how weird is that.
just plugged in the 3020 to do final tests on the phono and stuff, and its all distorted again, both channels,proper distorted and all i have done is put it away in a bag and taken it out agin, so what the hell is going on here do you think?
an do you know what is also strange, that start up noise has gone.
just plugged in the 3020 to do final tests on the phono and stuff, and its all distorted again, both channels,proper distorted and all i have done is put it away in a bag and taken it out agin, so what the hell is going on here do you think?
an do you know what is also strange, that start up noise has gone.
an update on the last post
i dont know whats going on here.i had 21v on both centres outputs on speaker terminals today.
yesterday i checked 2 of the transistors Q601 and Q602 and put them back as they were ok, but i put them back in the pin configuration shown on the board with the transistor flat as shown on the board and the instructions,but what i didnt check was that the ones fitted are the same as spec, and they are not, they had been changed by someone, so the emitter was on the opposite side(does that make sense?) so i have changed them round and the centre is back to around 0v, but the idle is 0v on both channels(with solder shorts removed) when it was 30v on both last night.🙁
so what was originaly fitted was a BC546 but what is actualy fitted is a MPSA05.
so back to square one agin with this one😕
i dont know whats going on here.i had 21v on both centres outputs on speaker terminals today.
yesterday i checked 2 of the transistors Q601 and Q602 and put them back as they were ok, but i put them back in the pin configuration shown on the board with the transistor flat as shown on the board and the instructions,but what i didnt check was that the ones fitted are the same as spec, and they are not, they had been changed by someone, so the emitter was on the opposite side(does that make sense?) so i have changed them round and the centre is back to around 0v, but the idle is 0v on both channels(with solder shorts removed) when it was 30v on both last night.🙁
so what was originaly fitted was a BC546 but what is actualy fitted is a MPSA05.
so back to square one agin with this one😕
If both channels start doing the same thing then that suggests a common cause such as a power supply problem.
The regulated supplies would be my first suspect from what you describe, and if there are no definite dries on Q901 and Q902 then I would just replace those two transistors. BD139 and BD140 should be suitable.
The diagram shows a BC549C for those other transistors you mentioned which is a high gain low noise transistor but the BC546 or MPSA05 should all work OK. The pinouts for the MPSA are 180 degrees different to the BC type. Base is still in the middle for both.
The regulated supplies would be my first suspect from what you describe, and if there are no definite dries on Q901 and Q902 then I would just replace those two transistors. BD139 and BD140 should be suitable.
The diagram shows a BC549C for those other transistors you mentioned which is a high gain low noise transistor but the BC546 or MPSA05 should all work OK. The pinouts for the MPSA are 180 degrees different to the BC type. Base is still in the middle for both.
Ill see if i get time later to have a look, if not it will be sometime in the week.today is dedicated to learning,and im sticking to it 😉
OK 🙂
(the old 2SD/2SB types like are used here do suffer from various strange intermittent problems. Usually a sudden increase increase in B-E forward voltage occurs as the junction becomes almost open circuit. Its weird but it happens to many of the TO126 outline devices of that era)
(the old 2SD/2SB types like are used here do suffer from various strange intermittent problems. Usually a sudden increase increase in B-E forward voltage occurs as the junction becomes almost open circuit. Its weird but it happens to many of the TO126 outline devices of that era)
Sounds like bond-wire issues, thermal cycling over time can detach them - perhaps the leadframe is more free to move in the small TO126 compared to larger packages exacerbating the risk.
Could be something like that Mark. It was a fairly frequent failure mode back in the TV servicing days, the clue was that there would be something like 1.5 or 2 volts across the B-E junction. TO220 packages never seemed to fail like this as far as I recall and certainly never TO3's
I think some of the BFxxx 'video outputs' were prone as well, and they were the same TO126 outline.
Long time ago now 🙂
I think some of the BFxxx 'video outputs' were prone as well, and they were the same TO126 outline.
Long time ago now 🙂
I do indeed. I worked for quite a while for the Thorn group (TTR, Thorn Television Rentals). They were good days 🙂
yeah i think i would have to agree with you, just generaly realy, these days its alltopo much stress and bottom lines!
thats why i love the old equipment,dont get me wrong new technology is great, but somehow it has no soul.
thats why i love the old equipment,dont get me wrong new technology is great, but somehow it has no soul.