Tek 465 Repair

okay so I have to start admitting that I have a problem because I ordered this thing off of ebay and I mean I probably don't use it I mean probably well this stuff's really strong in there um probably is definitely don't need it because I can't even imagine running music but it was at a ridiculously low price and I thought it would be an interesting experiment in trying to fix something so what I was able to score was one of the most popular oscilloscopes in all time I think a 465 from Tektronix which is in much worse shape than I thought it would be but like I said used not working according to the listing but we will see about that okay so let's plug this thing in and see if we can get it produce anything nice power cord wrapping around the back there plugs in power mmm lights up no light on the volts per division intensity focus scale illumination so something works their beam finder and uh no beam II yeah it looks like we're going to have to do something let's poke around a little closer okay so I got the case off and I think the first problem is the fuse here and if mmm if we can we see that can't see then but it's blown so that leads me to believe that it might have a problem with its power supply since since it's not producing any dot on the screen I'm not sure but this is the first place to start and I don't have any one-and-a-half amp fuses so I'll have to go to the electronics store and pick some of those up but yeah that's it for now okay so we've replaced the fuse now let's see what we get oh I should turn the power on though there we go scale illumination very good my volts per division light isn't coming on and can't speak on that mid and that mid beam finder still nothing still nothing in finder [Music] yeah there's something something that's not right yeah nothing nothing nothing still nothing so that's interesting a the scope is putting out a square wave on its calibration trigger I haven't quite figured out what the what the [Music] which is good news what means that there the power supply is probably working but what that does mean that it might be the the the tube that is gone or the high voltage supply and I just have to check the might have to check the tube now that's a that's a dangerous little endeavor getting in there with the seventy thousand seven thousand volts but uh yeah well just be careful and see what we can find out so now what we're going to do is we're going to test our low voltage supply so we have our test points arrayed here and we need to see a +5 at 499 we need to see plus 55 now plus 15 1497 that's good we need to see - eight - seven nine five that's good now let's book that upper range to our 200 volts we need to see plus 110 109 seven and plus 55 54 nine so low voltage supply is all good - the ability for this thing to measurement so now we go on to the next step in the troubleshooting diagram TP okay so you know what I'm not going to check the negative 24 50 volt supply because I have no way of checking that but push the beam finder and hold it in no trace is visible so now we check test point 1486 for an unblinking pulse plus 15 volts - depending on 75 depending on the intensity okay so there does seem to be a trigger waveform for the for the test point 1486 z-axis which leads us to a check CRT circuit hmm so checking the CRT circuitry means removing the high voltage cover for screws off it comes now remember to not be all pokey with your fingers in there okay so I did some googling and um well spend some time on the Googler and man oh man the the amount of extra IQ points you get having Google is absolutely amazing just like I'm just like they say on xkcd anyways the there's a couple of good resources a lots of good resources on the internet I found a copy of this to print out you saw that in a previous segment I found a copy of this to print out and on the on Yahoo there is a tech scopes group and googling for repairing they're searching for repairing a 465 brought up an excellent suggestion which is if this fuse blows which it does in this scope check two things Q fourteen eighteen and the components around it because if this or this capacitor are short well this capacitor in in particulars that is the critical one because if that shorts to ground then you're just got unregulated fifteen volts it'll blow that fuse so this is a tantalum capacitor capacitors are kind of flaky over time anyways this is an old scope so I am going to check this capacitor and this transistor to see if there's anything wrong with yet now where those are physically located in the circuit is up in the upper left-hand corner and we find that out by by looking at our grid location and the grid schematic which is this thing right here so up there we've got a test a couple of things let's see what is going on with that c1 14 16 and what's going on with this transistor which is mounted in a in a case and I don't know if I can get a good picture of it but I can remove it it's just got a couple of knots that are holding the heatsink on its nicely plotted or nicely jacked and you can just pull that puppy out like that and it gives us an easy way of testing that and then we can also test that capacitor okay so let's test the transistor what do we have here we do we have no okay diode drop there diode drop there it's either EB C or EB C but the base is the middle in any event so we have our diode drop there and we don't have a diode drop across the emitter to the collector I don't think and we don't have a short-circuit I don't think let's see yeah no short circuit so the transistor is okay onto the capacitor that's plus 15 going straight to ground and that should not happen so I'm thinking that it is the capacitor that has bit the bullet all right let's pop that off and replace it with what the guys on the googler say a 100 [Music] microfarad 50 volt 105 degrees C electrolytic and see if that helps okay let's try that all right no short-circuit or is there no there isn't once that capacitor charges up all right well let's see what we get when we turn her back on fuse goes in all right so pop the fuse back in plug the baby in and let's see what we get all righty it's a trace that pot seems a little fudgy focus turn the intensity down oh look at that I do believe have a functioning oscilloscope all right so what was the problem the tantalum capacitor that controls a power resistor that runs an oscillator that drives the charge pump for the high voltage circuit had shorted so replace the tantalum cap with a aluminum electrolytic and Bob's your uncle man oh man that was kind of fun yeah the plots are a little dirty but that's to be expected in something that's a as old as I am practically and so yeah so let's see if we can put a see if the calibration works and yeah Wow look at that we have a nice happy square wave yeah I guess the the next question is do I get this baby calibrated I think I might or do I go in and start doing all the cleaning of it the cover doesn't look too bad I don't know if I necessarily have to go too crazy about cleaning it up maybe just a toothbrush to get the gunk out of the the knobs but yeah hmm five for a dollar those capacitors so that makes it 20 cents repair

Channel: grtyvr

Views: 51,997

Rating: 4.8314605 out of 5

Keywords: Tektronix 465, DIY, electronics, repair

Id: 81UA49dOFa4

Length: 17min 5sec (1025 seconds)

Published: Sat Apr 08 2017