#83 Back to Basic Radio Troubleshooting

well hello everyone um my last video I made a call me about anybody would like to see me go through this radio and do some troubleshooting on it and return it that I was it well I cut a lot of responses out of that woman's betting to get a whole lot but it was very surprising and I even got several emails till I haven't answered yet because I have so many emails I first disclaim i'ma go ahead and say I don't walk on these radios I don't care to walk on these radios if you email me about working on these radios I may even know it I don't condone using these radios is an export they are shipped into the country they are illegal to operate on 11 meters and that's not my rules that's our federal government rules as a ham radio operator you can legally use this radio if you care to do so but you will have to do quite a bit of extensive modifications to it to get it to meet spectral purity that it needs to be done to use already air like this now this radio uses what's called an EPT 3615 be bored and you can see it right down down the bottom now these are also called cookie cutter radios we manufactured at Bill Steve if you look inside you'll see there's a lot of unpopulated parts and this radio comes in many many many many flavors so you this right here here is am/fm yeah I'll make sure I was right am/fm you can get this radio with the same board in it with single sideband you can get this radio with dual finals in it this one has a single but you see the slot here in the back for another final to be installed if we turn it over you can see an unpopulated area here where the second dual final will go on being that these radios are so versatile the way that they're made they have a lot of drawbacks to them and one of them is spectral purity and this is exactly why I don't care for these radios if you want to get out there and talk on multiple channels at a time this is the radio for you if you want to get on the air and talk and keep their ways clean stay far away from these how much weather have a good cope of 2900 something along those lines over 25 unit ends PC 66 Cobra 148 those is back when they made decent radios but this stuff that's coming overseas is basically crap the way they're built anyway enough of that I said before you know if you want to get into working on radios and you don't know how before you jump into a nice brand new Kim with two thousand or one of those $5,000 icon rigs you need to know what you're doing and this is a good platform to run offer now you will not be able to go online and find a schematic for a general AP hill but the galaxy DX 33 44 s and so forth all use the same board I'm it's very very close to your original board that was d I think it was the that didn't note the Levin board it was just a 11th day board and this board here has been copied from that 11 B board so we'll get right into it and go through it and I'll show you the steps on how our troubleshoot that's ready now the first thing I went ahead and did I've already verified this radio has no transmit and no receive we do have noise on the speaker but it's not receiving any singles and it's not transmitting English tables if you put a mic in it and you key the microphone you'll see the green light tx/rx light will not eliminate to read it it stays green but you can hear a popping in the speaker when you key the microphone also the meter is stuck in this you'll find a lot of these from bad meters in them but it does not show no indication and going into the transmit mode other than here in the electronic switching inside so that's telling me that it's trying to go in the transmit mode but it's not now a lot of times when this happens they see the voltage regulator has gone or there is a problem in the face lock loop now this thing has one of the crappiest phase-locked loops it's ever been built as you can see here it is your standard PLL chip under the channel selector there's two more IC chips and these are called adalah chips and that is in so it can cover such a wide band this radio goes from being a band F so it covers a wide spectrum but we're going to keep it right here on being D and play around with it so starting out with any repair regardless of what it was the first piece of test equipment that you want to start with is your basic senses that can tell you a lot about the condition and the shape of what you're going to find in the radio or any other piece of equipment that you're looking at so sight touch smell hearing will tell you a lot about what's going on like I said we've already done I've already done a transmit received test and found it to be completely dead as a doornail although that is noise from the speaker so the first thing you can do is like you need board that's in there take it loose put it aside and just go along inside the unit and look for obvious stuff burnt components missing components like say you know this was a flea market fine just tell them what has been cooking out of it but just look for anything out of the ordinary that you think you know could be a suspect problem a lot of times you might find caps have in it or you might find transformers Bronner but the gold is just look look around it anything and one of the first things I see that I didn't like what to start with if this cord is sitting right over here now you see somebody has spread this call open and this is part of the 50 for our future for megahertz trap so it's been spread open so it shows more power on the watt meter it's not that the radios doing more power it's just that you're letting more harmonics through and you're crazy dozy watt meter don't know the difference between what's coming out on the selected frequency regardless t other frequencies that it's generating so it just combines all those together the radio might not be doing but 10 was but it's seeing all these other harmonics and that meter is adding all those together and showing it on the watt meter so looking at the radio I don't see a whole lot inside of it that has been tampered with or anything that's blown or something now one thing that I do not like is you see this great big monster dome back here you know what this tab is for this is a reverse protection doubt and what happens is if you accidentally connect the red wire to ground and your ground wire to the fuse box or battery just doubt it's gone conduct in the wrong direction and what it's going to do is blow the fuse in the line cord if someone has the correct using or if they have it used at all and a lot of times today will short and what it does it stops the power right here at the power arm connector so that the reverse gravity does not get inside the radio and damaged components like the audio chip or blow subject traces up one up to the off/on switch now I've seen this so many times would a died what can completely fry and be blown out of it that's because they hooked it up wrong they didn't know what it wrong so they go ahead and grab a bigger fuse and stuck in it and it finally blows the doubt completely out next thing you know you've got components your audio chip so all the things I've even seen it blowed the top off of your little chip when someone had put a 35f use them so you'll see all kinds of things like this they put this big huge doubt in here then on what would you rather blow up the radio or an electrical system in your vehicle a bigger doubt it's going to build a handle whole lot load so the weakest links going to end up being these small wires that come with these things going back to your supply especially if you had the wrong fuse in it and those wires could you know overheat easily and such a vehicle on fire or damaged something in your fuse panel so not I don't like those I'd rather have the standard we voice protection David in there and let it do what it's supposed to do now as I'm looking through the radio I'm looking also for any mods that has been done to it a lot of times people get crazy with mods and they'll do some stuff that's just god-awful crazy and it's look right right there come on focus now you can see to your 32 has been removed this is a limiter if this was a single sideband radio this radio which can be completely useless on single sideband because this in a single sideband radio controls your ALC most of time back near the back of the radio is a another limiter that is for the automated modulation control and this is a 2 SC 945 transistor so that would have to be replaced and then the back does this add a jumper across it so it doesn't even have to you're 53 in this radio so they came here and they snatched out to your 32 which is not the way you need to run a radio this will give you flat topping pinched off audio and all kinds of distortion so next thing we would do is look at the bottom of the radio and just go through as much of this as you can and looking for cracks or joints bonk traces sort of blobs or anything the side of the ordinary and I can tell right here it looks like this has been worked on before and this is the transmitted mixer over here on this side if I turn the radio over see that little black icy layer it's actually a circuit board with pins on it and it's surface mount devices on it this is your trays Myint mixer so if we turn it back over and I'll get that back in frame you can see there's a lot of flux around these pins so this has been took out and even replaced or took out and tested at one time it's hard to say this is the original or not but this is this has been walked on and this is the only thing that I've seen this Walkman a few you know looking at rest of the board I'm not seeing this flux residue but it's only every pins so this has been walked on so the very first thing that we're going to do start looking at this radio is that we're going to check to receiver power supply rail now just because we hear static you know and we have a green light still doesn't mean that we don't have a problem in the receiver switching Network so as you can see right here on this schematic we have T or 36 there's a 2's a 1280 T and we should have somewhere around 7 to 8 volts on the collector of this transistor and just so go on through in this feeds our receive side the voltage that it needs to turn the receiver on them that transistor could be shorted loading down the whole supply and keeping everything from working okay I have power applied back to the radio but I remounted this more to keep it from flopping around and shorten everything out which would probably make some spectacular sport our favorites but we got that out of the way through it we won't see any fireworks on that but if you look down here in this front corner right behind the meter you can see three transistors down here and you'll see too short and I think it's a 2 SC 945 and then you'll see but that's two 2's a transistors and the one that's mounted right here this is part of your received power supply so we can go on the other side and we will find a collector and we're going to check the voltage on it okay so the point that we're going to check is down here I'm going to go to the ground plane don't use your chassis when checking voltage on these radios always you go to circuit board ground like chassis ground and T or 37 here so T or 36 is the next transistor here and a bit of center pin which is collector and we have eight point seven seven volts so we know our receive power supply real it's fine if it's real good so there's no problem there what do this thing we're going to do is come here to all PLL this part we will come over here to our PLL and we're going to check the voltage on pin 5 of the PLL which is I see 5 and we want to see somewhere around around 7 volts give or take a vote depends on how the voltage is looking over there again we're going to go to circuit board ground and we have a little over 8 volts there so that's good now this is part of supply coming in and if you find this here missing voltage at this point you can go back here to see 90 in the radio and a lot of times seen Oni will short and that would cause it to lose this voltage because you know capacitors fell all the time now there is a resistor in between these two I think it's our 22 I can't remember what the value is but a lot of times to that resistor could burn out and all the risks are can change over time they'll also not supply the voltage okay so now the next thing we're going to do is check our reference oscillator which is a 10-point to 40 megahertz crystal and we're not going to go to the crystal and check it we can come now here to IC 5 which is our PLL and we are going to look at 10 4 for our 10.2 40 megahertz single this way we'd only have to turn the radio over to find it go up here to the old BK and I'll probe in for and you can see we have all ten-point to 40 reference oscillator so we know we have an oscillator a reference oscillator going into the chip okay now next step we'll do is check our 16.4 90 mixer single and we're going to do that here at TP woman now you know I could pull up the book and go through this but there's no need oh it's simple enough and if you'll remember these steps you can go back and refer to the manual so go back to our frequency counter and we'll look for our 16.4 90 single this one is somewhere around 15 kill over 16 kilohertz slowly climb so we are missing our mixer single now when you're missing your mixer single we then have to wonder what's going on down here in the PLL circuit so probably what we need to do is go and check our VCO voltage and make sure we have voltage on my VCO alright so what we're going to now is a take off scope and we have our scope probe set - tans woman we're gonna come here like it's all 74 now guys you know I'm doing this live I'm doing it without any documentation what I'm doing it's just out of my head and what you're seeing is what I'm seeing for the first time so we're gonna come here we're gonna probe or 74 does a bear lead right here on the scope and we're going to look for nine point eight volts peak-to-peak for a VCO single okay let's go pull the bone there sure ain't no point eight votes there a lot of ripple there's nothing there all right what we're going to do now is check L 50 down here and there's a barrel lead on the old 50 it stands right out you can see it pretty good and we're going to look for to 2 volts peak-to-peak on the scope which is also part of our POA I mean our VCOs block voltage you can see that voltage is going to run off the cart I'm on five volts per division so we're up in about seven volts peak-to-peak so our VCO is running crazy okay so we're back on the schematic and you can see here this was TP three that we check start with that we had absolutely nothing this L 18 until you're 26 is the VCO buffer and TR 25 is the VCO so what we want to do want to go in the base of this transistor and see what kind of voltage we have okay I try to look at everything in the shot so you can see exactly what I'm doing I'm going to go to circuit board ground over here and then they just come right here to one of the points and we have zero voltage oh what's this and that's interesting I touched a pen I got eight point six eight volts if I touch anything else on the circuit trace I have zero voltage now you need to put this on the microscope and take a look we may have just found our problem that's easy okay so let me ask you you see anything there that looks kind of kind of strange look at it real good become the light off for you look right here right there in that area you see that crack there you go so we know it adieus we have a crack circuit board or socket trace we have bolted on the pin but we don't have any voltage so we're not supplying the VCO with any voltage whatsoever so we see can't we get this fixed all right so what I'm going to do is reflow that joint and get all these old sort of rock first and reflow it and put some fresh solder on it and never feel silicon the serine all right sorry about that we reflux this line and don't be scared to use books all righty okay I got a stone speaker antenna connector microphone plugged in just turn the radio on a little bit and I wanna do better you bother about hooking the single generator to either just going to keep the mic on another radio check one two it goes appear to be receiving see if we get a red light on the transmitter and we do okay we'll look at the what meters if we have any power out whatsoever and it's key in about 1 and 3/4 watts test one two testing one two one two three testing one two and that should win say ugly sight not that it's not putting out power but it's what I'm seeing on the scope in the spectrum analyzer okay you know I had to roll with me because the spectrum analyzers kind of pointed up and the scope is laying flat and they need to get them with both over we're over top of each other and make your screen shot a lot better the better see them but uh my cue to microphone let's go and just look at the spectrum analyzer right to start with you can see just now pay that spike on the far left no mind I'm on a kind of narrow so I know it up a little more as you can see right over here is all 54 megahertz single but I widen out on this right here and you can see the two side bands on either side of the main carrier but look at all these other spikes up and down here I'm going to look at the 54 megahertz single it's not too bad then you do gotta know we're going through about 40 DB of attenuation because I don't want any power at all getting into this spectrum analyzer but still it's not looking that good and the reason why the spike is so high you know I told you that that wind caused and spread apart like an accordion that is the result of that so I want to show you what happens when you remove the limiters in the radio and you go stretching cause and miss tuning your transmitter now you've probably seen this setup many times on other videos where people are doing this but I use a different way you know I pick off a demodulator audio and a rowdy audio onto the single so if I uh turn the tone generator off we look at over at the radio you'll see there's a plug in it with an audio cable and there's a PTT switch and I know y'all seen it before up here is a box that's more wire and X and this close to the wine X mode on the oscilloscope and what that box does is allows the carrier so if I key the radio up we can see a carrier and you can see the unmodulated audio writing on top of the carrier so imma turn the tone generator on and let you see what this single looks like and you can see that is just garbage it is not defined in any way it kind of beat your 4 to 1 ratio so anyway there you have it my friends a five bottle radio will work now you know the next thing that you would want to do to radio like this to just go through and do your basic tune-up in alignment and replace the missing limiters and straighten the calls back out like it's supposed to be but still you know these radios produce harmonics now you can do a lot of work to them and get that out but you know I'm not going to do that with this radio I'm following the next one I'll go through will go through a Cober 29 a good radio that you can follow along plenty of information on the net about it but I just wanted to give you just you know I straight up what to do with a radio that doesn't work it off anyway I hope you enjoyed this little video if you do you can always let me know by giving me a thumbs up and I'll leave a link down below to the website if you want to discuss the issue and go to the website and do so or you can leave your comments down below either way anyway thanks for watching and we'll catch you next time

Channel: The Radio Shop

Views: 54,140

Keywords: cb radio repair, trouble shooting, ham radio, no receive, no transmit, General AP Hil, The Radio Shop, VCO, PLL, phase lock loop, voltage control oscillator

Id: jga0oTGjLOw

Length: 34min 18sec (2058 seconds)

Published: Mon Dec 05 2016