| "Danny D." <dannydiamico@yahoo.com>: Aug 22 04:40PM On Sat, 20 Aug 2016 16:59:13 -0400, TekkieŽ wrote: > Thank government regulation. Just to report back, the sandpapered thermocouple has been working, so I have time to order the correct parts, probably from AO Smith themselves as they have an order number for parts: When I buy the pilot assembly, should I buy an anode? I have hard water (calcium carbonate rich). How often do you replace your anodes? |
| thekmanrocks@gmail.com: Aug 21 05:09PM -0700 Ron D. wrote: "in a 1972 Chevelle, the AC and Defrost was linked although it may have been possible that at full hot, the AC got turned off. I can't remember, but i suspect not. " I always made the simplistic assumption that the only difference between "AC" and "Defrost" modes was the direction the compressored air was ducted: either toward your face and feet(AC), or out the top side of the dash toward the windshield(Def). A lot of owners manuals suggest a temperature setting between "10 and 2 o'clock" when using Defrost, vs extreme/full cold or hot, respectively, for AC or Heater. |
| thekmanrocks@gmail.com: Aug 22 06:11AM -0700 On Wednesday, August 17, 2016 at 7:53:17 PM UTC-4, avag.ail.com wrote: > NO RECIRCULATE > recirculate is for a load of rotting fish. ___ Fresh air fanatics, are we? ;) |
| jurb6006@gmail.com: Aug 21 11:34AM -0700 >"* A better description is that the class B output stage includes >signal tracking supplies for each rail employing switching, buck >regulators. " The way I see it, the main thing it accomplishes is to get the filter out of the output line. >"The attraction of this example is the extreme simplicity and low >parts count - in part made possible by the use of Sanken power >Darlingtons rated at 70MHz. " What kind of frequency does that thing actually switch at ? Or didn't you check. No biggie if you didn't, I probably wouldn't. Were your bad connections on the outputs themselves or the regulators ? If on the outputs, your theory bout the thermal expansion is probably right, but if on the regulators I think the high frequency had an effect on it. However, of late it is starting to look like the HF has less of a deleterious effect on the unleaded solder than it did on leaded solder, though that is only supposition at this time, I don't have enough data. Not sure, but it is possible that even with all its faults, unleaded solder has a lower resistance than leaded, I don't feel like looking it up right now but that might explain it. In this newer stuff I am seeing good connections in the SMPS but bad one like at the display driver. And I get some strange ones, like in a microphone input that don't even respond to resoldering and I have to install jumpers. I'll get to the bottom of that one day but for now I just get the job out. By the way, do you use unleaded solder on repairs ? I don't. I remember there was a time when I used Tektronix 2 % silver bearing solder on certain critical spots. You didn't see them but we had the Magnavox (before Phillips bought them) T995 chassis TVs that were actually a fire hazard because of the yoke connections. I used it on them. But someone did ask on a forum and I said no, why would I use something that doesn't work as well ? That law is for manufacturers. I got a nice big pound roll of 63/37 that'll probably last me a lifetime. Another question - you said you had to unscrew all the transistors, was there no way to remove the heatsink with the board attached ? Or did they make it so you can't do that ? I swear sometimes I wonder how they manage to even build these things. I mean, if it is that cumbersome to take apart, how the hell did they achieve a decent production rate putting it together ? Since labor is such a "huge" cost they say, why not make it easy ? |
| Phil Allison <pallison49@gmail.com>: Aug 21 09:16PM -0700 > >"* A better description is that the class B output stage includes >signal tracking supplies for each rail employing switching, buck >regulators. " > The way I see it, the main thing it accomplishes is to get the filter > out of the output line. ** But it is not a class D amp in any case, just a basic class B design with a a pair of "helpers" to eliminate most of the heat. > What kind of frequency does that thing actually switch at ? ** About 200kHz, the pos and neg versions are not very symmetrical. You can see some residual riding on the output sine wave, along with minor crossover notches cos the output pair run zero bias. BTW You need a decent analogue scope to see any of this, forget using any recent, low cost DSOs with LCD screens which totally blur detail. > Were your bad connections on the outputs themselves or the regulators ? ** It was ALL the devices on the heatsink - including a pair of 1amp, 15V regulators. > By the way, do you use unleaded solder on repairs ? I don't. ** I have some 99% tin solder - but never use it. The stuff is just awful. > Another question - you said you had to unscrew all the transistors, > was there no way to remove the heatsink with the board attached ? > Or did they make it so you can't do that ? ** The power amp module was easy enough to get out and then you access the underside of the PCB by unbolting all the power devices. A common enough assembly method these days and one Yamaha uses in a few models. I was just trying to avoid doing that until I was sure there was a fault to be found there. It was amazing that with so many cracked joints, the PCB did NOT respond to hard impacts. .... Phil |
| jurb6006@gmail.com: Aug 22 04:19AM -0700 >"** But it is not a class D amp in any case, just a basic class B >design with a a pair of "helpers" to eliminate most of the heat. " Class B or AB ? Things can be class B, they, according to their publications speak of "musicality" or some such IIRC. Class B is not very warming to that, though my Phase Linear does run the actual outputs in class B. It is just that there is enough feedback and low ohm resistors from the drivers that make it sound good at low levels. If it is class B there will be no bias regulator transistors or anything to do with idle bias. Is that so ? The Phase Linear you set the bias for the drivers and they are actually the outputs up to a certain level. Is it like that or what ? >"** About 200kHz, the pos and neg versions are not very >symmetrical. " And you said something about self oscillating ? That sounds like a real bitch to engineer but I suppose it can be done. But from what I know about that topology is the collector voltage just stays a few volts higher than the output voltage. Actually in the past there were transistors that did not like that. An example would be the NEC N-965 VHS, which you probably have not seen. they had transistors for the reset the had 5 volts on the collector and then wanted 5 volts on the emitter so the put 5 volts on the base. They were a common failure. I determined that the problem was that the transistor could not maintain hfe with that low of a Vce. I replaced them with 2SD612Ks which were bias transistors and therefore made to work at low voltages. Never failed. Others had modifications running wires up to a heat sink, drilling hoes and putting the collectors to the 12 volt source. Fuck all that, but that is why I got the big bucks. So in a way I wonder if these class B outputs might not fail the same way. With the ones in the reset of the N-965 they seemed to fail with an open base. They read infinity every which way on the meter. Could have been an open emitter, no way to tell. >"** It was ALL the devices on the heatsink - including a pair of >1amp, 15V regulators" Well that pretty much clinches it that it was heat. Remember when STKs had the loops on the pins ? Obviously they were to eliminate that mechanical stress. I guess shit like that is too much trouble now. But hey, they paid the bill and you mad some money I hope. If nothing ever broke, we would be broke. >"** The power amp module was easy enough to get out and then you >access the underside of the PCB by unbolting all the power >devices. A common enough assembly method these days and one Yamaha >uses in a few models." So, after all that do you clean it and put new heatsink compound on ? (also known as bird shit) And then if there are insulators it is even worse. In fact I had a problem with that with a Yamaha, the insulators were big, one for the whole bank of transistors and it was stuck, no way to get it apart without damage. I was looking for a solution to that but quit that job and left them to their own device. It might be different in your country but here people like us are like gold. I know in Europe people know things and can fix things, but not in the US. They can't even change a flat tire. >"I was just trying to avoid doing that until I was sure there was >a fault to be found there. It was amazing that with so many >cracked joints, the PCB did NOT respond to hard impacts. " I am pretty goddamn good but I am not sure what to tell you about this. It must be that the mechanical was so strong that even a hard smack would not affect it. Maybe if you had pressed down on the PC board right near the heatsink really hard, not hitting but applying pressure, while in fault condition of course, you may have been able to tell without taking the whole damn thing apart. that reminds me I got a bunch of amps that have a channel cutting out and it is as if it is a bad connection, and AFTER the volume. I did prelims on them and thought it was the speaker relay(s) but found a couple which is wasn't. I see no bad joints but it has to be one, and I got it on either channel, we got 53 of these things. Not great amps, hundred a channel but can handle four ohms so two hundred a channel. HA, I AM factory service for these things and I have to operate like a boneyard. They all got a defect in the mechanical design. The bias transistor has no thing forcing it to make contact with the heat sink. Well we know what happens then. And the factory put heat sink compound on it so that means the design wants it. It was a SNAFU between the electronics end ans the mechanics end. But if we sell them like that they are all coming back and they will have to be refunded when, not if, they fry out. They do not want that. I had an idea with a wire clip, under a screw of the output to hold it down. I prefer that because it is plastic and you got no worries about the UL or anything but the boss was asking questions, like why are all these sitting here so I am considering using a paper clip. That is a FACTORY modification ! I have seen worse. |
| Phil Allison <pallison49@gmail.com>: Aug 22 05:18AM -0700 jurb > >"** But it is not a class D amp in any case, just a basic class B > >design with a a pair of "helpers" to eliminate most of the heat. " > Class B or AB ? ** It just happens to be class B = zero bias current in the output devices. The full manual and schem is available here: http://elektrotanya.com/yamaha_emx-2000_sm.pdf/download.html All outputs are Darlingtons, some forward bias voltage is provided set by two diodes and a resistor. > >"** It was ALL the devices on the heatsink - including a pair of > >1amp, 15V regulators" > Well that pretty much clinches it that it was heat. ** Yep. > > A common enough assembly method these days and one Yamaha uses in > > a few models." > So, after all that do you clean it and put new heatsink compound on ? ** The module has long strips of insulating material - the grey coloured silicone, re-inforced with fibreglass threads kind. I was able to re-use them with no problem, cos none of the TO3P devices dissipate really high wattages. BTW: I think the stuff is a poor heat conductor, compared to mica and white grease. ..... Phil |
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