2465CTS Parts Scope Lives! - Page 1
Forum section: electronics / testgear

author: mskobier
author_rank: Regular Contributor
timestamp: April 12, 2015, 07:26:00 pm
content: All,I had already posted this thread over on the Tek Scope Yahoo group, then realized Ihad not posted it here. So here it is for your reading pleasure.I posted some info in another thread about a couple of parts scopes I picked up a short time ago. Well, Now that the 2445B is back in service, I was able to spend some time today seeing just how bad of shape the scopes were in. I started with the plain 2465 serial number B013xxx (scope A) as it appeared to be in the best physical shape, and I was actually able to get a dot on the screen. The other is a 2465CTS serial number B029xxx (scope B) which seemed to be alive according to the control panel, but there was absolutely no indications of a trace,It appears scope A has an issue with the A5 board or something is keeping the processor from initializing properly. All voltages on it checked out ok.So while I was removing the channel 1 attenuator from scope B to make sure I answered correctly in another post, I checked the voltages at J11, and had no indications of the higher voltages (+87, +42.4). Anyway, I figured the power supply was toast. So, with a good power supply in scope A, I figured I would change the power supplies between the two units and see what happens. As I was dismantling scope B to remove the power supply (quite the pain removing all the CTS stuff), I discovered a power supply cable unplugged from the power supply. I thought to myself, it could not be that simple, so I plugged the cable back into the power supply board, put everything in a safe configuration, without the options board, plugged it in and looked for smoke. Well, I didn't see any smoke, and the scope actually came back to life! It has a nice sharp trace, and all four channels have a trace. I did test channel 1 and can get a signal trace, channel 2, I was not able to get a signal trace. Anyway, there is hope for this scope. It does have the TEST 05 FAIL 42 error which according to the manual is positive voltage too positive. So it looks like I will have to spend some quality time with the power supply in the near future. I haven't decided if I am going to reinstall all the CTS stuff, as I currently have no need for the GPIB option. It does have the FET voltage plug on the back, that I'll try and keep. I need to read up on what all options came with the CTS scope.Anyway, another Tek scope lives.Mitch

author: mskobier
author_rank: Regular Contributor
timestamp: April 12, 2015, 07:29:55 pm
content: Another poster on the Tek scope group (Siggi) posted that there is some internal differences between a regular 2465 and one with the options buffer board. Something to do with some pins on a couple of the plugs are jumpered, and those pins not jumpered caused the TEST 05 FAIL 42 error message on his scope. Anyway, I reinstalled the options boards and gave it a test. The scope worked, but still has the TEST 05 FAIL 42 message, and the triggering was unstable. TIme to do some more reading.Mitch

author: mskobier
author_rank: Regular Contributor
timestamp: April 12, 2015, 07:40:31 pm
content: I got to spend some more time with the scopes late yesterday and this morning. I have learned some interesting things. First and most importantly, there are significant differences between the normal 2465 and the 2465CTS version.There is a different back plane.There is a buffer board that the options plug into as well a the front panel and A5 board.There is some minor differences in the power supply, specifically the addition of a couple of notches cut in the circuit board and a couple of additional plugs that interface with the buffer board.The A5 board is significantly different , with an extra plug as well as the two plugs that the front panel plugs into. for all intents, the connections are reversed.The front panel is significantly different with only one cable going directly to the A5 board, and that connection is in a different location on the A5 board. The second cable goes to the buffer board on the back plane with a separate cable from the buffer board to the A5 board.That pretty much sums the major differences.Remember I acquired this scope already half disassembled with a number of the cables un-plugged from their respective connections. I found a web page with pictures of the inside of a 2465CTS as it was being dismantled. Many thanks to the owner of that page. M1KTA for the pictures. It would have been a lot more difficult to figure out the cabling without his pictures!Now, for the important stuff. I did quite a bit if swapping board and power supplies between the two scopes. Here is what I have found. Both power supplies work,, but have a bit more noise than I would like. I have already ordered two sets of capacitors to overhaul the power supplies. I figure one overhauled power supply will go into the 2445B, since it needs an overhaul too, the other will go into the 2465CTS.I swapped around the front panels, the A5 boards and the display boards. Here is the results of those tests. It appears there is a problem with the 2465 A5 board, as installing it and the associated front panel in the 2465CTS board gives the exact same results as when they were installed in the 2465. That tells me the 2465 A1 board is probably working correctly. The troubleshooting chart in the manual states the problem is either a bad processor or a couple of IC associated with triggering the data lines. It could also be the RAM or ROM. I pulled all four of the EAROM chips and read them with the programmer, then compared the BIN files with a set of BIN files for the same model downloaded from the net. There are no errors in the BIN files. That leaves the RAM or processor and associated IC's.The 2465CTS I was able to get partially functional has now been properly reassembled with the help of the previously mentioned web site. After assembly, I plugged it back in and ran some tests. No more TEST 05 FAIL 42 or any other error messages! Most everything worked as it was supposed to with the exception of channel 2's trace being distorted when displaying the internal calibrator signal. The other three channels displayed the internal calibrator square wave properly. I did have to turn on the <20MHZ band width filter to clean up the fuzzy traces. I figure a power supply overhaul should rectify that issue. But other than that, it looks like the scope is working properly.So, hopefully next weekend, the replacement capacitors will be here and I can dismantle the 2465CTS again and overhaul the power supply. Then I can sort out the channel 2 issue. I'll take a bunch of pictures when I next disassembly the 2465CTS.Anybody have any extra screws that will fit this scope they are willing to part with (sell). I can always use regular screws from the hardware store, but I would like to use original screws if possible.Mitch

author: MarkL
author_rank: Unknown
timestamp: April 12, 2015, 10:07:22 pm
content: Quote from: mskobier on April 12, 2015, 07:26:00 pmCongrats on bringing the scope back from the dead!I wouldn't bother re-installing the GPIB option. For one, the functionality is extremely limited. You can only read CTT values, cursor positions, display messages, and control settings the same as the front panel. You don't magically get automated measurements or screen captures (2465 is incapable of that). Second, the option card intercepts the cursor controls and there's a bug where it adds erratic movement to them when you try to change the position from the front panel. I know because I added a GPIB card to a 2465 and it was a net-minus. I've been too lazy to remove it because it was complicated to put it in.On the CTS version, that "FET voltage plug" on the back is for the P6407 16-bit Word Recognizer Probe. The CTS is supposed to come with that probe, unless someone swapped it out for an Option 11 probe power plug.A good place to start with the options on the CTS version, if you haven't already looked at it, is a Tek catalog from that era. The 1985 catalog has it (as well as others):http://w140.com/tekwiki/wiki/Tek_CatalogsSorry, I don't have any extra screws. But here's a place that will probably have something if you're not happy with the local hardware store selection:http://www.mcmaster.com

author: tautech
author_rank: Super Contributor
timestamp: April 12, 2015, 10:29:33 pm
content: Come to think of itSphere should have bucket fulls of screws for Tek's.http://www.sphere.bc.ca/

author: mskobier
author_rank: Regular Contributor
timestamp: April 12, 2015, 11:13:29 pm
content: MarkL,Thanks for the response. I had originally removed all of the options boards and cables. After I did that, I kept getting the TEST 05 FAIL 42 message. In discussions with another that has the 2465BCTS, he encountered the same problem when he went to remove the options. He informed me that a couple of the plugs have a couple of the pins jumpered on the normal 2465, and that I would have to find those pins and jumper them to make the error message go away. He did the same thing I did and reinstalled the options boards and interconnects. That resolved the TEST 05 FAIL 42 message. He did send me a link where he had posted about this issue on a different group, and listed the plug numbers that will have to be modified. However, I do not currently have a good schematic of the CTS A5 board and front panel to compare with the normal 2465 documents I have. If I can sort out the jumpered pin issue, I will remove the options boards and just use it as a normal 2465. That is a ways down the road at this point.Mitch

author: MarkL
author_rank: Unknown
timestamp: April 13, 2015, 02:19:46 am
content: So, you're trying to remove ALL the options?The A5 isn't special for CTS units, as far as I know. The magic is all in the option boards. The front panel is also the same in CTS and non-CTS versions. The only front panel difference is that there's an additional small board that holds the LEDs for the GPIB indicators that poke through holes in a modified name plate.I have a printed version of the 2445/2465 Option 06 and Option 09 service manual, and the 2445/2465 Option 10 service manual (both are for the plain, non-A/B version).I have attached a page out of the option 06/09 manual that talks about jumpers on P102 and P101 when removing all options for testing. When it says "extender kit cable jumpers", it's talking about 0.1" jumper blocks. The cables with numbers 1 through 14 are references to extender cables for testing cards out of the chassis.The Pxxx jumpers may be what the other poster was referring to.Hope this helps.I can scan other pages if you need something specific. I just don't have time to scan it all.EDIT: Reprocessed PDF. The scanner didn't make a PDF that was readable by many.

author: mskobier
author_rank: Regular Contributor
timestamp: April 13, 2015, 03:44:19 pm
content: MarkL,Thanks for scan of the pages from the manual. It clears up a few things. Now that I know which manual to look for, I found a hard copy on the net last night. It cost a little more than I wanted to pay, but I can always resell it if I part with the scope. PDF's are good, but its hard to beat a hard copy. It's kind of hard to scribble notes on the margins of the computer screen!I really do not care if the options are in the scope or not, as long as the basic scope works properly. I realize the GPIB is of limited use, as is the word recognizer. I'm still trying to figure out exactly what the Option 9 (Counter, Trigger, Timer) does. If it is of some usefulness to me, then I will try and keep it.I only know that of the two scopes I have, the 2465 and the 2465CTS, that the A5 board is different as well as the front panel connections to the A5 board being different. Maybe its a age difference between the two scopes. The 2465 is model number B0134xxx, and the 2465CTS is B 029xxx. I'll open up the two scopes tonight when I get home and take some pictures so you will see what I am referring to.Mitch

author: MarkL
author_rank: Unknown
timestamp: April 13, 2015, 06:44:35 pm
content: My 2465 started with no options, and later had option 06 (CTT), 09 (WR), and 10 (GPIB) added, in that order. So, I think you're probably right the differences in your A5 boards is an age thing.Interestingly, the WR was just the addition of the Lemo connector on the back going to the CTT board, and of course the probe itself. I only used the WR a few times in the 10 years the scope was in active service. I agree not to bother with it. Its usefulness has been way overshadowed by even the most rudimentary logic analyzers.The CTT, since you already have it, I think would be worth considering. It's like having a built-in fancy frequency counter. It allows you to do:- Precision time-interval measurement - much more precise than using the cursors.- Event and frequency counting - count pulses or frequency of a signal to 7 digits.- Delay-by-events triggering - trigger the sweep after the Nth trigger input.- Logic triggering - if you don't have the WR, you can do things like trigger A sweep if A&B trigger inputs are both true.Another nice thing is that because the CTT works off the trigger inputs, the edges of what it's measuring do not necessarily have to be on the screen. For example, it can always give you a frequency reading of a signal no matter what the horizontal sweep speed.I used the CTT a lot to measure pulse widths by setting up the A trigger for the rising edge and the B trigger for the falling edge (you can also do it with the ALT SLP setting).The printed manual you ordered details all this. You might like the CTT.

author: Howardlong
author_rank: Super Contributor
timestamp: April 13, 2015, 09:01:24 pm
content: I agree regarding the usefulness of the CTT, I have a 2465B without it and a 2467B with it, and it's part of the reason the 2467B gets used a lot more than the 2465B. You can measure approximate frequency without the CTT, but you have to wait a few seconds while it makes the calculation. With the CTT, it's there on screen right away if it's setup to display.Make sure though that you understand the limitations of the CTT: the specs for frequency measurement for <=50MHz are based on a signal of 1.5divs vertical minimum, and for 50 to 150MHz, you need the signal to show 4divs minimum. If you don't realise this, although the scope triggers perfectly well, the CTT frequency measurement will be unreliable. I'm just saying this because if you go from a DSO to this you might think the CTT isn't working correctly,

author: mskobier
author_rank: Regular Contributor
timestamp: April 13, 2015, 11:58:43 pm
content: MarkL,Ok, here is a set of pictures showing the differences in the front panel wiring and the A5 boards. The first two pictures show the differences between the A5 boards. Note the number of ROM chips, and the extra plug in the middle of the board. The third and fourth show the placement of the cables on the back of the control panel. The fronts are identical. Again, maybe its the age difference, but the boards and panels are definitely different.When the service manual gets here, I'll have a better reference to help me understand the cabling of the options on board.Any one have an idea why the square wave trace only on channel two would be distorted? Channel 1, 3, and 4 all work fine. I'm leaning to either the attenuator is messed up or the preamp is going bad. After I get the CTS stuff sorted out, I'll attack tat problem.Sorry about the quality of the pictures.Mitch

author: MarkL
author_rank: Unknown
timestamp: April 14, 2015, 01:21:00 am
content: Quote from: mskobier on April 13, 2015, 11:58:43 pmMy A5 board looks exactly like your second photo with the 2 EPROMs. My scope is vintage B0309xx. I didn't try peeling the stickers off the EPROMs because they were very stuck on, but Tek likely switched to a more dense EPROM for the later models and didn't need the other 2 socket positions.It also looks like your other A5 board can accommodate all the option connectors, including that one in the middle.On your two front boards, what is especially different is the white ribbon connector on the "CTS" labeled board. That connector is P651 which needs the extra length to get to the A20 buffer board to support the GPIB option.I wonder if Tek updated the design along the way to be more "option ready".Not sure what you're seeing on Ch 2; maybe a screenshot would provide some ideas.

author: mskobier
author_rank: Regular Contributor
timestamp: April 14, 2015, 02:56:45 am
content: MarkL,You are probably correct in regards to the ROM's between older and newer boards. Makes sense to me.On the first board, (blue ribbon cables). The short cable aligns with the bottom plug on the A5 board. On the second panel, (grey ribbon cables), the short cable aligns with the top connector on the A5 board. In other words the older panel will not work with a later A5 board and the later panel will not work with the earlier A5 board. The plug alignment is wrong and the short cables do not have enough reach to make the correct connections. Yes the grey cable is a bit longer to reach the options buffer board.The other thing to note is the plugs on the end of the cables. The short one on the later board (blue) is a narrower plug. On the earlier board (grey), the shorter cable has a wider plug.So now you understand what I was referring to when I said the boards and panels are different in the same basic model.Mitch

author: MarkL
author_rank: Unknown
timestamp: April 14, 2015, 06:02:01 pm
content: Perhaps I'm being dense; please forgive me if so.The length of the cables aside, what you have on the A5 board is a 26-pin connector on the top and a 20-pin connector on the bottom. Electrically, the connectors carry the same signals on old and new.From your pictures, it looks to me like either front panel board can plug into either A5. If you don't have the GPIB option, both the 26-pin *and* 20-pin ribbons from the front panel go directly to the A5 board.Only if you want the GPIB option does it matter. Then, the 20-pin (P651) ribbon from the front panel goes to the buffer board where the signals are duplicated and returned on another 20-pin ribbon, which plugs into the A5 (J651) in place of the one from the front panel.Only the "CTS" front panel card has a long enough 20-pin ribbon to reach the buffer board. So, this card must be used if you wanted the GPIB option, which you don't anyway.Sorry if it sounds like I'm beating a trivial thing to death, but I think you should be able to mix-and-match boards to get a working second scope (any needed firmware updates aside). A reading of the option 06 09 10 docs will no doubt be helpful when it arrives.

author: mskobier
author_rank: Regular Contributor
timestamp: April 15, 2015, 02:10:00 am
content: MarkL,You are not being dense at all. You have more experience with these scope than I do. I am just going by what I see on the different panels and A5 boards. The boards will probably work as you say. I do know when I had the cables from the panel and the A5 board to the buffer board swapped, the scope did appear to function but the triggering was all messed up and it was giving me TEST 05 FAIL 42 error message. As soon as the option service manual arrives, I'll verify the pin out on the CTS front panel and A5 board and compare them with the pin out from a normal A5 board. That should resolve the issue in my mind.Once I figure out what is causing all of the address pins on the processor to be locked high which is preventing the scope form operating, I'll be a able to try some parts swaps and see what happens.Mitch

author: mskobier
author_rank: Regular Contributor
timestamp: April 18, 2015, 11:43:58 pm
content: All,The Options 6 and 9 service manual came in the other day. I have had time to briefly look through the manual. I understand what MarkL was referring to in regards to extension cables and jumpers. I still have not had a chance to trace out the pins, hopefully in the next day or two.I finally found some suitable rear case screws. They are actually a Polaris ATV part, and I ended up buying a bag of 500! (cheap though!). These screws are 8-32, 1-1/4" long, plated steel, not stainless steel. They may have to be shortened a little since the manual calls for 1-1/8" long screws. Anyway, if anyone needs some of these long screws, drop me a line and I'll make you a heck of a deal.Mitch

author: mskobier
author_rank: Regular Contributor
timestamp: April 19, 2015, 08:01:12 pm
content: All,I have done some studying of the Options 6 and 9 service manual, and made up some jumpers to bypass the buffer board. All in all, it does not seem to have any effect. I'll have to work on that issue a bit more.It currently has two issues. The first is an intermittent TEST 05 FAIL 24 message, I can push A/B and it will clear and the scope appears to work fine. However upon further inspection, there is no triggering. I have tried all combinations of switch settings to get it to lock into trigger. This may be temperature dependent, as the scope is kept out in the garage where it is fairly cool (mid 50's F), and when I bring it into the house where it is warmer, at first it gives the error message, but after it has had time to warm up to, it no longer gives the error message. Possibly a bad solder joint, a cable not plugged in tightly, or possibly a PS caused issue. Don't know. I checked for the sine wave signal at pin 28 on U500, and get a nice sine wave, but at twice the specified voltage from the manual. Once the scope decides it is not going to give the error message, then the triggering works as expected. I'll figure that out eventuallyThe other is it appears I have a damaged input attenuator on channel one. When using the internal calibration source, both channel 1 and 2 work as expected using AC coupling, but when I switch channel 1 into DC coupling the wave form gets distorted. Almost as if it has a badly compensated probe. Channel 2 does not distort when I place it into DC coupling. I have switched the probes around, and it makes no difference. The leading edge of the square wave is significantly rounded when in DC coupling in channel 1. Here are a few pictures showing the traces and control settings. The top trace in all pictures is channel 1.Just one more thing to try and sort out.Mitch

author: MarkL
author_rank: Unknown
timestamp: April 19, 2015, 10:43:30 pm
content: Perhaps stating the obvious, but I would try to get to the contacts on the first relay inside the A11 attenuator. My first guess is that the DC coupling side is not making good contact.A couple of other tests to determine that would be: Is the distorted signal still AC coupled anyway? Change the offset of the input to find out.Or, if you turn on DC and 50ohm coupling at the same time, is the distortion the same? If the signal goes away completely, it's definitely not making contact since the 50ohm terminator relay is after the AC/DC coupling relay. 50ohms would kill any weak, capacitively coupled signal that made it through dirty contacts.I've never had the lid off one of the attenuators, so I don't know how serviceable they are. Maybe someone else can comment. There are also used, "tested good" ones on ebay.I can't find what "TEST 05 FAIL 24" means. Only FAIL 01, 02, 04, 22, and 44 are in the manual. Does your manual say anything about it?It seems that the TEST 05 flowchart paths all have to do with line triggering. It's probably checking the trigger system by making it trigger on line.And the flowchart also says to check U500 in all cases of the errors above. Since you have 2 scopes, you could try swapping U500. It's easy to remove and replace the big hybrids. (Use ESD safeguards!)

author: mskobier
author_rank: Regular Contributor
timestamp: April 20, 2015, 12:05:13 am
content: MarkL,Thanks for the response. I have run a few resistance tests on both channel 1 and 2 input. In ac mode on both channels, the input resistance is infinity (>20 Mohm) as measured by my old DMM. Which is expected with a capacitor in series with the input. In DC coupling mode, channel 1 still shows infinity, channel 2 shows .998 Mohm. In the 50 ohm setting, channel 1 still shows infinity and channel 2 shows 50.1 ohms. Well, that pretty much verifies that the channel 1 attenuator is toast. Now to figure out if it is repairable or just needs to be replaced. I do have a good used spare I picked up when repairing the 2445B. Just need to check if its a channel I or 2 attenuator. Apparently there are some differences between the two attenuators, what I do not know.I have a copy of the 2465 service manual. On page 6-11 there is a table of tests and exercise routines. It does not give a lot of info, just that that error code means "positive level not positive enough", and it has something to do with the triggering voltage. Since the channel 1 trigger pickoff is started in U-100, the faulty attenuator may be causing some issues with it.Here is a scan of page 6-11 form the manual.Mitch

author: mskobier
author_rank: Regular Contributor
timestamp: April 20, 2015, 01:50:22 am
content: Well, I changed out the channel 1 attenuator with the spare I had, and it appears to be working fine now. No more distorted trace. I ran the DC balance, to get things back to where they should be. Checked the internal calibrator, and both channels are reading within a few millivolts of each other in both AC and DC coupling.I dismantled the attenuator and could not see anything physically wrong with it., No burnt traces, over heated resistors, or corroded contacts that I could detect under high magnification or with a DMM. I checked the contacts and nothing seemed stuck or hanging up. I may change it back and see if it works now. Maybe it was a stuck relay?So far, I have not had any more error messages upon startup. Maybe I got both problems resolved?There is apparently a difference between the 2465 and 2465A/B attenuators. They are labeled with a significantly different part number. In comparing the two, the front X10 insulator is much thicker on the A/B series attenuators. Functionally, I do not see it being a problem, and it appears to be working fine.Mitch

author: MarkL
author_rank: Unknown
timestamp: April 20, 2015, 06:08:40 pm
content: A little gentle cleaning of the AC/DC Coupling relay contacts might be in order before you re-assemble the attenuator module. If you can get to the contacts, that is.I usually clean delicate contacts by wetting a small strip of paper with isopropyl and move it around between the contacts. The contacts should be engaged to put a little pressure on the paper.I don't think the bad attenuator has anything to do with the power-on trigger issue.I missed that table on 6-11, thanks! So, failure 24 maps to "Negative level too negative" and "Positive level not positive enough". In other words, the test trigger signal has too much of a negative offset.I've attached a capture of what I have on pin 28 of U500 (actually the capture is test point 46, but they're both the same). Putting the scope on a loop for TEST 05 doesn't change the waveform, but the offset does jump about +8mV (very tiny) each time the loop executes.I would still try swapping U500 as something very easy to try if it crops up again.Interesting that the channel 1 and 2 attenuators are different part numbers. I never noticed that. I wonder what the difference is? The manual says they're identical in operation and the schematic looks the same to me.EDIT: Fix typo.

author: mskobier
author_rank: Regular Contributor
timestamp: April 23, 2015, 02:40:17 am
content: MarkL,Nice display. Maybe someday I'll have a scope as nice as that (Scope Envy!)The other day when I swapped out the attenuators, I dismantled them and inspected what was inside. From what I could tell, they appear to be identical electrically. a couple of the SMD (yes SMD components from 1983!)components looked a little different, but the layout of everything was the same. When I had the original one apart, I cleaned all of the contact points with IPA, and put it back together.I reinstalled the original attenuator this evening. hooked everything back up and applied power. The attenuator now works perfectly. When I cleaned everything, I did not get any residue from the contacts on the Qtip, so all I can figure is that I had a stuck relay. Getting to all of the contacts is quite easy. All it takes to remove them is a couple of screws, and the relay module separates from the board. The contact strips will even come out of the housing if they needed to. I did not remove them. I did physically cycle each a couple of times to see if anything felt out of order. Everything was fine.I have not had the test error message since I re-seated all of the cables. Hopefully, it was just a bad contact. I am still getting a bit of HF noise in the trace, but that can be filtered out by using the <20mhz bw switch. I still need to do the capacitor service on the power supply, but that can wait for a while.I did note another minor thing with the channel 1 and 2 traces. when I have both channels active and both probes hooked up to the internal cal at the same time. The voltage readings are not the same. They are close, but you can see and measure the difference. It looks like about 4mv difference between the two channels. It's not the probes, because when I switch the probes between channels, it makes no difference. The scope will probably need a calibration tweak before I call this one complete.The part number of the attenuator in the 2465CTS is 119-1445-01(02). The part number of the attenuator I have spare is 119-2342-06 (from a 2465B). Yes I know it is a channel 2 attenuator, but the only difference is in which side of the attenuator the 3 pin plug comes out. The slots in the attenuator case is already cut on both sides.Mitch

author: mskobier
author_rank: Regular Contributor
timestamp: April 23, 2015, 03:13:29 am
content: All,A while back we were discussing replacement screws for these scopes. I stumbled upon a pdf that may be of interest to those of us who need factory style screws. Here's the pdf.Mitch

author: mskobier
author_rank: Regular Contributor
timestamp: April 25, 2015, 12:19:55 am
content: I've had an opportunity to work with the scope some more. It appears there is at least one other issue I need to sort out. Originally channel 1 attenuator was having some issues, which I was able to correct. Now that channel 1 is working correctly, it appears channel 2 has some issues too. The issue with channel 2 shows two symptoms. The first, is it does not want to trigger properly. It sometimes does and other times it does not trigger properly until I push one of the other buttons on the front panel. When I get it to trigger properly, if I push the <20Mhz BW button, it looses lock. When I disengage the <20Mhz BW, the trace returns to normal. Other times, it will give me multiple "ghost" displays on top of the main trace and slightly out of phase. What I am thinking, is the attenuator is not switching properly, and allowing multiple paths for the signal to the preamp. I need to go back to the manual and verify, but I think the BW filter is in each of the attenuators. Whatever it is only affects channel 2. It may be a few days before I can get back to work on it.Mitch

author: MarkL
author_rank: Unknown
timestamp: April 25, 2015, 02:17:59 am
content: That's pretty strange.The BW limiting happens common to both channels at the vertical output amp U600, fairly far after the attenuators.I don't think the channel 2 attenuator has anything to do with it, but you could try swapping it since you're an expert at that now.I would probably feed the same signal to 1 and 2, and start by comparing the various outputs of U100 and U200. Those are the two channel pre-amps and is where the trigger signal starts. If those look ok, keep going down the path all the while switching BW limit on and off.There is a signal associated with BW limiting (BWLB) coming into the trigger hybrid U500 via Q645, but I'd have to dig into the circuit more to understand what it's doing. It's conceivable the BW limiting switch is doing something to effect the trigger.EDIT: Typo.

author: mskobier
author_rank: Regular Contributor
timestamp: April 25, 2015, 08:01:12 pm
content: I studied the manual some more last night, and found the band width limiter is in U600. After a bit more thinking, and re-analyzing the data (slept on it!), it seemed the most probable location of the problem was the U200 preamp. So I had just a little time this morning, and swapped out the preamp with one from the other 2465 parts scope. Well, that solved the triggering and ghost problem. I did change them back to verify that it was indeed a faulty preamp. It is. The thought that triggered me to swap the preamps was remembering that on my 2445B that I recently repaired, there was no trace at all caused by the trigger pickoff in the preamp not working. So a replacement preamp has been ordered.I will use parts from the other 2465 parts scope, but I want to keep it as functional as I can so that when I troubleshoot it, I do not have a number of issues to resolve caused by scavenging parts. That scope has a problem on the A5 board. Once I am done with 2465CTS, I'll get back to sorting it out.Mitch

author: mskobier
author_rank: Regular Contributor
timestamp: May 05, 2015, 05:05:43 pm
content: All,The replacement preamp arrived yesterday, and I got a chance to install it and perform some tests. All basic functions on the scope now seem to work fine. Even some of the CTS functions (Frequency counter) were tested and work too. I input a 10.000000mhz signal and It displayed 10.000 mhz. Close enough for now. There is one additional issue I need to resolve. The displayed voltage amplitude between channel 1 and channel 2 are different. With channel 2 being a little lower than channel 1 for the same input voltage. I did replace the channel 2 preamp, so I probably need to tweak the channel 2 calibration to bring it back into spec. Other than that, I do not see any other issues that need to be sorted out. I'll do some more studying of the calibration procedure to see what it will take to bring it back into spec.Other than the calibration, the last things I need to do to this scope is to do the power supply capacitors and re-install the word reader plugs on the back panel. One of the plugs has a couple of broken wires at the plug that needs to be resoldered, then I can re-install them onto the back panel. From appearances, those broken wires are from the previous owners disassembly/repair activities.Won't be long before I can say this one is finished.Mitch