Damaged (?) HP 1741A (Here's looking at tekfan) - Page 1
Forum section: electronics / testgear

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 01, 2013, 10:56:42 pm
content: Good day, everyone!Tekfan, I just read your thread about your restoration of an HP 1741A oscilloscope and decided it'd be a good idea to post here to see if you had a solution. Others are welcome to chime in as well, of course--I just haven't been here long enough to know who's most experienced with what.Anyway, I recently bought an HP 1741A oscilloscope on ebay, supposedly in working condition. However, when I unpacked it and turned it on, all it did was display a green splotch on the screen--no trace. I set it to the basic test settings as given in section V (adjustments) of the manual, found here:http://cp.literature.agilent.com/litweb/pdf/01741-90911.pdf.I also hit the "find beam" button and the only response it gave was to dim the screen briefly, then when I released the button it went back to the way it had been. I was able to get rid of the green splotch, but there is still no trace (just a green screen). Again, I have all the controls set to the settings specified in section V of the manual.I am trying to figure out if this means it is damaged and will need repair, or if I have something set incorrectly. I have used analog scopes in the past, but it has been YEARS since I last used one.If anyone's got some ideas of what might be going on, and why the beam isn't showing up no matter what I do, I'd really appreciate any help!Thanks everyone!Regards,Matt

author: ddavidebor
author_rank: Super Contributor
timestamp: August 02, 2013, 12:09:52 am
content: Xy?

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 02, 2013, 12:16:52 am
content: Hi ddavidebor--I tried adjusting the vertical and horizontal position and it made no difference at all. I also adjusted the brightness, beam intensity, persistence, and other knobs and still had no luck.Thanks for the response.Matt

author: Unknown
author_rank: Unknown
timestamp: August 02, 2013, 01:27:37 am
content: I think he wondered whether you had XY mode enabled. That would give you just a dot.It would be useful to post a good picture of the front panel of your scope with the settings of all controls clearly visible.

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 02, 2013, 02:02:53 am
content: :facepalm: Sorry about that. Told you it's been a whilex/y mode is not enabled, though I tried it both ways and it made no difference at all.This is what the front panel looks like:It's exactly the same as the first hp o-scoppe tekfan tore down and restored in his thread, found here:https://www.eevblog.com/forum/testgear/hp-1741a-oscilloscope-restoration-project/This one is in much better condition, but still does not seem to work.If it was 10 or 20 years ago I might be able to figure the problem out, but I've been using digital scopes recently and forgotten a lot of the little tricks with the analog ones.Thanks for the replies, guys!Cheers,Matt

author: edpalmer42
author_rank: Super Contributor
timestamp: August 02, 2013, 06:39:04 am
content: This is a storage scope so it's somewhat different from an ordinary analog scope and much more complicated.For comparison, I have a 1744A that looks identical to your 1741A. It's apparently an enhanced version. Mine works properly so here are a few things I tried. Maybe it'll help you narrow down the problem.With BEAM INTENSITY set fully CCW so that I don't have a trace, the screen is uniform green.- BEAM FIND dims the screen.- BRIGHTNESS increases the intensity of the green color as I turn the knob CW.- PERSISTENCE decreases the intensity of the green color as I turn the knob CW.- pushing the ERASE button (on the PERSISTENCE knob) flashes the screen bright green.- The RESET LED appears to be on solid. Turning the TIME/DIV knob CCW causes it to start flashing. At the higher speeds it was flashing too fast to be seen.- Even with BEAM INTENSITY fully CCW, when the RESET LED is flashing, I can see a flicker on the screen. It shows up better when I turn up the BRIGHTNESS.- If I turn up the BRIGHTNESS part way and leave it, the screen will gradually brighten until it's bright green. Pushing the ERASE button will dim it down, but it will just start brightening again.- With the RESET LED flashing, pushing the AUTO/NORMAL button to the NORMAL position causes the RESET LED to go on solid.- With the AUTO/NORMAL button in the AUTO position, pushing the AUTO STORE button causes the screen and the RESET LED to flash bright green. The PERSISTENCE knob controls the time between flashes.- Pushing the STORE button darkens the screen and turns off the RESET LED.How does your scope react to these tests? I've never had to work on mine so I don't know how much help I can give you beyond this sort of comparison, but we'll see how it goes.Ed

author: ddavidebor
author_rank: Super Contributor
timestamp: August 02, 2013, 06:59:11 am
content: Quote from: The_PCB_Guy on August 02, 2013, 02:02:53 amYou need to set trigger to INTernal. One of the button on the right side.

author: robrenz
author_rank: Super Contributor
timestamp: August 02, 2013, 12:17:18 pm
content: Quote from: ddavidebor on August 02, 2013, 06:59:11 amThey bothareset to internal

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 02, 2013, 10:00:44 pm
content: Sorry guys, I should have mentioned that that is not an actual photograph of my scope, it's only one of the same model. I misunderstood your request. I'll take a photograph and post it in a couple of minutes. Both trigger buttons are set to internal.As for your instructions, Ed, here goes:QuoteMine follows that exactly.QuoteThis is where I lose you. My reset LED is not lighting up at all. I suppose it might be a bad LED, but I believe it was working briefly when I first got the scope, but haven't seen it light up since.QuoteTurning up the brightness slightly and leaving it, the screen does continue to brighten. Pushing the erase button brightens it, then it gets dim again, and does not continue to brighten anymore.QuoteStill no reset led flashing, and pressing the auto/normal button does not change anything at all.QuotePushing the auto store button causes the screen to dim, and the "auto erase" LED to turn on. Releasing the 'auto store' button (putting it in the "out" position) re-lights the screen, but the red LED next to "auto store" does not light. I don't believe I have ever seen it light since I got this scope.Thanks very much for your efforts, everyone. The seller of this scope has offered me a partial refund for repairs, if they are necessary. Hopefully I just have some settings wrong, but if not everything should be covered.Cheers,Matt

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 02, 2013, 10:27:06 pm
content: Here is an overall view of the front panel:Also, before you ask, changing the beam intensity doesn't change anything.Thanks,MattP.S. If you need any more close-up photos of a specific part of the panel, I have them on demand. I just didn't want to post 5 or 6 large photos in the same post

author: vk6zgo
author_rank: Super Contributor
timestamp: August 02, 2013, 10:35:22 pm
content: Have you noticed that your "WRITE" LED is on?In non-storage mode that should be off,if it is similar to my Tek 7613.

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 02, 2013, 10:47:41 pm
content: Quote from: vk6zgo on August 02, 2013, 10:35:22 pmIndeed, I did notice that. I have the option of it being on "write", "store" or "store and display", when the "auto store" button is "out". When I have it set to "store" only, the screen looks the same as if it is set to "write". When set to "store" and "display" (both orange LEDs are on), the screen is blank (not lit up at all).

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 03, 2013, 01:32:15 am
content: Well guys, turns out I should have followed Dave Jones' long-standing advice: "Don't turn it on, take it apart!"I finally got around to popping the cover off this thing and was greeted by a potent burning-electronics smell. A quick search on the boards turned up this:Thankfully the boards are modular and can easily be unplugged from one another. I should be able to remove it and give it a good cleaning, replace the capacitor (even if I have to bodge it in there), and hopefully have this thing up and running again!I'm still open to advice, tips, and instructions. For example, I have no idea how to discharge the CRT circuitry on one of these. I know how to do it in CRT TVs, but this is set up a bit differently.....Thanks!Matt

author: edpalmer42
author_rank: Super Contributor
timestamp: August 03, 2013, 03:06:52 am
content: Quote from: The_PCB_Guy on August 02, 2013, 10:47:41 pmThat's normal. These scopes don't have a non-storage mode. It's not described very well in the manual. The 1744A has a small Operator's Guide that gives a little more info. The typical mode of operation is with PERSISTENCE and BRIGHTNESS fully CCW. Use the BEAM INTENSITY knob to set the trace brightness. If your signal doesn't show up very well, start increasing PERSISTENCE and/or BRIGHTNESS. Too much and the screen will bloom. It takes practice.I like the scope. It takes a bit of fiddling, but my 1744A can do a single-shot capture of a 4ns rise time on a pulse. Good enough for me. Since I've got this scope I haven't been able to talk myself into buying a digital one. A few months back it stopped working but all I did was wiggle an IC in it's socket and it was fine. Oh, well.Matt, the fact that your RESET LED never comes on might mean that your timebase isn't working. If changing the capacitor doesn't fix it and there are no other obvious problems, that might be a place to look. A dead timebase should still give you a spot on the screen, but there could be multiple problems.Ed

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 03, 2013, 03:18:58 am
content: Thanks very much, ed. This blown capacitor is indeed on the timebase board. I still am not sure the best route to take--whether to try to repair the board itself, or to buy a new one (just the timebase board). Unfortunately several searches, both on google and ebay, did not turn up just the board for sale. I figure I'll try to repair it myself, though the traces are severely damaged. I'm not really sure how I'm going to do this. I'm an Electrical Engineering Technician by trade, so I expect I'll figure something out eventually.Thanks for all your help!Cheers,Matt

author: Electro Fan
author_rank: Super Contributor
timestamp: August 03, 2013, 07:10:15 am
content: Hi PCB Guy,Sorry about your scope - it looks very cool! - and I hope you get it running.Don't know if this might be a possible path to a fix, but I saw unit in the link below for sale on eBay. Not sure how feasible it would be from a shipping cost standpoint for you to purchase this and have the whole thing shipped to you but I bet for the price of what the seller is asking ($35) or possibly less he might just sell you the boards/parts (although I can't quite tell whether he has the board(s)/part(s) you want). Might not cost a lot to just ship boards/parts. Just a thought.http://www.ebay.com/itm/HP-1741a-Oscilloscope-not-working-as-is-for-parts-/321173784561?pt=BI_Oscilloscopes&hash=item4ac77307f1#ht_419wt_1093EF

author: dzseki
author_rank: Frequent Contributor
timestamp: August 03, 2013, 07:34:23 am
content: Quote from: Electro Fan on August 03, 2013, 07:10:15 amHuh, this one looks to be missing the entire time base unit, so won't help much I think -at least on the blown capacitor.

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 03, 2013, 03:48:00 pm
content: Hi everyone. I have opted to repair the board myself. I am documenting the process and will post it here when it is completed.Thanks for all your help!Regards,Matt

author: ddavidebor
author_rank: Super Contributor
timestamp: August 03, 2013, 04:04:58 pm
content: DON'T clean it before you have removed all the shit mecanically, like with a cutter or bisturi.If you clean it all board will become conductive.

author: c4757p
author_rank: Super Contributor
timestamp: August 03, 2013, 04:19:47 pm
content: A bisturi?

author: robrenz
author_rank: Super Contributor
timestamp: August 03, 2013, 04:29:37 pm
content: Scalpel in Italian

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 03, 2013, 05:22:03 pm
content: Thanks guys. Yes, I used an Exacto knife to clean all the corrosion off. I also cut back the damaged traces so that I can repair them with copper tape. Again, this will all be documented as soon as I can get the copper to do the repair.This isn't my first time repairing a circuit board, I do know what I'm doing when it comes to PCB repairRegards,Matt

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 13, 2013, 07:54:41 pm
content: Good day, everyone,Just a quick update on the repair process:I received the copper foil tape I'm using to repair the traces in the mail yesterday, so I was finally able to start fixing the thing. I've been taking photos and hope to be able to do a full write-up for the process. With luck, if my capacitor arrives soon, I'll hope to have it all up by tomorrow or the day after.Regards,Matt

author: Rigby
author_rank: Super Contributor
timestamp: August 14, 2013, 07:55:20 pm
content: Excited to see your progress.

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 15, 2013, 02:57:53 pm
content: So the capacitor arrived yesterday, and as luck would have it it was the wrong size.Ordered another one from Mouser, hoping to receive that by the weekend.Will keep you all updated, and thanks again for the interest!Best wishes,Matt

author: MrAureliusR
author_rank: Unknown
timestamp: August 15, 2013, 04:54:13 pm
content: Gotta love it when parts show up and they're not the ones you ordered or turn out to be fakes/cheapies...Please do post a full documentation of the repair!! Quite excited to see what happens, and if you get it working!

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 19, 2013, 11:57:37 pm
content: Good evening folks--The capacitor arrived today, this one the correct size. I soldered it in and finished up with the trace repair and popped the board back in its slot. I went to put the knobs back on and realized I had moved the contacts during disassembly.Before I can finish this repair, I'll need to know one thing: For the time/div knob (both inner and outer), what are the extremes? In other words, if both knobs are fully clockwise, what position should they be on? This should help me reinstall the rod properly, as I can adjust the inner contacts to their clockwise-most position, then position the knobs where they should be. I would assume the "delay" (outer) ring should be "off" in its fully-clockwise position, and main (inner knob) should be at 0.5uS?I can't help but feel I should know this, but it's been a whileThanks folks!MattEDIT: I figured it out, no need to reply to this post.

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 20, 2013, 12:58:42 am
content: Alright folks, as promised--A brief writeup of the repair process!Okay, so let's start from the beginning. A few weeks ago I purchased a HP 1741A digital storage oscilloscope on ebay for about $50 (came to $76 including shipping). My purchase was, of course, inspired by Dave's video about finding a perfectly decent scope on ebay for $50 or less. The 1741A is a 100MHz, dual channel scope, so I figured I'd jump on the opportunity to get a "new" scope (I donated my old one to a school, and have regretted it since).So about a week later I received the package. The box was quite large, and the scope was well-packed. I took it out and plugged it in eagerly. Unfortunately all that turned up on the screen was a large green splotch (as shown earlier in this thread).No amount of fiddling would change the screen at all. I eventually decided to do what I should have done in the first place, and followed Dave's advice--"Don't turn it on, take it apart!".I took off the cover and caught a strong whiff of burnt electronics. A brief scan of the timebase board revealed this:An electrolytic capacitor had blown out one end and severely corroded the surrounding board and traces. I contacted the seller and let him know that the scope did not work, despite what was claimed in the ebay ad. He was very kind and agreed to refund me the cost of the repairs.I'm not sure how many photos I can add per post, so I'll stop here and continue in another one.Matt

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 20, 2013, 01:29:39 am
content: The first part of the repair process was to remove the damaged capacitor and clean up the board. I desoldered the one remaining capacitor lead and removed it from the board. I then used an exacto knife to carefully scrape off the corrosion so I could get a better view of the traces. As expected they were practically non-existent, so I also made a cut through each trace just outside the corroded area. This allowed me to peel off the damaged traces and have a clean, solid trace to solder to. Once cleaned, the board looked like this:The board is still a bit discolored, but all of the corrosion was removed and was good to go. You'll notice in the photo that I also scraped off about 2-3mm of the solder mask from the end of each trace. This would allow me to solder to it more easily.The next step was to acquire some copper foil tape. Ideally one should use heat-activated tape, as it works best for soldering applications, but the merchant I bought some from shipped it way too slowly. At the time of this writing, I still have not received it, and it's been about 3 weeks.I ended up buying some tape intended for trimming stained glass pieces. Not ideal, but it will work.I cut out a piece just a little bit longer than the gap between the ends of the traces, where it would eventually be soldered. It's very important to cut it a little bit too long, otherwise you will not get a good connection later on when you solder it in.And after some trimming, it looks about ready to be stuck down:It's usually a good idea to tin the ends of the traces that you'll be soldering the tape to, just to make sure you have a good connection.After the ends are soldered in, I like to put averythin layer of solder over the entire trace, just to ensure there's a solid connection all the way across. The process is repeated for the second long trace that was damaged.Here they both are--stuck down on the board and soldered:In my next post, I'll show how to handle a trace that terminates in a solder pad.

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 20, 2013, 02:19:36 am
content: Before I continue, I'd just like to apologize for the bad photography. My camera is about 10 years old, and the camera I bought to replace it was even worse.Okay, so in some of the previous photos you'll see the short trace coming out from the contact traces. Just beyond that, you'll see a hole in the board. This is where one lead of the capacitor should be, but there's nothing to solder it to (except for a tiny pad on the underside). In this type of setup it's often best to solder both sides, once again to ensure a good connection. Repairing this trace and providing a surface to solder the capacitor to is very simple. First things first, cut the copper tape to size. I also trimmed the corners to round out the end over the hole. This ensures that solder won't "leak" over the edges as much and accidentally make contact with another trace.(Don't worry, I got rid of the scrap on the contacts before finishing it up)After the tape was stuck down, I used the tip of the exacto knife to cut a tiny hole in it so the capacitor lead can fit through.And we're ready for the capacitor!It was very difficult to read the label on the blown capacitor, as it was burnt and discolored. Thankfully the service manual (http://cp.literature.agilent.com/litweb/pdf/01741-90911.pdf) is in public domain and I was able to find it easily with a quick google search. I looked at the schematic and found that the capacitor I needed was a 100uF one, but there was no mention of the voltage. The capacitors around the damaged one were rated for 35v, but from what I COULD read on the label of the blown one, it looked like it said 50v. I decided to buy a 63v one so I'd be covered either way.I forgot to snap a photo of the cap before installation, but I'm sure you all know what a capacitor looks like. I soldered it to the board and finished the tin coating of the short trace. The cap is in!In the second photo, please note the 1-2mm space between the capacitor and the board. This allows for air circulation and better cooling. If the capacitor gets too warm, the electrolyte will dry up and it will fail, possibly in the same way as the old one did.That's pretty much the end of the repair process. Time to put it all back together....After trimming the capacitor leads and reinstalling the contact hardware (front and back):I had a spot of bother putting the knob back in, as mentioned a few posts ago, but I was eventually able to figure it out. I reinstalled the board to its socket on the main PCB and tightened the set-screws to make sure the knob doesn't slide out.And we're set! Moment of truth.....et, voila!Beautiful! Needs a bit of tweaking here and there, but it all seems to be working as expected!So that's it, a brief explanation of how to repair corroded traces on a PCB, as well as the replacement of a blown capacitorI wish I was a better writer and that I could have made this more interesting, but hopefully all the necessary information was provided and that someone else can learn from my experienceIf anyone's got questions or comments, I'm happy to answer them!Thanks for the interest!Best wishes and kind regards,Matt

author: robrenz
author_rank: Super Contributor
timestamp: August 20, 2013, 02:29:41 am
content: Very nice job! but resizing your pictures to 1024 x 768 or smaller would be much nicer to view and you could put more pictures per post that way.

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 20, 2013, 02:33:00 am
content: Quote from: robrenz on August 20, 2013, 02:29:41 amThat probably would have been a good idea. I'll see about resizing and re-uploading them.Thanks,Matt

author: edpalmer42
author_rank: Super Contributor
timestamp: August 20, 2013, 02:33:52 am
content: Congratulations!Enjoy your new toy.Ed

author: The_PCB_Guy
author_rank: Regular Contributor
timestamp: August 20, 2013, 02:34:58 am
content: Quote from: edpalmer42 on August 20, 2013, 02:33:52 amThank you kindly, Ed. Will do!