DR #29 - Carver TFM-6CB Repair - Part 2

thanks for coming back to part two my relay has not arrived yet but all of the new capacitors have so I'm ready to start to recap you might notice that the tops of all of the electrolytic SAR marked so I do that for a reason it doesn't really apply to unit like this it's more so two units that have a lot more capacitors usually ones that are more closely spaced as well as ones that are nearly identical in size but I do this as a as a habit to remind myself which capacitors have and have not been replaced it can be really easy to mix that up especially when you're doing larger units with many more capacitors but it's still just a habit of mine I do it on almost any recap I'm starting with the bulk caps the 6800 micro farad's at 50 volts the new ones are direct replacements but they are quite a bit larger in diameter however they do match the outline or the trace on the board perfectly so they're gonna fit just fine the old ones had the glue on there it wasn't difficult to get off but I was curious these don't seem large enough to me to warrant glue but I'm not an expert maybe there's someone out there who's been in some sort of design role that can tell me what's the typical standard size as in diameter and height of cab where you start to consider using glue let's see if I can get some of that glue off I got some of the glue off I couldn't get all of it but none of us near any of the through holes so I'm not concerned one thing that almost tripped me up on this units happened to me in the past is the electrolytic polarization label on the board so most of the units I'm used to working on labeled a negative lead however these this unit is labeling the positively these are the positive leads so it is critical to pay attention to the polarization or the orientation of the capacitor before you remove it so you don't install it backwards if you want to see what happens go to one of my Tektronix repair videos I can't remember which one but you can see what happens when you put one in backwards I'm done recapping the app module I'm just waiting on the relay to come in so I can install it and reinstall the ant module back into the unit previously I mentioned removing this PCB so I can clean the volume potentiometers but there's no need you get plenty of access on either side so I'm just going to clean it while it's installed I don't how to do it I blew this out with my air compressor and I got some of the dust out but there's still a lot of cleaning to do baby wipes again all right that's much cleaner now I would never claim that cleaning that like that would improve the performance or the longevity of this unit but I like to treat everything like it's my own everything was open it's exposed really easy to clean it took five minutes so that's just kind of the standard that I hold myself to all right while we're still waiting for the relay I'm going to remove and recap the power supply section trying to get this power supply board out I disconnected the few connectors that there are and remove the board from the four standoffs but these two wires right here are really really tight it's making it I think impossible to to kind of turn it over to expose the underside so I think I have to remove this front faceplate here and possibly remove or detach whatever these wires are attached to I believe it's the front power LED yep so just the four screws on the top four on the bottom and the front faceplate comes off and indeed the two wires do lead to the front power LED I'm hoping I can remove it from the front front faceplate and fish it through the chassis but it might be glued in place I hope not after a little maneuvering this is about as good as I can get it so that's enough of an angle for me to remove and reinstall new capacitors I finished recapping and reinstalling the power supply board it looks pretty good I have received the new relay that I ordered the electrical specs match or exceed the original so it's got a 12 volt coil it can handle up to 250 volts ac and it's got an actual higher current rating at 8 amps the original was only at 5 amps now the pin layout is obviously different from the original there's a large gap between the coil pins and the contact pins and if we look at the amplifier board we can see the outline for the original relays on the right it's very close to a square in shape now where I thought I'd be able to use the new rail a is on the left that the narrower outline however I did not measure I assumed based on the pin layout so I tried reinstalling it and the pin layout does not match through-hole layout so I cannot use that new relay that had ordered I did measure the distance between these contacts so between the pins on the board and they're very odd based on all of the the newer relays that I've seen at least on digi-key I've looked at I don't know 10 12 different styles none of them matched the the spacing on this I'm not sure what kind of relay this is or this was for and it certainly doesn't match any of the ones that I've seen so far I I have found a resolution that's gonna be interesting but I think it's gonna work here's the hopeful resolution to the relay problem this is not the 6eb that i've been working on this is a TFM 6c that i found online for a great deal the previous owner of this recapped it or had it recapped and ever since then it has not been working so this is a big win not only will I be able to use this unit as a donor unit for the relay which is an exact copy of course I'll I'll remove it and I'll clean the contacts properly this time without removing that precious surface material but the work has pretty much already been done for me it looks like they did a decent job on the recap they also use good quality caps so really all I need to do is install this relay or attempt to find a suitable replacement in the future and then identify what's wrong with the unit as well it should be something simple since it occurred during the recap all right here are the two relays you can see the one that I cleaned is on the right all of that surface material is has been removed from the contacts the one on the left is the the one I just pulled out of the 6e unit and you can see it's got some oxidation it's not terrible it's not as bad as the other one was but there's some decent oxidation on there that should be removed if possible I'm going to use the first method I think that was suggested which is just actually a pencil eraser and some contact cleaner I think that'll be the least invasive way to try and clean this if that doesn't work I'll move on to another method I didn't have much success using the eraser I think it might have worked except I wasn't able to put enough downward force to clean the contact without risking bending the pins that they're attached to and so I tried the next suggestion that was in the comments and that seemed to work really well I just used a standard piece of printer paper I soaked it pretty good in the contact cleaner and that way I was able to hold it on either end of the contact and rub it with quite a bit of force on either contact as well as so rubbing it on the internal the fixed contacts as well and that seemed to clean it pretty well you can see that the contacts are fairly clean but the surface material has not been removed like it was in the first one so that worked really well I'm gonna reinstall this everything is finally reinstalled and I have the unit plugged in although I don't have any input connected I'm ready to turn it on and we heard the relay engage the power LED is on so this is a good start I'm gonna hook up some audio now actually before I apply an audio signal I want to adjust the idle current according to the service manual procedure and so the first resistor to check across is RA 24 I have my multimeter hooked up now I just turned the unit on I'm gonna let that voltage stabilize all right the unit has been on for a while now and the voltage is starting to settle down we're at about 8.6 millivolts and that's pretty high the spec is 5 plus or minus 1 millivolt so I'm gonna see if I can just that down at TV are eight zero one right here pretty touchy there we go we're at about five we're well in spec now I'm gonna move on to the next checkpoint and we'll come back and check this later here's the second checkpoint this is our 924 this is the other side or the other channel and you can see we're well out of spec on this one we should be again at 5 millivolts plus or minus 1 millivolt the units been on for a few minutes and the voltage hasn't quite settled down yet but we're trending in the wrong direction so I'm gonna start adjusting this now this is TVR 9:01 wow that is so touchy okay so it's down into spec now I suspect it's gonna trend up a little bit as well as the unit warms up so I'm gonna turn the unit off and we'll check both test points again RA 24 + r9 24 all right the units been on for two or three minutes now and the voltage is starting to settle down I don't think it's going to stop here but it's really slowing down so I think we're gonna end up right in the middle of the spec they're really close to 5 millivolts on this channel let's go ahead and check the final channel one more time @ r9 24 alright the other channel has stabilized at about 4.8 millivolts well within the spec so I think we're good on idle current now I'm ready to hook up an audio signal and test alright time to turn it on test and make sure that our original failure mode is gone all right so they're really engaged both channels are on and they sound really good I'm gonna let this run for a while to make sure that we're running cool both sides of the heatsink are okay and we have no further issues down the road all right it's been running for about thirty minutes now it still sounds great both heat sinks are ice-cold so this one is all done thanks for watching [Music]