TSP #198 - Teardown, Repair & Analysis of an Anritsu MG3700A 6GHz Vector Signal Generator (Part 1)

[Music] hi welcome to the signal path in this episode we're going to try another repair a couple of patreon supporters ask me why i never review any unreal instruments and that's actually not something that i'm doing on purpose it's just that a relationship between andrutsu and i was never established i really never really heard from them but we've repaired on ritual equipment in the past of course on the website and i went ahead and i bought this one this is an unreached mg370 this is a six gigahertz arbitrary waveform generator plus synthesizer so it's a vector signal generator and it's a some pretty good specification and this one is actually fully loaded the only option it doesn't have is the rubidium standard which is interesting to know that this could actually have a rubidium standard this is a discontinued model of course but uh yeah i think would be good to take a look at it even if we can't fix it as always analyzing it and reverse engineering and figuring out how it works is always good see how the japanese built their vector signal generators so here this is plugged in if i go ahead and turn it on so i can hear the power supply start but uh then nothing else happens and i happen to know that it has more than just one problem that's how it was listed on ebay when i bought it so it's going to be quite a lot of investigation to figure out what's going on it just sits here like this so i hope it's not some kind of a weird firmware corruption because that might be impossible to fix so let's take a look inside of this instrument and see what's going on i'm not going to talk about the rf yet we can leave that at the end since that's not the issue right now there's some stuff at the top that's rf related and the main power supply at the bottom is a tdk lambda i've actually repaired one of those in a different video for a totally different instrument so let's take a look and see what we have here so here's the two boards at the top this is most likely the arbitrary wave from generator board we can see a tx tag over here from analog devices vertex 2 pro fpga memory on both sides so this is basically a streaming device it grabs data from here pushes it through this and then that eventually finds its way into the mixers on the output of the arbitrary waveform generator part so these two boards have to be pulled out there's a main motherboard over here where everything is pulled in it's interesting there's another connector over here which another board can plug into i'm not sure what that would be for because i don't think there's any option that this is missing but either way we're going to have to remove this to see what's underneath it because without that you actually cannot i see the main processor where the main firmware and everything resides and then on the other side of this and behind all of this from the bottom of the instrument is all the rf portion and we can take a look at that later if we get to it so that we can see how the instrument actually works so i have to fiddle around a little bit with this more to find out how to get to the processor and here's the main processor board i removed the car that was in front of it simply by sliding it out and you can see a lot of familiar components on here there's actually a lot of line driver components all around as well there's a 32-bit risk processor over here and a hitachi 32-bit arm processor this component here is labeled ax-51901 it's from axle i believe i have no idea what it is i couldn't find anything meaningful about it and there is an altera a6 fpga a bunch of memory static ram memory there is a max221 over here which is a serial port converter of course and there's a connector here so i wonder if there's a serial interface into one of these processors that could be potentially helpful and there's two flash memories here in a socket and one more over here and those could be the firmware or at least some kind of parts of firmware so if you maybe if that's the problem if you could have another one of these units we could maybe replicate that and see if that could help us but there's also a lot of voltages labeled on this board and a couple of leds in different places so we can still power it on like this and see if it does anything all right here we go the instruments turned on and the very first thing to note is that none of these leds a whole bunch of over here a whole bunch of them are there none of them are actually on no activity at all most of these components are also quite cold i can pull out the thermal camera and take a look but i don't feel anything on them there's a couple of voltages labeled here we can measure them here is 1.5 volts you see there we go that's nice 1.5 volt there's good and there was a whole bunch of them over here as well let me see here's the 3.3 volt backup voltage there we go 2.6 okay maybe the battery is a little bit low but i wouldn't worry too much about that there's an led up here for the hard drive is also not blinking here is 3.3 volts oh look at that 0.4 volts okay that's a good start here's a 5 volt supply 1.7 huh that is strange okay so something is indeed going on with the power supplies that's actually a good sign because that that could be the easiest thing to fix let's see there's a 12 volt here okay 12 volt is there there is a plus 12 volt header here at 12 volts this year that's interesting so here's if okay i see two fuses one fuse over here one fuse over here i'm gonna measure on the right side of this fuse i do see 3.3 volts that must be a separate one because this 3.3 volt is there there's the fuse over here on one side of the fuse i measure 1.7 and the other side of the fuse it's very difficult to reach that 5 volts oh that fuse is dead interesting okay this fuse is open because on one side of it i measure 1.7 and on the other side i measure 5 volts which i think i was just measuring a moment ago pretty sure it's there somewhere it's hard to reach it okay so if that fuse is there there it is here's five volt so if that fuse is actually not blown we have to look at why i see two dc-dc converters over here so this could be the reason i don't want to just replace the fuse i have to think about this a little bit more carefully now the the other side of the fuse where we see that the fuse is blown is not shorted because if it were we wouldn't see this 1.7 volt hanging there that means that it probably has some voltage from somewhere else being fed back to it because there's so many semiconductors here some are probably some back feet voltage coming into it so that could explain it well i'm going to take a look at this fuse a little bit more closely and find out if there's potentially we could supply this very slowly with an external power supply overriding the internal one in a safe way so we don't damage anything else in case that say this dc-dc converter is the source of the problem so let me set some things up here so this is the part of the circuit that we're dealing with this fuse is okay this fuse is not the five volt plane is existing on this side and it's fed to the other side and feeds these five volt part this also is sitting at 1.7 volts and i believe it's also running this dc-dc converter which is supposed to be 3.3 volts and that one is dropping down to 0.7 i think this is just simply not getting the kind of voltage it needs obviously in order to convert it to 3.3 volts so this failure of fuse is probably not allowing anything the rest of this figure to be powered on anyway and of course nothing works the question of why this is dead is still unknown so first i'm going to remove it obviously because it needs to be done and then we can think about maybe either powering this from an external 5v power supply which is the only supply you need to provide it here right after i remove this fuse and then we turn it all on synchronously and see what happens and we can current limit the fireball supply and if that doesn't work then we'll have to dig in a little bit deeper so let's go ahead and use the rod ensures ngp 800 power supply which is an absolutely fantastic power supply i have a set of five volts and two half amps this originally the fuse was at five amps so this is about halfway where it should be and of course it's going to current limit as necessary and i've connected it to the test points the fireball test point and the ground so i'm going to turn these on at the same time and see if we get anything interesting happening we can also have an eye on those leds and here we go oh leds and it's only drawing 1.3 amps leds it's flashing it's booting yes it's working okay good so it's only taking 1.25 amps so i think we're safe and yeah all the leds are turning on it's going through the boot process so looking good okay now we can turn our attention slowly to the rest of the unit okay here we go the fuse has been replaced now the cause of the failure of the old fuse may have been some transient effects or over time you know sometimes this does happen to fuses but given that we measured the current consumption of this portion of the circuit and it is below 2 amps and the fuse was for 5 amps i'm fairly confident that it's going to be fine all right here we go so the instrument now boots perfectly fine and don't see any particular problems with it if you go under utility and then we go under the hardware check you can see that the cpu module the if moisture and rf module all pass their own self-test which is great and go back to the frequency here you can see there's the oven cold is blinking that's probably something that takes a bit of time we'll keep an eye on it until the oven control crystal oscillator comes up to temperature so we're at one gigahertz zero dbm i have connected the output directly to the fslo spectrum analyzer which i repaired in the previous video there's no signal right now but the amplitude is set to zero dbms squamous enable it there we go there it is you can see that the signal is there if i do a new search you can see we do have a tone at one gigahertz minus 1.9 dbm being measured that is good okay let me turn this off let's go ahead and increase the frequency here let's go by a hundred megawatts at a time that's not what i wanted to do there we go 1.2 gig it's fine looks good let's go to 2 2.2 gigahertz let's do a new search yep 2.2 gigahertz minus 2 dbm that looks good let's go to 2.5 still okay 2.8 gigahertz 2.9 gigahertz and three gigahertz let's do a new search yep three gigahertz looks good oh there you go something happened so now we have an alc alarm and the output is gone if i do a new search you can see the signal is there 3.3 gigahertz minus 29 dbm so something is wrong here above three gigahertz you go higher your signal is kind of following so the synthesizers are fine there you go 4.1 gigahertz so the tones are correct alc alarm means that it's obviously not able to measure the output power coming out and this is definitely not from the attenuator because if it was the attenuator problem you would see it below three gigahertz also it's the same itineraries broadband so something else is going on it is likely that internally the architecture of this instrument splits the signal generation below and above three gigahertz differently that's probably why you probably can't read this from here but this mg 3700a is actually a three gigahertz synthesizer you can add the option which takes it from three to six as an additional thing and this one does have that that means there must be a separate piece and that's the part that's not working well this is a good opportunity for us to go and take a look at the rf part and see if we can clear this last problem with it and get it fully functional yeah the name can also try the entire basement generator these buttons are not very good there we go it's got it's got an entire arbitrary way from january actually has 120 megahertz of bandwidth from its own internal arm which is quite a lot so it is quite good especially for the age of the instrument so i'm eager to see if we can fix it up well after doing a lot of searching on the internet i did manage to find what appears to be some kind of a marketing document and in there there is the block diagram of the instrument a very rough one but it's going to be still quite a bit of help here for us so on the left side we have the iq baseband generator because this one obviously has that and then there is two d2a converters and some low pass filtering which generates our inq signals going into the iq modulator this would be the internal modulation path and this actually comes out of the instrument too so you can use and it has differential i and q apple which is fantastic and allows you to use the internal arbitrary wave from generator right at if and we've seen this from several different instruments and you can also put your own external iq input which can have even a slightly higher bandwidth going into the iq modulator core that is being fed from 100 megahertz reference which is multiplied by eight so that's what's coming out of the iq modulator up to about 800 megahertz or so and then we have some pulse modulation on top of this so you can pause modulate your signal that's coming out so if you have a long stream by pass modulation you can do some bursty transmissions all the good stuff that comes with pulse modulation then after that we have the alc so this alc is going to ensure that the signal coming from all the different ports that enters it are leveled and this is goes back to the variable gain amplifiers in different stages to make sure that when you tell the instrument produces 0 dbm it does internal loopback to make sure that 0dbm is as accurately as it can be considering it's on calibration so then after that things get a little bit more interesting we have a 4 gigahertz fixed oscillator that's fed under the first mixer and that allows the signal to be up converted and then from there we have a yig tuned oscillator and that the e2 oscillator is mixed yet again with that signal and this is how we get the tuning so some of the tuning is coming from here some of the 20s coming from here all of these were producer cw tone at the very end now if you look over this there's a dotted line around this block and that's the six gigahertz option so the signals between three to six gigahertz are produced with another two mixers after this so if you don't have this portion you obviously don't need the rest of this section they probably remove it and not populate it or maybe it's there and it needs a softer option but this is the part that most likely has an issue so we get our up to about three gigahertz roughly correctly you can see that we have detector here this detector is fed back to the alc module and then on this side we have another detector this detector also goes back to the alc module that's why the instrument knows that up at around three gigahertz you're not getting what you want anymore and that's precisely because this alc simply is not receiving the signal it's expecting to receive now the way it generates between three to six gigahertz is that it has yet another mixer and then yet another one in order to reach the higher frequencies and there is a doubler here that doubles the yictone oscillator frequency so that goes up fairly high actually in order to down convert eventually to the frequency you want it's a little bit similar to a spectrum analyzer the way the super heterodyne architectures work and there's a power amplifier over here too so we know therefore that the step attenuator has nothing to do with the problem as we saw from the measurement normally synthesizers have no knowledge of what the signal is at the output port they don't touch this one they don't look at anything after the step attenuator they assume that that's fairly predictable and reliable and you can even take that into account when you calibrate because you can put that lookup table inside the elc taking into account the step attenuator so if this guy is reporting that we don't have enough power above three gigahertz and this is this the problem is must be here it can be in this one it can't be the four gigahertz it can't be the yictune oscillator because all of these signals are necessary for the three gigahertz part to work and since that's working it is likely that none of these are the problem the problem must be in fact contained within this box so now we can go back to the unit and take a look at it and see if we can find out where that box is and then eventually find out what part of it is dyed if we can now you can also there's also some more details about how the basement works but there is a picture here which is the back of the instrument and if you look the iq output comes out of this connector which is so strange and why not put them onto bncs i mean there's lots of room over here this means that now you have to have another proprietary connector and then get that into coax it's just such a headache luckily in the front of the instrument you do have the iq input classical bnc connector so you could use that and i also now understand what this ethernet port in the front is it's actually just a bypass so there's only one ethernet in the back and then you can buy this little jumper cable connect this front to the here and then that brings the ethernet to the front of the instrument a little bit unusual but i guess it works okay good so let's go back to the unit and take it apart and here is the backer instrument where all the rf goodness is that is most of them are so here's the front panel connector over here and right over here we have our mechanical latener made by anritsu and this mechanical latino is controlled by this mechanical itinerary controller board which then itself is controlled by this port over here so i think the yiketone oscillator and some of the other oscillators are on the other side of the instrument and then they're brought in with these connectors at the very top so there's two main boards here the one over here and then one over here it's very obvious that this one connected to the chassis and has most of the signals going out of it is the primary iq modulator as well as the first mixer so the output of that is one of those outputs goes into this unit which is a mechanical rf relay which then switches between a low band and a high band below six gigahertz and above below three gigahertz and above three gigahertz if you look at this one over here it has four connections aside from its dc connection over here there's one two three and four one of them goes into this that's obviously it's output and the other three come from this board and those are the two loss that it needs as well as the input of course which then needs to get up converted to the appropriate frequency so what where we need to focus on our attention is this one to see if anything's wrong with this so we're going to take this cover off and look at the circuits underneath and then we can make sure that the signals we think are coming into it the four gigahertz as well as the yikton oscillator and everything is actually arriving here so we can find out exactly at what point in the signal flow it stops working and here is what is inside of our three to six gigahertz module which is a suspect module in this case and we know roughly how it works so it should be very easy to reverse engineer at this point so if you look at the four ports that coming into it they're actually labeled on the silk screen which makes it even easier we have the if port coming in this if port has already the modulation on top of it it already also has been applied first mixer from the other module to it and you can see that it enters the input port of this mixer the if port of it which means that this mixer is an upconvert mixer at least in most scenarios and the rf comes out of it now the yellow entering it is our first lo that's our four gigahertz fixed lo which has some bowtie filtering on it and it enters the yellow port what comes out is actually up converted so you may ask why would you up convert this what's the benefit of going way above the frequency you want so that you're going to have to use a much much higher low frequency and mixer to bring it back down what else has to do with at least one of the reasons has to do with fractional bandwidth of generally filtering things it makes filtering much easier now all of these filter structures you see these hair pins these bowtie filters they can be tuned to any standard frequency they will have of course varying performances but their fractional bandwidth is roughly the same so for example you build a bandpass filter at 10 gigahertz and you hit a fractional bandwidth of let's say 30 gigahertz that's a three gigahertz bandwidth around 10. now if you build the same filter now at six gigahertz it's going to have roughly the same fractional bandwidth about 30 percent but now that translates to only 1.8 gigahertz so when you go to higher frequencies it is a lot easier to build a bandpass filter that has a wider bandwidth and therefore can cover let's say the entire three to six gigahertz you're interested in so by up converting it first to a higher frequency and then filtering it very carefully you can isolate all the other frequencies you're not interested in and only keep the frequencies that you want which at the end translates to three to six gigahertz this is one of the reason why this is done now of course there's a disadvantage every time you do this means you have to go to higher frequencies components are more expensive they may be more lossy they may have more noise figure and in general there are other disadvantages but this strategy of what is called frequency planning is very common not just in test and measurement equipment but also in communication systems in general this harmonic rejection and so on is is very crucial especially if you have to abide by fcc regulation in communication systems so having said that the if comes in dlo comes in this gets up converted filtered some pinned out attenuation it looks like along the way and it goes through some hittite power amplifiers these guys are now quite a bit higher frequency of course and then the enters another mixer now it enters the mixer from its rf port and then the lo part of the mixer is coming from here and the if is now down converted between three to six gigahertz goes through an amplifier goes through a power amplifier this is a maycom part it seems to have a output saturated power of over one watt they're probably not using the entire range of course if you look carefully you can see this line thins out and then there's a coupler embedded right over here very thin line one side of that coupler is terminated the other side goes into a detector i believe this is where the alc circuit is and that's how it knows that we're not getting the power we want because nothing's coming out of this and eventually that makes it to this connector and that goes to the output after our mechanical relay over here we have our ektune oscillator second lo come in amplifier and then it goes through this component here which is a frequency doubler we saw that in the block diagram as well and this frequency doubler is passive meaning that it only has a diode in it can't really call it quite passive but it doesn't have any amplifiers built into it which means it has a huge conversion loss i think something like 15 to 17 db so it's a big big loss and after that therefore it needs two power amplifiers medium power amplifiers again to boost it back up so that it can enter the lo port of this mixer so that's it very very straightforward based on the block diagram you're going to have then down converter over here three to six figures so any of these components could be bad any of these amplifiers could be bad any of these ports could be bad but we have to break it down at some point and do it one step at a time first thing the most logical thing is to test to make sure all the signals entering it the yellows as well as the if are actually there at the correct value and if you're satisfied with that you will measure one step at a time using an active probe to find out where the signal eventually fails to go forward well let's go ahead and follow some of these signals on this six gigahertz board now i was going to use an active probe at first but i thought maybe i'll show you a slightly different way to do it which is not using an active probe it's much much cheaper but it also has huge limitations so you have to keep that in mind so here is what i have basically i have a dc block here and connected to the sma cable and on the other side i have a vertical sma connector these sma connectors are basically meant to be soldered onto a board and he has two screw holes so basically it will sit like this now with the advantage of this is that the pin is fairly sharp and you can actually trace and touch different places on this board the reason i have the dc block is because my spectrum analyzer doesn't support dc but if your spectrum analyzer is ac couple you don't even need this the disadvantage of this of course is that this is a 50 ohm interface and you touch it to something and you're going to load that line not only are you going to load it with something that has a 50 ohm termination you're going to load it in a really poor impedance actually because your ground isn't even connected you're just kind of making this really bad transition from these coplanar waveguides on the board into a coaxial interface it's not going to be good but it will tell you if a signal is present and you can couple a lot of power out of it it will mess the rest of the circuit up of course but in most cases it may not matter much much cheaper than using an active probe again has a huge limitation but let's try it out see if this works for us okay so here's the spectrum analyzer and yes i do recognize the irony of trying to save some money in an active probe while i'm using a keysight mxab that's fully loaded but of course this is just an example it's the one that's easiest to use and i really like the spectrum analyzer all right so let's go ahead and try this out i'm going to turn the instrument on and i'm going to tell you exactly where i'm probing and all of those probe locations are going to follow our block diagram analysis and the board overview i just did okay let's start with the frequency that's going to the doubler let's make sure that frequency is working so we're looking at i've set the instrument to three and a half gigahertz now that's going to create a series of low frequencies we need to expect so let's measure the yellow coming from the yick to an oscillator see if it's present here it is look at that it's nice 6.15 gigahertz this is the signal that's going to get amplified so i'm going to go past the amplifier here it is you can see it's now a bit larger nice i'm going to go past the doubler there it is you can see it's been doubled sitting over here now it's sitting at 12.3 gigahertz amplitude is quite a bit smaller because as i said this doubler doesn't have its own amplifier i'm going to go past the first amplifier after the doubler it should be much larger there you go very nice and i'm going to go past the second amplifier to the input of the mixer and it should be even bigger than that there you go there it is so it is basically a nice hello at 12.3 gigahertz going into our second mixer now let's go back to the first mixer the first mixer should have one of its lo be four gigahertz so let's measure that there you go four gigahertz coming in nice and large signal perfect now the if going into this mixer should be at 4.8 gigahertz you should be able to measure that it's going to be much smaller than amplitude near this 4.8 gigahertz so when these two mix together you get 8.8 and 8.8 is going to mix the lo signal which i measured this one it's going to mix with 12.3 and that's going to of course give us three and a half so let's look at the output of the first mixer that output now should be at eight point eight gigahertz i'm going to land on that and look at that so 8.8 gigahertz is somewhere around here this is actually our low feed through that we're measuring that's not good it's much much larger than it should be so let's go ahead and turn this picture off and let's put the marker at 8.8 gigahertz there it is so it's very very small now i don't really like that i don't like the fact that the signal is so much smaller than it should be so now if i go all the way to the rf input of the other mixer and i measure that and you can see the signal is essentially not even present so the signal is lost somewhere after the first mixer so let's do a bit of more analysis on this now what appears to be here is a pin diode or an attenuator most likely a pin diode switch this is on the yellow path of this first mixer when this entire part of the circuit is disabled this pin diode actually turns off and i'll show you that and this disables the lo signal from coming over here which means no up conversion happens right at the beginning and that quiets down the rest of the circuit it's probably to improve the isolation and the overall signal coming out but then there's also one over here one over here and one over here these are all in series in sequence of each other and all seem to be connected to each other in terms of biasing and the other unusual thing is that they never turn off even when this part of the circuit is not used so either they're being used maybe as an attenuation or maybe they're just always on it's a little bit weird so i'm not quite comfortable with that but nonetheless i started measuring the biasing on these and there is something a little bit unusual about one of them okay let's measure the biasing of the first one i'm going to put this on this bow tie stop here so you can see that the biasing gets zero now i turn the frequency to 3.1 gigahertz which enables this entire part of the circuit and let's see what happens there you go you can see that the diode is now forward biased and most likely this path is therefore turned on that's great now all of these other ones are always turned on so i'm going to measure the voltage on this one it should look very similar to the other one because there are identical parts you can see 0.49 i'm going to measure the one all the way down here 0.49 i'm going to measure the one up here 0.17 so that's different so it could be that this diode is dead and if this diode is dead the signal cannot travel through this path and of course if there is no signal there then you're going to see very little output so this could be a potential problem now this part has a marking on it of vw and no other information that i could find it's a bit of an issue because i cannot find a replacement for it but one thing i can do is i can remove it from the circuit we can measure it out of the circuit and then we can also bridge the gap between these two parts and see what happens and there are some challenges with removing a component like this and bridging across it so if i remove this and just connect this wire to this wire with a very very small piece of conductor this may appear like a nice transition because the distance is very small but keep in mind that this bow tie stop these open stops over here and the thinning of these lines these are done to maintain a good characteristic impedance of this line in the presence of the parasitics of this component if i remove this the parasitics are gone and if i bridge them the same matching networks now actually push you away from a nice characteristic impedance because there's nothing for them to compensate for but i think it should at least tell us if this component was a problem because we can monitor and see if the output signal becomes a lot stronger or not and that would be a good point to try so i went ahead and bypassed this diode and actually helped things quite a bit it helped by about 10 db which is a lot but we're still about 10 to 15 db below the output power of this entire instrument should be able to produce so something else is wrong along this path so i went ahead and just removed this entire path from the circuit by placing a coaxial cable using the ground connection over here maintaining 50 ohm into it and then going back down over here by passing again everything else and tapping right before this filter so this entire section is now out of the circuit this allows us to inject the signal directly from the mixer right at the very top over here so the up to the mixer directly comes out and goes to the input of this amplifier now if the rest of this works we should get a good signal and that just isolates that section now remember that we can't really leave it like this because those filters in the middle are there for a reason is to remove the images and some of the harmonics that may be present but it will still give us a good indication if this is working all right let's give it a try so here we are again below three gigahertz that's part of the circuit that's working the output is set to about zero dbm and you can see it has a nice clean tone now i'm going to increase the frequency and you should be able to hear here the switch to the upper band at some point two point nine three there you go switch the upper band look we're producing power it's exactly what we wanted to see now you can see there's so many harmonics here obviously because that first of all the cover is not on there and also i removed the whole bunch of the filters so it's going to look pretty bad but the power is correct which means all the mixers are working let's uh go higher and higher in frequency we should be able to hit about six gigahertz there you're going as it drops to minus seven dbm because i have removed so much of the circuit all the calibrations out everything's out but it is producing roughly the correct amount of power now so that was indeed the problem that entire section is faulty so yeah unfortunately we are kind of stuck because i can identify those parts to replace them i will put a high resolution photo of that part right in the video so in case you know what that is you can help me find it and hopefully replace it we can't go any further there's no point closing this back up and do any more testing because until we do this it's never going to meet this specification for harmonic rejection and everything else in linearity most likely will be really bad but nonetheless i thought this was quite an educational and interesting set of experiments and you can see the kind of tricks you can play to bypass things and while maintaining a reasonably good impedance environment so things at least roughly work so you can identify what's going on i even removed this over here and i injected my own signal at different ports just to make sure the mixers are working and everything seems to be okay it just seems that this path here made of those individual components something's gone wrong with it maybe a bias condition has gone really bad and destroyed them maybe related to the fact that the fuse was dead because all of these share the same bias network so it is possible that maybe they're all damaged in the same way either way i hope you enjoyed this let me know in the comment section i'd love to hear back your feedback and maybe in a future episode we can finally completely fix it

Channel: The Signal Path

Views: 13,734

Rating: 4.9797573 out of 5

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Id: VAiyqMESqPU

Length: 30min 44sec (1844 seconds)

Published: Sun Aug 08 2021

Reddit Comments

[u/zifzif]

If you can't find a service manual or a part number for that diode, measure the characteristics of one of the good ones. There are so many PIN diodes available that it shouldn't be too difficult to find a suitable replacement.