V3 would be the critical one in Patricks markings.
-32v should be high enough (high as in closer to zero) to turn the transistors on. The sim shows around -36v as being about the zone for conduction to begin although it will vary depending on the transistors themselves.
-32v should be high enough (high as in closer to zero) to turn the transistors on. The sim shows around -36v as being about the zone for conduction to begin although it will vary depending on the transistors themselves.
Go for it
Q405 reads good on both B-E and B-C junctions (0.683 V with pos. lead of DMM to B and neg to E, OL with pos to E and neg to B; equally for Collector
I also measured the voltages around Q402 which are in spec. and I measured after D406, which showed -42,6.
Yes.
Basic diode tests aren't always definitive proof though. A device can still have problems and yet seem OK.
If you have removed them (as you should for testing) then do not refit them at this stage.
Basic diode tests aren't always definitive proof though. A device can still have problems and yet seem OK.
If you have removed them (as you should for testing) then do not refit them at this stage.
I could put in a 2SC2240 instead of the 2SC1364 for Q406 (but the former's current rating is lower). Or a 2SD669. That's what I have here at the moment. Or a BC549, but then I'll mix up the pinout 🙂
Interesting. That's quite an unusual failure mode.
It has to be swapped then to prove it. Its not critical as long as the replacement is rated for the full rail voltage it will see when off which means -44v. So we are looking at 60v or higher device.
It needs to have a collector current rating of at least whatever the relay is drawing... quick calculation 😉 if the relay was zero ohms then it would see just the 680 ohm load which would be 44/680 which is 65 milliamps. So anything common that is say 200ma or more should be fine.
Gain is (could be) important although most modern devices are pretty decent.
What have you got lying around?
It has to be swapped then to prove it. Its not critical as long as the replacement is rated for the full rail voltage it will see when off which means -44v. So we are looking at 60v or higher device.
It needs to have a collector current rating of at least whatever the relay is drawing... quick calculation 😉 if the relay was zero ohms then it would see just the 680 ohm load which would be 44/680 which is 65 milliamps. So anything common that is say 200ma or more should be fine.
Gain is (could be) important although most modern devices are pretty decent.
What have you got lying around?
Just looking... 2SC2240. It seems a bit of a waste but it has the credentials I suppose.
2SD669 is a golden oldie, I'd go with that and see what gives 🙂
2SD669 is a golden oldie, I'd go with that and see what gives 🙂
I have put in two 2SD669s. That's a large enough margin. I only need to solder them to the tracks now.
OK. We need as much gain as possible but try them and lets see what happen. That first transistor needs to be high gain really.
But try 'em.
But try 'em.
neither with R412 back in place. shall I try the 2SC2240? I also have some used 2SC458 lying around. and diverse power transistors, maybe a pair of those. but maybe that still was not the fault... thanks for your patience and kindness to assist, Mooly!
Those Sony amps are so marginally designed. Sony has made powerful amplifiers that run really hot.
My experience with old Sony amps is that the boards get so hot that the driver transistors unsolder themselves. Once the base is open a chain reaction of catastrophes happen. The most spectacular meltdowns I've seen were ALL Sony amplifiers. I've seen lightning, smoke, and partial vaporization of transistors in Sony amps. I won't even fix them any more.
My experience with old Sony amps is that the boards get so hot that the driver transistors unsolder themselves. Once the base is open a chain reaction of catastrophes happen. The most spectacular meltdowns I've seen were ALL Sony amplifiers. I've seen lightning, smoke, and partial vaporization of transistors in Sony amps. I won't even fix them any more.
Leave R412 out. It has to work with that out.
I have to disappear for a while again I'm afraid but I'll look in later on.
Check the voltage on the base of Q405 as we did before using the -44 rail as the reference. You had -2v earlier. What is it now? If it is more like 1 to 1.2 then that is a good clue we are just short of gain with two of those 2SD669's.
Is Q406 getting hot/warm? If so then that is a sign it is not fully on (not enough gain for the meagre current available from the 150k)
If you suspect low gain then you could try dabbing something like a 47k across that 150k and seeing if that operates the relay.
I have to disappear for a while again I'm afraid but I'll look in later on.
Check the voltage on the base of Q405 as we did before using the -44 rail as the reference. You had -2v earlier. What is it now? If it is more like 1 to 1.2 then that is a good clue we are just short of gain with two of those 2SD669's.
Is Q406 getting hot/warm? If so then that is a sign it is not fully on (not enough gain for the meagre current available from the 150k)
If you suspect low gain then you could try dabbing something like a 47k across that 150k and seeing if that operates the relay.
That sounds impressive. I had a NAD 3150 burn twice... but managed to restore it... on my own even 🙂
In this case all is good on the boards. The tracks are of high quality, it's easy to unsolder, there is a lot of space around the components, the amp is very ergonomically built.
I'd say that in this particular case it's a joy to work on it. If only the fault(s) would reveal themselves.
The older SONYs are even better to work on. I have a STR-6050 as well.But back to work!