EEVblog 1395 - Onkyo Repair SUCCESS

hi in our previous episode our intrepid adventurer was repairing an onkyo tx sr 607 surround sound thingamajig receiver and it had a non-working vacuum fluorescent display on the front vfd although like the audio section worked and everything was fine and all the power supplies were fine except for one which was traced down to on a different board to the front panel vacuum fluorescent display board this is why we left the previous video because the intrepid adventurer didn't have time to finish it off that day but he's back today to determine to find this fault because it was traced down to this board here and the negative 35 volt supply voltage minus vp here which was not being generated which is the negative voltage required for the vacuum fluorescent display and that was not on the vacuum fluorescent display board it had to go through yet another board over here on the side and then through a right angle board uh into this uh power supply video mux it's actually got a video mux on there so it maxes all the videos and things like that so it was narrowed down to that and when we left off we had actually uh tested this uh transistor here so we had that and put it on an external transistor tester measured fine it detected it as a transistor it had gain but that doesn't mean it's necessarily good there could be some we obscure high voltage breakdown in the part when you've got semiconductors like this they can actually um do you know weird and exotic things if murphy's not on your side that day but anyway we're going to call that good we could put in a replacement but i think that's okay so it's got to be some other part here but unfortunately we can't power this all up and uh then start probing voltages the uh all the the transistor was on the top through hole but the other parts are surface mount on the bottom here and you can't do that because the board has to plug into this right angle board over here which then has to go over to the display board in the front which then also goes down to this bottom main power amplifier motherboard which also eventually goes over to the mains power supply soft start switch so in order to power the thing up um all these things have to be connected and it's otherwise it doesn't work it doesn't power it up so unfortunately unless we hack it it's not easy to do that so we're not going to bother to do that but i'm 99 sure that the fault's going to be within here we've tested this transistor i think i tested that zener although this is a 36 volt zener so unless you take that out of circuit and hook it up to an external power supply my 121 gw multimeter here only tests up to 15 volts so unfortunately yeah we won't be able to test that unless we hook it up to a power supply but anyway i did actually measure that and it was a diode in one direction so it's not like it's open or anything and these caps look okay although i haven't taken them out but really a cap like that wouldn't cause a complete failure in this so it's got to be one of the parts here i think i might have measured that diet and was okay but anyway i think what we've got left is we're going to go through and systematically test every single component in here until we find it we'll desolder every component if we have to so we'll bet we can measure the diodes we can measure the resistors although uh you know it's unlikely your resistors are gone open or something although this one up here this is curious it's got list here what this means is that it's a select on different model so we've got the sr607 up here so it should be a 2.2 ohm but i don't know why it's so drastically different look 2.2 ohms half watt or 82 ohms half watt it just seems ridiculous um that spread in values but anyway i don't know if anyone's got any info about that model and why it's 82 it's got a radically different type of display or something i i don't know anyway um yeah let's systematically test every part until we find the culprit thing if we don't find anything well then go deeper down the rabbit hole but i hope it's in there okay so let's just check that zener again we can at least uh check one direction yep see so it's you know it's at least a diode um so it's not obviously blown open or anything like that yet the other diode is on top here so it's a through-hole jobby that's good five five that's okay for a uh you know like a well yeah one in four double o three that's hunky dory let's not look at the caps let's measure the easy stuff we'll measure the resistors let's see if one if one of these is open that would certainly uh explain it okay we've got 220 ohms one watt r901 one watt here had to be on the front because the surface mount one water would be quite big 215 yeah good enough for australia and our 1910 and our 9010 we've got the sr607 so we need 2.2 ohms and it's that one there yeah that looks like 2.2 it's pain in the ass to get vertical one here not sure if you can see that that should be 2.2 hello i'm making contact with that is that open there and there there and there solder joints look good it's open we shot the pros together wow winner winner chicken dinner that one is open there it is 90 90 10 uh which is a 2.2 or what half a half watt so you know it's a power joby so this thing is going to heat up um and it it's gone open that would explain why we're not getting out negative vp here ah okay and now that's kind of embarrassing that was just uh two fixed exposure there because the white paper if you don't know you know you put the white paper in here then everything else is dark so you've got a like fixed exposure and overexpose the damn thing anyway don't count your chickens yet um but we've found an open resistor which should explain why we're not getting the voltage there so that's all it was all i had to do was not give up and just spend another five minutes on this but yeah i had other stuff to do yesterday so i released the video and uh yep that's a potentially all it is that's the culprit that explains it now i'm probably 90 percent confident if i replace that resistor it's going to work again um so yeah i don't think it's failed due to uh like you know over current somewhere else because our transistor measures fine our diode measures fine this resistor here measures fine so you know that is the main current path so you know and it's not particularly high power but there's nothing that sort of like shorted out and taking out that i think it's just you know it's just heated up and it's a poor quality resistor or whatever or it's just heated up for so long that it finally went died in the ass and went open um i've misplaced the transistor that i took out it was in the socket here and i measured it and i've come back today and i can't find it so our transistor is missing it's got to be within the 50 square meters of this lab i found it i found it there it is sitting on the sponge doll yes i know the sponge is dry so there is the culprit it's a little uh carbon composition jobby and uh yeah half a what it looks more like a quarter watt resistor to me it depends on the temperature i have done a video on this a lot of people don't know that just because a resistor is rated at a quarter watt or a half watt or one watt or whatever yeah it can survive at that wattage but you don't realize that that wattage is actually rated at a ridiculously high temperature so if you're dissipating you know half a watt in your half watt resistor it's getting damn hot yes technically it can survive it's rated for that but generally you don't want your components to get that hot so yeah anyway so i have to uh reassemble this unfortunately to test this i can't just power it up i've got to like physically go to the effort to at least do a modicum of reassembly to uh test our theory that that's a resistor and it should be i'm 90 plus percent confident unless murphy is uh awake today then well we could come in guts a bit confidence is hard i repeat confidence is high so it's not a lot of effort to put this back together i get or at least get it to a point where you can actually uh power the thing up and uh test your hypothesis but uh test your repair so anyway we'll just put a couple of screws back in there and just get the boards basically back and the soft start should power up again and yeah just a few screws just in case you don't want to come a gutsy and have to unscrew them all again and we'll see if murphy's sleeping today all right it's back together let's power it up i think i've got plugged in most stuff or there's a few oh hang on nice and the receiver in the bottoms uh flapping around in the breeze need to put a screw in that yeah you can't see it there but there is like a metal um rf uh tuner on the uh back and uh yeah that's a metal can and you don't want that flapping around in there because it's just secured on the back by two screws and if you don't put the screws in it just flaps around in the breeze in the back and lays on the top of the power supply board down there so yeah it didn't want that so that could ruin your day will it release the magic smoke will it work and not our standby leads on wha oh flashing now it's flashing wasn't doing that before wow just wondering if i forgot to plug something back in but anyway vacuum fluorescent display is not on but that's that that's just like a logic function it's detecting something it's not happy about um ah let me give it a once over again i may have forgotten to plug something in don't you wouldn't know what it was the back of the board here was touching that power supply which is grounded and um yeah i like well yep and it was uh it's let's not do let's not do it again oh no hang on now it's flashing i swear the display was working a second ago oh god what's going on i swear i held it up like this and it was working okay you can see the standby led's on hit that it's not flashing the display is working the display is working i swear look game it's very dim fox there you go tv tape it's working winner went well see no it just went and it flashed now there's there's some sort of intermittent connection thing something's happening because i physically just moved that then okay i'm going to put all these screws back in the back because they do hold all the boards in place and of course all the boards are right angle connected so you could have a dodgy connection just uh by leaving some of the boards flapping around in the breeze right so i screwed it all back together now um you know the top's not on but uh yeah everything's back in place so nothing should be flapping around in the breeze now and that's a problem with these designs when all the boards are basically held together with uh certain like physically with screws into the back uh panel and stuff like that so anyway let's power it up there we go we've got our standby which should be the default mode whereas before when we were actually uh playing around with this it would actually power up by default on so i don't believe that's the standard but i think this is correct so let's hit that volume it's very dim but that's common for vacuum fluorescent displays and i do remember it being very dim that just happens with age unfortunately yeah but anyway it's working again vcr dcr game aux it's good enough to make it usable like you can actually tweak the voltage and stuff for the vacuum fluorescent display to make it brighter with age but eventually you're going to come a gutser and they just fail it's a thing with vacuum fluorescent displays like this not my huge amount you can do about it we could modify it but i'm happy that it's working so that is a winner winner chicken dinner pretty sure it was dim like this originally it is a relative's one i do remember it uh yes slowly dying over the years it's pretty old it's like at least 15 plus years old i think so um yeah anyway there you go yep winner winner chicken dinner we fixed it it was in the end just a carbon film resistor that went open but i hope you enjoyed that uh you know trip down the rabbit hole the repair rabbit hole where uh due to the design and construction of this thing we just had to like you know slowly eliminate things one by one check things it was the last power supply that we actually measured let that be a lesson to you thou shall measure voltages and in terms of vacuum fluorescent displays there are ones that specifically negative 35 volt rail that was dead that uh powered the vacuum fluorescent display and that was it it eventually went open that happens with those carbon film resistors you know it is one of the failure modes um and yeah whether or not it's just poorly rated i mean half a watt for that looks like a standard quarter what joby to me so yeah not terrific so whether or not it gets hot and everything i don't know but anyway there you go it could be poor design could just be i don't know is this a standard fault in these sort of units but of course if you were repairing these all the time you'd you know get a like a database of common faults and things like that it's usually you know every product will have like a like a classic louis rossman repairing his macbooks like there's you know like half a dozen major things that fail and that's and that's pretty much it that covers like 95 of his repairs or something like that it's just like a handful of uh common fires and stuff like that so i don't know if you've got one of these and you've had a similar photo please let us know in the comments down below but yep that's an interesting exercise and certainly i don't think um in the end it was shorting against the chassis uh there it was i think it was just the the connections are because all the boards in here are basically held in place by like rear panel screws and stuff like that so we've got board to board interconnects and if there's any dicky contacts in there um when they're all like flapping around in the breeze you just move something it can you know move to other boards and it just yeah and the ribbon cables and stuff like that it's uh it's all a bit how you're doing but once it's all together that's fine that's rock yep still on rock solid there you go no wackers so that works a treat so anyway yeah in the end that was a real easy fix but sometimes you've got to go down that rabbit hole to find it so that being said if you liked it give it a big a thumbs up as always discuss down below catch you next time you

Channel: EEVblog

Views: 56,463

Rating: 4.9475508 out of 5

Keywords: eevblog, video, repair, onkyo, onkyo receiver

Id: rkKyqk1YQ60

Length: 15min 57sec (957 seconds)

Published: Fri May 21 2021