HP 1741A oscilloscope - restoration project - Page 1
Forum section: electronics / testgear

author: tekfan
author_rank: Frequent Contributor
timestamp: June 27, 2011, 10:06:17 pm
content: 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.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.

author: Bored@Work
author_rank: Super Contributor
timestamp: June 27, 2011, 10:31:14 pm
content: What did you pay for it on eBay?

author: saturation
author_rank: Super Contributor
timestamp: June 27, 2011, 10:44:11 pm
content: Very nice tekfan, if you photograph the before and after as you move forward, it would make a great documentary!

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: June 27, 2011, 11:15:45 pm
content: 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.

author: Unknown
author_rank: Unknown
timestamp: June 28, 2011, 12:01:58 am
content: Lovely scope, shame to the seller! Nice HV connection too. How much was it? Have you restored any valve scopes like...

author: tekfan
author_rank: Frequent Contributor
timestamp: June 28, 2011, 10:47:56 am
content: Quote from: BoredAtWork on June 27, 2011, 10:31:14 pmIt 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)Quote from: Kiriakos-GR on June 27, 2011, 11:15:45 pmIt 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.Quote from: Alex on June 28, 2011, 12:01:58 amI 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.

author: Neganur
author_rank: Unknown
timestamp: June 28, 2011, 11:06:15 am
content: Quote from: tekfan on June 28, 2011, 10:47:56 amOh, 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.

author: tekfan
author_rank: Frequent Contributor
timestamp: June 29, 2011, 07:38:30 pm
content: 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 accessibleTransformer 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.Quote from: Neganur on June 28, 2011, 11:06:15 amThe scope actually came from Stuttgart so I think it's safe to rule that one out.More later.

author: Frant
author_rank: Regular Contributor
timestamp: June 29, 2011, 08:56:52 pm
content: Quote from: tekfan on June 29, 2011, 07:38:30 pmBefore you continue the restoration, you should make sure it isn't asbestos or something like that.

author: tekfan
author_rank: Frequent Contributor
timestamp: June 29, 2011, 09:07:11 pm
content: Quote from: Frant on June 29, 2011, 08:56:52 pmI 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.

author: bilko
author_rank: Frequent Contributor
timestamp: June 29, 2011, 09:17:41 pm
content: 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.

author: tekfan
author_rank: Frequent Contributor
timestamp: June 30, 2011, 09:00:30 pm
content: 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 androute 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.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.

author: tekfan
author_rank: Frequent Contributor
timestamp: July 03, 2011, 02:30:15 pm
content: Now the scope is assembled. Knobs still have to be put on.All the tools and crap leftover after assemblyReady 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 hereShould I do the calibration procedure as well?

author: Unknown
author_rank: Unknown
timestamp: July 03, 2011, 02:36:31 pm
content: 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.

author: slburris
author_rank: Frequent Contributor
timestamp: July 03, 2011, 02:40:31 pm
content: Very nice! Of course while I'm staring at the photos, I can't help but noticethe Datron 1072 multimeter in the background. What's that, a 7 1/2 digitmeter?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 suspectinghigh ripple in the power supplies. Probably at least a nice recapping jobahead of me.Scott

author: tekfan
author_rank: Frequent Contributor
timestamp: July 03, 2011, 03:12:31 pm
content: Quote from: slburris on July 03, 2011, 02:40:31 pmIf it has a focus problem you might want to check this link out:http://www.cromwell-intl.com/radio/tek2445a.htmlIt 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.htmlThe 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

author: Unknown
author_rank: Unknown
timestamp: July 03, 2011, 06:49:22 pm
content: Hey tekfan, is that mica capacitor next to the rectifier for some sort of 'line trigger'?

author: ivan747
author_rank: Super Contributor
timestamp: July 03, 2011, 07:29:29 pm
content: I wish I had the experience to restore thingsThis looks awesome

author: tekfan
author_rank: Frequent Contributor
timestamp: July 03, 2011, 09:06:45 pm
content: Quote from: Alex on July 03, 2011, 06:49:22 pmYes! It is exactly that capacitor. It's tapped off the 120VAC secondary of the transformer.Quote from: ivan747 on July 03, 2011, 07:29:29 pmDon'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.

author: Unknown
author_rank: Unknown
timestamp: July 03, 2011, 10:14:48 pm
content: Quote from: tekfan on July 03, 2011, 09:06:45 pmI used to put them back together without the PCBs and everyone was wondering why they were so lightweight.

author: ivan747
author_rank: Super Contributor
timestamp: July 04, 2011, 01:39:07 am
content: Quote from: tekfan on July 03, 2011, 09:06:45 pmI 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.

author: tekfan
author_rank: Frequent Contributor
timestamp: July 10, 2011, 10:46:33 pm
content: The project continues:At last the CRT came from the US.Here are the broken one and the new oneFace of the old CRTFace of the new CTR. The graticule lines are slightly thicker than the old one.

author: MikeB
author_rank: Newbie
timestamp: October 08, 2011, 06:59:32 pm
content: 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!

author: Spiro
author_rank: Contributor
timestamp: October 08, 2011, 09:16:31 pm
content: How much was shipping from Germany?Does it work in the end?

author: amspire
author_rank: Super Contributor
timestamp: October 08, 2011, 11:08:38 pm
content: Quote from: MikeB on October 08, 2011, 06:59:32 pmI 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.pdfService:http://cp.literature.agilent.com/litweb/pdf/01740-90909.pdfApplication Note:http://cp.literature.agilent.com/litweb/pdf/5952-2040.pdfAlso the HP Journal article on the HP1740A is great:http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1975-12.pdfRichard

author: BravoV
author_rank: Super Contributor
timestamp: October 10, 2011, 07:38:22 am
content: 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.

author: tekfan
author_rank: Frequent Contributor
timestamp: October 10, 2011, 02:15:42 pm
content: 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).

author: appsman
author_rank: Contributor
timestamp: October 12, 2011, 06:10:17 am
content: 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.

author: dfnr2
author_rank: Regular Contributor
timestamp: October 13, 2011, 06:09:59 am
content: 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

author: tekfan
author_rank: Frequent Contributor
timestamp: October 16, 2011, 07:41:46 pm
content: 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 betterAfter some calibration:The trace is the pulse from the Jim Williams pulse generatorThe rise time is slightly over 2ns as opposed to the specified 3.5nsThis scope can easily display signals well beyond 100MHzThe 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 onAnd since it's a storage scope you can even play Etch A Sketch on it:

author: lowimpedance
author_rank: Super Contributor
timestamp: October 17, 2011, 03:15:49 am
content: 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 ??

author: vk6hdx
author_rank: Regular Contributor
timestamp: October 17, 2011, 06:55:22 am
content: Nice work and great result, thanks for sharing this restoration project with us.Troy

author: BravoV
author_rank: Super Contributor
timestamp: October 17, 2011, 07:04:32 am
content: Thanks for sharing this restoration job, well done and congratulations too !Btw, what Jim Williams pulse generator ? Link ?

author: tekfan
author_rank: Frequent Contributor
timestamp: October 18, 2011, 07:29:56 pm
content: Quote from: BravoV on October 17, 2011, 07:04:32 amhttp://cds.linear.com/docs/Application%20Note/an47fa.pdfPage 93-95I've tried to make it as small as possible for my self for the convenience. A little flimsy on the stripboard but it works:

author: BravoV
author_rank: Super Contributor
timestamp: October 24, 2011, 10:57:51 am
content: Quote from: tekfan on October 18, 2011, 07:29:56 pmThank 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 ?

author: Omicron
author_rank: Regular Contributor
timestamp: October 24, 2011, 05:06:31 pm
content: Quote from: tekfan on October 18, 2011, 07:29:56 pmBe 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.

author: tekfan
author_rank: Frequent Contributor
timestamp: December 28, 2011, 11:48:15 pm
content: 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 troughis 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.

author: FenderBender
author_rank: Super Contributor
timestamp: December 29, 2011, 02:45:44 am
content: 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.

author: BravoV
author_rank: Super Contributor
timestamp: December 29, 2011, 09:31:03 am
content: 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.

author: tekfan
author_rank: Frequent Contributor
timestamp: December 29, 2011, 02:19:13 pm
content: Quote from: BravoV on December 29, 2011, 09:31:03 amThe 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.

author: wkb
author_rank: Super Contributor
timestamp: December 29, 2011, 05:45:18 pm
content: Nice job Tekfan!Reminds me of the Tek 2213a that I have sitting here and still needs fixingIt 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?

author: tekfan
author_rank: Frequent Contributor
timestamp: December 29, 2011, 06:29:53 pm
content: Quote from: wkb on December 29, 2011, 05:45:18 pmFirst 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.

author: amspire
author_rank: Super Contributor
timestamp: December 29, 2011, 11:11:52 pm
content: Quote from: tekfan on December 29, 2011, 02:19:13 pmMy 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

author: tekfan
author_rank: Frequent Contributor
timestamp: December 31, 2011, 02:48:28 pm
content: Cleaning time for the HP1740AThis is how the front panel looks before cleaningAnd afterNow I just have to find a printer or something to rob it of its HP badgeFound some cold solder joints on the Z axis amplifier boardAnd this is what happens with a signal at the fastest time base settingThis should be a nice sinewave.

author: tekfan
author_rank: Frequent Contributor
timestamp: January 06, 2012, 06:57:36 pm
content: 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 HP1740AAfter 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 ICI 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.

author: firewalker
author_rank: Super Contributor
timestamp: January 06, 2012, 07:09:12 pm
content: Very nice!Results?Alexander.

author: BravoV
author_rank: Super Contributor
timestamp: January 06, 2012, 07:20:18 pm
content: Really enjoying your work on fixing old scope TekFan, its an epic.Quote from: tekfan on January 06, 2012, 06:57:36 pmI guess you're going to insulate the replacement transistor pins against touching those cut pins right ?

author: tekfan
author_rank: Frequent Contributor
timestamp: January 06, 2012, 07:25:38 pm
content: Quote from: firewalker on January 06, 2012, 07:09:12 pmI don't know yet. This is as far as I've come.Quote from: BravoV on January 06, 2012, 07:20:18 pmOnce 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.

author: wkb
author_rank: Super Contributor
timestamp: January 06, 2012, 10:20:57 pm
content: Quote from: tekfan on December 31, 2011, 02:48:28 pmHeh... thought of scanning my ol' HP corporate badge. But that won't do, you need the old, classic HP badge!

author: amspire
author_rank: Super Contributor
timestamp: January 06, 2012, 11:03:55 pm
content: 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.

author: tekfan
author_rank: Frequent Contributor
timestamp: January 19, 2012, 03:13:05 pm
content: Almost finished:When I got the oscilloscope it didn't have the HV power supply cover as someone was obviously trying to troubleshoot it.I used the cover of an old ATX power supply. It fits very nicely.This is what the step response looks like.I am feeding a fast risetime square wave from a Tek 106 generator (<1ns risetime) into the scope input terminated to 50 ohms at 50ns/div.There is a lot of overshoot. This can be compensated out by adjusting the HF response of the vertical output amplifier.Vertical amplifier compensated. The step looks much cleaner now.And the end result is another nice oscilloscope from the 70's

author: krivx
author_rank: Frequent Contributor
timestamp: January 19, 2012, 04:08:32 pm
content: This is really impressive!What are you using to clean the front panels? I have a Philips scope from this period that is more-or-less functional but is a bit grimy.

author: firewalker
author_rank: Super Contributor
timestamp: January 19, 2012, 04:19:06 pm
content: Excellent job! Look like new.Alexander.

author: Unknown
author_rank: Unknown
timestamp: January 19, 2012, 04:33:36 pm
content: Beauty!and nice photography too.

author: tekfan
author_rank: Frequent Contributor
timestamp: January 19, 2012, 05:16:48 pm
content: Quote from: krivx on January 19, 2012, 04:08:32 pmI almos always use window cleaner, a cloth, toothbrush with bristles cut short, cotton swabs and that's about it.

author: wkb
author_rank: Super Contributor
timestamp: January 19, 2012, 05:49:35 pm
content: My compliments! Beautiful job!

author: Kilroy
author_rank: Regular Contributor
timestamp: January 19, 2012, 10:40:14 pm
content: Awesome.I find it particularly fascinating that the finished scope is now a 1740A instead of the original 1741A.

author: ilikepez
author_rank: Regular Contributor
timestamp: January 20, 2012, 01:22:57 am
content: Quote from: Kilroy on January 19, 2012, 10:40:14 pmHe got a second one to restore.You did an amazing job tekfan. I hope to be that good with electronics someday. I don't know what it is about electronics from the 1970's but they all look gorgeous.

author: Teknotronix
author_rank: Regular Contributor
timestamp: January 20, 2012, 02:29:28 am
content: Great work!

author: snoopen
author_rank: Contributor
timestamp: January 20, 2012, 03:18:26 am
content: Great work mate! Nice hacks with the IC transistor and ATX PSU case!

author: siliconmix
author_rank: Frequent Contributor
timestamp: January 23, 2012, 09:47:00 pm
content: nice job

author: bsgd
author_rank: Regular Contributor
timestamp: January 24, 2012, 01:06:40 am
content: I just love the looks of old instruments!Too bad they cost a fortune here and Im stuck with cheap chinese stuff.

author: wkb
author_rank: Super Contributor
timestamp: January 24, 2012, 03:51:48 pm
content: Quote from: bsgd on January 24, 2012, 01:06:40 amAgreed! And the build quality of the older stuff is just so much nicer. OK.. the prices are another matter. I think the list price of my Tek 2465CTS was something like US$ 6800 in its day... Ouch

author: calin
author_rank: Regular Contributor
timestamp: January 24, 2012, 09:22:58 pm
content: I just grabbed one of these in a much much better condition of an craigslist ad .. if you can believe it .... for 50$ cash !!! insane !!I can't wait to see how is working cause right now is resting in the trunk of my car as I am @ work.

author: bsgd
author_rank: Regular Contributor
timestamp: January 24, 2012, 10:45:01 pm
content: Quote from: wkb on January 24, 2012, 03:51:48 pmWell agreed again! The quality on this stuff is really nice. Much better than any other electronics most of us can afford. And thats probably because these were very expensive on the past and we can glance at how well something could be engineered if price was not the single most important factor in manufacturing.

author: bsgd
author_rank: Regular Contributor
timestamp: January 24, 2012, 10:45:52 pm
content: Quote from: calin on January 24, 2012, 09:22:58 pmCan you post some pics? Please please please

author: mayeri
author_rank: Contributor
timestamp: December 09, 2012, 06:17:37 pm
content: Hi all, I has recently been registered in this site because I saw the HP 1741A restoration project. The published images reveal a very impressive professional knowledge about oscilloscopes.Not long ago I received a similar device from my acquaintance who has not used this about five years.Let us breathe life into the topic…

author: mayeri
author_rank: Contributor
timestamp: December 09, 2012, 06:20:06 pm
content: The storage mode seems ok…

author: mayeri
author_rank: Contributor
timestamp: December 09, 2012, 06:23:46 pm
content: These two problems with conventional mode. How do I get rid of them? Please, TekFan...

author: tekfan
author_rank: Frequent Contributor
timestamp: December 09, 2012, 07:38:04 pm
content: Quote from: mayeri on December 09, 2012, 06:17:37 pmWelcome to the forum! Hope you find some useful stuff on the forum.So, looking at the storage controls (PERSISTENCE and BRIGHTNESS) they are almost fully counterclockwise. In this case when the scope is in storage mode you should get a screen that is completely green. The trace should fade out very fast since the persistence control is almost at its minimum.In STORAGE mode the you should get the following displays with the control settings:PERSISTANCE min., BRIGHTNESS min. ---> CRT looks completely greenPERSISTANCE min., BRIGHTNESS max. ---> CRT looks completely green, slightly brighter trace and screenPERSISTANCE max., BRIGHTNESS min. ---> CRT no longer green, trace is stored on the screenPERSISTANCE max., BRIGHTNESS max. ---> CRT no longer green, stored trace is slightly brighterPressing the ERASE button causes the screen to flash brightly and erase the stored imageWhen the scope is in CONVENTIONAL mode, the screen shouldn't be green anymore and the trace should fade out almost instantly. The storage controls should have absolutely no effect in CONV mode.What may be happening is that one of the logic ICs on the storage board is defective, causing the flood guns and storage functions to be operatied in the CONV mode. This may also be caused by leaky transistors driving the flood gun control grids, collimator plates, collector mesh, and storage mesh.Check if the storage controls (PERSISTENCE and BRIGHTNESS) have any effect when the scope is in STORAGE and CONV mode.Those are all the ideas I've got at the moment.You may want to read the Theory of operation section of the service manual (onward from page 94):http://cp.literature.agilent.com/litweb/pdf/01741-90911.pdf

author: mayeri
author_rank: Contributor
timestamp: December 09, 2012, 10:36:54 pm
content: Hi TekFan,Thanks for the quick response. I thought it will not be too easy…In storage mode I get a good picture in only one position: PERSISTANCE min., BRIGHTNESS min.The storage controls (PERSISTENCE and BRIGHTNESS) do absolutely no effect in CONV mode. That’s ok.

author: mayeri
author_rank: Contributor
timestamp: December 09, 2012, 10:39:31 pm
content: I show the rest:

author: mayeri
author_rank: Contributor
timestamp: December 09, 2012, 10:59:40 pm
content: PERSISTANCE

author: SeanB
author_rank: Super Contributor
timestamp: December 10, 2012, 04:53:58 am
content: I have a dead storage scope mainframe somewhere....... Think the tube still works.

author: mayeri
author_rank: Contributor
timestamp: December 10, 2012, 09:05:08 pm
content: Does this phenomenon show an obviously defective tube? I would trust in the TekFan’s experience firstly…Tube replacement would be? Then the spot remains…Despite the spot it could be used in conventional mode.

author: tekfan
author_rank: Frequent Contributor
timestamp: December 11, 2012, 05:10:59 am
content: So first thing I would do wether the scope works or not is to measure the power supply voltages. If one of them is missing or low it may be causing problems in the storage system. Both my HP scopes had problems with the power supply.So take off the covers and start probing. The mains cabling is shielded away under a small plastic cover (near the voltage selector) so the risk of shock is very small. The HV power supply for the CRT is also under an aluminium cover. The test points for the supply voltages are clearly labeled on the power supply board. Check +15, -15, +5, +48, +120, +156 and -100 volt supplies with a multimeter (the case of the scope is ground). If they are there and stable then move onward.I strongly suggest reading the Theory of operation section of the manual. Try to follow the circuit diagram. If you look closely there are also important voltages written on some circuit diagrams.I wouldn't say the tube is dead just yet. If it behaves this strangely even in normal mode it's probably another fault.Besides HP never made a scope with the same CRT as the 1741 so replacement can only be done with the same tube.

author: mayeri
author_rank: Contributor
timestamp: December 11, 2012, 10:42:12 pm
content: Hi TekFan,You were right.The supply voltages are not ok. It seems at first glance that may be some problems with the power supply.The burned diode is almost certainly failed, the resistance may be not.Now I have to check in quickly in Theory of Operation section of the manual relevant parts of the schematic of the power supply.

author: tekfan
author_rank: Frequent Contributor
timestamp: December 11, 2012, 11:40:32 pm
content: Great work so farThe resistor and diode are used as a primitive voltage regulator. That's actually a 100V zener diode in series with the 3.3k resistor. The -100V supply is used exclusively by the storage circuit so that may very well be the problem. The diode would probably have a too high voltage drop to be tested by a multimeter so the only hope is actual in circuit operation. The orange Sprague 10uF / 200V capacitor looks like it overheated from the nearby resistor. It will probably work if you leave still leave it in the circuit. They are very tough capacitors, but be sure to replace it in the long term.Try to unplug the small board that interconnects all the boards in the scope. That way you can unload the power supply and see if the supply voltages rise to their nominal values. That way you can determine if there is a problem somewhere else in the scope. You can also slightly (or rather considerably) bend the boards out of the way so that you can connect the power supply to only one board at a time. That way you can isolate the problem at least down to board level.Be sure to check the +48, +15, -15 and +5 volt supples. It's also used by the storage board. The unregulated +15V supply looks fine. It can actually be as high as 25V. The high voltage inverter for the CRT uses this supply. The other voltages also seem to be within spec.I might add that both of my scopes had several faulty bridge rectifiers. When the scope is turned on you could hear the transformer humming loudly since the rectifiers had shorted. I also had problems with several shorted series pass transistors mounted on the back heatsink. Worth checking those with the diode test function. They are on connectors so no desoldering is needed.Just keep measuring the thing. You'll eventually find what's wrong.

author: mazurov
author_rank: Frequent Contributor
timestamp: December 12, 2012, 10:41:53 pm
content: Tekfan: How do you clean the controls? I have a Tek 7934 which works very well but some knobs and buttons are stiff and/or "sticky".

author: mayeri
author_rank: Contributor
timestamp: December 13, 2012, 12:30:18 am
content: Hi TekFan,I replaced the diode, the resistor ok, 3,3k. Really, this resistor and diode very primitive voltage regulator solution. There was not 100v Zener at home, so I soldered together three diodes temporary (56 v + 33 v + 12 v). All three diodes are heating little bit, so it may need to add a series-pass transistor. Anyway, tomorrow I will buy a 100v zener.I checked all the voltage again. It seems everything is ok (48, +15, +15, +5). I think so that each graetz works properly.

author: mayeri
author_rank: Contributor
timestamp: December 13, 2012, 12:31:26 am
content: The result: in CONV mode the spot has disappeared.

author: mayeri
author_rank: Contributor
timestamp: December 13, 2012, 12:34:00 am
content: I noticed a strange phenomenon in Conventional mode: The beam intensity does not function properly. When turning button the brightness increases linearly in the first period, then suddenly becomes brighter and then returns to its previous brightness level. From this point the brightness does not change any further turning of the button.

author: mayeri
author_rank: Contributor
timestamp: December 13, 2012, 12:36:29 am
content: Surely there is a problem in storage circuit.Turning brightness button:

author: tekfan
author_rank: Frequent Contributor
timestamp: December 14, 2012, 02:14:10 pm
content: Quote from: mayeri on December 13, 2012, 12:34:00 amThis is the screen protection kicking in. There's a maximum current limit trimpot in the HV power supply that sets the max current to the CRT. If this current is exceeded it will slightly reduce it by dimming the beam. If the spot on the screen is too bright it might permanently burn the metal storage meshes behind the screen.When in storage mode there is a very small area where the beam is visible and the entire screen being flooded by the excess electrons if the beam intensity is too great. So you must use the minimum intensity to get a nice, visible display.The brightness control is operating as it should. Somewhere in the middle position you should get a pre-fogged screen state (slight green spots appear).The storage CRTs age quite a bit more noticeably than regular non storage. That's why regular calibration of the storage circuit is very important.You can do a partial adjustment with only a screwdriver, multimeter and good eye. Look at page 43 where the storage adjustment section starts (especially paragraph 5-62). That will bring the brightness control back into the proper range. If you have another scope and a signal generator you can do a complete storage circuit calibration.It seem that in the pictures you took the delayed timebase is turned on. Turn it off by rotating the outer timebase knob fully clockwise before making adjustments or storing images. It really works only in conventional mode since the intensified spot on the trace causes the screen to flood in storage mode.

author: mayeri
author_rank: Contributor
timestamp: December 14, 2012, 06:07:38 pm
content: Thank you very much for your continuous support.Even I want to show this… the screwdriver was used enough.

author: mayeri
author_rank: Contributor
timestamp: December 14, 2012, 06:10:26 pm
content: Unfortunately, my another oscilloscope is broken too.EMG 1568/2A (2x50Mhz). Search it with Google, it is interesting look at him. This is one of products of an former, now defunct Hungarian electronics factory, it it called EMG. Power supply also was defective, but I am still hunting for the fault because the electron beam is missing.Do you know? I would not be so lucky…

author: timjimbaker
author_rank: Newbie
timestamp: February 07, 2013, 07:31:19 pm
content: Quote from: tekfan on December 28, 2011, 11:48:15 pmHey Guys, this is my first post. This is a great forum, I hope to frequent it now that I've found it...I need a bit of help. Just bought a 1740a. It's in decent shape except for one thing. Someone must have lubricated the time division switch with something they shouldn't have many years ago. Basically what ever it was has broken down and turned to glue... I fired some deoxit in there and it freed up the switch. I figured that had fixed the problem. The next day, the switch had re-glued its self again. I dismantled the assembly and took out the pcb that is sandwiched by the two halves of the switch. The glue/lube cleaned up nicely. My problem is that a few of the contacts have been pulled out of their slots on the switch. Tekfan was kind enough to post all of those great photos of his restoration. One of which is one half of the switch. It shows where the contacts for that side belong. I was hoping someone may have a photo or diagram of the other half so I can make sure the contacts get put back to where they belong.Thanks. Best regards, Tim.

author: tekfan
author_rank: Frequent Contributor
timestamp: February 07, 2013, 08:27:01 pm
content: Quote from: timjimbaker on February 07, 2013, 07:31:19 pmI'll dismantle the scope sometime during the weekend and post the pictures.Luckily they didn't use multi-wafer switches. That would be a real pain to clean up.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: February 07, 2013, 09:07:37 pm
content: I have a 1742 and a 1725 both of which need to be opened at some stage.But from my recollection if you look carefully you should be able to see from which positions the contacts had been mounted. You can see small wear marks.Hopefully you don't have any broken leaf springs. I have one broken one that I fixed with a banana plug and an angle grinder but It isn't a long term solution. I have some watch spring steel that I am going to use to fix it a bit more nicely. One day.

author: lowimpedance
author_rank: Super Contributor
timestamp: February 07, 2013, 11:13:05 pm
content: .QuoteThe lube/GLUE like goop is whats left of the original HP lube used on these series of CRO's.Does not age at all well as you have found, how ever its easily removed and new lube applied.I have cleaned half a dozen of these series oscilloscopes with this 'glue issue', and none of themhad been touched since new.

author: timjimbaker
author_rank: Newbie
timestamp: February 11, 2013, 04:42:27 pm
content: Sorry guys... Late reply. Busy weekend here...QuoteTekfan - That would be amazing but probably above and beyond the call of duty... I hate to take up that much of your time.QuoteHackedFridgeMagnet - Unfortunately no wear marks, not a trace to be seen. The PCB and wafers are in quite good shape aside from the glue problem.QuoteOne is broken. One of the prongs got torn off. I think I'll be able to fashion something to take it's place.QuoteLowimpedance - Wow! Now that you mention it, that makes total sense. The inside of the scope is in excellent shape. I couldn't figure out why that gloop was the only invasion... When someone does something dumb to modify equipment, they usually do more damage than that!I guess it was hard to HP to be able to predict how a particular lubricant was going to perform decades later... BTW, what did you use to re-lubricate the switches?Thanks everyone. Your help is appreciated. -Tim

author: tekfan
author_rank: Frequent Contributor
timestamp: February 11, 2013, 07:10:29 pm
content: Here are pictures of the switch contactsThe contact positions should be exactly the same for the 1741 and 1740 scopes. I think the 1741 has some slightly different resistor values for the slow sweep speed holdoff time. It's a bit longer since you don't want double triggers when storage mode.Main time base switchesDelayed time base switches

author: lowimpedance
author_rank: Super Contributor
timestamp: February 11, 2013, 11:09:06 pm
content: QuoteI used 'Electrolube brand' part no.SGB35SL (contact treatment grease) to carefully lube the contacts and also applied some to the axle hub.Any 'suitable' grease you can get for electronic use should be okay. (The one I used I purchased from Farnell some time ago, have not lookedto see if its still stocked!). I used IPA to remove the fossilized grease (be VERY careful with the switch contacts,they are delicate!).

author: timjimbaker
author_rank: Newbie
timestamp: February 12, 2013, 12:43:50 pm
content: Tekfan... Thanks so much! I appreciate you doing that for me. I'd be happy to return the favour anytime. BTW, nice Leslie in the background of one of your photos on this thread.Lowimpedance - Thanks, I'll find something that'll work.Take care guys...-Tim.

author: Martin.M
author_rank: Frequent Contributor
timestamp: February 14, 2013, 11:54:18 am
content: hello tekfan,great job, congratulations.The cold scopes are oftleny more complicated to restore then the glowing oldies.I start now the restoration of my second triple nickel :-)greetings from germanyMartin

author: timjimbaker
author_rank: Newbie
timestamp: February 14, 2013, 03:34:57 pm
content: I managed to fix the two broken contacts on the main time base switch. It is a bit tedious to get them just right. I got the spring steel from those stick on anti-theft tags that many stores put on their products. I think they are called "sensormatic" tags. Inside each one is two pieces of spring steel. One is a thicker gauge and it is pretty spot on the the gauge of the contacts. It is still thin enough to cut with a sharp razor blade. Far easier to cut out the shape of the contacts with that than a pair of snips... The spring steel in those sensormatic tags is real handy stuff. I always save those tags when I see them. Also, old windshield wipers have great spring steel in them for making small tools and the like... I grab that when I can too!Best regards, Tim.

author: peterpan
author_rank: Newbie
timestamp: February 14, 2013, 05:14:46 pm
content: Quote from: mayeri on December 14, 2012, 06:10:26 pmHello mayeri!Look here :http://elektrotanya.com/?q=hu/content/about-siteThe site language is hungarian, but you can write in english, if it is easier for youFor example :http://elektrotanya.com/?q=hu/content/emg-15682-szkop-sokszorozo-aramkoerebe-kondenzatort-keresek-500pf15kv-megoldva

author: RacerX
author_rank: Contributor
timestamp: December 21, 2013, 04:40:16 am
content: Quote from: lowimpedance on February 07, 2013, 11:13:05 pmSorry to resurrect such an old thread, but I just stumbled across it and it is relevant to an issue I recentlyencountered...I have a HP 1725A scope and have cleaned the switch contacts of the petrified grease HP applied over30 years ago. However, since I did not have any on hand I did not re-apply any contact lubricant.Should I be worried? HP put it there for a reason... am I going to quickly wear the gold plating away?I plan to apply some Electrolube in the near future but this thing will be OK for some normal usage inthe meantime, yes?

author: tekfan
author_rank: Frequent Contributor
timestamp: December 23, 2013, 12:36:30 am
content: I've heard that gold contacts have self lubricating properties. If you look at most multimeters there's no grease in the switches.

author: robrenz
author_rank: Super Contributor
timestamp: December 23, 2013, 01:34:42 am
content: Caig Deoxit G100L is tough to beat on gold contacts.

author: MuchMore
author_rank: Contributor
timestamp: January 26, 2014, 04:31:47 pm
content: HeyI am new to this Forum, so I guess a short introduction is necessary:I am:- a mechanical engineering student- 22 years old- from Austria (not Australia)- (have) some experience in electronics- quiet frustrated with my first oscilloscopeNow to my Problem:I recently bought my first oscilloscope an HP 1740. After some testing I figured the time/sweep assembly must have some bad switch/contacts. I carefully removed the main sweep board and immediately saw that there was someone in before me. After cleaning the contacts I spotted that one "flyleg" was bend so I brought it back to the standard position and recognized the metal was very weak, after a closer "look" it snapped off......does anyone have a good idea how to fix "my" mistake?? replacing the leg seams quite difficult. And I guess HP does not sell replacement parts!?!P.s.: All remaining grammar mistakes are placed on purpose, to ensure an pleasing reading experience...

author: tekfan
author_rank: Frequent Contributor
timestamp: January 26, 2014, 10:52:59 pm
content: Hi! Welcome to the forum.Probably your best bet on replacing the switch wiper is to find a similar sheet of metal and make the part yourself.The sheet metal is very thin so don't expect your local hardware store to have it in stock. It also must be quite springy so it doesn't deform when you turn the switch.You can ask in the hardware stores if they know where you can get spring steel sheet (''federblech'').You can also try to find a mechanical clock because the spring inside the clock is just the right material. It may be too thick but still worth a try. If you have a mechanical egg timer it probably has this type of spring inside. The only thing you need to do is to cut and bend it into the correct shape. You could also try to find a watchmaker or jeweler and as if he's got some similar metal.To disassemble the switch to get the wiper contacts out you will have to do the following:On the other side of the switch there are several marks where the two halves of the switch were sealed together by melting the plastic. You will have to carefully remove this plastic dimples so that the two switch halves can be separated. You can even try to drill out the plastic. Just be careful not to damage the rest of the switch.Once you have the switch apart you can remove the broken wiper contact and another one so that you know the exact shape of it.To put the two halves together you will probably have to use some sort of glue. It's easier to remove afterwards if it needs repair again.Here you can see the 4 melted plastic dimples that hold the two halves together:

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: January 26, 2014, 11:01:43 pm
content: Yes very light spring steel.I did one with a banana plug and an angle grinder, It worked but would have been no good, long term.I then got some spring steel and was set up to fix it when somebody gave me another scope which I then cannibalised for parts.

author: MuchMore
author_rank: Contributor
timestamp: January 27, 2014, 12:43:08 am
content: Heythanks for the fast replies.After some thinking I remembered that there was a useless Battery Tester in my drawer.And sure enough there where two flylegs inside.The idea of removing the molten nipples is risky, since the plastic is soooo old I fear it will shatter while Drilling.I came up with the idea of removing a pocked, with a dremel, on the front big enough to fit the new flyleg and glue it with epoxy.However if I mess this up it is over...Since the new flyleg is at least coated with copper is it a longtherm issue off rupping on the goldpats?I could get a Nickel-solution to make it like the other once..??P.s.: some rant from me: I HATE THE IMPERIAL SYSTEM, now I can go to an expensive hardware store to get does *** Hex keys that will fit the screws inside the knops.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 27, 2014, 06:39:37 am
content: The problem with the Imperial System is all the little inconsistencies,like the fact that US Gallons are smaller than British/Australian ones,so that a "44 Gallon drum" in Oz translates to a "55 Gallon drum" in the USA.They are both,thankfully,near as dammit to 200litres.Old Brit type equipment is likely to have Whitworth,UNC,UNF,BA (AAARRRGH!),or BSF (double AAARRRGH!) screws,while the smaller screw sizes used in US equipment are of a incomprehensible & completely incompatible series.In the larger sizes,UNF is pretty much common to both,some UNC,SAE,& Whitworth are compatible in very large sizes.Even metric screws have weird things,though.--- small Japanese metric screws were different to the same nominal size German screws---though this may have been sorted out in more recent times.

author: SeanB
author_rank: Super Contributor
timestamp: January 27, 2014, 04:19:35 pm
content: Metric at least has defined threads and pitches, and taps and dies are available for them all in a single series ( ok it is a 20 page pdf) for ease of use.

author: Kilroy
author_rank: Regular Contributor
timestamp: January 27, 2014, 05:57:00 pm
content: Quote from: MuchMore on January 27, 2014, 12:43:08 amThe biggest thing to watch out for is that surfaces of anything coming in contact with the gold is a totally smooth, polished finish. The slightest bit of surface roughness will tear the gold right up. Just because it feels smooth to the hands does not mean it is so. Check everything under at least a 12X loupe to be sure...smooth stuff can look particularly horrible under magnification. I use very fine Japanese waterstones for polishing wiper surfaces for these types of repairs. You can *not* use fine wet/dry sandpaper....3000 grit wet/dry will leave a much worse surface than a 3000 grit Japanese waterstone finish. Always carefully compare the finish on the original contact surface with the finish on any potential replacement material before you consolidate the repair. Any impatience or shortcuts in the procedure will reward you with a ruined switch surface.The HP 1740A/1741A machines are beautiful instruments, perform well beyond their specifications, nice to work on when/if the time comes, and well worth the trouble to repair them when they do require a bit of attention. I would plough ahead with the repair if everything else looks good with the scope. The experience alone counts for something.Incidently, since the board requiring the repair is the main sweep pcb, I would check the Sprague 109D 100uf 30v wet tantalum capacitor when your are in there. After much use this cap had a tendancy to fail, which kills the slower sweep speeds. It's usually not particularly catastrophic when it happens, but since the sweep board will be out anyway I would just go ahead and replace it. If it is anything other than a Sprague 109D then it has probably already been replaced....hopefully with an equivilent milspec substitute.

author: MuchMore
author_rank: Contributor
timestamp: January 27, 2014, 08:07:08 pm
content: @KilroyHeymhmm polishing the pad is a very good idea... however I was a Little bit fast. I already put in the new flyleg and glued it back together. (was a real pain in the ass job)I don't know if it is very practical to polish them when they are inside the Frame, or if it would break another one, and there is no way to separate them now (the epoxy is really tough)I have to think about that.About the cap: you mean C11 ?? I can't read the name on the part. If you mean C11 than yes it look really crusty, but the slow timebases work just fine (for now).I don't have the exact replacement part, however I can write it on a list for the next Mouser order.So it seams you know which parts are up for an replacement. It would be amazing if you can write a small list containing parts that are prone to fail?for now the scope works, but the knops for the vertical Settings are very "funky", means: you turn them and the line jumps around like crazy, but it is stable when you leave it alone. Is there an easy way to clean the pots, or do I have to replace those? (I have not jet removed the main vertical board)and the second Problem is, when I Change the Volts/div the ground Level jumps around. Is this an calibration issue or an Hardware failure??I really appreciate your help, (and I like the positive Response to the metric System)

author: lowimpedance
author_rank: Super Contributor
timestamp: January 28, 2014, 02:41:37 am
content: Neat refit job on the switch there.Sounds like you need to clean the vertical switches as well.Couple of things to check are the power components on the power supply (including the connectors for any fatigued joints and re flow any suspect looking ones. Also make sure you lubricate the mechanical surfaces of the timebase switches don't need much but will help with the "feel" of the switch detents when rotating. One other failure I have had was a power resistor in the vertical amp hybrid 'bias' go high in value killing all vertical signal getting to the vertical deflection stage.

author: Kilroy
author_rank: Regular Contributor
timestamp: January 28, 2014, 04:13:25 am
content: Looks like you used a wiper off something else for the repair so you should be fine, no worries there, and you saved futzing about fabricating a special part.C11 is the right one. Often fails open when it goes and you don't get much, if any, warning that it is near death. Suddenly your slower sweep speed is a flickering flat trace originating from somewhere mid screen. This cap is specified at 20v which I suspect is probably towards the low end of the requirement...possibly to keep leakage and ESR down as low as possible, since this tends to go up for equivilent capacitors having higher voltage ratings.You can replace the original Sprague 109D wet slug with a good solid tantalum if you prefer. I like the Kemet T140 as a substitute...not inexpensive but very low ESR, low DC leakage, good heat performance and stability. I usually go up a bit in the voltage rating but these HP 1740A/1741A machines are very solid, and would go for years and years with no trouble on the originally specified components so if you want to stick with the original 109D 20v cap there's no reason not to.Sounds like you need to go over all the controls and give them a good clean and flush with isopropyl.

author: MuchMore
author_rank: Contributor
timestamp: January 28, 2014, 10:11:36 pm
content: Ok I guess that I am not willing to spend 1/8 the money I paid for the scope on an cap the may fail in the future... and when it fails I will replace it with a good cap that will do the Job.@lowimpedance I can't find an power-resistor on the vertical-amp?? which one do you mean??The high voltage supply look not sooo good, can someone take a look and tell if there is a part that may be at the end of its lifetime??

author: lowimpedance
author_rank: Super Contributor
timestamp: January 28, 2014, 10:25:30 pm
content: That would be R3 on PCB A5 (see circuit diagram) fed from 43V rail. (HP1740)The High voltage PCB has a little 'soot' on it which is normal for circuits running at high tension (Old CRT TV's for example), so nothing from your photo's looks too bad actually.Maybe a gentle wipe with a soft cloth (and a little IPA) to remove the soot.Check the soldering for any suspect joints, one last inspection and put the cover back on , and don't worry about component failure until it does!!.Clean your vertical attenuators.

author: tggzzz
author_rank: Super Contributor
timestamp: August 29, 2014, 10:32:56 pm
content: I've recently restored a 1740 that was more-or-less functional before I bought it; it now works well. Nice machine.The remaining "suboptimality" is that the digits on the timebase knob/dial are hardly visible, partly due to grime on the transparent plastic, partly because the charaters are worn away. I'd like to clean the transparent plastic and replace the legend. How do I mechanically disassemble the knob/dial itself, so that I can access the legend?(To state the bleedin' obvious, I can get the dial out of the machine).Thanks.

author: tautech
author_rank: Super Contributor
timestamp: August 29, 2014, 11:27:18 pm
content: A 1740 manual should be available from one of the links in the first thread in theRepairboard.HP used retaining screws that require very fine hex keys to remove the control knobs, you will need the correct sizes. (imperial)Search other restoration threads as some senior members have unbelievable skills and tricks to do exactly what you need.I've also got a 1740 for a wet day project, had another a few years back before I got into DSO's.

author: tggzzz
author_rank: Super Contributor
timestamp: August 30, 2014, 03:44:00 pm
content: Quote from: tautech on August 29, 2014, 11:27:18 pmIt came with the repair manual, I'm pleased to say, but it is silent on disassembling the knob.I had a quick look a while ago, and couldn't be sure it was a hex screw; I wondered whether it was a foobar, where "foobar" is effectively an expanding coiled spring shaped like a very thick danish pastry. Now, if only I could remember the real name for a "foobar".Either way, I'll have another look, and thanks for your reply.

author: SeanB
author_rank: Super Contributor
timestamp: August 30, 2014, 04:34:08 pm
content: Roll pin........

author: tautech
author_rank: Super Contributor
timestamp: August 30, 2014, 09:04:10 pm
content: Quote from: tggzzz on August 30, 2014, 03:44:00 pmJust checked, they are definitely hex grub screws that hold the timebase knobs on.2 sizes, 1/16 and 0.050.the 1/16 is easy to acquire, the 50 thou not so easy.Both sizes came in a cheap Fuller set #130-8030 metric & imperial to 10mm/3/8 that I have no hesitation to recommend for workshop/lab use.

author: tggzzz
author_rank: Super Contributor
timestamp: September 01, 2014, 10:08:25 am
content: Quote from: SeanB on August 30, 2014, 04:34:08 pm<sigh>Thanks!</sigh>

author: coppice
author_rank: Super Contributor
timestamp: September 01, 2014, 10:51:23 am
content: I think the 1741A was the only really satisfactory analogue storage scope ever made. Their only big problem was premature failures of the tube. As long as it failed in under 90 days it was a warranty replacement, so HP paid the bill. If the tube failed out of warranty you threw the scope away. The tube was most of the cost of the scope.

author: David Hess
author_rank: Super Contributor
timestamp: September 01, 2014, 01:22:45 pm
content: Quote from: coppice on September 01, 2014, 10:51:23 amWhy do you say this? I really like some of the Tektronix analog storage oscilloscopes with the notable exceptions of the 464/466 and operating any of their variable persistence tubes in bistable storage mode.

author: coppice
author_rank: Super Contributor
timestamp: September 01, 2014, 01:32:29 pm
content: Quote from: David Hess on September 01, 2014, 01:22:45 pmThe Tek scopes had a number of problems, but the bleed alone was enough to make them pretty awful. I always thought that was rather odd, as they had the bleed totally controlled on their graphics terminals. You could turn one of those off on Friday, and on Monday morning the same 4096x3072 resolution image was still there in its full glory.

author: David Hess
author_rank: Super Contributor
timestamp: September 01, 2014, 04:29:48 pm
content: Quote from: coppice on September 01, 2014, 01:32:29 pmI have never had a problem with this on the ones I have used but maybe I do not understand the issue. I find the stored image retention on my 7834 rather annoying actually.Maybe this is an aspect of their storage transfer CRTs which allow very fast single shot writing rates?

author: tggzzz
author_rank: Super Contributor
timestamp: September 03, 2014, 02:52:05 pm
content: Quote from: tautech on August 30, 2014, 09:04:10 pmThe hex keys have just arrived and the 050 fits nicely. Thanks.But the grub screw is frozen in position sufficiently tightly that I don't want to break the key or strip the headI've doused the screw in WD40, and will see if that has any effect. Then it will be a light machine oil or penetrating oil.If that doesn't work, are there any standard techniques I could use?

author: SeanB
author_rank: Super Contributor
timestamp: September 03, 2014, 05:05:07 pm
content: Try tapping gently on the hex key to shock the screw in the shaft, and if that does not work take a soldering iron and heat up the hex key and thus the grub screw to loosen the oxides that are holding it, or loosen the locking compound. Heat it till it just starts to smell, then try to turn it loose, and if no turning try to tighten then loosen. Then hit it with freezer spray to thermally shock it and it should come loose.

author: David Hess
author_rank: Super Contributor
timestamp: September 03, 2014, 05:25:45 pm
content: Quote from: tggzzz on September 03, 2014, 02:52:05 pmMy ordered list of methods to remove set screws is:1. Applying light machine oil and waiting.2. Using a soldering iron to heat the screw.3. Sacrificing the screw and replacing it once it is out.I have a special 1/16 hex key where I filled down the flats on the end to make it into a hollow ground 0.050 hex key so it fits very tightly and will not strip the screw.

author: calmtron
author_rank: Regular Contributor
timestamp: September 03, 2014, 05:30:34 pm
content: I have a 1742A that have/had the same problem with the grub screws. The solution that worked for me was to use high quality hex keys, not-so-gentle tapping and lots of patience. Unfortunately i used cheap hex keys (one hung low ones) first and managed to strip the heads of the screws on one of the the timebase knobs.I don't think there's any locking compound on the screws, it just looked like a bad case of galling / oxidation. Heating the screw seems like a good idea to try.

author: tautech
author_rank: Super Contributor
timestamp: September 03, 2014, 09:43:48 pm
content: The timebase shaft goes through 2 plug-in PCB's and have grub screwed shaft retaining collars.Form memory the manual describes a method to remove these PCB's that entails removing that shaft, and that will allow you to clean the dials.

author: tggzzz
author_rank: Super Contributor
timestamp: September 03, 2014, 09:55:46 pm
content: Quote from: tautech on September 03, 2014, 09:43:48 pmThat's the mechanism, but the grub screws holding the knob onto the shaft is the problem - the legend is "between" the two knobs and shielded/protected by transparent plastic.

author: tggzzz
author_rank: Super Contributor
timestamp: September 04, 2014, 03:22:17 pm
content: Thanks for all the suggestions. The problem has now been circumvented...The original 0.050" grub screws are still as immovable as ever, despite gentle thumping/heating, WD40, gentle force. I didn't want to apply too much of any of those since the knobs were functional and I was afraid I would melt/break adjacent plastic parts of the knobs.In the end theothertwo grub 1/16" screws on the delayed timebase were persuaded to turn, which allowed me to disassemble the knob and insert a replacement legend. Sure the font and colour aren't right, but at least I can read them!

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 01, 2016, 08:50:43 pm
content: Tekfan I need your help! I need to know if the focus unit of 1740A is the same as the 1741A.I bought an unit of 1741A that the seller said me that, the problem was in the focus unit and I do have a dead one 1740A.

author: AlienRelics
author_rank: Unknown
timestamp: April 17, 2016, 12:36:15 am
content: Wow, this is a long-lived thread.I was just given two 1741A 'scopes for free. I have no idea what is wrong with them, other than that they do not work. I'll be posting pictures and progress.

author: tggzzz
author_rank: Super Contributor
timestamp: April 17, 2016, 06:33:36 am
content: Quote from: AlienRelics on April 17, 2016, 12:36:15 amIf you don't have one and need to open it the 1741, strongly consider getting the service manual fromhttp://artekmanuals.com/manuals/hp-manuals/

author: AlienRelics
author_rank: Unknown
timestamp: May 10, 2016, 04:39:23 pm
content: Thanks!I did find a free source for a PDF of the service manual.

author: techie1234
author_rank: Regular Contributor
timestamp: July 09, 2016, 12:47:28 pm
content: Keeping this thread alive...I'm working on a 1743A and am having problems with TIME/DIV controls. The main control won't rotate more than a couple of positions CW or CCW - sounds like it might be a bent contact in the rotary switch or perhaps some hardened grease. Also the delay TIME/DIV knob cracked off, but at least the shaft rotates easily by hand. And those grub screws in the knobs are a pain - wish they would have milled some flat surfaces into the shaft so the set screws could mate flush. Seems like this is a weak point on these scopes. Will be having a closer look inside...My main question is: is there a version of the 1743A manual that has as much detailed repair information as the 1740A one? The 1743A manual on the Agilent site:http://cp.literature.agilent.com/litweb/pdf/01743-90905.pdfhas a BoM and exploded diagrams but not a schematic, repair procedures, etc.Also, are there any recommendations on who sells various parts (like the aforementioned cracked delay TIME/DIV knob) for the 174x series?

author: tggzzz
author_rank: Super Contributor
timestamp: July 09, 2016, 02:15:08 pm
content: Quote from: techie1234 on July 09, 2016, 12:47:28 pmSphere (Canada), QService (Greece, US), ebay.It is useful to have exact part numbers, which you can find in the service manual.

author: tautech
author_rank: Super Contributor
timestamp: July 09, 2016, 09:15:25 pm
content: Quote from: techie1234 on July 09, 2016, 12:47:28 pmIIRC a 1740 I had at one time did the same and I'm pretty sure it's a result of incorrect reassembly, at least it was in mine....I'd had it apart.The timebase shaft goes through a # of selector wafers on a # of plugin PCB's and if the wafers aren't in the correct positions you end up "hamstrung" as you describe. Some careful fiddling should sort it out. One wafer might be 180 out.Thinking back.....the timebase shaft is withdrawn from the front panel, knob and all after the shaft retaining collars are loosened on the shaft, each retaining collar hex grub screw retained IIRC.

author: tggzzz
author_rank: Super Contributor
timestamp: July 09, 2016, 10:52:03 pm
content: Quote from: tautech on July 09, 2016, 09:15:25 pmI'll second that, having had similar experiences on my hp1740.It is surprisingly difficult to get both knobs, both shafts and both rotors in the right position. It is even worse if, like me, you had also moved the knobs on the shaft in order to add a more visible legend to the timebase control.

author: techie1234
author_rank: Regular Contributor
timestamp: July 10, 2016, 12:55:06 pm
content: Quote from: tggzzz on July 09, 2016, 10:52:03 pmTurned out you both were pretty close - the boards appear to have been knocked around a bit at some point. The side of the boards closest to the case were all about 10 degrees flexed towards the back of the case, relative to the side of the chassis. As such, the middle board (for the main TIME/DEV) was askew relative to where it mated with the shaft. A careful bit of forward pressure and "pop" - all three boards returned to perpendicular, unjamming the main TIME/DIV shaft. All is now good. They should really have had slots on the case side for each board to slip into so they weren't just held in place by the one edge connector. Now to find those knobs...

author: tggzzz
author_rank: Super Contributor
timestamp: July 10, 2016, 01:12:50 pm
content: Quote from: techie1234 on July 10, 2016, 12:55:06 pmGood stuff!For future reference, my A timebase was faulty and I traced it to two problems. A faulty 100uF electrolytic was easy, but some PCB tracks had been abraded and needed replacing.The tracks in question areinsidethe rotary PCB switch. To access them, remove the board, slide off the spring clip so the two black switch halves can be removed from the PCB, but don't drop the internal spring contacts!. The edges of those black halves rub against the PCB at their periphery, and eventually sever the PCB track. The track(s) can be replaced with fine wire and careful soldering - try to avoid getting solder on the gold contacts.

author: atlacamani
author_rank: Newbie
timestamp: December 12, 2018, 07:22:25 pm
content: Hello guys.sorry for my english, i use the google translator to communicate with you.A friend gave me a disassembled oscilloscope hp1741a. I want to collect itbut I do not know where to connect some wires. Help please. Look at the photo please.

author: atlacamani
author_rank: Newbie
timestamp: December 12, 2018, 07:32:43 pm
content: general picture

author: lowimpedance
author_rank: Super Contributor
timestamp: December 12, 2018, 10:58:00 pm
content: Here are some pictures of my HP1741 showing the wire locations.If you need any further pictures now's the time to ask before I put the covers back on !.BTW when needing to service any module or switch assembly, make sure to take many photos before anything is undone !. (I'm sure you already have that in mind now).

author: lowimpedance
author_rank: Super Contributor
timestamp: December 12, 2018, 10:58:58 pm
content: last set !.

author: peterpan
author_rank: Newbie
timestamp: March 26, 2019, 09:34:21 am
content: Listen to my friend!HP makes your job easier: there is a number for each wire connection, eg. 956. Equal to the color of the matching wire according to the resistance color scale: 9white, 5green, 6blue equal to white wire with blue and green stripe. I tak dalee ...Hi. PP

author: atlacamani
author_rank: Newbie
timestamp: December 05, 2019, 05:59:27 pm
content: Quote from: lowimpedance on December 12, 2018, 10:58:58 pmlowimpedance, you really help me, sorry for long silence, it was not my fault.. My oscilloscope waiting me for a year)))only one wire left:

author: atlacamani
author_rank: Newbie
timestamp: December 05, 2019, 06:01:35 pm
content: Quote from: peterpan on March 26, 2019, 09:34:21 amthank you friend))

author: jeno
author_rank: Newbie
timestamp: April 21, 2021, 06:49:55 pm
content: Hi, I just got a HP 1741a oscilloscope, and the power supply is bad, none of the voltages match their rating, i replaced two burnt resistors, one of the power tranzistors and some capacitors and still nothing, anyone help?

author: lowimpedance
author_rank: Super Contributor
timestamp: April 22, 2021, 10:29:44 am
content: What voltage is coming out of the bridge rectifiers ?, they do have a hard life so check for dry joints etc .Also the transistor connectors for the pass transistors on the rear panel maybe not making good contact.Just tossing a few ideas, perhaps a few good pictures of your power supply PCB if you think it useful unless its pristine.One other point to note is odd symptoms can also be caused by resistors that have drifted high upsetting critical bias points in the DC coupled circuits, both power and signal paths.

author: jeno
author_rank: Newbie
timestamp: April 22, 2021, 09:42:03 pm
content: After replacing the bridge rectifier for the +15v rail bridge rectifier, all of the filter caps after the bridges, I have all good voltages at the diode bridges, +5v, +15v, -100v rails are fine but the +48v is reading 26volt and the +120v is at 188v, at the +48 and the +120v the 2w resistors were totally burned i replaced them but still not ok, for the -15v my regulator ic is bad, ill try to put an LM723 for that. But I noticed that the horizontal output board is also has some burnt parts, but I dont have the schematic for that, even for the power supply I paused Dave's video when he showing the schematic.

author: jeno
author_rank: Newbie
timestamp: April 22, 2021, 09:43:38 pm
content: I also need to get somehow the values of theese components, or the horizontal output schematic

author: lowimpedance
author_rank: Super Contributor
timestamp: April 23, 2021, 12:25:14 am
content: Thats quite some bbq-ing there, I assume its now clean though !. The manual on this site is ok and has the Horizontal op circuit.https://elektrotanya.com,scroll down for the search window. Read the supply circuit descriptions etc.Given the damage you really need to isolate the LV power supply from the rest of the unit to fully debug it first as the 120 and 48V rails arereferenced to other supplies and if those are not fully functional things will go bad quickly. So best to trouble shoot in isolation then when workinglook for other damage (beyond the horizontal OP PCB as well). So just to confirm you only get 26V across C5 and 188V across C3 ?. Does that change whenthe supply PCB is isolated from the res of the instrument ?. BTW be mindful of the voltages your playing with in the 1741 and follow best safe practices.

author: jeno
author_rank: Newbie
timestamp: April 23, 2021, 06:16:14 pm
content: Thank you very very mutch, this manual is very useful, i was searching it for days but couldnt find it, whithout the manual it was very hard to understand the working principle, now I vill start measuring all the resistors and all components one by one, I really want to get this boy up and running. Thank you very mutch.

author: jeno
author_rank: Newbie
timestamp: April 26, 2021, 05:19:20 am
content: Can someone recomend me some good modern day replacement tranzistors for the A11 board? Only one of the tranzistors survived there, and I cant find any information for those Iwas thinking about BD439,Bc547 and their PNP brothers but Im not sure that those will be fine.

author: jeno
author_rank: Newbie
timestamp: May 02, 2021, 07:41:30 pm
content: Now my three main supplyes are good, I had to make some little adapters for the LM723 from DIL14 to TO100package, I couldn't get TO100ones, But my +120v and +48v rails are busted, I'm measuring +186volts at the +120v and 26volts at TP5 across C5 I have 78volts, but betwwen the negative side of C5 and GND I'm measuring -52 volts. Across C3 I have 186volt, and betwwen the negative side of c3 and GND I'm measuring -7.5volts. These measurments does not change id I disconnect the power tranies, the power supply is disconected from the rest of the circuits. All the transistors seem fine, what can cause this problem?

author: jeno
author_rank: Newbie
timestamp: May 03, 2021, 06:48:18 pm
content: I finaly managed to fix the power supply. All the voltages are oke, when the LVPS is isolted from the rest of the scope, but when I connet it I see no trace, the LEDs are working, and the 48v rail drops to zero. Can I get in contact whits someone for help, or some tips, what can cause that? Thank you.

author: lowimpedance
author_rank: Super Contributor
timestamp: May 04, 2021, 02:43:43 am
content: Quote from: jeno on May 03, 2021, 06:48:18 pmSo the whole power supply is working when isolated from the rest of the chassis?. And only the 48V rail collapses when reconnected, all others remain in spec.?.OK, try loading the 48 V rail with suitable values of resistance to see if it can deliver a decent amount of current (within its current limit of course, ~400mA ? i guess) without the rail collapsing.That will test its operation and thus if any transistors/components etc are still faulty. Check the other passive are in spec.If it is working correctly there is a short somewhere in the scope on that rail. best to use the interconnecting diagramin the manual (page 8-48 to 8-50) to see where the 48V rail is routed to and then isolate those modules and measure for shorted components, ie transistors, cap's etc.Did you repair the Horizontal O/P stage.

author: jeno
author_rank: Newbie
timestamp: May 04, 2021, 08:12:34 pm
content: I found out thet there is problems whit A7 as well as A17. On the A7 board U2 (that shiny gold one) is getting warm, removing it does not change the current draw. But I cant find any schematic for thet board to trace out what can be problematic, any ideas? Later I will move on to A17

author: lowimpedance
author_rank: Super Contributor
timestamp: May 05, 2021, 12:05:40 am
content: Quote from: jeno on May 04, 2021, 08:12:34 pmOk A7 from the interconnect diagrams refers to circuit diagram numbers 7,9,11,12 as seen on the bottom right of the manual schematics , ie multiple schematics make up the overall A7.A17 is circuit diagram 3.Does the 48V rail work ok with an appropriate resistive load ?.Be mindful that there is a number of custom HP parts (eg U2 ) and you should use proper handling procedures when out of circuit. Hopefully none of those are broken. BTW that IC U2 is running off the 5V rail.Use the interconnect diagrams to find which schematic sections use the 48V rail and work through likely failures.Remove A17 and check the 48V rail (possible A1 output amp failure which uses 48V).

author: jeno
author_rank: Newbie
timestamp: May 24, 2021, 06:58:49 pm
content: I think I managed to repair A1 and A17 (not 100% sure) now all my voltages look Ok when the LVPS is connected to the rest of the components, I also managed to get somthing in the screen, it's all green, none of the buttons doind anything, On the vertical preamplifier I measure 9.23volts at TP1, What can be now the problem?

author: electronix27
author_rank: Contributor
timestamp: August 09, 2024, 11:34:13 pm
content: Hi everyone, bit late to the party here. Just picked up an HP 1740A, and enjoyed reading this post. There are a few circuit issues but the CRT is in great condition. Figured I’d start with a good cleaning. Bit stumped on how to remove the sweep dial from the shaft. Appears to be a small C clip on the notched shaft or maybe something I’m missing. Appreciate your help.Much Thanks

author: factory
author_rank: Super Contributor
timestamp: August 10, 2024, 10:12:53 am
content: Quote from: electronix27 on August 09, 2024, 11:34:13 pmThose counting dials are used on a few HP scopes & plug-ins, it needs a special tool for the nut, the alternate is to make one, as I did.David

author: electronix27
author_rank: Contributor
timestamp: August 10, 2024, 09:05:21 pm
content: Thank you sir. I suspected this may be the case, but have not seen this on a potentiometer. A tremendous help knowing, I’ll have to make one like yours.Much appreciatedRussell