#191 Home Brew Curve Tracer Repair

well hello everyone just a short video too long but I'm going to do a little troubleshooting today and as you can see here on the bench we have an HP justice D 1205 a oscilloscope and it is a very low bandwidth so scope now being that the bandwidth at this scope is that it's pretty much useless as using an oscilloscope then you might say well why worry about fixing an old scope like this then you can see right here [Applause] dual-trace you look back of oscilloscope 500 kilohertz so not a very good candidate to use on the beach for repairing electronics now the way while back I joined mr. Carson on patreon and picked up some good stuff up there and one of the projects he had was turning an oscilloscope into a corrupt racer so that has what I have done to this oscilloscope but you can see I have removed the Bing farm switch and put a high-low switch in here and came between the trace alignment and the power indicator which has to be replaced cause this does not work and put a potentiometer and that is your gain control so you see when I short the probes out we don't have a vertical rise but I'm having some issues for this thing now this scope does need to be recapped and some cleaning done to it but the scope came from my working environment and I want to go ahead and get the conversion done to it and then do the restoration of the scope I put a doubt in here you can see I'll turn the gang down and you can see the knee of the day which first time zone but the problem with this is that I can't go much further because the gain is so high on this scope that I can't see the full thing and then you can start seeing and start to double trace also when I found out that for some reason when I try to go anything above 0.2 on the Volt's per division this is what happens I completely lose all trace on the screen and that's on channel P and channel a now this trace of board is connected to both ports in fact it's complete the input of the scope is completely disconnected from channel a you can use channel be like a normal scope if you wanted to but have redirected the inputs and put the input of the tracer here on channel a so I'm not able to shrink the trace down the size to see all the detail that I wanted to see on the kart racer and you know which of them high to low is not gonna help anyway so I wanted to get in here and do a little troubleshooting and see if I can find out why I cannot switch to 0.5 this goes setting goes from 0.5 out to 20 and this way from point to down to points it was the or 5 volts per division and both channels is like that being that both channels are independent of the self you would think that maybe there was an external issue that boat channels wouldn't show the same problem and that's what I thought to begin with so I started checking through the power supply I looked at the 180 of old rails and the plus and minus 50 volt rail and everything looks good no problems at all so it looks like we need to go in here find out what is happening on these volts per division controls well good evening everyone on the bench today we have a HD 1205 a dual-trace oscilloscopes now this oscilloscope as you can see it's not very useful for anything on the bench working on now as you walk around close to DC cause it's only up on a kilohertz but one piece of equipment I have always wanted to have here in a shop was a color tracer and there's a reason why I wanted to get a core tracer and that is for teaching troubleshooting on how to use a couple trace a curve tracer for finding faults on a circuit board because but for kart racer you can do a a lot of things that you just couldn't normally see with components still mounted on the board this curve tracer or signature tracer will help identify the Bayer components especially using of IC chips and stuff it works real good for that and comparing diodes and different components and now you can even check transistors and so forth with a color tracer now what got me on this project was that you know while back I joined uh mr. Coston slab on patreon and he the circuit showing how to turn an oscilloscope into they call tracer for the past few days I went ahead and edged out the board and built it and cut it installed in their source code let's go did come from a working environment but it does need a good overhaul there are a lot of capacitors in here that probably needs to be checked well I'm going to say really probably needed to be changed out there's really no probably about it now they do need to be changed out HP did use high-grade components in their electronics in this error but you know while I'm Sprague and you know just good name stuff but it's not about showing you how to build a kart racer I will not be doing that with this project what we need to do is get this code tracer working like it's supposed to so anyway along with that I will take the probes and will short them together we see we get a vertical line and if we put a diode in here and we turn the gain up you can see the knee of the toes start to come in the field and we can turn it down and you can see exactly where it goes now here's a port in the back so you can connect a voltmeter up I'll go ahead and do that okay so I got to voltmeter plugged into the back and you can see the voltmeter there see if I can get everything in the shot and as we turn the gain up you start watching here right where the knee starts to come in and you can see that David is turning on at about 0.6 three volts so that is looking real good now the issue with this scope is if I try to turn the gain on up I can get more detail we can see that it goes completely I'll screen not a problem right as you can see I can turn the Volks for the vision low and it gets bigger and bigger and bigger the problem is is once I advanced test point two votes on either channel a or channel B my screen goes completely blank and it does it on both channel a and channel B now the curve trace the board is tied into the channel a and channel B and we have it set to a versus D this is kind of like XY mode on this scope so I can't shrink the trace down to to get all the detail this is a zero load so we should have a you know the knee on this the Union that come up should have a curve going towards the top but we're not able to see that because I cannot set the scope to point five so what we're going to do is take the schematic and we'll take a look at the schematic and see if we can figure out what is causing this issue so we're looking at general a schematic assembly of the most per division board and you can see here we got - ground and positive now this scope does have dual inputs on both channels you got a minus input and a positive input and we're tied into the positive input and ground so as you look at this we'll scroll down to the positive input it is completely identical to the negative input so we'll just go ahead and look at the positive input now I'll zoom in on just a little better so you can see it this is our input coming in it goes through our coupling switch off AC and DC and you can see the only stiffness is between DC and AC DC is directly coupled AC goes through a point 1 micro farad cap and then we have a switch here that will select either of the couplings it goes right on into the attenuator and when we select 0.2 all the way to 0.5 it is using this part of the circuit now in attenuates from point 2 to point 1 0 5 2002 0.01 and point O and it does it through resistance and it goes right on over here to this side and then into the first amplifier of the scope now when you select from 0.5 to 1 2 5 10 and 20 volts per division you see we we come through we have a ceramic input capacitor going to ground we didn't go through this compensation circuit which is a ceramic capacitor and a 990 k resistor we didn't have a resistible in the ground and a 200 picofarad capacitor going to ground so we know that this part of the circuit is working and this part is working because we can go to anything from 0.2 to 0.005 and the tracer has a display on the screen but when we select 0.5 to 20 volts per division we cannot get nothing on the display so it has to be something in here that has gone bad I'd also have switched the probe over to two negative sides and I got the same results also channel B has this same issue we cannot select the 0.5 so the first thing come on mine will but it has to be something outside of the board that is causing this issue it's just seems kind of strange that the same problem would be on both channels well first of all you got to think about how old this unit is and I went ahead and checked all the power supply rails and everything is real close yes the caps need to be placing we're going to do that in another video when we do a full restoration and alignment on this piece of equipment but right now we're concerned about getting this circuit working so we can go from 0.5 to 20 volts per division so one of the first things you have to wonder is that the 990 K resistor across this capacitor and the compensation adjustment is that a problem or has something else here shorted to ground and it calls this part of the circuit fails on all four inputs so if this problem whatever this problem is on this one is probably going to be the same problem on the other three inputs now this scope has two main power suppliers in it a low voltage and a high voltage power supply the low-voltage handles plus and minus fifty volts up to 180 volts the high voltage supply is up to two kkv so if you're working on something like this you're doing so at your own risk it is very dangerous whenever you're messing with high voltage and mains power so be very careful luckily the high voltage side is a little bit definitely using a double circuit with our ceramic capacitor so very seldom do they convey it so that part of the power supply would just need to be checked inspect it make sure everything's look good and there's no problems in it I have seen none as of yet so what we're gonna do is turn the scope off and just let it bleed off the caps and we're gonna get in here and do some testing on the channel a volts per division if you saw this old supply here in the back this is an old what's called a project board dual variable power supply is got it set to 15 volts on one side and 15 volts negative on the other side and that is what's feeding the curve tracer board I do have to build the supply which I've already ordered all the ports along with the capacitors for the HP 1205 scope so I'll be getting that built and installed here before long I'm gonna do a little hand hill here with the camera for a second you can see the most per division section here with all the wafers for channel a and that is the channel 8 board and you can see it's pretty much mirrored on both sides here this is positive input and negative input then over here in the middle you'll see another one it is just like it that is channel B so that way for switch assembly is buried below that which means we got people this board out to get in there and check those components but we'll go ahead and start with channel a forest and see can't we get this up and running so with the scope upside down I'm gonna use my poor man bench cookies which is just rows of Kim wicks sort of wick and we've set it up on the side and just been running under there they make perfect bench cookies and they should for about thirty eight bucks a roll well since our tracer board has its own signal we do not have to put anything into the input of the scope to trace this out with another scope in fact you can actually use the oscilloscope to troubleshoot itself by using the other channels but the bandwidth is a little higher on just scope I'm using so a little bit easier now I'm got the scope probe connecting to the input and if we look over here we can see our signal on the Tektronix scope and it's not fully locked in on the trigger so we can go ahead and pass through here and see where we're losing our signal we're so we're basically tied into right here on the beginning of the input just after the coupling switch now you can see here we have a variable capacitor here and here and to show you where there are at on the scope you can see these large ceramic capacitors here no chances of those going bad it's going to be very slim those things just last forever so my first guess you can see right here in the compensation adjustment circuit there's a 990 K resistor now f5 someone has put the wrong signal into the front of this oscilloscope it's a good chance that this resistor has gone a low tolerance they'll remember that there will be four of these resistors in here for both channel a and channel B because both channels we have two inputs a positive and a negative input now it's a little bit strange that someone would have sit there and did that to all four channels because it's you know should have been if you get put it on the positive side it should have took out the positive resistor if you came up and you put it on the negative side it should have took out this resistor on the negative side and not both resistors so we'll check this resistor just to be sure and we'll check the one on this side but still looking at this circuit the first thing that I see that could be a problem it's just 200 Pico farad capacitors are going to ground and I'll show you why in just a moment what I'm gonna do now is go ahead and take the oscilloscope they go ahead and couple right to the front end of this amplifier circuit and see if you know if their signal there and I'll move our connection on the input of the coupling to the input of the amplifier and there we have our signal because I rotate through all the lower settings we can see we have signal as soon as I go to 0.5 you can see we have no signal so there's definitely nothing is getting through from point 5 all the way up to 20 and then back to point 2 so I have this cope shutdown in Fitness everything bleed off and when we go ahead and check these 990 K resistors that are in parallel with the ceramic cap now where these are located that is on the backside this is the positive input and this is the negative input so this will be the first resistor under this cap only positive input so in other words this is your input trim capacitor and the one behind it is your conversation trimming capacitor so we can get the voltmeter and see if we can't check that off 990 younger sister okay do you want me to connect it in and we have nine hundred and ninety-one ohms that one and this other one is a little bit tough to get to all the negative input and it's at 989 ohms so it looks like those resistors or okay now that we know that our resistor is good like I said chances of these big caps being bad is very slim now you could have this resistor could be shorting to ground but I really don't think though and I expect this 200 picofarad cap my Atlas es or 70 will not check the lows when microfarad and you can probably some of your high end flukes we'll check the pass once this load but waka pass a law like this and I'll show you why as I said it would before why this would be suspect and there's our capacitor right here which is a 200 picofarad and the reason why that would be suspect is that is a molded micro capacitor and capacitors dis low and valued or notorious or going open or shorty so there is the number one suspect of what this problem is so I've got one end of the capacitor removed we'll say it's a cross state 10k resistor and we'll go ahead and check this capacitor anyway just to see if there is a problem with it now this old client tools multimeter will test these capacitors and we'll go across it and see what we get and it shows absolutely nothing let's switch it to our continuity and that capacitor is shorted so we now know what was causing the problem with 0.5 to 20 volts per division so what I'm going to do now this is gonna be a bit intense and work goes this one's not too bad to get to the one that's up here it's way back in the back I Polly can remove the board and get it real if removed we definitely had to remove the board for channel B so we can get in there and change the amount so I'm gonna go ahead and do all of that off-camera as you can see I have channel B for the vision board poured out and it was simply just removing the knobs off the front and removing the one nut from the main shaft and disconnecting see the seven eight nine ten wires and also we William the wetlands on the side and able to pull the unit completely out and this time this gives me a good opportunity to get in here and clean these wafers which just like they need to be also and I'll go ahead and replace these caps while I'm in here and also we'll go ahead and check those resistors and make sure everything is in tolerance on this board now the good thing about the electrolytic that are on here you see that's to 10 microfarad caps here they are able to be removed from the topside since they're soldered directly to the DES traces so they're real easy to pull out now I've checked these with the atlas and they are spot-on the ESR it's like 23 so no problems with those but they will get replaced here in the future as soon as the parts come in now those molded mica caps out and I'll quote my bad deeds the one out of channel a and both of them or bad so these things feel quite often you got you know radio like the A's and the FT 101 back in that series we found that home to $10 radio that the c-13 the morning between the driver and the final was bad these are notorious and going bad so if you run across those sometimes if they're you know below 100 microfarads anything below 100 microfarads down to 200 pico farads or below they need to go out and be replaced I've got the color traces all back together and we have a Zener diode if you get no the traces good crisp and clear and it looks like the camera for us it a little bit cuz it's trying to have it a hard time focusing on it but I turn it down just a little bit and we'll go ahead and we'll switch to one volt per division and see what happens and there's all trace I got a game cup just about all the way down we'll return the color tracer gain up now and we can see our legs starting to come up and now you see our leg that's going down so our coach Acer is now working like it's supposed to before you just couldn't get the range down enough to shrink D trace down on the screen and it was because of these old micro caps in there that's going bad but now it seems to be working no problems so now now our card coasters working you know what can you do with it Oh sniffle you know if you saw a while ago we used diode and we can see where our diode turns on it and if we connect the voltmeter to the input on the back we can see what the tonal voltage is and this will also work in circuit so that was a diode and a but now if you short the two leads together you'll get a straight vertical bar so what happens if you put a resistor in line as you can see you go a ball that's tilted to one side represents a resistor and just a simple one capacitor will show up as they circle depending on the capacitance so what does a bear capacitor do what I happened to have a on a micro farad at 200 volt electrolytic capacitor let went bad in a unit we hook this up you can see it shows they dead short so that is a bad capacitor so there we go you can see I'll cut racers now working like it's supposed to and this is a great piece of equipment to have on any tax bench especially at troubleshooting because like I say you can go in troubleshooting board without even putting power on the board you can go in and do a signature comparison of components and Eco tracer will show you that now for right now if you go online you can find all kinds of information on building color of tracers like say this particular board is one that uh Paul that mr. Carson's lab designed and if you're interested in the illness where you can get that right now is to join him on patreon and you can download all the files and so forth I don't move maybe one day you don't go public with it we'll just have to wait and see but if you find the core of trace so he the kid made a few again is a great piece of equipment to have on the bench anyway when enough all my parts kitty and I'll let you guys right along with me as we rebuild this old 500 kilohertz hewlett packard scope you know there's a lot of these old scopes on the market that off just low bandwidth and not really good but for our do you know DC the idea it's bottomless thing they're good for by taking the scope and putting a circuit in like this you get to repurpose it or a another wonderful piece of test equipment on the bench but when we get the parts in will go through this one and restore it get everything back to where it's supposed to be and we'll have a great piece of equipment here on the bench okay also wanted to give an update on the last video for the Yazoo if the old 101 repair in the giveaway I'm oh I'm normally respond to just about everybody that replies and I have it on this video and there's a reason for that when I go to select the winner it pulls my name up in the pot as one of the contestants and right now there is 126 comments so if I responded to everybody that would make it up over 250 comments and I didn't want to tie off everything but after the draw when I will go back and respond to any comments on the video also I had made a post here that was a sticky I got 15 people that have replied under this post not sure if that program will see your names when I did a test run there was about eight people that had replied under my comment and it did not show up when I get a test run on the random picker so those of you that have replied under here you may want to go back and just start your own comment just to be fired to make sure that everybody gets a chance at a wedding the Heathkit back in till voltmeter so anyway uh that will conclude this video for now until we get ports to go ahead and do the complete restoration if you found the video interesting and useful to you you can show so by giving me a thumbs up leave your comments down below thanks to all my patreon that I come on board y'all support helps to build and do things like this so thank you very much to my patreon supporters so hope everyone had a wonderful holiday and little idea just being off of work was a big blessing waiting to happen it's been been a while since we had time off anyway we'll catch you in the next video

Channel: The Radio Shop

Views: 8,658

Rating: 4.9460917 out of 5

Keywords: curve tracer, me carlsons lab, electronic repair, oscilloscope, ham radio, troubleshoot, theradioshop, the radio shop

Id: h4ZJSSWw8OA

Length: 37min 59sec (2279 seconds)

Published: Sun Nov 25 2018