#153 Heathkit IT-12 Signal Tracer repair and restoration

today here on the bench a hiss get signal tracer model i teat worth which has never been used and we need to take it back into service welcome to tear expand okay and let's right go here into the videos so you see this is really IT 12 in a very good condition and i was able to acquire it because the owner told me it doesn't work so it is without function and he did this kit i don't know 30 years ago and he tried it out and it doesn't work so he put it by site and over the decades he has forgotten that it is somewhere in his shelves and now he said okay really I don't need it any longer and I was not able to find the problem when I built this signal tracer and therefore he sold it and now we have it and that means this this model or this device seems to have complete new valves and you you you see that yeah the shape is like it comes from factory so I mean here we have some scratches maybe from the shelf I don't know but anyways let's test it out so let's test it interest let's take it into service and let's see if it works and you all may know that if you have a product like this you have to be very very careful because you really can this try the complete unit you really can blow it if you simply plug it into your main circuit and to switch it on so that is really what you never should do so we really have to take some precautions to take it really carefully back into service and let's see if it works or not and of course we have to give it a full inspection because it was a kit so it has been built so I have no clue what the workmanship is so I have not had it open but well so let's very very carefully start our testing here okay and this here is the u.s. model so that means it runs with 117 volt which is no problem because we have adapters like this year so you can get it for very little money on the internet and you can easily plug your US socket ear to a European one which then will it make what was what then make it possible to operate this unit on a European mains network so that is not a problem but for our first step of course we will put it to our isolation transformer and we will put some current-limiting bulbs in front of it so let's prepare here our test setup and then let's start the unit ok and of course we are using here our bulbs to be able to take our signal tracer safely back into service if you don't know how it works so the bulbs are limiting the current and if there is a short inside our unit then all the bulbs will light up and will protect our circuit so it is like I can shortly demonstrate it so you see I have here my both wires which will supply here our unit with 117 volt AC and if there would be a short inside our circuit we would not get a problem as you know our bulbs here jumping in and they will limit it our current through the unit the voltage drop will at our bulbs and will therefore really protect our whatever is shorted out here in our signal trace or maybe a truffle transformer or such and therefore this is always a good idea if you want to know a bit more about it simply watch my video number 48 there I explain a little bit more how it works sorry it is video 43 right it is video 43 where I explained a little bit about how it works here with our protection circuit and of course we have here our isolation transformer over there and so we can do our first steps okay so it is connected this way here all right so we have our bulbs in between now I can switch on the unit but our transformer are isolating transformer is turned down so we do not have a voltage here so we can see it here on our power analyzer and we can see that there is no amps and no vats and you see no voltage and when I now start here cranking up our voltage so you directly see yeah something is obviously happening so six VAT and ninety milliamps it is dropping because of course 60 volt is definitely too low so that is only the procedure more important is of course now let me see if I can bring it here a little bit more together of course we are interested in our in our metric I is it working or not so that will be an indication and now I will go ahead with cranking up here our voltage and let's see oh I already hear it humming so that is interesting because remember as a foetus scription was that it doesn't work okay so let me crank it slowly up and we watch our parts here because if there is something wrong they will light up and you hear we have already hum and it is really coming here from the unit so that is promising okay so let me go and you see everything is fine no problem and by the way the unit is rated with maximum 25 VAT so that is always important to observe and for the moment in time you see we have 11 but at 87 volt and I will crank it up to let me say it 120 as long nothing goes wrong here but let's have a mirror look to the unit so we see we have already here our magic eye coming up but we have not yet reached our target voltage and as I said let me go up to 120 volt so now that is set is just fine here so you see we are drawing you 180 milliamps at 19 VAT and yeah we can hear is humming and the speaker and we see here our magic eye and it is already shining very nicely so that is promising - so no problem whatsoever so let's see what we have here and it is working it is really it's really working and yeah I don't know what's really going on because the unit was salt as no function at all so I'm wondering what's really going on so all our parameters are still good so a 20 but at 180 milliamps 120 volt and I'm sure our voltage here at the input is lower than 120 remember so we definitely have a voltage drop here at our boards but we leave it in this configuration because whatever happens this will protect our circuit here okay so that is really funny and I can switch it to RF it's all working fine and I can hear ya short hear our probe and now the hum is gone which is good as well all right so what does that mean we really have a let me switch it off because we have not tested our electrolytic capacitors so we really do not nothing so we we have to open the unit and we have it we have we need to give it a full inspection because there must be a reason why the pre owner told me that the unit is not working and I carried it by car here into my lap and so that is all what I did okay so let's open the unit let's see what's really going on so there may some really nasty components inside especially capacitors and that is what we need to check before we go ahead okay so that is relatively easy so we only have to take off here this both screws and then according the assembly instruction we should be able to take off here our housing and he should have directly access to our unit and so it is let it get it through here okay and remember so we have here a capacitor so that is what I directly see and this capacitor capacitor can potentially still charged so be careful maybe we have not maybe we have to check it first and then we can ahead but anyways here on the first look it really looks like new so really really nice but yeah we give it a full inspection okay and as already set so we need to make sure that there is no load anymore so ground is our chassis and as we discussed before so this is our electrolytic capacitor and let's see if there is a load and yeah five volt so that is not dangerous here we have obviously also five volt so there is a little rest load but that is not very dangerous so I will simply connect it here to ground which means I'm able to discharge it and now let's test it again and so that is nothing at all so that means the load is gone and well the very first what we should do is testing our electrolytic capacitor because I'm not entirely sure but this unit must be from the late 60s or the early 70s so let's assume it is from 1970 so we really have here a vintage unit and even it has never been used because our owner thought there is a problem with the unit and he found it not working asked after assembling it we have to expect that there may be a problem here with electrolytic capacitors because capacitors 40 years or older are always a problem I mean this capacitor never get heat I mean you see here a tube is very close to the capacitor and that means if this unit is running and believe me in workshops this unit were running the whole day the whole weeks a whole months a whole year and after I don't know 10 years or so you definitely have four problems here with the electrolytic capacitors but I mean this has never been used and I can believe it because it really looks never touched so maybe this is fine but we have to test it and let let us start there and then we look after a problem because our owner told us that pre owner told us it will not work and the question is why so what really is the problem okay while our capacitor tester is calibrating we can take here our magic eye out of the way so that will make it easier to get access year to our electrolytic capacitor now I believe we yeah so now we have a much better overview and we can check out here our circuit a little bit and we can test here our electrolytic capacitor well meanwhile we can have here first look on our tube sockets and what have we so you can see here there is obviously a coupling capacitor which needs to be tested or we have to swap it out but it does not look like one of this VAX capacitors which has been used but maybe in the 70s they already didn't use VAX capacitors so that looks like a much more modern type and yeah when we have here our carbon resistors and of course we have to test this resistors because maybe they moved out of Tolerance so that is an important step as well and of course we have to test here this capacitors because there are some coupling capacitors as well and having here look onto the schematic you can easily see here our transformer so that is the mains transformer for 170 volt AC and then we have here a silicon rectifier diode so that is not a tube any longer so that is already a silicon diode and then we have here 1 2 C 7 and I've seen it it's a triple package capacitor C 7 oops you come to see it and we have here our bypass capacitor of 20 Mike referred our belief so that is a common value for a bypass capacitor here at our audio amplifier so yeah we have this both of 50 micro farad and then the 20 micro farad in one package and of course this year is a critical coupling capacitor because this is really connected here to the grip of a grid of our tube here or amplify audio amplifier tube and you see this is connected here at the anode of our double triode tube so two tube tubes in one package it is a 12 ax7 and the 12 is already an indication for the heating voltage so is working with 12 volt so as our amplifier audio amplifier as well so it is a 12 CA v and our magic eye is 1629 and that is as far so that is V 3 and we see it here at our power supply so this year is for our tubes and the V 3 is then of course also the 12.6 12.6 heating world heating system alright and yeah let's start with our electrolytic capacitors and of course here our coupling capacitors I mean this coupling capacitors are really really important as if this capacitors are leaking current DC current then we never would get here zero vault at the grid it is a g1 of our final tube because we always would get a leakage of the supply voltage for this portion of our double packet you see 76 volt DC and this would directly get to the grid here of our amplifier tube and that means this this tube would get out of its it's working point and the tube would then really draw heavy current and therefore yeah it is important that our coupling capacitors are not leaking a bit so that is really crucial to check and of course we are testing for ears are and therefore I put one clip here to ground maybe I can take ground here better would be really here at the ground point and we know our capacitor is 50 micro farad and it has 150 wallet and according to our list so we have to take here like me see all 47 and let me check here with 100 volt we should not go over 0.7 home and with 250 0.8 so we are in between so maybe 0.75 so as long we are below 0.7 the ears are is just fine and you can take care our reading and what we can see here our first 50 micro farad is 338 milli ohm so we are far below 0.7 ohm and that means this portion is really fine okay and let's go to the second capacitor in this package it is again a 50 micro farad 150 volt and you already sees reading so we are even lower so 0.29 3 which is which is really fine it looks like that this capacitor is as new and now our third part which is let me double check in the schematic it is our 20 micro farad type and it is 25 volt so that means we should not exceed 2 point 1 ohm and yeah you see it is 2.1 let me double check it is 2.1 you see it is moving and jumping around here a little bit so it is within its specs but maybe we need to support it a little bit we will see later I mean as I said this is only the bypass capacitor for our final audio amplifier and those yeah let's see what we need to do but other than that it really looks fine so really I would not expect that this capacitor is really doing any trouble here in our circuit okay next step will be I mean you you know obviously that we can't check for capacitor capacitance as therefore we need to have the capacitor taken out or at least we have to take off all the wiring because otherwise we are not able to test for C but I just want to check in the next step I just want to check here the wiring and I just want to check here our resistors so I try to check the values of the resistors and yeah this year is our final amplifier and so I just go through our circuit and yeah let me get back if I have maybe finding or yeah with our next steps I mean we have to check of course and that is what I already said this coupling capacitor even it looks a more modern type but this is really really important and I believe if this you see if you can see it here so there you see the marking so the white bar and this may show the foil end of our capacitor and if it is really indicating the foil and I mean we have to check it out but if it is indicating the foil and then this capacitor is the wrong way around so you may know that the foil and always have to go to the lower impedance and of course the output of our pre-staged here is lower impedance than the input of our final audio amplifier so that it's a higher impedance and according to the law that always our foil and of a capacitor has to go to the lower impedance this is wrong so it needs to get flipped over and if I have it out anyways because I have to test it I would replace it anyways with newer capacitors just in case because yeah we need a very good DC blogger over okay and I've taken my time and I inspected the circuit very very carefully and see what we found so have a look I go as close as I can here to this point and what you see is that this has never been soldered here to the socket this little wire and when we go here into our schematic we are here you may see it at our audio output tube so let's see audio amplifier right and when we go here into our schematic you see that exactly this point here so this is pin 1 so that is the cathode of our amplifier tube and you see this is pin 1 so let me go closer so this is pin 1 2 3 4 so 3 & 4 is our heating system and you see this is here definitely pin 1 and pin 1 is a cathode and that has not been soldered so this solder point joint is missing and of course if our pin 1 is not connected here to our tube that is clearly reason why the complete system won't work so that can already be the reason why the system wasn't working and today I mean you you clearly see this is a brand new contact here from our tube socket right so you easily can see that never solder has been on that contact here so and you see I can move it here up and down and if there was no contact then of course the system was not functioning so that is definitely the explanation for what the owner was telling me this system is not working so that is most likely the reason and well while I was carrying the unit of course it got checked here a little bit and it might got contact so that the system was working here in our first test right okay so that means of course we have to solder it down so that we have a proper connection but I have another nice finding so let me flip here the unit around as I told you I just wanted to check the resistors and that is what I did and this here is a 68k resistor and we know this resistors has here a silver ring which means 10% tolerance and well so maximum 68k plus 10% would be seventy four point eight Kate and when I test it here so you see this is definitely out of Tolerance so this resistor went too high over the years so what we need to do is we have to replace this resistor for sure and of course we have to check here if it is the right way around so I will take this out as well and I've taken out here my tube and what you can see here so I mean this does not necessarily mean anything but as this tube sockets are known for making a trouble we really have to check this tube socket or maybe it is already the best idea to simply replace it I have to over think it and I am a little bit unhappy here with the ground connections because this is here you can see it this is here all main ground all right so you see this here is directly our wiring here out of our transformer and so this is ground all right and then you see we have here can you can you see it or not I don't know let me check if I can show it any better so when you definitely have here a ground point as well I'm see maybe you can see it here I mean we have here all the ground leads and then it is the connected to ground and here as well you see a ground is tied here to this point so we have here different ground points and that is never a real good idea I have to check if we can leave that so we need to give the circuit better or more complete testing but here for the first step we need to keep it in mind that maybe that is not the best idea and I go ahead now with replacing the resistor and of course here our our capacitor here okay so we did hear some modifications and first of all you remember that we had here an open connection and I have here now a nice old point on our cathode of our audio amplifier and of course I have changed here our capacitor to modern one and it is even a higher DC voltage what this capacitor capacitor can take even it is not necessary because we have here maximum I believe 80 80 volts or such so that is now new entities now the right way round so we have our foil and here at this side and it is now pointing here to the lower impedance site which is of course right and I've tested it so I didn't rely here only on as little marking here so I really tested it and sure this marking is really foil and so that is fine by now then what had we had we out so I replaced here our resistor which was gone out of Tolerance so that is new and I found here this ground this ground point here was completely loose due to the fact that it was not really screwed here to the chassis and that means this was wiggling around and yeah as we already discussed I'm not really happy with the ground wiring here but we will check it I will first now replace back here our magic eye and if set is back in and and I know I have done here some solder points where a thought maybe it is good to reflow it so that is what I've done now yeah as I said let me put back here our magic I to the unit and then we can do a performance test I mean you know it is always important to have here a high gain so a very high amplification so that is really important if you are probing in RF circuits because remember you may have very tiny tiny signals and to hear this tiny signals rectified here by our crystal diode if it is switched to RF right then the little diode here inside will rectify it and to rectify it means in this regard it is a demo the modulator and you will then have your audio which is on your RF signal and it is always in an RF circuit very tiny and therefore you really need a huge gain and that is a reason why we have here our two tubes connected in cascada configuration or cascode I do not really how to pronounce it it simply means that this bar stools are tubes are switched behind each other and really brings up a high gain to our final stage and yeah is therefore we really need to check the performance that means for me it is always an indication for quality or for fully working or whatever you want to call it if we can minimum probe a signal at minus 40 DB M or even lower because that is already real tiny tiny signal and that means you can feed your receiver for instance with a very low signal or for antenna input minus 40 DB M is not low so that is already very high so it is s 9 plus 30 32 DB I believe if I'm did sir Massa writing my in my head so that is already a very high signal at the antenna input but for a probe it is not really a big signal so therefore we like to be able to probe already at our antenna input a signal off let me say minus 40 DB M right and then we can follow along in the circuit and go a step by step and then we can determine if our circuit is amplifying the signal or not so we can really go stage by stage and therefore that is really an indication for performance of a signal tracer if the signal tracer is even possible is even able to pick a very little RF signal and can de modulate it and can really amplify it and secondly to that is that signal tracer like this is able not only let me say shortwave signals which is maximum at 30 megahertz so it is interesting or it is formally important to be able to pick even 50 or 145 or maybe 400 30 megahertz signals I mean you know that this signal traces were never developed for taking signals in in in the 400 something megahertz area and not even for the 2 meter band 140 or so so you know in in the past it was a matter of fact that this signal tracers are already struggling with let me say 100 megahertz or so in the FM radio for FM radio stations which are around 195 up to 100 115 megahertz so it was a matter of fact that you know signal traces like this was failing and so it is really indication of performance if you can really pick a very tiny signal right and additional to that a very high frequency and that will be our performance test so let me reassemble it let's see if the basic basic functions are given and then we go and pick really tiny signals to see how this unit works all right so our magic eye is installed back here into the unit and well here it looks pretty nice now we have to check if we need to adapt it a little bit okay so then let's try to switch the unit on I see that the unit is pulling current so uh and magic eye is coming up very nice so of course I have here shorted out our probe and now our first test so now crackling no hissing only a little bit in the background so let me see if I take the ground and so what is obviously working as far as I can see it we need to adjust here or tube just a little bit to have it more or less here in the middle I don't know if that is now fine maybe I have to check it and let's see symmetrically is working as well as you may see and it is really nice and bright and by the by the way I have of course tested all the tubes with my tube tester so here for instance I have here my test cards for the 12ax7 and I can tell you that all our tubes here in sight our unit are showing up 100% so all that is again an indication that we really have another used unit so that all makes sense so all tubes are really really in a good condition according to my tube tester ok that all seems to be really good and I really can yeah so that is all just fine and even on RF there is only a little humming here in the background and that is clear because our housing is not on and don't forget we have really here a circuit with a very very high gain and Zeus it is clear that there is a bit coming on our position on audio it is dead quiet and we check here or a tube for microphonic no so our tube is just fine no microphonic effects and you really hear it is nice and quiet so another chance what we wanna do is for the moment in time our noise function is switched off by the way I can switch off here my speaker and you may hear but it is easily working okay what I just wanted to know is if we get our approximately 90 or 100 volt to our probe for the noise or for the crackling test so therefore we have 100 volt DC at our probe and that is what I want to test as well and I've prepared here my test setup so now our noise is off noise function is off and I read I read 3 volt so maybe there is this which I have cleaned as a switch then maybe there is still a little bit of our di oxide here my get contact 60 maybe that there is still a little bit but anyways so let me switch now the noise function on and you see I really have 180 vault and that is used for our crackling test so if you have a noisy component or so that you can test it here with this feature so you see that is working as well and even it is 100 volt it is not really dangerous to your life because the current is limited limited to one milliamp I I believe so I wouldn't touch it because one vault is a lot but you know it is you you do not really need to touch it you may get hurt a little bit but it is not finally dangerous to your life so we know that function is given as well and ah what if I may have forgotten to tell you I've of course tested here our triple capacitor package and all the capacitor values I mean capacitance wise are in the limits so they are a little bit about 50 money microfarad and everything is fine so you really see that it is another used unit and those the restoration work was not so happy so we really were able to get it back here in to work with just some little steps okay now let me put back the housing that we have a bit better shielding and then let's see the performance of our unit here okay and here is so unique back in the housing and yeah maybe some of you have already or wondered already why I was not changing here the power cord and I have three reasons for that because first of all I use this adapter which will adapt from 230 volt to 110 115 and in this unit there is no fuse installed and I have not installed a fuse here into our unit because if I would have installed here a fuse it should it would have made sense to use a three wire power cord to connect ground tear to the chassis to make it more safe but once again first of all I use this converter here and I have fuse here in my little converter so the unit is fused here by my little converter so that is first secondly I will make clear to everybody who is may use this unit that it is the American American version and Zeus it is a 110 volt or 120 volt version so that is the second reason and the third reason here is that I use the unit in my internal isolation supply network so I use as well here my scope is used with an isolation transformer so that it's a reason why I can test on AC lines and so forth and so forth and therefore this will get to the isolation transformer installation as well and maybe a last point for collectors so I leave it original but if you do not use it on a isolation transformer please do you own favor and replace this original court with a safety three via court and put one so the ground lead here to the chassis that if something happens here in the unit that your fuse will break so that is very important only here in my installation I can take the risk because it is no risk and leave it as it is so you really should know what you are doing because it is not funny to get an electric shock here by a unit which is 40 okay but now let's go over to our performance test okay and my probe is set to RF and you can hear that it is working alright I have here my corks cable and so that my port is going here to my signal generator and you see I really start off in the 10 meter band right and I have set it to -4 DBM so that is not really a very low level so that is really a high level especially for receiver input so you really would float receiver with such a strong level and now let me here switch it on so now it is on and I'm here of course with my probe and I just want to take here yeah and you can clearly hear our strong and nice I'm able to read here my my ten meter Bend and even with very low settings so that is only on 10% when I go down here to the test point all right so that means performance means let me see how much I can go down so let me go let's say 2 minus 10 and let's test it again and you still can hear it no problem whatsoever so let's go to 20 okay so now you can recognize the volume is going down but I can increase it here with my little volume control and you hear it is gute again so let's go to let me say 30 and ya volume is going down and I go higher with and you still can hear it very very good I am at what is it 55% and we are at minus 30 DBM and you hear that it is no problem to hear our signal okay and I mean minus 30 DBM is already yeah how can I say it or it is still 7 millivolt if you like and yeah let's go down to minus 40 DB M and that is already a little challenge for a signal tracer but let's see and aha so we can still hear it so I advanced him a volume and it's definitely no problem to hear this signal and minus 40 is only 2 milli watt so let's see let me go down to 50 I mean that is really a little bit low because this is only 700 micro volt and I mean now I'm on 100% here alright so you see it is fully cranked up but I'm still able to pick the signal and to to be awesome attitude to be honest I mean that is awesome so that is really a great preferable performance let me see - 55 and you still can hear - 55 awesome - 60 now I don't believe that we can hear that maybe a little bit in the background but now no but - 55 we can hear - 55 and that is 447 sorry it is 398 microvolt so that is really low so that performance is great as we talk about sensitivity so it is really sensitive here our tracer and that is what I meant with performance but now let's start to do here or trick a little bit different so let me go up to let me say 50 megahertz and of course we change it to am 50% and let me go here too I don't know let's start with minus 20 can we hear this signal and we can easily no problem so let's go back to our minus 50 because we know okay we have to advanced our volume and still we can without a problem okay so let's go into the 2 meter band and again let's switch to am and let's go here to minus 20 DBM let's hear and I should switch on here my generator oh no problem let's go down to minus 50 and we can still hear it and remember we are already in the 2 meter area right and that means a lot of older tracers are giving up because they cannot handle it and even my modern digital one you may have seen it in one of my earlier videos is simply not able to pick 145 mega roots with minus 50 DBM no way but this one is doing it okay now let's try what I really can't believe if it would work okay a.m. and 50% and let's go up as well too let me start with minus 20 let me switch it on and let's see come on are you kidding me so that is working so let's go down to minus 50 and yeah I know now it starts a struggling year I mean minus 50 on 430 so but minus 40 is working here without any problems alright so let's see yeah you can hear it four hundred thirty megahertz at minus 40 DB M so that is awesome that means it is easily possible to trade signals in a 70 centimeter transceiver without any problem so this is so unbelievable sensitive and it is really a broadband unit so yeah you have seen it and that is what I mean with performance so that means I really can use this unit for all the radios I'm normally working here on in my in my lab without a problem and you see this iskut models are really awesome and especially here the last a tube addition so that it's definitely the last tube edition edition we had to model t4 which looks the same it's a little bit different but not much circuit wise and the AI t12 is really the last version with tubes and remember it is important to use a tube circuit because we have the high input impedance which we want that we really do not load down a signal with you know a high impedance because that would happen and even with my scope I'm not really able to trace down signals on four hundred and thirty megahertz and therefore I really can say is this little restoration is really a success I have here a unit which is working like new it is really sensitive down to minus 55 DBM and we can go up to 430 megahertz there we have our limit at minus 40 DB M but hey so that was not expected so if you talk to an older radio technician he would tell you okay 100 megahertz is maybe the maximum what this tracers can handle but you see what is possible and that is really a nice addition here to my bench okay what can I tell you more so this is really a nice invest to anybody's bench so if you come if a unique light like this comes across your way just grab it maybe if it is the t4 version you have to do a little bit more rest raishin and even ite a12 which worked for 30 years then you have to expect that you need to change your capacitor your electrolytic capacitors and maybe your tubes are worn out and so on so yeah you you need to do a bit more restoration than I was needed to do here on this unit but anyways if you find I t12 then go for it it is really an excellent tracer okay so though that's it for today I hope it was a little bit interesting for you even it was not a full restoration because we were lucky and therefore yeah if you liked it please give me a big thump up and yeah catch you next time bye

Channel: TRX Lab

Views: 43,322

Keywords: HAM Radio, 2way radio lab, Funkwerkstatt, Amateurfunk, DARC, repairshop, CB Funk, Amateur Radio, ICOM, Kenwood, Yaesu, Flex Radio, Drake, Alinco, Maas, CRT, Albrecht, Midland, Superstar, Cobra, Snakeradio, Hilberling, Team-Com, Elektronik, HF-Technik, hf technik, CB Reparatur, Funkgeräte, Kurzwelle, President, Uniden, Stabo, SSB, LSB, USB, AM, FM, Modulation, Audio, Driver, PA, Sendeendstufe, Brenner, Linear Amplifier, TRX, TX, RX, Röhren, Transistoren, MOS-FET, MCU, DSP, Bird RF Meter, TelePost LP-500

Id: 2tJzMlf0SCA

Length: 72min 40sec (4360 seconds)

Published: Sat Oct 14 2017