New LeCroy 9304AM, display is squeezed horizontally, some broken knobs - Page 1
Forum section: electronics / testgear

author: RedOctobyr
author_rank: Contributor
timestamp: December 30, 2014, 09:03:26 pm
content: Hi all,I'm new at this (not an EE), and just bought my first oscilloscope, a used LeCroy 9304AM. 200MHz, 4 channels, 100MS/sec sampling.It's got a few issues, but I got a great price on Craigslist. It should be plenty for my purposes, and looks like a nice tool. I don't have any lofty goals for it, primarily using it to help look at some stuff with my radio-control equipment. I wanted a DSO instead of analog, to help capture glitch-type issues. It has firmware 06.4.4, the printer and floppy drive, along with listing soft options of "WP01 WP02 CKIO", and hard options of "GPIB R232 CLBZ CENT I2C". I'm not sure yet what all of those mean.The obvious issue is with the CRT display. It was squeezed a lot horizontally, only filling maybe 1/3 of the width of the screen. It seems fine vertically. I found the service manual online, and tried the Horizontal Size adjustment. But even with that maxed out, it still only fills about 1/2 of the screen width. At least it's more usable now. Any suggestions on ways to help resolve this? I can use it as-is, but if I can get it to fill the screen without accidentally destroying the unit, great!Also, 2 knobs are broken off. Their shafts broke off below the faceplate, making them hard to turn. One is the Volts/div knob (obviously important), the other is the horizontal Zoom knob for Zoom + Math, which I haven't started exploring yet. If I turn the Volts/div knob with tweezers, it works. Is there a knob I can put onto these to make them more usable (looks aren't important)? I saw an eBay 9304AM listing where someone included a aftermarket knob that could apparently be moved to any of the 3 broken shafts on that scope.Some of the other knobs are a bit finicky, sometimes not registering, or going slowly in the wrong direction, or jumping, but they are usable for my needs. I don't know if they can perhaps be cleaned; I've used DeOxit to clean exposed potentiometer strips on servos, which helped reduce glitching.Any insight would be appreciated. Thank you!

author: nctnico
author_rank: Super Contributor
timestamp: December 30, 2014, 10:35:25 pm
content: There is probably something bad in the horizontal section of the CRT circuitry. It could be a power supply problem but it can also be the HV transformer dying.

author: RedOctobyr
author_rank: Contributor
timestamp: December 30, 2014, 11:35:09 pm
content: 3roomlab, I know they're not much, but a few pictures I'd taken of the internals are attached. Particularly the areas I was interested in, the video-related boards. Also one showing a broken control knob shaft (not very interesting, I realize).nctnico, thank you. Is there anything specific I could try to check for this? Forgive me, as mentioned, I'm not an EE or a repair tech, unfortunately. Do you mean the main power supply for the whole scope? Or something on one of the video boards themselves?In trying it out a little more, I noticed two things that seem odd.- When I calibrate the probes with them set to 1X, everything is fine. They are eBay P6100 probes. Nothing fancy, I know, but from what I read they're at least OK for lower-frequency stuff. But when I set them to 10X, I see sporadic spikes off the top or bottom of the 1V P-P calibration square wave. The spikes are at the beginning of the wave's pulse, either when going up to 1V, or down to 0V. You can see two of them in one of the attached pics. Both probes do this. The spikes are less-frequent if I attach the reference clip to the shell of the calibration BNC connector, but they still happen.- When reading 110V AC, the wave doesn't look quite the way I'd have expected. The tops and bottoms aren't quite a proper sine wave. Is this something I should be concerned about? I'm reading an extension cord, not directly out of an outlet. I can't do this test with the probes in 1X mode, as the amplitude is too big to display (it only goes up to 5V/division).Those pictures also shows the horizontally-compressed display.

author: RedOctobyr
author_rank: Contributor
timestamp: December 31, 2014, 01:23:50 am
content: I have no context for this vs other scopes, but I like it so far. I'm sure more-recent scopes are much better, but I don't need it to the best, just to work for what I want. My only other exposure was a USB scope (Hantek 6022BE) that I bought a few months ago. I tried it out, but returned it, due to the numerous limitations.I've been looking to try a real scope instead. Despite the CRT issue, etc, I'm hoping this one will work out for me. I can deal with the screen issue if it stays like this. The grid is projected by the CRT (rather than being a separate screen or etched on the glass), so I can still measure things by divisions, fortunately.I don't know what's on the screen. Dried clear something. Water didn't take it off, neither did isopropyl alcohol, but I wasn't comfortable trying anything stronger. But at the moment that's low on the list of priorities.Edit- Just saw your added question. I paid $30. I think I did quite well, given that it at least functions, and I can use it as-is. However, I don't plan to try a $200 replacement CRT, or things like that. Part of the appeal is that it's a low-cost way to get access to a real scope, for someone who is not designing their own devices, etc. Low- or no-cost screen fixes, if I can do them myself, sound good. But I am not looking to sink a bunch of money into it. I hope that doesn't sound dumb or shortsighted. Otherwise I'll be happy with it working as-is, and I'll figure out something for the broken knobs.

author: tautech
author_rank: Super Contributor
timestamp: December 31, 2014, 01:36:55 am
content: Get the Tek troubleshooting pdf from the first thread in the Repair board.I would start checing the horizontal output stages asnctnicosaid.Depending on how the Service maual is laid out, there might be DC voltages listed at test points to check against a certain scope setup. These are very helpful if you are without another scope for locating the problem area.Some reading and study required.Share the manual link with us please.

author: RedOctobyr
author_rank: Contributor
timestamp: December 31, 2014, 01:56:43 am
content: Thanks, I have some homework to do. My apologies if I should have posted this in a different forum sectionIn case they help anyone else, this site has a bunch of LeCroy documents, including the service manual:http://www.ko4bb.com/manuals/index.php?dir=LeCroyMore docs, including the operator's manual:http://exodus.poly.edu/~kurt/manuals/manuals/LeCroy/This is the Hands-On Guide for the 9300 series:http://www.opweb.de/en/model.php?id=79989304A and 9304AM service manual direct link:http://www.ko4bb.com/manuals/download.php?file=LeCroy/LeCroy_9304AAM_Digital_Oscilloscope_Service_Manual.pdf9304, 9310, and 9314 operator's manual direct link:http://exodus.poly.edu/~kurt/manuals/manuals/LeCroy/LECROY%209304,%209310,%209314%20Operation.pdfThe service manual does describe checking the voltage for an item W303 on the video board (page 7-33). It's supposed to be 2V +/- 0.1V, it measured 1.97V, I think. I didn't make the changes they described first, in part because I wasn't sure which was the intensity potentiometer. So I just checked the voltage "non-invasively", and simply measured the existing voltage, to minimize the things I could mess up.

author: SeanB
author_rank: Super Contributor
timestamp: December 31, 2014, 04:44:39 am
content: On the CRT main board ( not the driver, though the caps there probably would be better if replaced) you will find some non polarised electrolytic capacitors. Replace with the same value film units and the width will probably be back. the rest of the capacitors there ( especially any with a 100V or more rating ) will likely also need replacing.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: December 31, 2014, 05:15:39 am
content: It's been a while since I worked on a CRT, but is it just me or is that tube in there sideways and the yolk too? So his horizontal problem is really like a vertical problem on an old monitor. Note the inductor below the yolk connector says "V-SIZE" on it where on all these ones that is the thing that controlled the horizontal width?If so then it's not nearly so much of a problem. For the OP: the horizontal signal on old CRT monitors was used to drive the flyback coil which supplied the high voltage and a bunch of other voltages. It was stressed out and since it had so much stuff hanging off it a little failure here or there would take it down. The vertical circuit on the other hand was much simpler.

author: RedOctobyr
author_rank: Contributor
timestamp: December 31, 2014, 01:58:16 pm
content: I really appreciate the help and insight, thank you allI'm embarrassed to admit that much of this is going over my head, sorry.tautech, I read through the Tektronix troubleshooting guide you referenced. I'm probably just being too literal (or not making the conceptual connections for how it would apply to my situation), but I kept getting hung up on the fact that much of the troubleshooting *appeared* to tie into how the actual scope trace functionality works. Starting a troubleshooting test by setting the scope to certain conditions (1 sec/div, etc), maybe then also using Beam Find. In my case, the CRT is of course drawing everything including menus, so I can't really use trace settings to help, I think. And it doesn't have a Beam Find button, so I can't use that as a test.SeanB, do you mean what they call the Video Board, mounted to the back of the CRT itself? Or what they call the Deflection Board, which has the different adjustments for H-Size, V-Size, apparently has the HV transformer, etc?Paul Moir, I can get better pictures of the CRT itself, or the boards, if that's helpful.Just being realistic, it's looking like the best thing for me might be to simply leave it alone for now. If it stays like this, I can live with it, and I can use the scope. If in the future it fails completely, I may as well try something, as I'd have nothing to lose. But my fear is taking a usable-but-flawed piece of equipment, and turning it into junk by trying to improve things with a bunch of surgery.Please understand, I'm not trying to ignore good advice! Merely trying to avoid destroying something useful through my own good intentions and lack of expertise

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 31, 2014, 02:40:14 pm
content: Quote from: RedOctobyr on December 31, 2014, 01:58:16 pmForget that guide, this is for analog scopes only and completely irrelevant to your 9304AM which is a DSO.QuoteQuite frankly, you should get it fixed as otherwise you may struggle to see if there are any other issues. And seeing stuff on a compressed graticule isn't much fun, either.Don't take this as offense but my impression is that you went a bit over your head when buying this scope. Don't get me wrong, the 9304AM was a good scope more than 20 years ago but these days the specs are way outdated (100MSa/s is maybe good enough for 20MHz or so for non-repetitive signals which is very poor, which only makes the full bandwidth useful for repetitive signals), the plastic parts start to crack/disintegrate, and (based on your description of jumpy/non-registering knobs) the scope very likely needs a new set of encoders (an illness with the 9300 Series). Unless it has been done already the scope will also need the modification (removal) of the power-sense section of the power supply, as this can cause malfunction (there's an old LeCroy Service Note describing the procedure which applies to 9300 and LC Series scopes).LeCroy scopes are great, in many areas the best you can get, but these days a 20+ year old 9304AM is simply a very poor choice for an every-day scope. The fact that yours needs repair which seems difficult for you to provide only makes matters worse, especially as you'd likely need another (working) scope when trying to fix yours. Especially as a starter you don't want your learning to start by fixing complex test gear, you should start with simple stuff to build up your knowledge and skills.But sine you already have it, all I can do is to recommend that you ask around in the Yahoo! group for LeCroy scopes, where you're more likely to get help in getting your scope fixed. There are quite a few people around that tinker with old 9300 Series scopes and know them inside out.Good luck!

author: RedOctobyr
author_rank: Contributor
timestamp: December 31, 2014, 03:38:52 pm
content: Quote from: Wuerstchenhund on December 31, 2014, 02:40:14 pmThat makes sense.QuoteDefinitely a fair point, and noted.QuoteHeh, don't worry, I won't be offendedOver my head in terms of starting out with troubled equipment? That's definitely true. The specs are certainly not up to current standards, but I don't think I'd be looking at things that would be beyond the specs. And I don't have useful electronics-repair knowledge of any meaningful level. Maybe that will change with time. But it *is* a DSO, which I wanted (vs analog), and having 4 channels might be helpful. So at least in that sense, plus price, it was a useful choice.For now, I'll probably try to live with the quirks. I do understand what you mean, though. In another hobby, I see similar situations, people buying old obsolete equipment for starting out, and I know the challenges and headaches it will cause for them.I wanted to gain exposure to using a real (not USB) scope, most definitely on a budget, since this is primarily an area of curiosity (and wanting to learn) for me, not a profession or hobby by itself. Even $350 for a basic Rigol DSO is beyond what I was looking to spend. And the other used scopes around here are $100-300, and are still just analog. So I fall into the "beggars can't be choosers" category, I guess. I will learn something with this, at least, and if I get to a point that it's holding back what I want to do, I will look at other options.QuoteThanks! I am in the process of trying to join that Yahoo group. In the meantime, I'd figured I'd also ask the experienced users here.I appreciate your honest feedback.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 31, 2014, 03:44:22 pm
content: Quote from: RedOctobyr on December 31, 2014, 03:38:52 pmYou're welcome. My guess is that you'll find more people knowing these scopes in the LeCroy group, who can certainly help you to quickly diagnose where the problem is and maybe even supply you with a cheap replacement part which would be the easiest route.In their file section is also a description of how to replace the encoders (which isn't very difficult) including a list of parts you'd need, and the LeCroy Service Note for the input auto-sensing circuitry (again not difficult if you can solder a few wires in place). One member also sells the option GALs which enable the wide range of very advanced options in these scopes for little money, which is always worth doing.Try to get the scope fixed, so even when the specs aren't great you have at least a working piece of equipment which is invaluable especially for a beginner. It's old but especially with all the options is a really interesting piece of kit, and it gives you a glimpse in what you can do with a modern LeCroy scope.

author: tautech
author_rank: Super Contributor
timestamp: December 31, 2014, 06:03:25 pm
content: Quote from: Wuerstchenhund on December 31, 2014, 02:40:14 pmLooks like that IS the case as your scope seems to have a deflection yoke not electrostatic deflection as most other CRO's.Repair will be more attune to repairing a TV.However always start with checks that the PSU is to spec and ripple is within limits.Further study might point in the direction SeanB has suggested.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 31, 2014, 08:47:58 pm
content: Quote from: tautech on December 31, 2014, 06:03:25 pmBut you *DO* realize that the LeCroy 9304AM is a *DSO*, not an analog scope, right?Just to be sure.

author: tautech
author_rank: Super Contributor
timestamp: December 31, 2014, 09:09:43 pm
content: Quote from: Wuerstchenhund on December 31, 2014, 08:47:58 pmYeah DSCRO.

author: crusader66
author_rank: Contributor
timestamp: December 31, 2014, 11:04:38 pm
content: I had a friend that repaired an old HP scope that had a "squeezed in"display picture. The fix was replacement of a single capacitor attached to a uPC chip. It seems like it was a 22ufd cap. He actually did this on two of these TV type displays. Your problem seems very similar even though it is a Lecroy rather than a HP. Wish I had more specific details but this is all I got. I just thought I would mention it so that you knew that this might not be a very difficult fix.

author: SeanB
author_rank: Super Contributor
timestamp: January 01, 2015, 04:48:30 pm
content: That is right, low value caps will cause that. If it is the vertical then it will be a bootstrap capacitor on the driver in the board not attached to the back of the tube, but attached with a 4 wire loom to the deflection yoke. That is the board behind the front of the scope, next to the CRT front itself. The big black heatsink will have this in a big flat pack on it. Just look for capacitors attached to the chip directly and replace them all.While you have the board out please also resolder the pins of the LOPT and the output transistor, along with the driver transformer for it. Those pins run with heavy loads on them, and as they get old they tend to dry joint, so a general clean up and resolder there is good for reliability.

author: RedOctobyr
author_rank: Contributor
timestamp: January 01, 2015, 09:37:09 pm
content: Thank you for the suggestions.I checked the main power supply output voltages with the scope running in Auto-trigger mode, they were all within-spec per the service manual. Though I did forget to check one item while I was in there, I did not check the difference in the +5.10V line when in Auto-trigger vs Stop (there is supposed to be less than a 30mV difference between the two states).I can't check ripple, unless I use the scope to measure its own power supply. That's not something I feel comfortable doing, unless it's definitely safe, and won't damage the scope. I watched Dave's excellent video about how to not blow up your scope (by misuse of the reference clip, etc), but I'm afraid this scenario wasn't coveredI'd have to pull out the deflection board (the one behind the front panel) and spend some more time figuring out which some of these parts are, to relate them to the info you guys have offered.There is a large black component, flat on one side, cylindrical on the other. Per the pics I took, there are 2 black heatsinks. One has items Q5 and Q10 mounted to it (top-left of the "Deflection board bottom" pics). I can't read the label for the other, it's in the bottom-right of "Deflection board bottom A" pic, I can't see the whole marking on the board, just "...DS", there is a 3-legged chip on the other face of the heatsink.I was able to join the Yahoo LeCroy users group. I asked there as well, someone replied and suggested checking the deflection board for bad solder joints. He also said he's seen issues on other equipment (not LeCroys) caused by a bad LM3080 "transconductance opamp", he said I should check if this uses one. He didn't specify if he'd seen it cause the same issue, or something different. Per the service manual, pages 8-167 and 8-171, there is an LM3080 on the deflection board, item U1.I found it in the "Deflection board bottom A" pic, attached, it's the lowest of the (3) 8-pin chips. The schematic shows a pair of 0.1uF caps connected to it, C4 and C5, they are the blue items above it. He said that CA3080 could be used as a replacement.I don't know what that component does, or whether it makes sense as a possible cause, but I wanted to pass along what he shared.Thank you for being patient with my lack of knowledge (even if it may feel like trying to explain economics to a goat), I'm trying to keep up

author: Guni
author_rank: Regular Contributor
timestamp: January 01, 2015, 10:34:58 pm
content: Quote from: RedOctobyr on January 01, 2015, 09:37:09 pmThis is high voltage transformer (voltage multiplier) for kinescope's anode supply. If you don't know that maybe better to ask some for help. It's extremely dangerous to work around this part.I don't want to say: don't repair your scope by yourself but your lack of knowledge can be deathly dangerous in this case.

author: monkeysuncle
author_rank: Contributor
timestamp: January 01, 2015, 10:55:31 pm
content: I assume the faulty monitor is just that--a video monitor. Any idea what the sweep frequencies and signal levels are? If what is most important to you is getting a working scope, rather than the fun project of debugging the broken monitor, what about munging the video signals into an external monitor? Check if the sync signals are compatible, if you can, but you might try grafting vsync, hsync and video into an RGB cable.Maybe you can pick up an old CRT monitor at a thrift store that you don't mind frying if things go haywire.

author: RedOctobyr
author_rank: Contributor
timestamp: January 01, 2015, 11:49:28 pm
content: Guni, thank you, it makes sense that it's the transformer. I appreciate the advice; honest truth can hurt a bit, but a mistake when poking around inside something can hurt much worse!monkeysuncle, my goal is a usable scope. It's a very good idea to isolate the issue. I don't know what the signal specs are, but there's some info on it in the service manual if I need to explore that more in the future.I may simply leave it alone for now. It's usable for my needs as-is. I'd like the screen to be working properly, but not at the expense of accidentally breaking the scope, or hurting myself. Having it fixed professionally is almost certainly too expensive to be worth it for my uses. If I really need undistorted views of certain signals, I can save them to a floppy disk, or send them to a PC using the serial port.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: January 02, 2015, 01:26:41 am
content: Monkey's Uncle: It looks to be a little unique compared to an old standard composite monitor. No doubt it has some odd resolution or timings or something (I'm too lazy to read the specs). So a direct swap might be impossible.Page 8-167 is the horizontal schematic. The problem is with something on this page or something supplying it. The normal order of investigation would be to check the supply voltages (particularly the +15 and -15) with a multimeter. You can also usually check the ripple with a multimeter by putting it on it's AC range. Note the CM3080 is there as part of the signal path, and that's a good lead you got.Another thing that makes me suspicious is C14 which is right on the horizontal (X) output. If this is a can type capacitor (electrolytic) these are always suspect in older equipment because they fail with time and temperature.Of course, you could always crank up R23 (Size) and see what happens. That increases the amplification at the op-amp right above it in the schematic. That will give more signal to the coil drivers beyond it.SeanB - Just to make sure, you've got that this horizontal problem is what would normally be a vertical problem right? The tube and deflection coils are sideways.

author: Guni
author_rank: Regular Contributor
timestamp: January 02, 2015, 01:35:39 am
content: RedOctobyr, I can give you some general advice:1. Check all voltage - some of the value are printed on PCB. If you have scheme there should be check points with correct/reference values2. Make detailed visual inspection - especially on electrolytic capacitors, overheated resistor or some damaged components3. In addition to pt.2 check cold solder jointFrom my experiences most probably some of the electrolytic capacitor loose capacity - it's very, very often. It's very simple to check with ... oscilloscopeSeriously it's common practice to replace most important /bad looking/ leaked etc. electrolytic capacitors in first step.Last thing. IMHO you don't need high qualified oscilloscope specialist. Good TV repair man should solve you problem quickly.UpdatePaul Moir have right to suspect C14 - according to what I've told about el-caps

author: monkeysuncle
author_rank: Contributor
timestamp: January 03, 2015, 07:07:05 pm
content: Paul Moir, you are right that this isn't composite, but the timings look a lot like they would be eaten by a multisync VGA monitor. Compare the timings on page 4-12 of the service manual to VGA timings given here:http://javiervalcarce.eu/wiki/VGA_Video_Signal_Format_and_Timing_Specifications.(remebering, as noted, that the vertical and horizontal have been reversed). The only likely problem that I see on the sync side is that the polarities are reversed. I seem to remember that VGA monitors are often tolerant of inverted polarities on the sync signals, so that may not be an issue. If it is, that can easily be fixed with a 74LS04, since the signals are TTL level.What I haven't found in my quick perusal of the manuals is what level the scope uses for video. The source I linked says that VGA is 0V (black) to 0.7V (max).--Dan Menes