »
Crystalised deposits from water damage (probably). It is not salt and doesn't smell of anything. Maybe mineral content from hard water?
Before you continue the restoration, you should make sure it isn't asbestos or something like that.
 

Offline tekfanTopic starter

  • Frequent Contributor
  • **
  • Posts: 385
  • Country: si
Re: HP 1741A oscilloscope - restoration project
« Reply #9 on: June 29, 2011, 09:07:11 pm »
Crystalised deposits from water damage (probably). It is not salt and doesn't smell of anything. Maybe mineral content from hard water?
Before you continue the restoration, you should make sure it isn't asbestos or something like that.

I think it's very unlikely because the scope is very well sealed. Unless it was mixed with water dripping onto the scope. Who knows. Anyway it's too late now because the thing is cleaned and doesn't pose any real threat now.
One can never have enough oscilloscopes.
 

Offline bilko

  • Frequent Contributor
  • **
  • Posts: 405
  • Country: 00
Re: HP 1741A oscilloscope - restoration project
« Reply #10 on: June 29, 2011, 09:17:41 pm »
It looks like the scope may have been stored in a damp basement. Good look with the restoration and its great to see the progress shots.
 

Offline tekfanTopic starter

  • Frequent Contributor
  • **
  • Posts: 385
  • Country: si
Re: HP 1741A oscilloscope - restoration project
« Reply #11 on: June 30, 2011, 09:00:30 pm »
More progress.

The vertical preamplifier board removed. One custom HP hybrid can be seen in the middle of the board.


Gold plating has to be cleaned on the vertical attenuator contacts.


Attenuator cam switch gold plated fingers. These move up and down in a certain sequence when turning the volts/div knob and
route the signal trough attenuators and compensation networks.


Bare frame without any circuit boards ready for assembly.


Front panel being cleaned. Looks nice without too many scratches ;D.


The things that go around the buttons being cleaned. The LEDs are probably going to be replaced because they are now 30 years old and quite dim.
One can never have enough oscilloscopes.
 

Offline tekfanTopic starter

  • Frequent Contributor
  • **
  • Posts: 385
  • Country: si
Re: HP 1741A oscilloscope - restoration project
« Reply #12 on: July 03, 2011, 02:30:15 pm »
Now the scope is assembled. Knobs still have to be put on.


All the tools and crap leftover after assembly


Ready for a power up without the CRT. A few knobs are still missing because I had to drill out the screws because they rusted and couldn't be removed normally. The knobs will be tapped and a slightly larger screw will be used.


First power up. The transformer makes a terrible buzzing noise. The problem was a shorted rectifier.


No rectifier available. What now? Four diodes of course! It looks ugly but it works. Four 1N4007 diodes were used. The reverse breakdown voltage and current is higher than the original rectifier so they should work nicely. After that the scope turns on and all the power supply voltages are present and nicely regulated.


I connected the output amplifiers that originally connect to the deflection plates to another oscilloscope in XY mode with differential inputs.


Here I'm feeding a sine wave into channel 1 input and YAY!!! The amplifiers work and I get a display on the external scope.


Scope in a scope. This is what I would see if the CRT were in the scope. Now I just have to be patient and wait for the CRT to come from America Hope it doesn't break on the way here :'(


Should I do the calibration procedure as well?




One can never have enough oscilloscopes.
 

alm

  • Guest
Re: HP 1741A oscilloscope - restoration project
« Reply #13 on: July 03, 2011, 02:36:31 pm »
The service manual may give give more details, but I would at least expect that you have to go through geometry and storage circuit adjustments after a CRT replacement. If you have the equipment, you might as well do a full calibration for peace of mind.
 

Offline slburris

  • Frequent Contributor
  • **
  • Posts: 542
  • Country: us
Re: HP 1741A oscilloscope - restoration project
« Reply #14 on: July 03, 2011, 02:40:31 pm »
Very nice!  Of course while I'm staring at the photos, I can't help but notice
the Datron 1072 multimeter in the background.  What's that, a 7 1/2 digit
meter?

I'm about to try for a scope repair myself, on a Tektronix 2246.  It works,
but the trace is noisy, even when the input is grounded, so I'm suspecting
high ripple in the power supplies.  Probably at least a nice recapping job
ahead of me.

Scott
 

Offline tekfanTopic starter

  • Frequent Contributor
  • **
  • Posts: 385
  • Country: si
Re: HP 1741A oscilloscope - restoration project
« Reply #15 on: July 03, 2011, 03:12:31 pm »
Very nice!  Of course while I'm staring at the photos, I can't help but notice
the Datron 1072 multimeter in the background.  What's that, a 7 1/2 digit
meter?

I'm about to try for a scope repair myself, on a Tektronix 2246.  It works,
but the trace is noisy, even when the input is grounded, so I'm suspecting
high ripple in the power supplies.  Probably at least a nice recapping job
ahead of me.

Scott


If it has a focus problem you might want to check this link out:
http://www.cromwell-intl.com/radio/tek2445a.html

It looks like this is a common problem in the bigger analog Tek scopes. The resistor opens up as it is right on the limit of its power rating. And yes the capacitors should definitely be replaced with low ESR types.

Here's what can happen to the capacitors in the SMPS (German but you get the picture):
http://www.spurtikus.de/basteln/tek2432_reparatur/index.html

The Datron 1072 is actually a 6 1/2 digit meter but 7 1/2 with averaging and filter on.
Here's a review/teardown I did a while ago: https://www.eevblog.com/forum/index.php?topic=3013.msg41015#msg41015
One can never have enough oscilloscopes.
 

Alex

  • Guest
Re: HP 1741A oscilloscope - restoration project
« Reply #16 on: July 03, 2011, 06:49:22 pm »
Hey tekfan, is that mica capacitor next to the rectifier for some sort of 'line trigger'?
 

Offline ivan747

  • Super Contributor
  • ***
  • Posts: 2045
  • Country: us
Re: HP 1741A oscilloscope - restoration project
« Reply #17 on: July 03, 2011, 07:29:29 pm »
I wish I had the experience to restore things  :'(
This looks awesome
 

Offline tekfanTopic starter

  • Frequent Contributor
  • **
  • Posts: 385
  • Country: si
Re: HP 1741A oscilloscope - restoration project
« Reply #18 on: July 03, 2011, 09:06:45 pm »
Hey tekfan, is that mica capacitor next to the rectifier for some sort of 'line trigger'?

Yes! It is exactly that capacitor. It's tapped off the 120VAC secondary of the transformer.


I wish I had the experience to restore things  :'(
This looks awesome

Don't be afraid to buy old non working stuff. This is how I got started in electronics. Well that and taking things apart to see how they work never to put them back again! Looking at a schematic and trying to identify the faulty part can be a very rewarding learning experience itself.
One can never have enough oscilloscopes.
 

Alex

  • Guest
Re: HP 1741A oscilloscope - restoration project
« Reply #19 on: July 03, 2011, 10:14:48 pm »
taking things apart to see how they work never to put them back again!

I used to put them back together without the PCBs and everyone was wondering why they were so lightweight.
 

Offline ivan747

  • Super Contributor
  • ***
  • Posts: 2045
  • Country: us
Re: HP 1741A oscilloscope - restoration project
« Reply #20 on: July 04, 2011, 01:39:07 am »
Don't be afraid to buy old non working stuff. This is how I got started in electronics. Well that and taking things apart to see how they work never to put them back again! Looking at a schematic and trying to identify the faulty part can be a very rewarding learning experience itself.

I have just tossed away a radio that looks from the 80's after taking it apart. I took the pots and interesting, expansive and hard to find components. I hate cheap bakelite PCB's. If it only depended on me, I would be buying this kind of stuff on eBay on a weekly basis, but I don't pay them and the shipping of this huge test equipment is as huge in cost as the equipment itself.
 

Offline tekfanTopic starter

  • Frequent Contributor
  • **
  • Posts: 385
  • Country: si
Re: HP 1741A oscilloscope - restoration project
« Reply #21 on: July 10, 2011, 10:46:33 pm »
The project continues:

At last the CRT came from the US.

Here are the broken one and the new one


Face of the old CRT


Face of the new CTR. The graticule lines are slightly thicker than the old one.
One can never have enough oscilloscopes.
 

Offline MikeB

  • Newbie
  • Posts: 1
Re: HP 1741A oscilloscope - restoration project
« Reply #22 on: October 08, 2011, 06:59:32 pm »
Hi Tekfan, this is my first post to this site. I did a similar resto to you - only mine was not quite so bad - still have one problem though.
The 'X' scan sometimes just scans half the screen - tapping some buttons can sometimes restore it - any ideas?

I do not have the manual yet!

Great resto BTW!
 

Offline Spiro

  • Contributor
  • Posts: 34
  • Country: cs
Re: HP 1741A oscilloscope - restoration project
« Reply #23 on: October 08, 2011, 09:16:31 pm »
How much was shipping from Germany?

Does it work in the end?
 

Offline amspire

  • Super Contributor
  • ***
  • Posts: 3802
  • Country: au
Re: HP 1741A oscilloscope - restoration project
« Reply #24 on: October 08, 2011, 11:08:38 pm »
Hi Tekfan, this is my first post to this site. I did a similar resto to you - only mine was not quite so bad - still have one problem though.
The 'X' scan sometimes just scans half the screen - tapping some buttons can sometimes restore it - any ideas?

I do not have the manual yet!

Great resto BTW!

I use an HP 1740A as my analog scope. Bought it cheaply with a dead power supply and fixed it. A really nice oscilloscope.

The operator and service manuals (including schematics) can be downloaded from Agilent:

Operator:  http://cp.literature.agilent.com/litweb/pdf/01740-90911.pdf
Service:  http://cp.literature.agilent.com/litweb/pdf/01740-90909.pdf

Application Note: http://cp.literature.agilent.com/litweb/pdf/5952-2040.pdf

Also the HP Journal article on the HP1740A is great:

http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1975-12.pdf

Richard
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf