Tektronix 2230 or 2235? (more details inside) - Page 1
Forum section: electronics / testgear

author: ms4sman
author_rank: Newbie
timestamp: February 10, 2022, 03:11:02 am
content: Alright folks, I am getting my first real oscilloscope and I have two options available to me. To keep things simple, I have been offered to choose one of them for FREE. But not both, so I need to choose between them. So cost is not really an issue in this case.The first is a Tek 2235. From my understanding, this is an analog only 100MHz scope. It seems to be in quite good working order from my testing so far, and the CRT is quite bright and using the focus knob, it gets quite crisp and sharp. I don't have a ton more to say about this one. The front panel is not in as nice of shape. It shows more wear, and the time div knob has a crack and all three of the clear plastic number rings are also cracked, but still otherwise fine.The other is a Tek 2230. At a glance, this one seems like it should be the better option. It's analog and digital, and has storage capabilities. Otherwise, it seems very much the same as the 2235. However, while it seems cleaner and in better shape outside, I am not positive about its working condition.- First, from reading online, I see some folks (I think even on a thread on this forum if I recall) saying the digital functionality of this scope is not that great, so it's best to just stick with its analog functionality.- Also, the CRT seems...iffy. I can't seem to get the trace to ever focus down to nearly the bright crisp line as the 2235. Also, when I have the the Storage/Readout knob set so the voltage/time division and other readout details are displayed, I can not get them in focus at the same time as the trace. If one is in focus, the other is not. Also worth noting is that the readout stuff at the bottom of the CRT can be made pretty crisp and sharp...more than the trace can.- I understand that the cursor control on this scope can tend to go bad. I don't know yet if this one is any good. I haven't really had the chance to learn to use the digital/storage functions yet.- This one also does have what I understand to be an optional add-on, the RS-232 interface card. I have not tried it, so I don't know if it works.Any advice on which of these scopes I should get? I'm also just new to oscilloscopes. I've wanted one for my bench for many years but never been able to afford one until these two opportunities came along. I am not sure what all else I should be looking out for in choosing. What else should I test on them? Are the problems with the 2230 CRT easily fixable?As I said, the 2230 seems much more feature rich, but the CRT stuff concerns me. Also I don't know if having storage capabilities will be that much of a benefit to me, and as mentioned I know some have said the digital capabilities aren't that great on it anyway.I think that covers the main details I had to give. Feel free to ask any other questions you may have about them.Thanks for any help in advance!

author: bdunham7
author_rank: Super Contributor
timestamp: February 10, 2022, 05:50:43 am
content: How far apart are the readout and trace focus on the 2230? Does turning the BW limit on help?

author: adam4521
author_rank: Regular Contributor
timestamp: February 10, 2022, 11:23:45 am
content: I'd be a little bit worried about the display issues. On my 2245A I don't have trace blurring, but I do have some 'speckle' on the line which goes away if I turn the readout knob below a threshold. I think these scopes just have to work really hard to draw/refresh the characters while also tracing one or more signal lines. So you could experiment a bit more with the focus with the readout on and off. The 2235 will be more straightforward but it is a shame about the cracked controls -- if it was a keeper you would want to get a parts unit to fix it up. You'll have to jump one way or the other! Good luck!

author: ms4sman
author_rank: Newbie
timestamp: February 10, 2022, 12:44:59 pm
content: Thanks for the replies guys!Quote from: bdunham7 on February 10, 2022, 05:50:43 amThey aren't so far apart that it is unusable. I tried to get a picture/video to show it, but it doesn't show well in the video. If I get the trace as sharp as I can, the readout is fuzzy, but can be made out. It's just a bit frustrating to try to see both at once. Turning on the BW limit does seem to help a tiny bit, but not a lot.To be clear, I wouldn't say that having the readout turned on makes the trace focus worse, the trace can't be focused to a sharp line either way, but having the readout on and focused means that the trace is even further from its "best" focus I've achieved. Hopefully this makes sense?I also noticed this morning while testing your BW limit suggestion that depending on the time/div, the readout becomes very jittery and the focus even changes as the screen redraws. I'm guessing the jitter has to do with the fact that all of this is being drawn with a single gun right? So it's having to divide its time between drawing the trace (or even two!) AND drawing the readout? When the draw is slower, the readout jumps from fuzzy to sharp and back rapidly. Again, hopefully I'm making myself understandable here. I'll try again tonight to get a video or something to demonstrate this. Maybe some pics to show the difference in "best" focus I can achieve on both scopes.Quote from: adam4521 on February 10, 2022, 11:23:45 amYeah, on the 2230 if you turn the readout knob all the way to zero, it switches off and then you can turn the knob back up and it stays off. If you turn to zero again, it turns back on. Turning it off does stabilize the trace a bit (I assume since the gun isn't having to share its time to also go down and draw the readout across the bottom). But as mentioned above, the "best" trace focus isn't really any worse with the readout on, it just can't be achieved at the same time as the "best" focus on the readout.One final question, if I could somehow get my hands on both scopes to keep for myself (I can have one free, but if I got a good price for the other or something) are their internals similar enough that I could switch some components from one to the other to make a "best parts" scope? For example, I don't understand enough of what's going on with the focus issues to know if this is a problem with the CRT or not, but if it was, and they used the same CRT (I don't know that they do) could I theoretically put the better CRT from the 2235 into the 2230 to resolve the focus issues? Or is it much more complex than that and I'm oversimplifying? Obviously I know that if I kept both, I could at least take the non-cracked controls from the 2235 and put them onto the 2230, they appear to be identical parts. Would it be worth trying to combine the best parts of both, or would I just be wasting an otherwise good scope that someone smarter than me could possibly still fix?I am just trying to figure out if I am going to wish I had the digital functions of the 2230 or its saving functions. Right now, the bench work I do isn't anything too crazy, my current "obsessive" hobby is restoring old tube radios and test equipment. While this isn't exactly a modern scope, it's definitely far more modern than the stuff I've been working on so it's well beyond me. Would the 2235 and its analog only and no storage functions be more than sufficient for the kind of thing I'd be doing? I guess I'm not sure what kind of situations/work I'd have to be doing to start wishing for the digital and storage stuff...Thanks again, and hopefully I'm making sense in my explanations. I'm pretty new to scope technology, but I'm happy to learn!

author: adam4521
author_rank: Regular Contributor
timestamp: February 10, 2022, 02:16:17 pm
content: I don't think it's going to be the CRT. It lights up, there's a dot, the scope can steer it. Feels like a focusing problem, shape of the dot, compensation etc at the extremity of the screen, etc. So something about the driving circuits around the CRT is causing the problem. I wouldn't weigh the storage feature too highly -- modern DSO, even the lowest cost are far more capable for that scenario of non-repetitive waveforms. But for tuning up and aligning analogue circuits, say with a signal generator, you can get see what is going on perfectly well by using the oscilloscope in the traditional, interactive way without storage.

author: bdunham7
author_rank: Super Contributor
timestamp: February 10, 2022, 03:14:39 pm
content: To answer a few of your questions:Both scopes do use the same CRT, although I've seen nothing so far that would indicate you have a CRT problem with either.Some of the Tek 22xx series had an issue with the CRT focus ladder resistors. I'm not 100% sure the 2230 is one of the affected models, but I think it is. It is a straightforward repair that just takes a bit of disassembly and attention to detail. I'm wondering if some of the 2230 symptoms you are seeing might be a very early instance of this failure.As far as which scope is better for you, the 2235 is a simpler device and easier to repair while the 2230 has the digital feature set, but is a bit more cumbersome to work on. Buying something of this age and type means that you should anticipate doing some repair work sooner or later. OTOH, the basic digital capabilities on these scopes like the 2230, although not directly comparable to modern DSOs, can be quite useful.One thing worth checking--does the focus of the trace--using a straight-line with the input set to GND--change as you move it up and down the screen? The readout characters are at the top and bottom, so any difference in focus between them and the trace could be due to a general focus issue related to position.

author: ms4sman
author_rank: Newbie
timestamp: February 10, 2022, 03:28:59 pm
content: Again, thank you both for the replies!Quote from: bdunham7 on February 10, 2022, 03:14:39 pmI am not at home right now, but I will probably go home for a break in a few hours and I will take a look at the scopes then, and I will check this out.As for doing some repair work, I'm more than willing to give it a shot if its something like replacing resistors that would fix the focus! I mostly just will need lots of help with knowingwhatto fix since I don't have a good enough understanding of the inner workings of these to necessarily know the problem and fix myself.From what I'm understanding here, it sounds like if it comes down to it, the 2235 would be perfectly sufficient for what I'd be using it for, but if it turns out that whatever is wrong with the 2230 is a fairly easy repair (and nothing else major is wrong with it) it might be worth giving it a shot just because the digital storage features could be nice to have, since its available...I will also need to figure out enough of how to use those features to be able to test out that cursor issue I saw mentioned on the Tek Wiki...I guess the cursor knob tends to go bad. I would think that should be an easy enough part to replace, IF one can find the replacement part...Thanks!

author: ms4sman
author_rank: Newbie
timestamp: February 10, 2022, 03:57:07 pm
content: Ok, got impatient and went home early for a break and to look at the scopes. Couple interesting things to note.First is that when I put a straight line trace down near the bottom of the screen near the readout, it doesn't seem to make any difference to the focus. The difference in focus is the same. BUT, I did find something else interesting in the process. Turning the intensity of the trace down to about 2/3 from full, the line crisped up and I can find a balance point where the trace and readout are both in focus. But with brightness up all the way, it seems to blow out the focus and make it not possible to fully crisp up the line.This is not the case on the 2235 though. When I do the same on it (obviously it has no readout) but changing the intensity does not change focus at all. The line looks exactly the same all the time, just brighter or dimmer. But the 2230 reaches a point where any more brightness just blows out the line and makes it fat and fuzzy.I am continuing to tinker here but thought I'd share that finding...UPDATE: Another interesting finding with the focus...when I pop out the Waveform/menu select button to show the menu on screen, parts of the menu are in different focus than others here too. The top and bottom parts are blurry while the menu items themselves are sharp. The top and bottom appear to have their intensity controlled by the same knob as the readout, and turning down its intensity clears them up. But for reference, the readout on the waveform was sharp at full intensity on that knob. I'm just getting more confused by the minute here by this focus thing. Maybe nothing is wrong with it at all, and my expectations are just wrong, and its normal to just have to adjust the intensity and focus frequently to sharpen things up as the screen displays change. I'm just not familiar enough with this thing to know...

author: ms4sman
author_rank: Newbie
timestamp: February 10, 2022, 04:29:47 pm
content: Yeah, the more I play around with it, the more I'm feeling silly for posting this. I think maybe I just had the wrong expectation in my head of how it would work. By dialing back the intensity on the main trace and the readout, I can easily get everything focused fine at the same time and plenty bright enough to see. I guess I just didn't expect that the max intensity would blow out the focus like it did. Is that normal, or is something likely still wrong?I did figure out how to get into the menus and navigate around some, and the cursor knob seems to be working well enough for me. It's not super responsive but it seems easy enough to select what I'm after. The button on the knob also works, so I think all is good there.One other thing I saw on the Tek Wiki is that the firmware on the EPROM can begin to fade after many years and they have firmware images on the site there. How would I know if it's beginning to fail, just not acting right basically? How do I go about reflashing that if I needed to?Sorry if this is turning out to be sort of a pointless thread. I did try to do quite a lot of tinkering and reading about it before posting, but it seems to always be that way. As soon as I ask for help, suddenly I start finding the answer myself then...

author: bdunham7
author_rank: Super Contributor
timestamp: February 10, 2022, 05:12:51 pm
content: Quote from: ms4sman on February 10, 2022, 04:29:47 pmI didn't think of the brightness issue, and yes max brightness will typically 'blow out' the focus on a properly operating scope like that. There is a round 'anti-penumbral' circle around the trace dot if that you can see if you slow down the trace enough. Set the input to GND, the trigger to AUTO and the timebase as slow as possible to see what I mean. Don't do that very long as it is hard on the phosphors. Is the 2230 brighter than the 2235 by chance? And yes, you may have to adjust the brightness and focus as it warms up and under different conditions. For example, at high repetition rates and slower trace speeds, you might want the brightness down, but for a low-repetition signal at faster sweep speeds, you would need to turn the brightness up--perhaps to the max. There's a reason those controls are on the front panel and are separate for readout and trace.QuoteNot pointless at all. I think you've probably determined that the 2230 is the scope for you.

author: ms4sman
author_rank: Newbie
timestamp: February 11, 2022, 03:01:02 am
content: I gotcha! Well I'm glad to know that's to be expected. I spent quite a bit more time playing around with the scope tonight and its starting to really make a lot more sense now.Tonight I just finished up re-capping an old Eico signal generator and used the scope to test it out! Beautiful waveforms.Thanks for the help folks, I think I'll be keeping the 2230 and I'm very excited to have it!

author: m k
author_rank: Super Contributor
timestamp: February 11, 2022, 10:31:54 am
content: One thing.How long you are going to use it and what kind of problems you don't like to have with it?

author: David Hess
author_rank: Super Contributor
timestamp: February 11, 2022, 05:33:03 pm
content: Quote from: ms4sman on February 10, 2022, 03:11:02 amThe 2235 was the first model of oscilloscope in that series of oscilloscopes. The 2230 is literally a 2235 with an added storage board on top, like the 2236 is a 2235 with an added multimeter and counter board on top. There is a lot of part commonality between all of them.One issue with the 2230 is that because the storage board must be removed to gain access, it is difficult to work on. The 2232 which replaced it solved this. I am not sure about how the 2236 handled it.QuoteThe design of the 2230 straddles the all analog and DSO worlds, but except for its user interface, it operates very much like a modern DSO, albeit with limited performance because of its 20 MS/s maximum sampling rate. It automatically supports equivalent time sampling so working with repetitive signals up to the bandwidth limits of 100 MHz is not a problem.One interesting consequences of the 2230 design is that the bandwidth limit does not apply to storage mode.QuoteFrom your description of the blooming, the CRT on the 2230 may have a lot of hours and be nearing the end of its operating life.Quote from: ms4sman on February 10, 2022, 04:29:47 pmMaximum intensity on my 2230s and 2232s only widens the trace a little bit, and the readout brightness does not affect the trace and the trace brightness does not affect the readout.QuoteThat has been more of a problem with mask ROMs from that era, but flashing the EPROM just means pulling it, erasing it with an ultraviolet eraser, using an EPROM programmer with the image, and then reinstalling it. I think there is a self test to check the EPROM CRC, but it would not detect impeding failure.Quote from: bdunham7 on February 10, 2022, 05:12:51 pmThe perfectly round halo surrounding the beam spot is caused by secondary emission from the beam hitting the phosphor screen. The electrons bounce back into the CRT and then are drawn back to the phosphor screen by the high anode voltage.If you look closely, there is another irregular spot which follows and then precedes the beam spot horizontally across the screen. This is caused by electrons scattered from where the electron beam intercepts the scan expansion mesh. Presence of this spot is an easy way to tell if the CRT has a scan expansion mesh.

author: nctnico
author_rank: Super Contributor
timestamp: February 11, 2022, 05:49:52 pm
content: Quote from: David Hess on February 11, 2022, 05:33:03 pmHaving some hands-on experience with 2230 myself I must say it isn't that bad. You can flip the acquisition board up because it is mounted on a frame with hinges. IIRC there is even some kind of lever you can pull out to keep it upright. I wouldn't want to take the PSU out though. That is buried deep inside. This scope is pretty much packed with electronics.Given the choice between storage and non-storage, I'd choose the Tek 2230.

author: m k
author_rank: Super Contributor
timestamp: February 11, 2022, 06:53:49 pm
content: What special problems there could be?Failing components inside the PCB obviously not.Battery backed memories with unique information?Manufacturer special and not available components?Failing components burning with considerable flame?Corrosive fluids leaking components?Design faults carbonizing circuit boards?Something else?

author: nctnico
author_rank: Super Contributor
timestamp: February 11, 2022, 07:00:09 pm
content: Probably all of the above. These oscilloscopes are from the 80's. If you get these in working order for free, excellent! Use it until it no longer works and then decide to try and fix it or buy something more modern. I have sold my Tek 2230 about a decade ago while it stilled worked.

author: David Hess
author_rank: Super Contributor
timestamp: February 11, 2022, 07:25:12 pm
content: Quote from: nctnico on February 11, 2022, 05:49:52 pmMaybe I did it wrong, but my problem was having to mechanically disconnect all of the front panel switches before the storage board could be lifted.QuoteEven on an old DSO like the 2230, the storage is a game changer. I consider the 2230 to be the first digital storage oscilloscope worth having because it was the first to include peak detection, which is good down to 100 nanoseconds.Quote from: m k on February 11, 2022, 06:53:49 pmThe most common failure with these oscilloscopes is probably the aluminum electrolytic capacitors in the power supply drying out due to age.

author: nctnico
author_rank: Super Contributor
timestamp: February 11, 2022, 07:40:09 pm
content: Quote from: David Hess on February 11, 2022, 07:25:12 pmNow you mention it, I think it required pulling out the top row of push-buttons but that wasn't too hard to do. I have taken mine apart a couple of times. In the end it turned out a previous repair in the timebase circuit had damaged a trace on an internal layer. I had to add a wire to get that working properly again. I vividly recall how elegant the (digital) design is; not a gate or pin gets wasted!