Vintage Radio Restoration Part1

[Music] [Music] do [Music] hi everyone my name is tony durrant um i've been asked if i can repair four radios the gentleman who owns these radios said well i'd like to learn about repairing radios but he said i don't know where to start so i said well you know we could get together in my workshop we can go through it together if you like but of course this damn virus that's about makes this awfully difficult so at that point i decided that what i would do is try and make some youtube videos showing through my thought processes showing how to repair them which would help him and it may help some other people as well so i thought first of all i want to just tell you what radios i've got and what my approach is going to be what this video is not it's not about this is the fault therefore the problem is this what it's going to be is to try and help you to understand how to fault find some of the kit that you'll need which isn't terribly extensive um and try and get you to work your way through it in the same way that i'm gonna work my way through it and hopefully i'm gonna end up with these four radios in working condition but we will see what you need to understand first of all is that these three radios it's a bush dac 90a and a bush dac 90 and a bush vhf 80c is what i would call one class of radio and this decker dmr 88 is another class of radio now what makes those different well the point is that this radio has got an isolation transformer in it and it makes the world of difference in the way that you start to fault find it's an isolation transformer it runs on ac only all these three run on dc this radio therefore can earth the chassis it means that if you want to connect an oscilloscope to it and you connect your earth to the chassis that's absolutely fine but you do have to take great care with these ac dc radios what happens is one side of the mains is connected directly to chassis and when these were manufactured um people were not too worried about whether it's alive or the neutral is connected to chassis which is a bit of a concern so if you then plug this radio in and you come along with your scope and you connect the earth on the chassis and the chassis is live well say no more you don't want to do that so one of the things you need to do with these three radios first of all is to make sure it's the neutral connected to chassis and if you're going to work on it i'd recommend the use of an isolation transformer now i'm fortunate i've got an isolation transformer and i just use it as a matter of course i don't need it for this one but actually if i've got it why not use it so anyway the first radio i'm going to look at is this decker one [Music] i was told that this radio was working fine and then suddenly there was a bit of a pop and it didn't work anymore uh and also there is something leaking all right now that's what we know about it so where do you start you know when you get a radio do you plug it in what do you do firstly for me the answer is no you don't plug it in right what i want to do is to take the chassis out get it all set up on the bench but also you need to get the circuit as well now most of the time you can download the circuit for more or less nothing on the web it might cost you a couple of pounds but not a great deal i've got a circuit for this one here why do you need the circuit well it tells you a lot about it um you can start fault finding you do need the circuit even if you're not that good with circuits get hold of the circuit it tells you it tells you quite a lot so with this circuit i can tell that that this is an isolated radio as i said earlier how do i know that well the turkic shows me an isolation transformer that's the first thing the second thing is all the valve heaters are in parallel whereas with the ac dc radio they're all in series okay why is that important well it means that when you do eventually turn it on what you're looking for is all the valves glowing whereas if they're all in series of course if any of them were filed you wouldn't you wouldn't see any of them go um so i'm look i can check each one individually to see whether see whether they're glowing or not um that's the first thing um and then you know just take it from there so that's the next thing i'm going to start taking this radio apart and um lay it out on the chassis show you on the on the bench i'm going to show you how i've got it set out and we can work from there okay so i've got things set up on the bench um i've got an isolation transformer here which you don't need for doing this type of radio but as i've got it i like to use it it means then you know i can earth the chassis so the chassis is earth i like to do that it means then that if i've got a scope or anything and something goes wrong current's going to go through that earth wire and not through the scope um the other thing is i've done i don't know if you can see this let me just see whether you can i've just made a slight extension lead here for the speaker uh just a couple of crocodile clips so i can run the thing but most importantly i've got anything called lamp limiter now this is not my idea i can't claim credit for this but it's quite a clever one what it is is that when you switch this radio on you don't know if it's going to go bang you don't know if it's going to take a lot of current um but what the idea is if you put 100 watt light bulb in serious with the mains 100 watt light bulb the filament resistance is something like about uh 40 ohms when it's cold but when it's hot it's much higher so if you turn the radio on with that lamp in series well the radio isn't going to take very much current you're not going to drop very many volts across the bulb and at least it will protect it if something does go wrong if it starts to draw current then you'll get a lot of volts across a light bulb the light bulb gets hot and you can't actually draw too much current and then when you're happy that things are going there's a little switch here which just short circuits the bulb it's very very simple i'll put the schematic up you can download it you know it cost me what about five or six pounds to make it well worth doing i think because uh you don't quite know what's going to happen when you first switch on a radio anyway uh let's switch on and see what happens now what i do know is that when something is leaking i should give you a close-up shot of this if i can but there is a capacitor in here which is very dodgy it looks like it's leaking to me but i'm not sure i can't see that but i'm not sure but anyway i want to know what's going to happen when i turn on now what i'm the first thing i'm going to check for when it when it does go is are all the valves align remember these valve heaters are in parallel so if one isn't working then i should be able to detect it the filaments open circuit therefore you need another valve but let's have a go and see what happens so my isolation transformer is on what i will do is put this onto medium wave band because i haven't got an fm aerial plugged in but if something happens and i and i do get some sound out of it i should be able to scan across and should be able to get something um let's see what happens so radio turned on uh that's the on off yeah turned on so this is my armor let's see what happens out now did you see the light bulb come on and go off again now what that's doing is when the filaments of the of the valves are cold it takes a bit more current so it takes a current and then let's go again so what i'm looking for now is to see if any valves are a light and it's a little bit hard in this light so this might go a bit dim but i'm just going to turn the light out and see see if i can see i can see i can see all the valves are alight which is a good thing just going to put the light back on but what's worrying me now i'm going to turn off in a sec that is glowing which means it's starting to take a lot of current and i'm not hearing any sound i could hear a pop when i turned it off i wouldn't really expect that light bulb to be glowing that bride so i'm now thinking do you know what i think there's something something going on here i think we need to take a look underneath okay i know i'm going to be out of shot for the minute but it doesn't matter i wanted to show you the radio um have a look at this folks have a look at this two capacitors somebody's fitted so that leaking capacitor which i saw on the front uh somebody has been doing some work on this radio and if i look at the circuit there is a capacitor so i just switched off now let me do that there is a metal can capacitor and it's actually got three capacities in it and it shows me that on the circuit um it's three 32 mic caps and somebody has replaced two of them so i'm wondering what's going on now uh anyway what this what the schematic shows me is it gives me some voltages on those three capacitors so i think that's probably the next thing what i should do is measure those voltages and let's start having a look at some of the dc conditions uh at the minute i'm going to switch on with the light bulb in series but to actually get accuracy i really should short circuit but it depends how bright it goes because it is taking a lot of current this this thing so let's give it a go i'm on the first point now there goes a light bulb coming on that's all right right volts are coming up now of course the valve is warming up 290 let's just close that then 350 but it's going down c 60 i've got a 3 3 6. let's move on to the next one c 59 is 2 6 2 roughly let's move on to the next one which is c53 oh something's going on with my meter it does that now and again i must have pressed the hold hold on c53 that's two two one c53 is two two one right let's just turn off a moment and have a little think so the values are wrong right i mean the values are wrong there's no doubt about that so let's try and work out uh what the current should be in r26 and r25 so let's say should be ir26 should be 360 minus 310 equals that 50 50 volts across 1k is 50 milliamps and then the current in r 25 should be 310 minus 240 equals 70 divided by 2.7 k should be 26 milliamps but what we've actually got is something rather different let's see what we've actually got the current in our 26 is [Music] uh when we are 336 minus 262 so the 74 volts across there divided by 1k is 74 milliamps currents much too high in that ir25 is 262 divided by 226 that's 36 volts divided by 2.7 k is 13 milliamps current is too low in that so what does that tell you it means that the current going down into the output transformer is significantly higher than it should be it should be 50 minus 26 which is 24 milliamps and actually what it is is 74-13 is actually 61 milliamps question is where is it going so what we have to do now is we're going to pull out el 84 valve the output valve and once we do that then there should be no current going down that branch which means the current in r26 and r25 should be the same right let's do that v5 removed here we go let's pull this and pull it out okay valve's out now let's put my switch back on right let's turn back on uh why is it not going on yes it is give me a moment c60 i'm getting what's even lower now oh hang on let me just close the switch go back to where we were well it's definitely up 368 volts c59 is 308 what's going down 3-0 damn it's really going down 286 i'm going to turn off i'm worried i'm worried okay the point is if on c53 that was going down then something is going wrong it's either going down the output transform but it can't be so therefore it's going down the capacitor and i would expect them to get what warm but they're not which is a bit odd oh ah the original capacitor is getting warm i wonder i can see what's happened whoever's done this repair where they've replaced c59 they haven't disconnected the old capacitor so the old capacitor is getting warm and that's why these voltages are wrong right okay i've now got to go and disconnect that do a little bit of soldering and then we'll come back and we'll measure some more voltages let's see how we get on okay guys um moment of revelation here i've just started to disconnect things that's that's the replacement capacity somebody has done and i've just measured these two resistors and um one of them should be 1k which is that one the other one should be 2.7 k look i mean it's a bit black you can't really tell what it is but i've just measured it and it's 1k and it doesn't look original so i think somebody who said all volts are a bit low uh but i'll reduce the resistor a bit so i've got a we've got to replace that with a 2.7 k the real reason that the volts were low is because they hadn't disconnected the dead capacitor in the first place so we've got to replace that 2.7 k it says two and a half watt by a two watt i like to put a bigger one in if i can um and then we need to put it all back together but i haven't got those bits so i'm going to order that resistor i'll also order uh another capacitor because if two of those are dead in that can let's not muck about let's put the third one on so let's do that when i've got those bits well then we'll put it back together and see how we get on okay i've had a bit of a chance to work on this radio now and i've done a bit of rewiring inside i'm just going to show you what i've done um this is this old triple capacitor which was leaking i remember they put the wrong somebody put wrong resistor in at one k resistor so what i've done is they had uh there's a lot of holes in this chassis so i've managed to get a complete new piece of tag strip in there because i wanted to disconnect this old capacitor and connect it to something and i needed to just just needed some connection so i've got a tag strip i've managed to bolt it in there so there's the 1k resistor which is now correct that's the 2.7 k which was they had a 1k in there incorrectly as we discovered uh and then these are the two replacement capacitors which were already there and this is the third one which i've now added so the next thing to do in a minute is we're going to switch on and we're going to see whether these voltages are anywhere near correct okay you might not be able to see what i'm doing here but uh you'll get you'll get the gist of it so i'm going to do i'm going to measure these voltages now on c60 c59 and c53 and the schematic tells me it should be 360 volts 310 and 240 but first i'm going to switch on with my light bulb in series because i really want to know uh whether anything nice is going to happen so let's do that okay light bulb in series and turn on i can see a light bulb so that's good so i'll just wait for the valves to warm up okay volts are coming up now i can see my light bulb is glowing a little bit but i'm going to have to short circuit that now to get anything like the correct voltages so but it doesn't seem to be getting any brighter particularly i don't think let's go for it and i have got it's going down a bit but anyway 355 should be 360. let's move on to the next one and that's two nine seven it should be 310 a bit low but maybe it's all right oh hang on i can hear something and 240 i should get and i'm getting two four seven well the other thing i've done is i have plugged in a little bit of an fm aerial here just in case we get anything and the sign is that it will so i'm going to put this on the ihf oh i can hear something um yeah that's true sarah thank you for that and from kate i turned 60 in early february as a 59 year old that's encouraging exactly which is so freeing and exhilarating but i've also just started i think okay excellent right let's try another wave band let's try medium see if we can get anything on that i think the switch is a bit dicky we might need to spray something in that i can't seem to get much on medium wave let's try long wave let's just try medium wave again i suspect the switch it's definitely a bit bit iffy so i'm going to try and spray that anyway let's turn off for a moment and we'll need to turn it over to have a look at that okay this is going to be hard for you to see but here is the waveband switch and it's going to be very very difficult to clean and we can only do what we can do um you know you can't don't start disconnecting wires or anything like that all you can do is to try and put some switch cleaner on it and let's do what you can do you want to try and get all the contacts if you can and move it as you do it obviously make sure it's switched off and just keep doing as much as that as you can on all the contacts if possible just try and work it in there's normally a main contact in the center of these things sometimes you can't even see where you're spraying it but and then just make sure everything is just leave it to dry before you switch on yeah it might be worth leaving five minutes or so just keep working it in okay right let's i'll leave that to dry and we'll come back in a bit well it's all back together now uh and it's all working nicely the only other things that i've done to it is i've just cleaned the volume control a bit it was just a bit crackly again just spray the switch cleaner in that and i've replaced the y capacitor now if you don't know about x and y capacity it's very easy an x capacitor is one that is put right across the live and neutral of the mines and a wide capacitor goes between live and earth and then another one between neutral and earth now not all radios have these some only have x capacity y capacitors this radio has just got one wide capacitor between live and earth and i'll put a photograph of it up now and the one i'm going to replace it with now the reason that i always replace an x and y capacitor if they've got them is they are notoriously unreliable they are you know they see the mains voltage and you know they they just wear out and sometimes they can go off bang but if you buy a modern one now which is x-rated or y-rated it's to do with the failure mode and uh you know just just do it as a matter of course it's very easy and that's it that's the only thing i've done to it and i'll just show it working now i've got it on got an fm at the moment [Music] that's radio 3 i think oh just got to the end of something i believe in [Music] [Applause] and then if i go a long wave i should better get radio [Music] [Applause] turn it down very very happy with that that went quite well uh it's certain radio which didn't work into something which does work so i'll put all the documents up uh you can have a look at them and uh i'll be back with some more radios to repair you know do subscribe if you want to and communicate tom tell me whether this is useful whether it's not useful what you'd like to see i'm going to be pressing on repairing more radios putting more videos up bye for now [Music] you

Channel: Tony Durrant

Views: 28,222

Keywords: DMR88, DAC90, DAC90A, VHF80, valve, bush, Decca, lamp limiter, restoration, radio, Restoration

Id: -3DWGVifTbc

Length: 28min 6sec (1686 seconds)

Published: Mon Nov 23 2020