AE#15 Tektronix TDS 460 Frankenscope - It's Alive!

greetings this is already from artifact electronics in this episode we'll be revisiting this Tektronix tds 460 scope we looked at the scope in episode number 4 and if you haven't seen episode number 4 i'd suggest you watch it before watching this because i think things will make more sense but we found that there was some capacitor leakage on the acquisition board and the front end board and that got cleaned up capacitors got changed and eventually i found that two of the voltage regulators had their traces eaten through on the acquisition board and once that was fixed it came back to life and it worked very well so i put it back together and i've been using it since on the bench I mean I do have a better scope but what good is it fixing all of these things if you don't use them so I make it a habit to try to use things that got repaired as much as possible I really enjoy the scope it's very nicely built it's not in color and it has a CRT but it's very easy to view and its functionality is is very good especially for a scope of this age which is what is it's an early nineties scope but what happened a few a few days or a few weeks ago I should say is that I started using it and from one minute to the next all of the buttons stopped to work everything including the rotaries which are essentially buttons also and it all happened at once so it wasn't like oh there's a 30 button or maybe even the 30 row of buttons or a row or column but diode has gone out no the buttons just all stopped to work and after playing around with it for a bit and rebooting it some of the buttons started to work but very intermittently and so it was time to have a look at the front panel board now last time I looked at this I did not pull the front panel board using the if it ain't broke don't fix it approach but I may have had to have a look at it what I am suspecting is that since I saw some pretty extensive capacitor leakage on the acquisition boards that we may find the same thing in the front panel or on the front panel board and hopefully we'll be able to clean it up and find if it's eaten any traces or caused any discontinuities in there and bring the scope back to life these scopes are relatively service friendly well serviced mechanically service friendly I should say because they open up an access to the board's isn't that difficult you take off the case you then unsnap the front plastic bezel which is held in place with four plastic tabs careful so you don't break the tabs and then you can there's a tab on the side of this that you push in and then it swivels out and is easily removed and once you take out there's four ribbon connectors connecting it to the rest of the instrument and it's free so let's have a look at it now and I hear a collective gasp coming from the audience but we'll talk about this abomination in a minute what I found in here was that the capacitors have leaked pretty badly and they had leaked even worse than they had leaked on the acquisition board so things things were not in good shape over here I did I did a lot of cleaning up of course I pulled the caps out first I did a lot of cleaning up in here and there was a fair amount of crud that came off I did not however find any any specific defects or discontinuous traces what I did find though was that as I was testing it the buttons kind of after I cleaned it up the buttons started to work over here but they were still sort of intermittent and so as I looked more and tried out things I hooked up the probe to the calibration signal and the calibration signal wasn't there anymore it wasn't working at all now looking at this and again schematics aren't available the calibration signal goes out on this connector and so it was the calibration signal was getting generated in this area over here and for some reason even though there is no capacitor electrolytic right here the closest one is over here this area was hit the worst I mean there were there were totally encrusted components here that I couldn't even identify and I made I removed some made some guesses and the bottom line was I could not get the calibrator to work anymore no matter what I did no matter what I replaced it just would not come back to life but you know it's the calibrator it doesn't have to be very exact so but you need to calibrate er on here what I did was I threw together a simple 555 based oscillator here that generates a square wave and and it's just got the three wires on here power ground and of course it goes to the actual calibrator connector over here it works fine the biggest problem for me was how do I mount this but if I ended up mounting it on these two rotary switch casing casings and gluing it into place so now I cleaned up again and now the buttless seemed to start to work again not having found any sort of a defect other than this the calibrator circuit not working and I put it back the calibrator was working and the buttons and the e rotaries were working everything seems to be okay I actually separated this from the front panel itself and went in and put contact cleaner on through all the buttons and contacts and the things just kind of started to work but the the soft buttons were the buddies the soft buttons surrounding the screen were still not working correctly and and they were intermittent and I opened it up and I think I claimed like the top two buttons with alcohol and put them back and let's see to improve things a lot so I said alright let's give this thing a good cleaning and that is when disaster struck the button that was most obstinate was the clear Menu button over here so I thought I'd give that an extra good cleaning I didn't do anything different I cleaned it the same way I had cleaned all the other buttons but after two or three swipes with a q-tip dunked in isopropyl it took off and made this ugly mess it basically took off everything on the Affleck's PCB down to the base material so I'm looking at this and it was really really strange because there was no residue on the q-tip it just kind of poof made it disappear I won't even I won't even guess what happened but the closest thing to me is that the corrosion wandered here and since this is probably the most used button of all of the soft buttons over here it just for reacted or maybe something came in something some liquid was spilled on it I I really don't know all I know is that using alcohol essentially took everything off and this is somewhat of an intricate design with some insulators on the sides so this is not a simple matter of getting conductive paint and getting it back to work again so after I stopped being angry at myself and the alcohol and the world in general I continued looking at this and trying to figure out a plan of attack because I the one thing that I did know was I had to get the sculpt back into working condition and if we look at this basically this strip this flex PCB is has is glued onto the metal frame so of course the first thought was wow let's just gently remove this and buy a replacement so gently remove it I used an exacto knife to start peeling it off and as it was peeling off it is extremely brittle it cracked all the way across from the corner to the bad area I was beyond the getting excited about this anymore but yeah I wasn't it wasn't a good day but of course I went and did some online research to see if I could buy the replacement membrane I guess you'd call this and then it would be a simple matter of removing the old one regardless of what I was got to break it and tear it it didn't really matter I was gonna put in a new piece anyway and so my search started this is what showed up on my doorstep today I found this advertised online and it was essentially advertised the piece of that didn't work right but the small print said I can't really give you any more detail the screen lights up but it is so dim it is very difficult to read it was it was only $49 and the better part was the shipping was only 16 dollars so for $65 I got this of course as usual my gripes were that it was somewhat dirty and gross so I spelled spent quite a good amount of time cleaning and up getting rid of black marker all over it and stickers and unidentified substances as you can see it's missing the handles it's missing the feet two of the BNC connectors it was dropped somehow I mean this corner is loose and it was dropped and they were they are no longer round and more elliptical than round and you can't even plug a BNC connector into them not a big deal they can be replaced and you can't really see it in the in the video but there's a lot of residue on the control panel over here and but other than that was I did I did boot it up and the seller wasn't lying it's the screen was super dim I mean m'p it did boot up and give me an error report but it was so dim I could make out that there was an error report but I couldn't really tell what it said so using my knowledge I have from my 460 I navigated the menus to the screen intensity and I could make out that the screen intensity was set really really really low so I cranked up the screen intensity the the trace and the grid and everything it turned out that I had a beautiful screen beautiful sharp screen it came up so I rebooted it and pretty much anything that was related to the acquisition boards front-end acquisition boards was tagged as was tagged as failing and I was able to plug in a probe into the channel one and yes it was not doing anything but so here's a scope the front panel works so I have to go in and check all of the low voltages but the CRT is good on it and so the big if was what does the front panel membrane look like the case was bent pretty severely that took me quite a bit of time to get it to get it to slide off this thing had been dropped several times and it showed but it opened up and the nice thing is it's got a beautiful soft key membrane on it and since it ran I already saw it running that should be that should be our new membrane of course I also took off the front panel board and surprisingly this doesn't it doesn't show any corrosion the the caps are good oh and I also test that the calibration circuit and that works too now of course the astute observer may have noticed that I left out a big part here and that is this is not a 460 but rather a 420 now my logic behind it was of course this was the cheapest I found and second of all since I'm only interested in the via membrane and also interested in the front panel and this one just seems to have no corrosion on it so this one's plug-and-play is it gonna work as total guesswork at this point but I don't think I'm pretty sure that it will work because the functionality of the scope is the same the 460 has a higher bandwidth but other than that everything is the same so the acquisition boards are going to be different the firmware on the processor board is going to be different and all of that but the parts that I really need should be compatible the only other thing is is as I mentioned before there's a lot of tape residue on here and but other than that the only difference is is that the the help over here is in gray and for the 460 the help is an orange over here but since this cleaned if the 460 front panel is really clean I'm probably gonna use this front panel and Transplant it over to this assembly and that of course brings us back to the rest of the instrument which it isn't really that interesting because I've decided to use it as a donor but again there was even though the acquisition boards have a problem that was very little capacitor corrosion there is some on the some on the acquisition board in the front end port but not nearly as much as I saw on the 460 of course for the 460 those pores are useless because they're not going to be fast enough but I think this this one the scope lived a healthier life as far as capacitors were concerned so let's come up with a plan of attack originally I was thinking I might have tear everything out of this and end up with a naked frame with the membrane on and then transplant everything from the 460 to it except of course the the front panel board itself but since this came up and the screens beautiful on it I did some power supply measurements and they're all good so essentially the power supply and the CRT are not going to have to get transplanted what I do have to transplant of course is the front-end board and I mean I have to transplant the phone on board anyway because these BNC connectors are bent and won't accept won't accept any BNC cables the the acquisition board itself which is underneath here and the CPU board the DSP board and one other board that is in the card cage I'm not gonna risk miss king mixing and matching those but rather I'm gonna replace all of those and and then we'll power it up and see if we have magically transported transformed this frame into a 460 with working buttons here's the bottom of the 420 I've started removing a bunch of connectors and screws and everything but I think the most important part of this is to clearly label the boards as to what they are there's lots of numbers on them but none of them are easily identifiable as 420 or 460 so this way if a bunch of boards get to remove and they end up in a pile I will be sitting there forever wondering if I've got the correct boards inserted this of course is the acquisition board and one thing you'll see is one the main repair I did on the 460 was on on the two voltage regulators over here which had lost connectivity over here but our this and again you can see this this does not have any capacitor leakage on it but obviously there's something else blown up on here that keeps that keeps making the scope complain about it so here's a 425-cc connector on the back there is these flex connectors which you have to remove and very carefully thread through the slot in the board and there's also a header connector over here that connects to the rest of the boards all of those removed and it came out another nice thing was that the case was bent and the showing that the the instrument was dropped or mishandled in some way or other but fortunately the the case the actual frame is in good shape there's no bends there's no damage there's no corner dings on it so this should work out very well next we have the front-end board things are mostly removed from here one more screw remaining I have also removed the Flex connector over here everything looks good in here the caps look pretty clean and it's a shame that something must is wrong with this set of boards but something to worry about some other time but again this is also labeled and and this definitely looks cleaner than the 460 board I mean I wish I could use this but I do not know what the difference is between the boards are giving the 460 the extra bandwidth so I'm not gonna try to reuse this board and with that gone the bottom of the case is clear and it's ready to accept the 460 boards now took a bit of manipulating to get this to come through in one piece but it's not torn or bent and basically place it on the air connector and gently push it into place making sure that none of the pins got bent and of course then we have our assortment of screws that need to go in to hold us in place and not to forget we also have this wire that needs to be soldered back and the next candidate is the is the 460 front end and kind of hurts me to have to put this back in because of the corrosion over here but it was clean so many times and it has survived many hours of work so I think I got this one so we should be good and of course best of all the BNC connectors are straight on this and all except the NC cables so this one I'll go a lot easier it doesn't have a slot for the Flex connector but it just slides in and also has of course an assortment of screws that hold it in place and one of them by the way is hidden under here so if you're doing this in you're wondering where it went to it is well hidden so let's put this one back and I'll continue fastening this and then we'll have a look at the cards in the card cage okay everything's screwed in let's make sure that everything is there this board is held down with five screws no one two three four five six screws this connector has to be soldered back to the board and I don't recall what that's the auxiliary trigger input over here this one got plugged in for the front-end board this one got plugged in and this is held in place from the top with four screws these three and one right underneath here this also takes additional screws in front for the probe auto-detection a PCB and we will get to that but let's try and see or replace the boards in the card cage more boards to pull so first let's get rid of the header plug and start with the lowermost board which I've loosened so it's got a plug going to the front panel and a battery plug now that board the board we just removed is the 68 old 20 on it and lots of flash ROM so I bet you this is the this is what execute the the main OS and that would be what computer code wise distinguishes the 420 from the 460 next we take this guy it has the ribbon cable connecting it to the power supply and this seems to be doing as to a dg2 21 zone there well it's to 2100 to 22 to the other side chip so along with the TMS 34 Oh 61 which is a display processor and that's because this is a VGA board it's probably no need to swap this but since we're at it we might as well take this out and last but not least we have this board that has a national ad G 500 be e on it and lots of NIC on nine parts and it is also connected to its own battery so this has two batteries in it alright those three boards are back in and screw it into place and of course as I put it back I realized that there's two batteries in here and I should probably measure them now they're really really well insulated it's like impossible to measure them anything anywhere other than actually on the board so the first one's easy because of the board connector is I can't see it anyway the board connectors on the other side of the board over here and let's see what this reads 38.1 which is plenty and this one's a little bit more difficult to get to and even more difficult to show so I just have to take faith that I'm actually measuring the battery here and that one is what did I see two point two point nine so the batteries still have plenty of power they lasted this long they'll last for a good long time longer right thing so we are good there so what do we have so far is we have all of the card cage cards back in we are going to need to reinsert the inner board connectors here and you go to here they are at the right side right orientation yes it is it's all of these guys are connected together now another thing I want to do is with the luck I've been having lately remove all of the tape I put on here and that's because with my luck I got tape on this large chip over here and it's probably gonna cost some thermal abnormality that'll make the chip blow up so I'm gonna give this no excuse to fail on me so all of the tape comes off so at this point all of the board swapping is done and what is left for us to do is the front panel so for the front panel what we're gonna do is here is the 420s front panel and the front panel it's kind of dirty and tape and everything on it so but the electronics are good in here so what I'm going to do is use the electronics in here and but transplant this front panel from the original 460 over to here so everything will look just great and now for the front panel what we got to do here is do the faceplate transfer I'm going to use a sister for 20 I'm going to use everything in here except the actual faceplate because there's a bunch of papers to do in here and it doesn't exactly match the four sixties panel mainly because of the test legend here is right on the 460 and also the Year shade of grey used here is different so anyway let's open this one up not open it up but let's separate it and the way to do that is first we have to remove all of the protruding buttons and the service manual gives you this procedure where you're supposed to stick screwdrivers underneath the button here and lift it and well if I do that kind of stuff I'm just gonna scratch the front panel tape residue or not and what I found is easier to do is you just turn it around and press the buttons through from here with a flat surface like a flat bladed screwdriver with no damage or no risk of damage to the front panel and these two my fingers are sticking to the front well these can probably just push through my finger but nodes too much of it I'm trying to be careful I really don't want to break anything so let's try this and there we go buttons are out and in order to separate the PCB from the panel is there are more tabs more plastic tabs one here one here and one right in the middle you lift it and gently pry the board off so we want to keep this board this is our final board probably want to keep the membrane layer and since this worked so well we might as well keep the rotary inserts here that are going to come out easy and they are and then it was just do the whole thing in Reverse using the original 460 front panel I can't turn it because all the buttons will fall out but we'll just reassemble everything in here and that seems easy enough I could do that here let's remove the rotary inserts here but the old ones back ended they're actually there's a ball bearing in there which seems to match up with that and another one which matches up like that so now we need to put back the membrane right side up hopefully and follow it by the PCB that just shook just snap back in one click - and that's already clicked then so here is our repaired 460 front panel make sure that all the buttons travel freely and insert the mobs well this one who doesn't want to go in so let me figure that one out all right misunderstanding between me and the panel resolved we got these in and that is followed like one more and we're done old face new electronics okay straighten things out of it yeah so this is a lot better looking and more confidence instilling then this obviously so alright next step is to set this up right side of that and for all the connectors backing and we need this to this of course grows all right here wait a minute I haven't inserted all the screws quick that's in place now I want to put this stuff this one nice and long so is this one and of course this is the spare part that it was all about now I put in the inputs finally we are left with this one and that fits into place hinge this in and press it into place now we need some screws to hold down the input panel and I will make a final pass - and make sure that all of the screws are inserted well in this case we were going to install the front plastic vessel so I better make sure that these screws are all in and they are now let's get the plastic bezel preferably the right one that says a 460 on it and it has the membrane inside and it's also held in place with tabs okay I need to spend some time with the front bezel again it didn't want to snap into place every time I press things into place they would go in in the minute I let go that popped back out again so I removed it and went for a few rounds with it and finally I had things just aligned perfectly and it's not been to place one other thing I did was the ax workbench was getting rather messy at this point so I decided to do a little bit of cleanup and that is that the remainder or the remaining parts of the other front panel were all over the desk and I decided to put this back together again and not that I want to use this in its entirety but here's my parts front panel for the TDS series and I found a few more odds and ends on the workbench first one through these guys which are board brackets that hold the boards in place and align them properly I guess so let's sleep where that goes that goes yeah this one goes here doesn't want to click clicks when I come through not there was kind of a half-assed click but it did go in and finally this one I won't win him nicely and I think something a lot more important than this that I found is the the interconnect between the acquisition board in the front end board that wouldn't have worked too well without it this one is properly labeled 460 doesn't really matter because it's a it's a passive interconnect board and even the number is matched to the four 20s but let's keep things consistent and with that said and done everything is in place I don't see any extra pieces flying around so let's put this into position for the final test I went ahead and double-checked some more would be kind of a shame if I turned it on and I went up in magic smoke just to catch some obvious or stupid mistakes but couldn't find any I couldn't find any smart mistakes either so no more procrastination let's take a power cord and see what happens power switch on the back is on and [Music] liftoff or countdown I should say fans running lights are on screens obviously working wow this is great let's see if it makes the galloping sound testing the acquisition board right on cue that's good lights one off things are running and boom self-check past fantastic so let's see if we can adjust the screen brightness a little bit at this point and of course for that all we'll put some text on the screen and we go to intensity and overall intensity is at a 90 percent let's crank that a bit I'm gonna crack that to 95 text on the red graticule we'll leave that at 75 aa little less than that you don't need that much 65 and the waveform itself believe that at 70 and the button works fantastic we got a better put the case back on and give it some input but it looks as if the pork transplant was successful and that at least might be love at 460 is back in full health I mean I got a walk through all the buttons and turn all the knobs with signals applied to it but if it continues performing like this I guess that will be the fun part one more thing to note is when putting the case back on since we had removed the front bezel these pieces of the EMI shield all came out and they need to be reinserted into the channel and is actually do a really good job of reducing extraneous noise it's a bit fiddly to put them back in but it's well worth it there's four pieces and you can normally see from the wire memory where they belong and again you just put them in and press them down into place and once you put the case on it'll make contact with that and again you only need to do this after having removed the front bezel because when you remove the case these generally don't come out okay looks like we're back in business they did run a calibration cycle on it I'm not showing it because it's kind of boring to watch the screen goes dim and there's all sorts of things happening on the screen that that aren't very interesting to watch but what that did is basically made sure that the reference levels these little arrows over here match exactly where the signal is and the signal looks a bit noisy right now so what we can do is go to the acquire menu and tell it to use a high-res display and that gives us a nice analogue looking straight line in here so let's see what our compensation signal looks like and there's a compensation signal and the little indicator showing us where it's triggering from you can turn that off if B comes in the way but there's channel 1 for you we then move on to channel 2 turn off one turn on two and let the scope do that work for us by pressing Auto set and there's Channel two over three turn off to turn on three it's almost there but let it Otto said it so if that's probably because the trigger source wasn't was still set to tube and it couldn't trigger properly for Channel three because there was nothing on - and finally we'll go to channel 4 time three or four on what kind of the same results we don't even have to auto set this we can just go to the trigger menu and set the source to channel 4 and everything looks great let's measure the signal coming out and it's the frequency and a peak to peak which is here so it's it's very close to 1 kilohertz which it's supposed to be and peak 2px 520 males which is a little higher than specified but it's nice to see that the original calibrator circuit is working in here and this was by no means an in-depth test but it does show that it's pretty functional and since I'll be able to use this on my bench again from now on time will tell if everything else works well thanks for watching and I hope you enjoyed this at least a little bit as much as I did after seeing the scope come back up again it was I was pretty angry at circumstances when the thing went when those contact traces disappeared but nothing that time and money can't fix right well go ahead and if you liked it give me a thumbs up and if you haven't already subscribe go ahead and subscribe there'll be lots more stuff like this coming up see you later

Channel: Artifact Electronics

Views: 6,029

Keywords: Tektronix, oscilloscope, tds, 460, 420, transplant, repair, capacitor, electrolyte, corrosion, screen, intensity, cleanup, calibration

Id: Z8obX_dsP_I

Length: 55min 17sec (3317 seconds)

Published: Tue Sep 12 2017